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For 50 years of data collection and kinematic reconstruction efforts, plate models have provided alternative scenarios for plate motions and seafloor spreading for the past 200 My. However, these efforts are naturally limited by the incomplete preservation of very old seafloor, and therefore the time- dependence of the production of new seafloor is controversial. There is no consensus on how much it has varied in the past 200 My, and how it could have fluctuated over longer timescales. We explore how seafloor spreading and continental drift evolve over long geological periods using independently derived models: a recently developed geodynamic modelling approach and state-of-the-art plate reconstructions. Both kinematic reconstructions and geodynamic models converge on variations by a factor of 2 in the rate of production of new seafloor over a Wilson cycle, with concomitant changes of the shape of the area– age distribution of the seafloor between end members of rectangular, triangular and skewed distributions. Convection models show that significant fluctuations over longer periods (∼1 Gy) should exist, involving changes in ridge length and global tectonic reorganisations. Although independent, both convection models and kinematic reconstructions suggest that changes in ridge length are at least as significant as spreading rate fluctuations in driving changes in the seafloor area–age distribution through time.
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... transpressive boundaries) are also discussed in the Supplementary information ( Supplementary Fig. S1). Also shown in Fig. 1a is a Mesozoic-Cenozoic SPR curve (Coltice et al., 2013) based on the plate model of Seton et al. (2012). Because M16 is partly an update of Seton et al. (2012), the SPR curve of Coltice et al. (2013) and the 0-250 Ma segment of the M16 SAF curve are not entirely independent, but their similarity underscores the expected equivalence of the time-dependent SAF and SPR. ...
... Also shown in Fig. 1a is a Mesozoic-Cenozoic SPR curve (Coltice et al., 2013) based on the plate model of Seton et al. (2012). Because M16 is partly an update of Seton et al. (2012), the SPR curve of Coltice et al. (2013) and the 0-250 Ma segment of the M16 SAF curve are not entirely independent, but their similarity underscores the expected equivalence of the time-dependent SAF and SPR. ...
... The M16 SAF (and the SPR of Coltice et al., 2013) is characterized by relatively low, modern-day-like rates (~2-4 km 2 yr −1 ) in the Triassic to mid-Late Jurassic (250-150 Ma), high rates (> 4 km 2 yr −1 ) in the latest Jurassic and Early Cretaceous (150-100 Ma), and a general decline from high rates to modern-day rates through the Late Cretaceous and Cenozoic (100-0 Ma) (Fig. 1a). The V15 SAF curve exhibits a similar trend between 180 and 0 Ma, showing a moderate SAF in the Early-Middle Jurassic (180-160 Ma) and Late Cretaceous to Cenozoic (80-0 Ma) separated by high rates in the Late Jurassic and Cretaceous (160-80 Ma). ...
Article
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Ascertaining the cause of variations in the frequency of geomagnetic polarity reversals through the Phanerozoic has remained a primary research question straddling paleomagnetism and geodynamics for decades. Numerical models suggest the primary control on geomagnetic reversal rates on 10 to 100 Ma timescales is the changing heat flux across the core-mantle boundary and that this is itself expected to be strongly influenced by variations in the flux of lithosphere subducted into the mantle. A positive relationship between the time-dependent global subduction flux and magnetic reversal rate is expected, with a time delay to transmit the thermal imprint into the lowermost mantle. We perform the first test of this hypothesis using subduction flux estimates and geomagnetic reversal rate data back to the early Paleozoic. Subduction area flux estimates are derived from global, full-plate tectonic models, and are evaluated against independent subduction flux proxies based on the global age distribution of detrital zircons and strontium isotopes. A continuous Phanerozoic reversal rate model is built from pre-existing compilations back to ~320 Ma plus a new reversal rate model in the data-sparse mid-to-early Paleozoic. Cross-correlation of the time-dependent subduction flux and geomagnetic reversal rate series reveals a significant correlation with a time delay of ~120 Ma (with reversals trailing the subduction flux). This time delay represents a value intermediate between the seismologically constrained time expected for a subducted slab to transit from the surface to the core-mantle boundary (~150–300 Ma), and the much shorter lag time predicted by some numerical models of mantle flow (~30–60 Ma). While the reason for this large discrepancy remains unclear, it is encouraging that our novel estimate of lag time represents a compromise between them. Although important uncertainties in our proposed relationship remain, these results cast new light on the dynamic connections between the surface and deep Earth, and will help to constrain new models linking mantle convection, the thermal evolution of the lowermost mantle and the geodynamo.
... An ongoing lively discussion indicates some uncertainty about the models used to estimate the ages of oceanic crust. Coltice et al. (2013) argue that over the last-250 myr, sea floor production rates varied significantly, by a factor of 2 to 3, contrary to the estimates based on present day preserved oceanic crust by Rowley (2002). Based on spherical numerical simulations focusing on the influence of continents on mantle convection, Coltice et al. (2013) postulate that the rates of crustal production are related to cycles of supercontinent amalgamation and break-up. ...
... Coltice et al. (2013) argue that over the last-250 myr, sea floor production rates varied significantly, by a factor of 2 to 3, contrary to the estimates based on present day preserved oceanic crust by Rowley (2002). Based on spherical numerical simulations focusing on the influence of continents on mantle convection, Coltice et al. (2013) postulate that the rates of crustal production are related to cycles of supercontinent amalgamation and break-up. Their simulations show that supercontinent amalgamation contributes to rectangular-like distributions of the oceanic floor with low production rates, whereas supercontinent break-up contributes to triangular distributions of the oceanic floor, which eventually develop into skewed distributions, as progressively newer crust forms at the expense of older crust. ...
... However, Norton and Lawver (2014) challenge the models by Müller et al. (2013) and Coltice et al. (2013). Rapid spreading in the Pacific Ocean contributed to the subduction of enormous areas of crust. ...
Article
Full-text available
A better understanding of how zircon ages vary with time requires sophisticated statistical analysis of U/Pb isotopic ages from both bedrock and detrital zircon databases. Researchers mostly interpret variation in the preserved zircon age distribution as representing periods of enhanced production of continental crust coupled with recycling of older crust. Yet, estimates from several global databases show considerable variation, which suggests the need for standardizing sampling and statistical analysis methods. Grid-area sampling and modern sediment sampling are proposed for future database development with the goal of producing statistically consistent estimates of zircon age distributions at four scales – global, continental, regional, and intra-basin. Application of these sampling methods and detailed statistical analysis (time-series, spectral, correlation, and polynomial and exponential fitting) indicates possible relationships among continental and oceanic crust formation, large igneous province (LIP) events, the supercontinent cycle, geomagnetic polarity and geomagnetic intensity. Results show a strong correlation of zircon and LIP age spectra with major peaks at 2700, 2500–2400, 2200, 1900–1850, 1650–1600, 1100, 800, 600, and 250 Ma, with a pronounced cyclicity in both events of about 274 million years. Cross-correlation analysis indicates that LIP peaks precede zircon peaks by 10–40 million years. Furthermore, oceanic crust age peaks at 170–155, 135–125, 115–100, 80–70, 55–45 and 33–15 Ma correspond to zircon-LIP peaks. Also correlation analysis indicates a link between the zircon-LIP events and geomagnetic reversal frequency, as well as a possible link between geomagnetic polarity and paleointensity. Improved quantification of geological and geochemical measurements should help solve lingering questions about why time-series records of continental and oceanic crust, the supercontinent cycle, and global LIP events indicate evolution in quasi-periodic episodes.
... For the past 84 Ma (since the end of the Cretaceous Normal Superchron), the SPR can be calculated directly and with confidence from marine magnetic anomalies (e.g. Coltice et al. 2013), whereas prior to that we must turn to indirect means. One possible indication of a change in SPR is a change in sea level, and the 'standard' estimate of SPR in the GEOCARBSULF climate model is estimated from sea-level inversions before the Jurassic (Berner, 2004;Royer, 2014). ...
... (c) Subduction flux calculated from a full-plate model for the past 410 Ma (red line: DomeierMatthews et al. 2016). Subduction flux estimates are compared with a seafloor production curve for the past 200 Ma (blue line:Coltice et al. 2013). The stippled blue line is the GEOCARBSULF standard curve for normalized seafloor production (ƒ SR parameter) and here normalized to theColtice et al. (2013) estimate of present-day seafloor production. ...
... Subduction flux estimates are compared with a seafloor production curve for the past 200 Ma (blue line:Coltice et al. 2013). The stippled blue line is the GEOCARBSULF standard curve for normalized seafloor production (ƒ SR parameter) and here normalized to theColtice et al. (2013) estimate of present-day seafloor production. ...
Article
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A half-century has passed since the dawning of the plate tectonic revolution, and yet, with rare exception, palaeogeographic models of pre-Jurassic time are still constructed in a way more akin to Wegener's paradigm of continental drift. Historically, this was due to a series of problems – the near-complete absence of in situ oceanic lithosphere older than 200 Ma, a fragmentary history of the latitudinal drift of continents, unconstrained longitudes, unsettled geodynamic concepts and a lack of efficient plate modelling tools – which together precluded the construction of plate tectonic models. But over the course of the last five decades strategies have been developed to overcome these problems, and the first plate model for pre-Jurassic time was presented in 2002. Following on that pioneering work, but with a number of significant improvements (most notably longitude control), we here provide a recipe for the construction of full-plate models (including oceanic lithosphere) for pre-Jurassic time. In brief, our workflow begins with the erection of a traditional (or ‘Wegenerian’) continental rotation model, but then employs basic plate tectonic principles and continental geology to enable reconstruction of former plate boundaries, and thus the resurrection of lost oceanic lithosphere. Full-plate models can yield a range of testable predictions that can be used to critically evaluate them, but also novel information regarding long-term processes that we have few (or no) alternative means of investigating, thus providing exceptionally fertile ground for new exploration and discovery.
... 16 years later, this aim is still not reached, but the progresses in this direction have led to the emergence of numerical models of mantle convection which display a surface dynamics similar to that of the Earth, at first order (Moresi & Solomatov, 1998;Moresi et al., 2000;Richards et al., 2001;Stein et al., 2004;Bercovici, 2003;Tackley, 2000b;Van Heck & Tackley, 2008). Although the mechanisms of plate generation are still not clearly understood, these models are realistic enough to study the dynamics of seafloor spreading (Coltice et al., 2012(Coltice et al., , 2013, the long-term motion of continents Yoshida, 2010) or the repartition of plate sizes and the dynamics of specific tectonic features (Mallard et al., 2016). ...
... Several further developments have been proposed to obtain a surface dynamics closer to the Earth, such as taking into account the viscosity variations with the concentration of fluids in rocks, grain size and the deformation history . However, for the time being, a composite rheology with a Newtonian component of the (Coltice et al., 2012(Coltice et al., , 2013, studies on the supercontinent cycle , and on the distribution of plate sizes (Mallard et al., 2016). ...
... Significant progress has been made in the past 10 years on modelling convection that produces more realistic surface tectonics. Convection with a pseudo-plastic rheology generates surface tectonics with a plate-like behaviour (Moresi & Solomatov, 1998;Moresi et al., 2000;Stein et al., 2004;Bercovici, 2003;Tackley, 2000b (Coltice et al., 2012(Coltice et al., , 2013. This opens the way to producing a mantle circulation model using convection models with plate-like behaviour, under the observational constraint provided by tectonic data. ...
Thesis
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This dissertation focuses on the developpement of data assimilation methods to reconstruct the circulation of the Earth's mantle and the evolution of its surface tectonics for the last 200~Myrs. We use numerical models of mantle convection in which the surface dynamics is similar to the Earth's. By combining these models with plate tectonics reconstructions, it is possible to estimate the structure and evolution of the temperature field of the mantle. So far, the assimilation of plate tectonics reconstructions was done by imposing specific boundary conditions in the model (force balance, imposed velocities...). These techniques, although insightful to test the likeliness of alternative tectonic scenarios, do not allow the full expression of the dynamical feedback between mantle convection and surface tectonics. We develop sequential data assimilation techniques able to assimilate plate tectonics reconstructions in a numerical model while simultaneously letting this dynamicalfeedback develop self-consistently. Moreover, these techniques take into account errors in plate tectonics reconstructions, and compute the error on the final estimation of mantle circulation.First, we develop a suboptimal Kalman filter. This filter estimates the most likely structure and evolution of mantle circulation from a numerical model of mantle convection, a time series of surface observations and the uncertainty on both. This filter was tested on synthetic experiments. The principle of a synthetic experiment is to apply the data assimilation algorithm to a set of synthetic observations obtained from a reference run, and to then compare the obtained estimation of the evolution with the reference evolution. The synthetic experiments we conducted showed that it was possible, in principle, to reconstruct the structure and evolution of the whole mantle from surface velocities and heat flux observations.Second, we develop an Ensemble Kalman Filter. Instead of estimating the most likely evolution, an ensemble of possible evolutions are computed. This technique leads to a better estimation of the geometry of mantle structures and a more complete estimation of the uncertainties associated.
... En géométrie sphérique à trois dimensions cependant, une loi de viscosité dépendante de la température, de la profondeur et de la contrainte seuil selon une rhéologie visco-plastique, reste la meilleure solution, à ce jour, pour générer des plaques tectoniques en surface d'un modèle de convection. Les codes numériques intégrant ces caractéristiques rhéologiques, et en particulier StagYY [Tackley, 2008] (Fig. 1.10), permettent désormais de reproduire convenablement de nombreuses caractéristiques terrestres, telles que l'évolution des âges de la lithosphère océanique [Coltice et al., , 2013, la géométrie et la migration des zones de subduction [Crameri and Tackley, 2014], ou la formation et la dispersion de supercontinents . Ce type de modèles de convection apparaît donc particulièrement adapté à la prescription de vitesses de plaques. ...
... Dans la majorité des modèles publiés utilisant StagYY, E = 23.03 ce qui permet 5 ordres de grandeurs de variation de la viscosité avec la température [Tackley, 2008;Rolf and Tackley, 2011;Rolf et al., 2012Rolf et al., , 2014Coltice et al., 2012Coltice et al., , 2013. Elle correspond à 60 kcal/mol ce qui est encore inférieur aux valeurs expérimentales [Karato et al., 1986;Karato, 2010b]. ...
... For instance, rheological parameters used in former studies are not consistent with the velocities imposed at the surface : in studies with none to small temperature dependence of the viscosity, the surface should be deformable and toroidal motion negligible whereas in studies with larger temperature dependence of the viscosity, convection should be in a stagnant lid regime [Solomatov , 1995]. In recent years, 3D spherical models of convection with plate-like behavior have been developed [van Heck and Tackley, 2008;Yoshida, 2010;Rolf and Tackley, 2011], producing convection models more consistent with Earth's surface tectonics [Coltice et al., , 2013Rolf et al., 2014]. These models are in principle closer to Earth's dynamic regime, with stiff mobile plates and narrow shear zones where deformation is localized. ...
Thesis
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Since its formation, the Earth is slowly cooling. The heat produced by the core and the radioactive decay in the mantle is evacuated toward the surface by convection. The evolving convective structures thereby created control a diversity of surface phenomena such as vertical motion of continents or sea level variation. The study presented here attempts to determine which convective structures can be predicted, to what extent and over what timescale. Because of the chaotic nature of convection in the Earth’s mantle, uncertainties in initial conditions grow exponentially with time and limit forecasting and hindcasting abilities. Following the twin experiments method initially developed by Lorenz [1965] in weather forecast, we estimate for the first time the Lyapunov time and the limit of predictability of Earth’s mantle convection. Our numerical solutions for 3D spherical convection in the fully chaotic regime, with diverse rheologies, suggest that a 5% error on initial conditions limits the prediction of Earth’s mantle convection to 95 million years. The quality of the forecast of convective structures also depends on our ability to describe the mantle properties in a realistic way. In 3D numerical convection experiments, pseudo plastic rheology can generate self-consistent plate tectonics compatible at first order with Earth surface behavior [Tackley, 2008]. We assessed the role of the temperature dependence of viscosity and the pseudo plasticity on reconstructing slab evolution, studying a variety of mantle thermal states obtained by imposing 200 million years of surface velocities extracted form tectonic reconstructions [Seton et al., 2012; Shephard et al., 2013]. The morphology and position of the reconstructed slabs largely vary when the viscosity contrast increases and when pseudo plasticity is introduced. The errors introduced by the choices in the rheological description of the mantle are even larger than the errors created by the uncertainties in initial conditions and surface velocities. This work shows the significant role of initial conditions and rheology on the quality of predicted convective structures, and identifies pseudo plasticity and large viscosity contrast as key ingredients to produce coherent and flat slabs, notable features of Earth’s mantle convection.
... Some authors have argued that the rate of seafloor production (and thus the subduction flux) has not varied significantly for the past 180 Ma (e.g. Rowley, 2002;Cogné and Humler, 2006), but that view has been repeatedly refuted by examination of extant marine magnetic anomalies (e.g., Larson, 1991;Conrad and Lithgow-Bertelloni, 2007;Seton et al., 2009;Coltice et al., 2013) and both continental (e.g., Engebretson, 1992) and full-plate tectonic models Torsvik et al. 2020). A particular triumph of the view that the seafloor production rate varies has been the recognition of a conspicuous peak in seafloor production in the Early Cretaceous (Seton et al., 2009). ...
... Degassing since 250 Ma: Rates of crustal production and destruction vs. subduction lengths Back to 83 Ma, seafloor production rates can be calculated with a high degree of confidence from oceanic lithospheric age-grids derived from marine magnetic anomalies. Coltice et al. (2013) estimated Mesozoic-Cenozoic seafloor spreading rates (f SR ) by computing the 0-8 Myrs area from oceanic age-grids, as a moving average over the studied period, using an extension of the Seton et al. (2012) full-plate model. Normalized to today (=1), their estimation of f SR shows modern-day-like rates (within a factor of ±0.3) between 250 and 160 Ma, peak rates in the Late Jurassic-Early Cretaceous, and then, after 120 Ma, a gradual decline to modern-day rates (blue curve in Fig. 6a). ...
... In our models developed using GPlates, seafloor production rate and subduction flux must be equal due to the continental area being held fixed, and so any differences observed between them are due to the application of filters (see below). The subduction flux calculated from the same but unfiltered full-plate model used by Coltice et al. (2013), when compared against their seafloor production curve, yields a Pearson r-correlation (P r ) of 0.8 and 0.9 over the 0-250 Ma and 0-160 Ma range, respectively (where P r can range from À1 to 1 and P r = 1 denotes a perfect positive relationship). Although expected, this confirms that the rate of seafloor spreading and the subduction flux, as computed from the same model, closely correspond (Fig. 6a). ...
Article
Long-term carbon cycle models are critical for understanding the levels and underlying controls of atmospheric CO2 over geological time-scales. We have refined the implementation of two important boundary conditions in carbon cycle models, namely consumption by silicate weathering and carbon degassing. Through the construction of continental flooding maps for the past 520 million years (Myrs), we have estimated exposed land area relative to the present-day (fA), and the fraction of exposed land area undergoing silicate weathering (fAW-fA). The latter is based on the amount of exposed land within the tropics (±10°) plus the northern/southern wet belts (±40-50°) relative to today, which are the prime regions for silicate weathering. We also evaluated climate gradients and potential weatherability by examining the distribution of climate-sensitive indicators. This is particularly important during and after Pangea formation, when we reduce fAW-fA during times when arid equatorial regions were present. We also estimated carbon degassing for the past 410 Myrs using the subduction flux from full-plate models as a proxy. We further used the subduction flux to scale and normalize the arc-related zircon age distribution (arc-activity), allowing us to estimate carbon degassing in much deeper time. The effect of these refined modelling parameters for weathering and degassing was then tested in the GEOCARBSULFvolc model, and the results are compared to other carbon cycle models and CO2 proxies. The use of arc-activity as a proxy for carbon degassing brings Mesozoic model estimates closer to CO2 proxy values but our models are highly sensitive to the definition of fAW-fA. Considering only variations in the land availability to weathering that occur in tropical latitudes (corrected for arid regions) and the use of our new degassing estimates leads to notably higher CO2 levels in the Mesozoic, and a better fit with the CO2 proxies.
... In other words, if the strontium flux ratio doubles, as it does going from the present-day back to 100 Myr, then the rate of ocean floor production also would have doubled over the same time interval. Coltice et al. (2012Coltice et al. ( , 2013 modelled different area-age distributions for ocean floor as a function of the number and size of continents. They concluded that on model earths with plate-like behaviour, the average area-age distribution is nearly a linear function, and that the average area-age of the ocean basins is directly correlated with the average spreading rate (Coltice et al., 2012), Following previous approaches (Cogné and Humler, 2004;Becker et al., 2009;Coltice et al., 2012Coltice et al., , 2013, we use a least-squares method (Fig. 5) to fit a linear equation to the area versus age relationship of the present-day oceanic lithosphere from Seton et al. (2012). ...
... Coltice et al. (2012Coltice et al. ( , 2013 modelled different area-age distributions for ocean floor as a function of the number and size of continents. They concluded that on model earths with plate-like behaviour, the average area-age distribution is nearly a linear function, and that the average area-age of the ocean basins is directly correlated with the average spreading rate (Coltice et al., 2012), Following previous approaches (Cogné and Humler, 2004;Becker et al., 2009;Coltice et al., 2012Coltice et al., , 2013, we use a least-squares method (Fig. 5) to fit a linear equation to the area versus age relationship of the present-day oceanic lithosphere from Seton et al. (2012). In Fig. 5 we illustrate our linear areaage distributions for the present-day and for 100 Myr, which was a time with higher crustal production. ...
... One of the most important assumptions of our approach is that the first-order linear ocean age distributions shown in Fig. 5, are a valid approximation of the present-day. In Fig. 5, we compare our linear approximation with the estimation of Coltice et al. (2013), who used the ocean age grids of Seton et al. (2012) sampled at time intervals of 5 Myr. This figure highlights the excellent first-order fit between a linear function and the present-day area-age distribution. ...
Article
Full-text available
The eustatic sea-level curves published in the seventies and eighties have supported scientific advances in the Earth Sciences and the emergence of sequencestratigraphy as an important hydrocarbon exploration tool. However, validity of reconstructions of eustatic sea level based on sequence stratigraphic correlations has remained controversial. Proposed sea level curves differ because of site-to-site changes in local tectonics, depositional rates, and long-wavelength dynamic topography resulting from mantle convection. In particular, the overall amplitude of global Phanerozoic long-term sea level is poorly constrained and has been estimated to vary between ~400m above present-day sea level to ~50 m below present-day sea level. To improve estimates of past sea level, we explore an alternative methodology to estimate global sea level change. We utilise the Phanerozoic-Neoproterozoic 87Sr/86Sr record, which at first order represents the mix of inputs from continental weathering and from mantle input by volcanism. By compensating for weathering with estimates of runoff from a 3D climate model (GEOCLIMtec), a corrected 87Sr/86Sr record can be obtained that solely reflects the contribution of strontium from mantle sources. At first order, the flux of strontium from the mantle through time is due to increases and decreases in the production of oceanic crust through time. Therefore, the changing levels of mantle-derived strontium can be used as a proxy for the production of oceanic lithosphere. By applying linear oceanic plate age distributions, we compute sea level and continental flooded area curves. We find that our curves are generally within the range of previous curves built on classical approaches. A Phanerozoic first order cyclicity of ~250 Myr is observed that may extend into the Neoproterozoic. The low frequency (i.e., on the order of 10 to 100 My) sea level curve that we propose, while open for improvement, may be used as baseline for refined sequence-stratigraphic studies at a global and basin scale.
... More complex models with plate-like behaviour and continental rafts reproduce the distribution of seafloor ages on Earth, uncovering Zhong et al. (2007b), represented as isotherms (cold in blue and hot in yellow): a) a degree-1 planform leading to continental aggregation over the region of downwellings, and b) a degree-2 planform leading to dispersal of a supercontinent. Source: Modified from Zhong et al. (2007b) why subduction affects oceanic lithosphere of all ages (Coltice et al., , 2013. These two studies show that the shape of continents geometrically imposes that the age of subduction on the adjoining oceanic plate varies along the trench. ...
... These two studies show that the shape of continents geometrically imposes that the age of subduction on the adjoining oceanic plate varies along the trench. Coltice et al. (2013) also show that these models display a significant time-dependence of the average spreading rate, which alter the age vs. area distribution of ocean basins. Increasing continental area enhances spreading rate and associated fluctuations . ...
... Increasing continental area enhances spreading rate and associated fluctuations . Plate reorganisations produce spreading rate changes that can reach a factor of 2 (Coltice et al., 2013), along with variations of the length of mid ocean ridges, and changes in the shape of the area vs. seafloor age distribution (Fig. 12). These predictions by convection models are consistent with the plate reconstructions for the past 200 My. ...
Article
The concept of interplay between mantle convection and tectonics goes back to about a century ago, with the proposal that convection currents in the Earth’s mantle drive continental drift and deformation (Holmes, 1931). Since this time, plate tectonics theory has established itself as the fundamental framework to study surface deformation, with the remarkable ability to encompass geological and geophysical observations. Mantle convection modeling has progressed to the point that connections with plate tectonics can be made, pushing the idea that tectonics is a surface expression of the global dynamics of one single system: the mantle-lithosphere system. Here, we present our perspective, as modelers, on the dynamics behind global tectonics with a focus on the importance of self-organisation. We first present an overview of the links between mantle convection and tectonics at the present-day, examining observations such as kinematics, stress and deformation. Despite the numerous achievements of geodynamic studies, this section sheds light on the lack of self-organisation of the models used, which precludes investigations on feedbacks and evolution of the mantle-lithosphere system. Therefore, we review the modeling strategies, often focused on rheology, that aim at taking into account self-organisation. The fundamental objective is that plate-like behaviour emerges self-consistently in convection models. We then proceed with the presentation of studies of continental drift, seafloor spreading and plate tectonics in convection models allowing for feedbacks between surface tectonics and mantle dynamics. We discuss the approximation of the rheology of the lithosphere used in these models (pseudo-plastic rheology), for which empirical parameters differ from those obtained in experiments. In this section, we analyse in detail a state-of-the-art 3D spherical convection calculation, which exhibits fundamental tectonic features (continental drift, one-sided subduction, trench and ridge evolution, transform shear zones, small-scale convection, and plume tectonics). This example leads to a discussion where we try to answer the question: can mantle convection models transcend the limitations of plate tectonics theory?
... An ongoing lively discussion indicates some uncertainty about the models used to estimate the ages of oceanic crust. Coltice et al. (2013) argue that over the last-250 myr, sea floor production rates varied significantly, by a factor of 2 to 3, contrary to the estimates based on present day preserved oceanic crust by Rowley (2002). Based on spherical numerical simulations focusing on the influence of continents on mantle convection, Coltice et al. (2013) postulate that the rates of crustal production are related to cycles of supercontinent amalgamation and break-up. ...
... Coltice et al. (2013) argue that over the last-250 myr, sea floor production rates varied significantly, by a factor of 2 to 3, contrary to the estimates based on present day preserved oceanic crust by Rowley (2002). Based on spherical numerical simulations focusing on the influence of continents on mantle convection, Coltice et al. (2013) postulate that the rates of crustal production are related to cycles of supercontinent amalgamation and break-up. Their simulations show that supercontinent amalgamation contributes to rectangular-like distributions of the oceanic floor with low production rates, whereas supercontinent break-up contributes to triangular distributions of the oceanic floor, which eventually develop into skewed distributions, as progressively newer crust forms at the expense of older crust. ...
... However, Norton and Lawver (2014) challenge the models by Müller et al. (2013) and Coltice et al. (2013). Rapid spreading in the Pacific Ocean contributed to the subduction of enormous areas of crust. ...
Article
Full-text available
A better understanding of how zircon ages vary with time requires sophisticated statistical analysis of U/Pb isotopic ages from both bedrock and detrital zircon databases. Researchers mostly interpret variation in the preserved zircon age distribution as representing periods of enhanced production of continental crust coupled with recycling of older crust. Yet, estimates from several global databases show considerable variation, which suggests the need for standardizing sampling and statistical analysis methods. Grid-area sampling and modern sediment sampling are proposed for future database development with the goal of producing statistically consistent estimates of zircon age distributions at four scales – global, continental, regional, and intra-basin. Application of these sampling methods and detailed statistical analysis (time-series, spectral, correlation, and polynomial and exponential fitting) indicates possible relationships among continental and oceanic crust formation, large igne-ous province (LIP) events, the supercontinent cycle, geomagnetic polarity and geomagnetic intensity. Results show a strong correlation of zircon and LIP age spectra with major peaks at a pronounced cyclicity in both events of about 274 million years. Cross-correlation analysis indicates that LIP peaks precede zircon peaks by 10–40 million years. Furthermore, oceanic crust age peaks at 170–155, 135–125, 115–100, 80–70, 55–45 and 33–15 Ma correspond to zircon-LIP peaks. Also correlation analysis indicates a link between the zircon-LIP events and geomagnetic reversal frequency, as well as a possible link between geomagnetic polarity and paleointensity. Improved quantifica-tion of geological and geochemical measurements should help solve lingering questions about why time-series records of continental and oceanic crust, the supercontinent cycle, and global LIP events indicate evolution in quasi-periodic episodes.
... Some authors have argued that the rate of seafloor production (and thus the subduction flux) has not varied significantly for the past 180 Ma (e.g. Rowley, 2002;Cogné and Humler, 2006), but that view has been repeatedly refuted by examination of extant marine magnetic anomalies (e.g., Larson, 1991;Conrad and Lithgow-Bertelloni, 2007;Seton et al., 2009;Coltice et al., 2013) and both continental (e.g., Engebretson, 1992) and full-plate tectonic models Torsvik et al. 2020). A particular triumph of the view that the seafloor production rate varies has been the recognition of a conspicuous peak in seafloor production in the Early Cretaceous (Seton et al., 2009). ...
... Degassing since 250 Ma: Rates of crustal production and destruction vs. subduction lengths Back to 83 Ma, seafloor production rates can be calculated with a high degree of confidence from oceanic lithospheric age-grids derived from marine magnetic anomalies. Coltice et al. (2013) estimated Mesozoic-Cenozoic seafloor spreading rates (f SR ) by computing the 0-8 Myrs area from oceanic age-grids, as a moving average over the studied period, using an extension of the Seton et al. (2012) full-plate model. Normalized to today (=1), their estimation of f SR shows modern-day-like rates (within a factor of ±0.3) between 250 and 160 Ma, peak rates in the Late Jurassic-Early Cretaceous, and then, after 120 Ma, a gradual decline to modern-day rates (blue curve in Fig. 6a). ...
... In our models developed using GPlates, seafloor production rate and subduction flux must be equal due to the continental area being held fixed, and so any differences observed between them are due to the application of filters (see below). The subduction flux calculated from the same but unfiltered full-plate model used by Coltice et al. (2013), when compared against their seafloor production curve, yields a Pearson r-correlation (P r ) of 0.8 and 0.9 over the 0-250 Ma and 0-160 Ma range, respectively (where P r can range from À1 to 1 and P r = 1 denotes a perfect positive relationship). Although expected, this confirms that the rate of seafloor spreading and the subduction flux, as computed from the same model, closely correspond (Fig. 6a). ...
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The validity of sea level estimates based on stratigraphic correlations has been debated since the 1990s as relative sea level curves differ between sites due to local tectonics, different deposition rates and changes in dynamic topography. Here, we offer a new eustatic (global) sea level curve for the past 520 million years (Myrs) based on observations of global flooding. We use paleogeographic reconstructions to measure the area of today’s exposed land that was flooded in the past (modern-land flooding). We then apply the modern global hypsometric slope to reconstruct the sea level history. We find minimum sea levels (comparable to today’s level) towards the end of Pangea (210 Ma) and peak levels (∼280 m higher than today) at 80 Ma when Pangea was widely dispersed. A first-order “supercontinent” cycle of 250 million years (Myrs) is recognized but we also document a second-order cycle of 37 Myrs that was previously thought to be undetectable using the hypsometric method. The hypsometric slope is critical for reconstructing past sea levels, and steepening the hypsometric slope during Pangea assembly implies dramatically larger sea level fluctuations. Our new sea level curve shares strong similarities with stratigraphic constraints and correlates with seafloor production proxies throughout the Phanerozoic. Measurements of global flooding represent averages across great continental extents, making them less sensitive than stratigraphic analyses to regional-scale vertical land motion, such as from dynamic topography and hence more reliable for estimating eustatic sea level. This method can also help to identify local deviations caused by regional uplift or subsidence and serves to constrain geodynamic mechanisms for sea level change. Our new sea level reconstruction usefully tracks global variations in Phanerozoic eustatic sea level, but also opens opportunities to estimate such variations in deeper time.
... 1). Подтверждением этого может быть резкое замедление скорости образования новой океанической коры [5], которая в период 120-110 млн лет уменьшилась в 1,6 раза (рис. 2). ...
... Наклон оси вращения Земли [11] с упрощением. Скорость образования океанической коры [5]. Вектор смещения точки (50° с. ш. и 140° в. д.) на плите Изанаги относительно Сибири: направление стрелки указывает азимут, длина -скорость (см/год), рассчитано авторами по программе GPlates-2.1 согласно реконструкциям [15]. ...
Article
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The paper seeks to explain in new ways the change in the geodynamic regime at the eastern margin of the Eurasian paleocontinent in the Early Cretaceous from the convergent type of plate boundary to the transform boundary. Certain global geodynamic characteristics were analyzed in the 200-65 Ma interval, which reflect the processes both at depth and on the Earth’s surface and are seemingly unrelated directly to the formation of the transform boundary in the east of Asia. The change of geodynamic regimes is found to occur within the 115 to 110 million years ago time range.
... Most of our understanding of subduction over geological timescales has come from estimates and proxies of subducting seafloor area at convergent margins. This has been achieved using methods of long-term sea level inversion (Gaffin, 1987), plate reconstruction and mantle convection models (Coltice et al., 2013;Engebretson et al., 1992) and seismic tomographic imaging (Shephard et al., 2017). However, the volume of slab material being consumed at subduction zones (slab flux) has received less attention, with the exception of the study by Wen and Anderson (1995). ...
... Green line shows the seafloor production rate curve presented by Gaffin (1987), based on the inversion of long-term sea level change. Bright blue line shows a more recent seafloor production rate curve derived from the plate tectonic reconstructions of Seton et al. (2012) derived by Coltice et al. (2013). The pink line depicts the area of seafloor subducted annually according to relative plate motions within a fixed-hotspot reference frame (Engebretson et al., 1992). ...
Article
Subduction is a fundamental mechanism of material exchange between the planetary interior and the surface. Despite its significance, our current understanding of fluctuating subducting plate area and slab volume flux has been limited to a range of proxy estimates. Here we present a new detailed quantification of subduction zone parameters from the Late Triassic to present day (230–0 Ma). We use a community plate motion model with evolving plate topologies to extract trench-normal convergence rates through time to compute subducting plate areas, and we use seafloor paleo-age grids to estimate the thickness of subducting lithosphere to derive the slab flux through time. Our results imply that slab flux doubled to values greater than 500 km³/yr from 180 Ma in the Jurassic to 130 Ma in the mid-Cretaceous, subsequently halving again towards the Cretaceous-Paleogene boundary, largely driven by subduction zones rimming the Pacific ocean basin. The 130 Ma spike can be attributed to a two-fold increase in mid-ocean ridge lengths following the break-up of Pangea, and a coincident increase in convergence rates, with average speeds exceeding 10 cm/yr. With one third of the total 230 - 0 Ma subducted volume entering the mantle during this short ∼50 Myr period, we suggest this slab superflux drove a surge in slab penetration into the lower mantle and an associated increase in the vigour of mantle return flow. This mid-Cretaceous event may have triggered, or at least contributed to, the formation of the Darwin Rise mantle superswell, dynamic uplift of the South African Plateau and the plume pulse that produced the Ontong-Java-Hikurangi-Manihiki and Kerguelen plateaus, among others. The models presented here contribute to an improved understanding of the time-evolving flux of material consumed by subduction, and suggest that slab superflux may be a general feature of continental dispersal following supercontinent breakup. These insights may be useful for better understanding how supercontinent cycles are related to transient episodes of Large Igneous Province and superswell formation, and the associated deep cycling of minerals and volatiles, as well as leading to a better understanding of tectonic drivers of long-term climate and icehouse-to-greenhouse transitions.
... We ascribe a similar scenario to the peak of carbon subduction in the Late Jurassic and Early Cretaceous, consistent with MD18. During this period oceanic crust that formed during the Triassic and Jurassic in warm bottom water temperatures begins to be subducted, and there is an increase in mid-ocean ridge and subduction length as a result of the breakup of Pangea, resulting in more consumption of oceanic crust (Figures 8D, 9D; Coltice et al., 2013;Van Der Meer et al., 2014;Müller et al., 2016). ...
... Although we do not explicitly measure seafloor production rates, we can estimate them as carbon storage in the upper oceanic lithosphere is broadly proportionally related to spreading rate (Figure 11F), as the thickness of oceanic crust is approximately constant. Our estimates are similar to both those of Coltice et al. (2013) (Figure 11F, black line with purple boxes), and the combined spreading rate and ridge length predictions of MD18 (Müller and Dutkiewicz (2018) their Figures 2B,C). Following this, assuming that carbon degassing is approximately linearly proportional to seafloor production rates (e.g., Kerrick (2001), though we note that CO 2 content of magmas are not constant across the globe), the relative shape of any carbon degassing curve should follow the seafloor production rate curve, providing a first-order estimate of degassing from midocean ridge systems. ...
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The subduction of upper oceanic lithosphere acts as a primary driver of Earth’s deep carbon and water cycles, providing a key transportation mechanism between surface systems and the deep Earth. Carbon and water are stored and transported in altered oceanic lithosphere. In this study, we present mass estimates of the subducted carbon and serpentinite flux from 320 to 0 Ma. Flux estimates are calculated using a full-plate tectonic reconstruction to build a descriptive model of oceanic lithosphere at points along mid-ocean ridges. These points then track the kinematic evolution of the lithosphere until subduction. To address uncertainties of modeled spreading rates in synthetic ocean basins, we consider the preserved recent (83–0 Ma) spreading history of the Pacific Ocean to be representative of the Panthalassa Ocean. This analysis suggests present-day subducting upper oceanic lithosphere contains 10–39 Mt/a of carbon and 900–3500 Mt/a of serpentinite (∼150–450 Mt/a of water). The highest rates of carbon delivery to trenches (20–100 Mt/a) occurred during the Early Cretaceous, as upper oceanic lithosphere subducted during this period formed in times of warm bottom water and the Cretaceous period experienced high seafloor production and consumption rates. Additionally, there are several episodes of high serpentinite delivery to trenches over the last 100 Ma, driven by extensive serpentinization of mantle peridotites exposed at slow spreading ridges. We propose variations in subduction regimes act as the principal control on the subduction of carbon stored in upper oceanic lithosphere, as since 320 Ma the volume of stored carbon across all ocean basins varies by less than an order of magnitude. For pre-Pangea times (<300 Ma), this suggests estimates of seafloor consumption represent a reasonable first-order approximation of carbon delivery. Serpentinite and associated water flux at subduction zones appear to be primarily controlled by the spreading regime at mid-ocean ridges. This is apparent during times of supercontinent breakup where slow spreading ridges produce highly serpentinized crust, and is observed in the present-day Atlantic, Arctic and Indian oceans, where our model suggests upper oceanic lithosphere is up to ∼100 times more enriched in serpentinite than the Panthalassa and Pacific oceans.
... The crustal structure, age, and origin of the main tectonic blocks are not well enough resolved to make definitive conclusions [72]. However, some analyses have concluded that there may be a trapped piece of Jurassic ocean floor within the basin [73] The Pacific Basin has one possible area for a remnant. The Jurassic Magnetic Quit Zone (JQZ) in the south western Pacific has no or very weak magnetic striping. ...
... Drilling projects have determined the age of the surface lava within the JQZ to be 167 Ma [73]. This would indicate that the JQZ formed after the breakup of Pangea unless eruptions continued for millions of years after its initial creation. ...
... 2. The area of seafloor at different ages not only depends on the production rate of seafloor, but also strongly depends on the history of seafloor destruction at subduction zones [Parsons, 1982]. As a result, variations in the seafloor production rate in the past 180 Ma are still debated, ranging from an approximately constant production rate in some reconstructions [Cogne and Humler, 2004;Parsons, 1982;Rowley, 2002] to variations of a factor of 2 or 3 in others [Coltice et al., 2013;Demicco, 2004;Seton et al., 2009] over the past 180 Ma. 3. There are some discrepancies between seismically determined oceanic crust thickness and the thickness of magmatic crust produced by partial melting [Cannat, 1996]. ...
... The time evolution of melt production (which we define here as the volume of melt produced per unit time) at mid-ocean ridges and the production rate of oceanic crust have been widely investigated. One important method is through measuring the volume and age of Earth's accessible oceanic crust [e.g., Coltice et al., 2013;Larson, 1991;Seton et al., 2012]. The thickness of oceanic crust can be inferred from seismic Mid-ocean ridges, however, are not isolated systems and they interact with the Earth's deep mantle through mantle convection. ...
Article
The Earth's surface volcanism exerts first-order controls on the composition of the atmosphere and the climate. On Earth, the majority of surface volcanism occurs at mid-ocean ridges. In this study, based on the dependence of melt fraction on temperature, pressure, and composition, we compute melt production and degassing rate at mid-ocean ridges from three-dimensional global mantle convection models with plate motion history as the surface velocity boundary condition. By incorporating melting in global mantle convection models, we connect deep mantle convection to surface volcanism, with deep and shallow mantle processes internally consistent. We compare two methods to compute melt production: a tracer method and an Eulerian method. Our results show that melt production at mid-ocean ridges is mainly controlled by surface plate motion history, and that changes in plate tectonic motion, including plate reorganizations, may lead to significant deviation of melt production from the expected scaling with seafloor production rate. We also find a good correlation between melt production and degassing rate beneath mid-ocean ridges. The calculated global melt production and CO2 degassing rate at mid-ocean ridges varies by as much as a factor of 3 over the past 200 Myr. We show that mid-ocean ridge melt production and degassing rate would be much larger in the Cretaceous, and reached maximum values at ∼150–120 Ma. Our results raise the possibility that warmer climate in the Cretaceous could be due in part to high magmatic productivity and correspondingly high outgassing rates at mid-ocean ridges during that time.
... Our model predicts major changes in seafloor age distributions through time (Figure 6). Such dramatic changes now have a firm geodynamic underpinning, based on the recent work of Coltice et al. (2012Coltice et al. ( , 2013, who used fully dynamic mantle convection models to show that over a Wilson cycle there are variations by a factor of two in the rate of production of new seafloor, with concomitant major changes in the age-area distribution of the seafloor. In their models, supercontinent dispersal is accompanied by a skewed distribution, reflecting the progressive creation of new crust at the expense of much older crust being subducted, whereas the triangular distribution we observe today reflects a near constant production of oceanic lithosphere compared to what is destroyed (Coltice et al. 2013), as our reconstructions illustrate. ...
... Such dramatic changes now have a firm geodynamic underpinning, based on the recent work of Coltice et al. (2012Coltice et al. ( , 2013, who used fully dynamic mantle convection models to show that over a Wilson cycle there are variations by a factor of two in the rate of production of new seafloor, with concomitant major changes in the age-area distribution of the seafloor. In their models, supercontinent dispersal is accompanied by a skewed distribution, reflecting the progressive creation of new crust at the expense of much older crust being subducted, whereas the triangular distribution we observe today reflects a near constant production of oceanic lithosphere compared to what is destroyed (Coltice et al. 2013), as our reconstructions illustrate. ...
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Open-access digital resources: http://www.earthbyte.org/ocean-basin-evolution-and-global-scale-plate-reorganization-events-since-pangea-breakup/ ftp://ftp.earthbyte.org/Data_Collections/Muller_etal_2016_AREPS We present a revised global plate motion model with continuously closing plate boundaries ranging from the Triassic at 230 Ma to the present day, assess differences between alternative absolute plate motion models, and review global tectonic events. Relatively high mean absolute plate motion rates around 9–10 cm yr-1 between 140 and 120 Ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time. A ~100 Ma event is most clearly expressed in the Indian Ocean and may reflect the initiation of Andean-style subduction along southern continental Eurasia, while an ~80 Ma acceleration of mean rates from 6 to 8 cm yr-1 reflects the initial northward acceleration of India and simultaneous speedups of plates in the Pacific. An event at ~50 Ma expressed in relative, and some absolute plate motion changes around the globe and in a reduction of global mean velocities from about 6 to 4–5 cm yr-1, indicates that an increase in collisional forces (such as the India-Eurasia collision) and ridge subduction events in the Pacific (such as the Izanagi-Pacific Ridge) play a significant role in modulating plate velocities.
... 1). Подтверждением этого может быть резкое замедление скорости образования новой океанической коры [5], которая в период 120-110 млн лет уменьшилась в 1,6 раза (рис. 2). ...
... Наклон оси вращения Земли [11] с упрощением. Скорость образования океанической коры [5]. Вектор смещения точки (50° с. ш. и 140° в. д.) на плите Изанаги относительно Сибири: направление стрелки указывает азимут, длина -скорость (см/год), рассчитано авторами по программе GPlates-2.1 согласно реконструкциям [15]. ...
Article
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An attempt to provide a new explanation for the change in the geodynamic regime in the Early Cre-taceous is presented below. It accounts for data on a number of global geodynamic characteristics in the range of 200-65 Ma reflecting processes both deep in the Earth and on the surface, and seemingly directly unrelated to the formation of a transform margin in Eastern Asia. It has been found that the geodynamic regime changed in the range of 115-110 Ma.
... Here, we use 3D spherical models of mantle convection to uncover the geodynamical processes that drive the tessellation of tectonic plates. Our dynamic models combine pseudo-plasticity and large variations in viscosity ( Fig. 1; see Methods), which generate a plate-like behaviour self-consistently [9][10][11] , including fundamental features of sea-floor spreading 12 . In our models, pseudo-plasticity is implemented through a yield stress that represents a plastic limit at which the viscosity drops and strain localization occurs, producing the equivalent of plate boundaries. ...
Article
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The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years4 suggests that this layout is probably a long- term feature of Earth, but the forces governing it are unknown. Previous studies primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection. Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size–frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected.
... Convection with a pseudo-plastic rheology generates surface tectonics with a plate-like behaviour (Moresi & Solomatov 1998;Moresi et al. 2000;Tackley 2000;Bercovici 2003;Stein et al. 2004;Van Heck & Tackley 2008;Bercovici & Ricard 2014). Recent models display seafloor spreading and continental drift comparable to that of the Earth to first order: seafloor age distributions and the time scale of spreading fluctuations are consistent with what has been inferred for the Earth for the last 200 Myr (Coltice et al. 2012(Coltice et al. , 2013. This opens the way to producing a mantle circulation model using convection models with plate-like behaviour, under the observational constraint provided by tectonic data. ...
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With the progress of mantle convection modelling over the last decade, it now becomes possible to solve for the dynamics of the interior flow and the surface tectonics to first order. We show here that tectonic data (like surface kinematics and seafloor age distribution) and mantle convection models with plate-like behaviour can in principle be combined to reconstruct mantle convection. We present a sequential data assimilation method, based on suboptimal schemes derived from the Kalman filter, where surface velocities and seafloor age maps are not used as boundary conditions for the flow, but as data to assimilate. Two stages (a forecast followed by an analysis) are repeated sequentially to take into account data observed at different times. Whenever observations are available, an analysis infers the most probable state of the mantle at this time, considering a prior guess (supplied by the forecast) and the new observations at hand, using the classical best linear unbiased estimate. Between two observation times, the evolution of the mantle is governed by the forward model of mantle convection. This method is applied to synthetic 2-D spherical annulus mantle cases to evaluate its efficiency. We compare the reference evolutions to the estimations obtained by data assimilation. Two parameters control the behaviour of the scheme: The time between two analyses, and the amplitude of noise in the synthetic observations. Our technique proves to be efficient in retrieving temperature field evolutions provided the time between two analyses is ≲10 Myr. If the amplitude of the a priori error on the observations is large (30 per cent), our method provides a better estimate of surface tectonics than the observations, taking advantage of the information within the physics of convection.
... Modern numerical studies of mantle convection have addressed many of the unexplored complexities from the earlier studies, including: nonlinear temperature-dependent rheology (Torrance and Turcotte, 1971;Parmentier et al., 1976;Richter et al., 1983;Solomatov, 1995); compressibility (Jarvis and Mc Kenzie, 1980;Leng and Zhong, 2008;King et al., 2010); three-dimensional geometry (cf. Gable et al., 1991;Tackley et al., 1993;Lowman et al., 2001Lowman et al., , 2003Lowman et al., , 2004; self-consistent equations of state King, 1994, 1998;Nakagawa et al., 2009); spherical geometry (Schubert and Zebib, 1980;Hager and O'Connell, 1981;Bercovici et al., 1989;Tackley et al., 1993;Bunge et al., 1997;Wen and Anderson, 1997;Zhong et al., 2000); and the role of plates and slabs (Gurnis and Hager, 1988;Gur-nis and Zhong, 1991;Zhong and Gurnis, 1992;King and Hager, 1994;Bercovici, 1995;King and Ita, 1995;Christensen, 1996Christensen, , 2001Chen and King, 1998;Trompert and Hansen, 1998;Tackley, 2000;Bercovici, 2003;Billen and Gurnis, 2003;Billen and Hirth, 2007;van Heck andTackley, 2008, 2011;Billen, 2008Billen, , 2010Lee and King, 2011;Coltice et al., 2013Coltice et al., , 2014. ...
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Calculations of mantle convection generally use constant rates of internal heating and time-invariant core-mantle boundary temperature. In contrast, parameterized convection calculations, sometimes called thermal history calculations, allow these properties to vary with time but only provide a single average temperature for the entire mantle. Here I consider three-dimensional spherical convection calculations that run for the age of the Earth with heat-producing elements that decrease with time, a cooling core boundary condition, and a mobile lid. The calculations begin with a moderately hot initial temperature, consistent with a relatively short accretion time for the formation of the planet. I fi nd that the choice of a mobile or stagnant lid has the most signifi cant effect on the average temperature as a function of time in the models. However, the choice of mobile versus stagnant lid has less of an effect on the distribution of hot and cold anomalies within the mantle, or planform. I fi nd the same low-degree (one upwelling or two upwelling) temperature structures in the mobile-lid calculations that have previously been found in stagnant-lid calculations. While having less of an effect on the mean mantle temperature, the viscosity of the asthenosphere has a profound effect on the pattern of temperature anomalies, even in the deep mantle. If the asthenosphere is weaker than the upper mantle by more than an order of magnitude, then the low-degree (one or two giant upwellings) pattern of temperature anomalies results. If the asthenosphere is less than an order of magnitude weaker than the upper mantle, then the pattern of temperature anomalies has narrow cylindrical upwellings and cold downgoing sheets. The low-degree pattern of temperature anomalies is more consistent with the plate model than the plume model.
... Our models use the estimates from GEOCARB II (Berner, 1994) (Fig. 6b ), because these were used by the model of riverine Sr (Lear et al., 2003 ). However, other estimates suggest a 4–15 % decrease over that past 20 Myr (Coltice et al., 2013; Conrad and Lithgow-Bertelloni, 2007; Muller et al., 2008 ). The modelled effect of a monotonic 15 % decrease in the hydrothermal flux over the past 20 Myr is ≤ 0.02 ‰ on δ 26 Mg (due to the lack of isotopic leverage the hydrothermal sink exerts), and a ∼ 6 % increase in N Mg . ...
Article
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Magnesium is an element critically involved in the carbon cycle, because weathering of Ca-Mg silicates re-moves atmospheric CO 2 into rivers, and formation of Ca-Mg carbonates in the oceans removes carbon from the ocean-atmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and iso-topically heavy Mg during calcification, show no correla-tion between the Mg isotope composition (δ 26 Mg, relative to DSM-3) and temperature, Mg / Ca or other parameters such as carbonate saturation (3). However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ 26 Mg inferred from the foraminiferal record de-creased from ∼ 0 ‰ at 15 Ma, to −0.83 ‰ at the present day, which coincides with increases in seawater lithium and oxy-gen isotope ratios. It strongly suggests that neither Mg con-centrations nor isotope ratios are at steady state in modern oceans, given its ∼ 10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers) and Mg sinks (dolomitisation and hydrothermal alteration). Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ 26 Mg of seawater, while hydrothermal Mg removal and the δ 26 Mg of rivers are more minor controls. Using Mg riverine flux and isotope ratios inferred from the 87 Sr / 86 Sr record, the modelled Mg removal by dolomite formation shows min-ima in the Oligocene and at the present day (with decreasing trends from 15 Ma), both coinciding with rapid decreases in global temperatures.
... We finally computed solutions with pseudoplasticity and continental rafts (named PLC for plate-like behavior and continents), following Rolf and Tackley [2011] but with Earth-like shapes and starting from a configuration similar to Pangea, 200 Myr ago. The combination of plate-like behavior and continental rafts produces mantle convection that matches, to first order, basic tectonic features observed on Earth [Coltice et al., 2012[Coltice et al., , 2013. Large-scale convection is also developed in these simulations ( Figure 1d) ...
Article
Reconstructing convective flow in the Earth's mantle is a crucial issue for a diversity of disciplines, from seismology to sedimentology. The common and fundamental limitation of these reconstructions based on geodynamic modelling is the unknown initial conditions. Because of the chaotic nature of convection in the Earth's mantle, errors in initial conditions grow exponentially with time and limit forecasting and hindcasting abilities. In this work we estimate for the first time the limit of predictability of Earth's mantle convection. Following the twin experiment method, we compute the Lyapunov time (i.e. e-folding time) for state-of-the art 3D spherical convection models, varying rheology and Rayleigh number. Our most Earth-like and optimistic solution gives a Lyapunov time of 136±13 My. Rough estimates of the uncertainties in best guessed initial conditions are around 5%, leading to a limit of predictability for mantle convection of 95 My. Our results suggest that error growth could produce unrealistic convective structures over timescales shorter than that of Pangea dispersal.
... Based on a similar model as presented here (but e.g. Dg R = 1), Coltice et al. (2013) suggested that such weak basal heating has only a small effect on surface velocities and seafloor spreading rates. If basal heating dominates the heat budget though, localisation of deformation in the lithosphere and thus plate-like behaviour may be more difficult to achieve, at least in the absence of continents (e.g. ...
Article
Earth’s continents drift in response to the force balance between mantle flow and plate tectonics and actively change the plate-mantle coupling. Thus, the patterns of continental drift provide relevant information on the coupled evolution of surface tectonics, mantle structure and dynamics. Here, we investigate rheological controls on such evolutions and use surface tectonic patterns to derive inferences on mantle viscosity structure on Earth. We employ global spherical models of mantle convection featuring self-consistently generated plate tectonics, which are used to compute time-evolving continental configurations for different mantle and lithosphere structures. Our results highlight the importance of the wavelength of mantle flow for continental configuration evolution. Too strong short-wavelength components complicate the aggregation of large continental clusters, while too stable very long wavelength flow tends to enforce compact supercontinent clustering without reasonable dispersal frequencies. Earth-like continental drift with episodic collisions and dispersals thus requires a viscosity structure that supports long-wavelength flow, but also allows for shorter-wavelength contributions. Such a criterion alone is a rather permissive constraint on internal structure, but it can be improved by considering continental-oceanic plate speed ratios and the toroidal-poloidal partitioning of plate motions. The best approximation of Earth’s recent tectonic evolution is then achieved with an intermediate lithospheric yield stress and a viscosity structure in which oceanic plates are ∼ 10³ × more viscous than the characteristic upper mantle, which itself is ∼ 100 − 200 × less viscous than the lowermost mantle. Such a structure causes continents to move on average ∼ (2.2 ± 1.0) × slower than oceanic plates, consistent with estimates from present-day and from plate reconstructions. This does not require a low viscosity asthenosphere globally extending below continental roots. However, this plate speed ratio may undergo strong fluctuations on timescales of several 100Myr that may be linked to periods of enhanced continental collisions and are not yet captured by current tectonic reconstructions.
... The pseudo-plastic approximation produces plate-like behaviour self-consistently over a restricted range of parameters (van Heck & Tackley 2008;Foley & Becker 2009). Such models reveal the dynamic origin of some fundamental properties of plate tectonics on Earth at the present day, such as the size distribution of plates (Mallard et al. 2016) and the seafloor age versus area distribution (Coltice et al. , 2013. However, their potential for tectonic predictions and reconstruction remains unexploited. ...
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Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough for an accurate prediction of instantaneous flow, but not for a prediction after 10 My of evolution. Therefore, inverse methods (sequential or data assimilation methods) using short-term fully dynamic evolution that predict surface kinematics are promising tools for a better understanding of the state of the Earth's mantle.
... Even if we add the 9000 km of 'collision zones,' the figure is still only half that of the 'spreading centers' (Smoot, 1997a;Pratt, 2000). This is evidenced with other data showing that the total length of the world's ocean ridges is: >50,000 km (Ito and Dunn, 2009); ~60,000 km (Courtillot, 2002); >60,000 km (Fowler, 2004;Coltice et al., 2013;Gale et al., 2013); 65,000 km (Garrison and Ellis, 2014;Sen, 2014); >65,000 km (Elders and Friðleifsson, 2015); 80,000 km (Ludhova and Zavatarelli, 2014); >80,000 km (Hendrix and Thompson, 2014); and others. It is generally accepted that the total length of the mid-ocean ridge system is ~80,000 km and the continuous mountain range is ~65,000 km; but in contrast, subduction zones and the volcanic arcs formed above them extend across approximately 40,000 km over the Earth's surface ( Syracuse et al., 2010). ...
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The main problems of the plate tectonics model are discussed in the paper. It is shown that the idea of mantle-wide convection, as well as convection within any thick mantle layer, violates the laws of physics and is therefore impossible. Analysis of the forces postulated for the model reveals that their values are very low and would be incapable of forming and supporting any significant tectonic processes (e.g., obduction, orogeny, uplifting of lithospheric block, subduction, and others). There is no clear definition of the forces operating in plate tectonics and movement of plates; and even their application is incorrect, as they violate physical laws by ignoring friction and strength limits. Formation of a new oceanic lithosphere in spreading centers violates physical laws, because it is not possible to have a plate which would independently form all its main layers of the oceanic lithosphere over tens to hundreds of millions of years in underwater conditions, building up in ~1 cm long, 50 km thick and thousands of kilometers wide increments each year, all to combine into a thousands of kilometers long solid oceanic plate, separated into its layers. There are inconsistencies between the total lengths of mid-ocean ridges (total length of the mid-ocean ridge system is ~80,000 km and the continuous mountain range is 65,000 km) and the total length of trenches (30,000-40,000 km) on the sea floor, but according to the plate tectonics model the total length of trenches should be twice as long as that of mid-ocean ridges (~130,000-160,000 km). There is also data indicating the impossibility for subduction to take place around the Atlantic (except a few locations) and Arctic oceans. Any oceanic lithosphere plate (slab) with a thickness of ~50 km is composed of three main layers: brittle upper layer with a temperature less than ~573 K; elastic middle layer with temperatures within the range of ~573-873 K; and plastic lower layer with a temperature of over ~873 K, and cannot be considered rigid. Analysis of possible density of subducting slabs shows that under any circumstances the average density of an oceanic lithosphere plate cannot be greater than rocks of the upper mantle, and formation of negative buoyancy should therefore not be possible; even transformation of the entire crust of any region into eclogite would be insufficient to form a negative buoyancy of even 0.01 g/cm3. It is shown that the subduction process requires presence of gigantic external force. An oceanic plate has an average geothermal gradient of ~50-86 K/km, and a temperature of about 1573 K (or 1603 K) at the point of contact between its lithosphere and asthenosphere, so it cannot technically be considered cold. There are also numerous questions in the model unanswered thus far. Formation of UHP rocks cannot be accomplished within a subduction zone under lithostatic pressures alone. Analysis of causes for the formation of significant overpressure shows that only the decomposition of rocks (foremost the serpentinization of peridotite) can generate such giant forces capable of horizontally moving oceanic plates. It is clear that the plate tectonics model is inconsistent as a model, violates numerous physical laws, and is based on a large number of false postulates and assumptions.
... Such an evolution is very likely linked to changes in conditions at the base of the mantle, influencing heat flow across the core-mantle boundary that is ultimately responsible for driving the geodynamo (McFadden and Merrill, 1984). Since ~200 Myr may be an emergent timescale of mantle convection (Coltice et al., 2013), it is tempting to view the Devonian as analogous to the Middle Jurassic weak-field hyper-reversing state (but probably more extreme and longer lasting) in a similar ca. 200 Myr cycle occurring previous to the most recent one. ...
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The Devonian has long been a problematic period for paleomagnetism. Devonian paleomagnetic data are generally difficult to interpret and have complex partial or full overprints– problems that arise in data obtained from both sedimentary and igneous rocks. As a result, the reconstruction of tectonic plate motions, largely performed using apparent polar wander paths, has large uncertainty. Similarly, the Devonian geomagnetic polarity time scale is very poorly constrained. Paleointensity studies from volcanic units suggest that the field was much weaker than the modern field, and it has been hypothesised that this was accompanied by many polarity reversals (a hyperreversing field). We sampled Middle to Upper Devonian sections in Germany, Poland and Canada which show low conodont alteration indices, implying low thermal maturity. We show that there are significant issues with these data, which are not straightforward to interpret, even though no significant heating or remineralisation appears to have caused overprinting. We compare our data to other magnetostratigraphic studies from the Devonian and review the polarity pattern as presented in the Geologic Time Scale. Combined with estimates for the strength of the magnetic field, we suggest that the field during the Devonian might have been so weak, and in part non-dipolar, that obtaining reliable primary paleomagnetic data from Devonian rocks is challenging. Careful examination of all data, no matter how unusual, is the best way to push forward our understanding of the Devonian magnetic field. Paleointensity studies show that the field during the Devonian had a similar low strength to the Ediacaran. Independent evidence from malformed spores around the Devonian-Carboniferous boundary suggests that the terrestrial extinction connected to the Hangenberg event was caused by increased UV-B radiation, supporting the weak field hypothesis. A fundamentally weak and possibly non-dipolar field during the Devonian could have been produced, in part, by true polar wander acting to maximise core-mantle heat flow in the equatorial region. It may also have influenced evolution and extinctions in this time period. There are a large number of paleobiological crises in the Devonian, and we pose the question, did the Earth’s magnetic field influence these crises?
... Their models support that a stable supercontinent is accompanied by a rectangular age-area distribution (Fig. 1A), with breakup and dispersal leading to a skewed distribution (Figs. 1B-1D), reflecting the progressive creation of new crust at the expense of older crust being subducted, while the triangular distribution we observe today reflects a near constant production of oceanic lithosphere compared to what is destroyed (Coltice et al., 2013). Therefore, the main conclusions of our paper are robust, supported by independent geodynamic models, and not dependent on geological uncertainties. ...
... An interesting alternative is the use of the "yield-stress" rheology (e.g., Tackley 2000) which has been demonstrated to lead to plate-like behavior without the requirement of prescribing the geometry of the plates. While it is still a question whether plate-like velocities can be modeled with this approach, recent advances using continental rafts suggest Earth-like convective vigor may be in reach (e.g., Arnould et al. 2018;Coltice et al. 2013;and Rolf et al. 2018). ...
Article
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Abstract Mantle tomography reveals the existence of two large low-shear-velocity provinces (LLSVPs) at the base of the mantle. We examine here the hypothesis that they are piles of oceanic crust that have steadily accumulated and warmed over billions of years. We use existing global geodynamic models in which dense oceanic crust forms at divergent plate boundaries and subducts at convergent ones. The model suite covers the predicted density range for oceanic crust over lower mantle conditions. To meaningfully compare our geodynamic models to tomographic structures, we convert them into models of seismic wavespeed and explicitly account for the limited resolving power of tomography. Our results demonstrate that long-term recycling of dense oceanic crust naturally leads to the formation of thermochemical piles with seismic characteristics similar to the LLSVPs. The extent to which oceanic crust contributes to the LLSVPs depends upon its density in the lower mantle for which accurate data is lacking. We find that the LLSVPs are not composed solely of oceanic crust. Rather, they are basalt rich at their base (bottom 100–200 km) and grade into peridotite toward their sides and top with the strength of their seismic signature arising from the dominant role of temperature. We conclude that recycling of oceanic crust, if sufficiently dense, has a strong influence on the thermal and chemical evolution of Earth’s mantle.
... This low-temperature basalt alteration would then have preferentially removed 18 O from the seawater, decreasing the icefree δ 18 O sw value towards more recent times 93,94 . However, there is no consensus if seafloor spreading rates were truly higher in these hothouse climates, as tectonic reconstructions and model simulations find conflicting results [97][98][99] . In summary, elevated δ 18 O sw in the early Eocene deep ocean can be ascribed to several factors. ...
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The early Eocene hothouse experienced highly elevated atmospheric CO2 levels and multiple transient global warming events, so-called hyperthermals. The deep ocean constitutes an assumed setting to estimate past global mean temperatures. However, available deep-sea temperature reconstructions from conventional benthic foraminiferal oxygen isotopes and magnesium/calcium ratios rely on uncertain assumptions of non-thermal influences, associated with seawater chemistry and species-specific physiological effects. Here we apply the carbonate clumped isotope thermometer, a proxy not governed by these uncertainties, to evaluate South Atlantic deep-sea temperatures across two hyperthermal events in the early Eocene (Eocene Thermal Maximum 2/H1 and H2; ~54 Myr ago). Our independent reconstructions indicate deep-sea temperatures of 13.5 ± 1.9 °C (95% CI) for the background conditions and average hyperthermal peak temperatures of 16.9 ± 2.3 °C (95% CI). On average, these absolute temperatures are three degrees warmer than estimates from benthic oxygen isotopes. This finding implies a necessary reassessment of (1) the Eocene seawater isotope composition and (2) pH changes in the deep ocean and its potential influence on benthic foraminiferal oxygen isotope records. South Atlantic deep-sea temperatures across two early Eocene hyperthermal events, reconstructed from clumped isotope thermometry on benthic foraminifera, were around 3 °C warmer than suggested by previous estimates based on oxygen isotopes.
... We model the seawater LIE using dynamic box models that have been used with varying complexity for modeling other time periods (34,42,45). As a starting point for modeling the seawater Li isotope evolution, we assume that the hydrothermal input can be constrained from mid-ocean ridge spreading rates, with the PETM hydrothermal input between 1.15× and 1.4× that of the present (46,47). The maximum effect of this range in hydrothermal input on steady-state seawater  7 Li is 0.5‰. ...
Article
The Paleocene-Eocene Thermal Maximum (PETM; ~55.9 Ma) was a geologically rapid warming period associated with carbon release, which caused a marked increase in the hydrological cycle. Here, we use lithium (Li) isotopes to assess the global change in weathering regime, a critical carbon drawdown mechanism, across the PETM. We find a negative Li isotope excursion of ~3‰ in both global seawater (marine carbonates) and in local weathering inputs (detrital shales). This is consistent with a very large delivery of clays to the oceans or a shift in the weathering regime toward higher physical erosion rates and sediment fluxes. Our seawater records are best explained by increases in global erosion rates of ~2× to 3× over 100 ka, combined with model-derived weathering increases of 50 to 60% compared to prewarming values. Such increases in weathering and erosion would have supported enhanced carbon burial, as both carbonate and organic carbon, thereby stabilizing climate.
... The connection between tectonics and sea-level oscillations may come from changes in directions and rates of seafloor spreading and subduction (Cogné and Humler, 2004;Coltice et al., 2013), intraplate stresses related to rearrangements of global plate motions (e.g., King et al., 2002;Müller et al., 2016;Embry et al., 2018;Müller and Dutkiewicz, 2018), and pulsations of convection (Lovell, 2010) or mantle-plume activity (e.g., Sheridan, 1987). Mjelde et al. (2010) reported evidence for major peaks in intraplate volcanism in the last 70 Myr ( Table 1) that seem to be global in extent, and which have an average~9-Myr to 10-Myr spacing similar to the spacing of stratigraphic sequence boundaries (e.g., the ''10-Myr-flood" cycle of Embry et al., 2018). ...
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We performed spectral analyses on the ages of 89 well-dated major geological events of the last 260 Myr from the recent geologic literature. These events include times of marine and non-marine extinctions, major ocean-anoxic events, continental flood-basalt eruptions, sea-level fluctuations, global pulses of intraplate magmatism, and times of changes in seafloor-spreading rates and plate reorganizations. The aggregate of all 89 events shows ten clusters in the last 260 Myr, spaced at an average interval of ~ 26.9 Myr, and Fourier analysis of the data yields a spectral peak at 27.5 Myr at the ≥ 96% confidence level. A shorter period of ~ 8.9 Myr may also be significant in modulating the timing of geologic events. Our results suggest that global geologic events are generally correlated, and seem to come in pulses with an underlying ~ 27.5-Myr cycle. These cyclic pulses of tectonics and climate change may be the result of geophysical processes related to the dynamics of plate tectonics and mantle plumes, or might alternatively be paced by astronomical cycles associated with the Earth’s motions in the Solar System and the Galaxy.
... Mismatches can partly be reduced by increased seafloor production ratesan important time-dependent plate tectonic degassing parameter (f SR ) in the GEOCARBSULF model. Variations in seafloor production (e.g., Coltice et al. 2013) can be calculated with sufficient confidence for the last 83 Myrs (after the Cretaceous Normal Superchron) from oceanic lithospheric age-grids estimated from marine magnetic anomalies. Before that time this approach has much larger uncertainties, but because the subduction flux must equal the seafloor production rate (to first order), we can use estimates of the subduction flux derived from full-plate models as a proxy for plate tectonic degassing. ...
Chapter
Most hotspots, kimberlites, and large igneous provinces (LIPs) are sourced by plumes that rise from the margins of two large low shear‐wave velocity provinces in the lowermost mantle. These thermochemical provinces have been quasi‐stable for hundreds of millions years and plume heads rise through the mantle in about 30 Myr or less. LIPs provide a direct link between the deep Earth and the atmosphere but environmental consequences depend on both their volumes and the composition of the crustal rocks they are emplaced through. LIP activity can alter the plate tectonic setting by creating and modifying plate boundaries and hence changing the paleogeography and its long‐term forcing on climate. Extensive blankets of LIP‐lava on the Earth's surface can also enhance silicate weathering and potentially lead to CO2 drawdown, but we find no clear relationship between LIPs and post‐emplacement variation in atmospheric CO2 proxies on very long (>10 Myrs) time‐scales. Subduction flux estimates correlate well with zircon age frequency distributions through time. This suggest that continental arc activity may have played an important role in regulating long‐term climate change (greenhouse vs. icehouse conditions) but only the Permo‐Carboniferous icehouse show a clear correlation with the zircon record.
... Such an evolution is very likely linked to changes in conditions at the base of the mantle, influencing heat flow across the core-mantle boundary (CMB) that is ultimately responsible for driving the geodynamo (McFadden and Merrill, 1984). Since ~200 Myr may be an emergent timescale of mantle convection (Coltice et al., 2013), it is tempting to view the Devonian as analogous to the Middle Jurassic weak-field hyper-reversing state (but probably more extreme and longer lasting) in a similar ca. 200 Myr cycle occurring previous to the most recent one. ...
... where ν is the global rate of seafloor spreading, A oc is the surface area of Earth's oceanic crust (A oc = A Earth − A cc ), and  and  max are the age of the oceanic floor and its maximum value, respectively. It has been suggested that the observed triangular distribution of the present-day seafloor age is a deviation from the theoretical rectangular distribution due to the presence of continents (Coltice et al., 2013). ...
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The water content in Earth's mantle today remains poorly constrained, but the bulk water storage capacity in the solid mantle can be quantified based on experimental data and may amount to a few times the modern surface ocean mass (OM). An appreciation of the mantle water storage capacity is indispensable to our understanding of how water may have cycled between the surface and mantle reservoirs and changed the volume of the oceans through time. In this study, we parameterized high pressure‐temperature experimental data on water storage capacities in major rock‐forming minerals to track the bulk water storage capacity in Earth's solid mantle as a function of temperature. We find that the mantle water storage capacity decreases as mantle potential temperature (Tp) increases, and its estimated value depends on the water storage capacity of bridgmanite in the lower mantle: 1.86–4.41 OM with a median of 2.29 OM for today (Tp = 1600 K), and 0.52–1.69 OM with a median of 0.72 OM for the early Earth's solid mantle (for a Tp that was 300 K higher). An increase in Tp by 200–300 K results in a decrease in the mantle water storage capacity by 1.19−0.16+0.9 –1.56−0.22+1.1 OM. We explored how the volume of early oceans may have controlled sea level during the early Archean (4–3.2 Ga) with some additional assumptions about early continents. We found that more voluminous surface oceans might have existed if the actual mantle water content today is > 0.3–0.8 OM and the early Archean Tp was ≥1900 K.
... This interpretation of the preserved seafloor spreading record was debunked by Demicco (2004) who demonstrated that the decreasing area with increasing age of preserved ocean floor does not necessitate a steady-state model of ocean-floor spreading and destruction through time. Both mantle convection models and tectonic ocean basin reconstructions result in major changes in the age-area distribution of ocean floor between rectangular, triangular and skewed distributions (Coltice et al., 2013), suggesting that long-term global tectonic cycles result in significant fluctuations in mid-ocean ridge length, spreading rates and thus ocean basin volume through time. ...
Article
Long-term variations in eustatic sea level in an ice-free world, which existed through most of the Mesozoic and early Cenozoic eras, are partly driven by changes in the volume of ocean basins. Previous studies have determined ocean basin volume changes from plate tectonic reconstructions since the Mesozoic; however, these studies have not considered a number of important elements that contribute to ocean basin volume, such as regional differences in sedimentation, or uncertainties within the plate tectonic model itself, such as spreading asymmetries and the incomplete representation of back-arc basins in the Mesozoic. Additionally, studies on long-term changes in sea level related to the extension and rifting of passive margins have not been performed on a global-scale and likely significantly underestimated the influence of this process. In order to improve reconstructions of sea level on geologic time scales and assess the uncertainty in deriving the volume of ocean basins based on a global plate kinematic model, we investigate the influence of back-arc basins, spreading asymmetry, large igneous provinces (LIPs), sediment thickness, and passive margins on ocean basin volume since 200 Ma. We find that less-constrained plate tectonic elements, such as the presence of back-arc basins or spreading asymmetry, may contribute up to ~120 m or ~ 150 m to sea level respectively. Changes in the sea level related to sedimentation and LIPs are respectively ~75–165 m and ~ 45 m. Changes in sea level associated with passive margin formation are almost negligible at present-day, though were much larger in the Cretaceous, and the assumed sedimentation style strongly influences the rate and magnitude of sea level change. We incorporate predictions for these components during times where ocean basins are predominantly synthetic reconstructions and find that sea level driven by fluctuating ocean basin volume has changed by ~200 m since the Jurassic, which is comparable to previous estimates. Our revised estimates will need to be combined with other processes driving long-term sea-level change, including mantle convection-driven dynamic topography and glacio-eustasy for constructing a complete eustatic sea level curve. Understanding and quantifying the uncertainties in the volume of ocean basins has implications for modelling subduction flux, the oceanic carbon cycle, and heatflow, and is important for exploring Earth's evolutionary cycles, especially during times in the geologic past where much of the ocean basin history has been lost.
... An interesting alternative is the use of the 'yield-stress' rheology (e.g., Tackley 2000) which has been demonstrated to lead to plate-like behavior without the requirement of prescribing the geometry of the plates. While it is still a question whether plate-like velocities can be modelled with this approach, recent advances using continental rafts suggest Earth-like convective vigor may be in reach (e.g., Coltice et al. 2013;Arnould et al. 2018;Rolf et al. 2018). ...
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Mantle tomography reveals the existence of two large low shear velocity provinces (LLSVPs) at the base of the mantle. We examine here the hypothesis that they are piles of oceanic crust that have steadily accumulated and warmed over billions of years. We use existing global geodynamic models in which dense oceanic crust forms at divergent plate boundaries and subducts at convergent ones. The model suite covers the predicted density range for oceanic crust over lower mantle conditions. To meaningfully compare our geodynamic models to tomographic structures we convert them into models of seismic wavespeed and explicitly account for the limited resolving power of tomography. Our results demonstrate that long-term recycling of dense oceanic crust naturally leads to the formation of thermochemical piles with seismic characteristics similar to the LLSVPs. The extent to which oceanic crust contributes to the LLSVPs depends upon its density in the lower mantle for which accurate data is lacking. We find that the LLSVPs are not composed solely of oceanic crust. Rather, they are basalt rich at their base (bottom 100--200~km) and grade into peridotite toward their sides and top with the strength of their seismic signature arising from the dominant role of temperature. We conclude that recycling of oceanic crust, if sufficiently dense, has a strong influence on the thermal and chemical evolution of Earth's mantle.
... Finally, in addition to the parameter choices, the degassing forcing is resampled every 10 Myrs from the uncertainty window of Mills et al. 37 . This allows for quite rapid changes in degassing rate, but not above the rates of change that have been suggested for more recent time periods 50 . ...
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The diversification of complex animal life during the Cambrian Period (541-485.4 Ma) is thought to have been contingent on an oxygenation event sometime during ~850 to 541 Ma in the Neoproterozoic Era. Whilst abundant geochemical evidence indicates repeated intervals of ocean oxygenation during this time, the timing and magnitude of any changes in atmospheric pO₂ remain uncertain. Recent work indicates a large increase in the tectonic CO₂ degassing rate between the Neoproterozoic and Paleozoic Eras. We use a biogeochemical model to show that this increase in the total carbon and sulphur throughput of the Earth system increased the rate of organic carbon and pyrite sulphur burial and hence atmospheric pO₂. Modelled atmospheric pO₂ increases by ~50% during the Ediacaran Period (635-541 Ma), reaching ~0.25 of the present atmospheric level (PAL), broadly consistent with the estimated pO₂ > 0.1-0.25 PAL requirement of large, mobile and predatory animals during the Cambrian explosion.
... Corroborating this hypothesis, the North Atlantic seafloor spreading rate (NASSR) exhibits a clear decreasing trend from high values in the Early Eocene (55-50 Myr) to a very low rate for most of the Oligocene (Mosar et al. 2002;Le Breton et al. 2012). On the other hand, recent studies seem to converge towards a significant 250-200-Myr period variation of the seafloor spreading rate Viaggi Progress in Earth and Planetary Science ( 2 0 1 8 ) 5 : 8 1 Page 27 of 37 (Becker et al. 2009;Coltice et al. 2013). Becker et al. (2009) proposed a spreading rate long-term slowdown since 140 Myr with minor cycles superimposed over time, such as a relative increase at~50 Myr and a minimum at~32 Myr. ...
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The global LR04 δ18O, the tropical ODP Site 846 sea surface temperature (SST), and the global ΔSST stack records were investigated using the advanced method for time-series decomposition singular spectrum analysis to outline the quantitative role of orbital forcings and to investigate the nonlinear dynamics of the Pliocene and Pleistocene climate system. For the first time, a detailed quantitative evaluation is provided of the δ18O and SST variance paced by long-period orbital modulation, short eccentricity, obliquity, precession, and half-precession cycles. New insights into the nonlinear dynamic of the orbital components suggest considering astronomical signals as composite feedback lagged responses paced by orbitals and damped (Early Pliocene) or amplified (Mid-Late Pleistocene) in a range of − 100 to + 400% the forcing. The Early Pliocene asymptotic decay of the δ18O and SST response sensitivity up to − 100% observed for the first time in all orbital responses is interpreted as damping effect of a wide global forest cover along with a possible high ocean primary productivity, through the CO2-related negative feedbacks during time of global greenhouse. An anomalous post-Mid-Pleistocene Transition (MPT) sharply declines to near-zero in obliquity response sensitivity observed in both global δ18O and tropical SST, suggesting an attenuation mechanism of the obliquity driving force and a reduction of the related feedback amplification processes. It is hypothesized the post-MPT obliquity damping has contributed to the strengthening of the short eccentricity response by mitigating the obliquity “ice killing”, favoring a long-life ice sheet sensitive to a synergistic ~ 100-kyr amplification of positive feedback processes during the time of a global icy state. The global δ18O, the tropical SST, and the global ΔSST trend components, all explaining ~ 76% of the Plio-Pleistocene variance and significantly modifying the mean climate state, appear to be related to the long-term pCO2 proxies, supposedly controlled by plate tectonics through the global carbon cycle (CO2 outgassing, explosive volcanism, orography and erosion, paleogeography, oceanic paleocirculation, and ocean fertilization). Finally, singular spectrum analysis provides a valuable tool in cyclostratigraphy with the remarkable advantage of separating full-resolution time series by variance strength.
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Spectral analyses of past relative sea-level oscillations as represented by the ages of 57 Phanerozoic (the last 545 Myr) stratigraphic sequence boundaries from the Canadian Arctic show a strong spectral peak at 32 Myr (>99.9% confidence). These findings concur with previous reports of significant cycles with periods of around 30 Myr in various records of fluctuations of sea level, and in potentially related episodes of tectonism, volcanism, climate, and biotic extinctions. Sequence boundaries commonly coincide with stage boundaries based on biostratigraphy, and are correlated with episodes of extinction and times of flood-basalt volcanism. The connection between tectonics and sea-level variations may come from changes in rates of ocean-floor spreading and subduction, intraplate stresses from plate-reorganizations, and pulsations of hotspot volcanism. These coordinated periodic fluctuations in tectonics, sea level and climate may be modulated by cyclical activity in the Earth’s mantle, although some pacing by astronomical cycles is suspected.
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Reconstructions of past seafloor age make it possible to quantify how plate tectonic forces, surface heat flow, ocean basin volume and global sea-level have varied through geological time. However, past ocean basins that have now been subducted cannot be uniquely reconstructed, and a significant challenge is how to explore a wide range of possible reconstructions. Here, we investigate possible distributions of seafloor ages from the late Palaeozoic to present using published full-plate reconstructions and a new, efficient seafloor age reconstruction workflow, all developed using the open-source software GPlates. We test alternative reconstruction models and examine the influence of assumed spreading rates within the Panthalassa Ocean on the reconstructed history of mean seafloor age, oceanic heat flow, and the contribution of ocean basin volume to global sea-level. The reconstructions suggest variations in mean seafloor age of ∼15 Myr during the late Palaeozoic, similar to the amplitude of variations previously proposed for the Cretaceous to present. Our reconstructed oceanic age-area distributions are broadly compatible with a scenario in which the long-period fluctuations in global sea-level since the late Palaeozoic are largely driven by changes in mean sea-floor age. Previous suggestions of a constant rate of seafloor production through time can be modeled using our workflow, but require that oceanic plates in the Palaeozoic move slower than continents based on current reconstructions of continental motion, which is difficult to reconcile with geodynamic studies.
Article
The oceanic crust that enters a subduction zone is generally recycled to great depth. In rare and punctuated episodes, however, blueschists and eclogites derived from subducted oceanic crust are exhumed. Compilations of the maximum pressure-temperature conditions in exhumed rocks indicate significantly warmer conditions than those predicted by thermal models. This could be due to preferential exhumation of rocks from hotter conditions that promote greater fluid productivity, mobility, and buoyancy. Alternatively, the models might underestimate the forearc temperatures by neglecting certain heat sources. We compare two sets of global subduction zone thermal models to the rock record. We find that the addition of reasonable amounts of shear heating leads to less than 50 °C heating of the oceanic crust compared to models that exclude this heat source. Models for young oceanic lithosphere tend to agree well with the rock record. We test the hypothesis that certain heat sources may be missing in the models by constructing a global set of models that have high arbitrary heat sources in the forearc. Models that satisfy the rock record in this manner, however, fail to satisfy independent geophysical and geochemical observations. These combined tests show that the average exhumed mafic rock record is systematically warmer than the average thermal structure of mature modern subduction zones. We infer that typical blueschists and eclogites were exhumed preferentially under relatively warm conditions that occurred due to the subduction of young oceanic lithosphere or during the warmer initial stages of subduction.
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Subduction is a fundamental mechanism of material exchange between the planetary interior and the surface. Despite its significance, our current understanding of fluctuating subducting plate area and slab volume flux has been limited to a range of proxy estimates. Here we present a new detailed quantification of subduction zone parameters from the Late Triassic to present day (230 – 0 Ma). We use a community plate motion model with evolving plate topologies to extract trench-normal convergence rates through time to compute subducting plate areas, and we use seafloor paleo-age grids to estimate the thickness of subducting lithosphere to derive the slab flux through time. Our results imply that slab flux doubled to values greater than 500 km3/yr from 180 Ma in the Jurassic to 130 Ma in the mid-Cretaceous, subsequently halving again towards the Cretaceous-Paleogene boundary, largely driven by subduction zones rimming the Pacific ocean basin. The 130 Ma spike can be attributed to a two-fold increase in mid-ocean ridge lengths following the break-up of Pangea, and a coincident increase in convergence rates, with average speeds exceeding 10 cm/yr. With one third of the total 230 - 0 Ma subducted volume entering the mantle during this short ~ 50 Myr period, we suggest this slab superflux drove a surge in slab penetration into the lower mantle and an associated increase in the vigour of mantle return flow. This mid-Cretaceous event may have triggered, or at least contributed to, the formation of the Darwin Rise mantle superswell, dynamic elevation of the South African Plateau and the plume pulse that produced the Ontong-Java-Hikurangi-Manihiki and Kerguelen plateaus, among others. The models presented here contribute to an improved understanding of the time-evolving flux of material consumed by subduction, and suggest that slab superflux may be a general feature of continental dispersal following supercontinent breakup. These insights may be useful for better understanding how supercontinent cycles are related to transient episodes of large igneous province and superswell formation, and the associated deep cycling of minerals and volatiles, as well as leading to a better understanding of tectonic drivers of long-term climate and icehouse-to-greenhouse transitions.
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A global carbon cycle model covering the Late Jurassic Period to Recent (150–0 Ma) with subaerial metamorphism and continental and oceanic hot spot volcanism was constructed. The model's results indicate that the OAE1a and Valanginian OAE (OAE: oceanic anoxic event) in the Cretaceous Period are related to increased atmospheric CO2 level due to hot spot volcanism. Furthermore, the model results based on high-resolution geochemical records demonstrate that decreases in CO2 associated with the termination of the OAE1a, OAE2, and perhaps the Valanginian OAE are attributable to a large amount of organic carbon burial. Moreover, the model results indicate that enhanced continental weathering and carbonate precipitation contributed to the decrease in atmospheric CO2 during the OAE1a period.
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Plain Language Summary The question of whether the speeds of tectonic plates vary over time is controversial but has big‐picture implications for our understanding of the forces inside the Earth that drive the plates, the role of volcanoes in controlling climate change over millions of years, and the rise and fall of sea level. At mid‐ocean ridges, two plates move apart, and the volcanic rocks that comprise the ocean crust are created. Magnetic minerals in the rocks record their age of formation and therefore the relative speeds of the diverging plates. However, this record is incomplete because seafloor is destroyed at subduction zones. We used the preserved seafloor magnetic record to calculate diverging plate speeds over the past 19 million years. We find that the relative plate speed at almost all divergent plate boundaries has slowed down, with a major inflection point at 15–16 Myr. As a result, the rate at which new ocean crust is created also slowed down, by roughly 35%. We speculate that there is not a single explanation for the nearly global slowdown in plate speeds but rather several unrelated tectonic events, such as the emergence of the Andes.
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GPlates is an open‐source, cross‐platform plate tectonic geographic information system, enabling the interactive manipulation of plate‐tectonic reconstructions and the visualization of geo‐data through geological time. GPlates allows the building of topological plate models representing the mosaic of evolving plate boundary networks through time, useful for computing plate velocity fields as surface boundary conditions for mantle convection models and for investigating physical and chemical exchanges of material between the surface and the deep Earth along tectonic plate boundaries. The ability of GPlates to visualize sub‐surface 3D scalar fields together with traditional geological surface data enables researchers to analyze their relationship through geological time in a common plate tectonic reference frame. To achieve this a hierarchical cube map framework is used for rendering reconstructed surface raster data to support the rendering of sub‐surface 3D scalar fields using graphics‐hardware‐accelerated ray‐tracing techniques. GPlates enables the construction of plate deformation zones – regions combining extension, compression and shearing that accommodate the relative motion between rigid blocks. Users can explore how strain rates, stretching/shortening factors and crustal thickness evolve through space and time, and interactively update the kinematics associated with deformation. Where datasets described by geometries (points, lines or polygons) fall within deformation regions, the deformation can be applied to these geometries. Together, these tools allow users to build virtual Earth models that quantitatively describe continental assembly, fragmentation and dispersal and are interoperable with many other mapping and modelling tools, enabling applications in tectonics, geodynamics, basin evolution, orogenesis, deep Earth resource exploration, paleobiology, paleoceanography and paleoclimate.
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Concurrent changes in seawater chemistry, sea level, and climate since the mid-Cretaceous are thought to result from an ongoing decrease in the global rate of lithosphere production at ridges. The present-day area distribution of seafloor ages, however, is most easily explained if lithosphere production rates were nearly constant during the past 180 m.y. We examined spatial gradients of present-day seafloor ages and inferred ages for the subducted Farallon plate to construct a history of spreading rates in each major ocean basin since ca. 140 Ma, revealing dramatic Cenozoic events. Globally, seafloor spreading rates increased by ˜20% during the early Cenozoic due to an increase in plate speeds in the Pacific basin. Since then, subduction of the fast-spreading Pacific-Farallon ridge system has led to a 12% decrease in average global spreading rate and an 18% or more decrease in the total rate of lithosphere production by the most conservative estimates. These rapid changes during the Cenozoic defy models of steady-state seafloor formation, and demonstrate the time-dependent and evolving nature of plate tectonics on Earth.
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Previous mantle convection studies with continents have revealed a first-order influence of continents on mantle flow, as they affect convective wavelength and surface heat loss. In this study we present 3D spherical mantle convection models with self-consistent plate tectonics and a mobile, rheologically strong continent to gain insight into the effect of a lithospheric heterogeneity (continents vs. oceans) on plate-like behaviour. Model continents are simplified as Archaean cratons, which are thought to be mostly tectonically inactive since 2.5 Ga. Long-term stability of a craton can be achieved if viscosity and yield strength are sufficiently higher than for oceanic lithosphere, confirming results from previous 2D studies. Stable cratons affect the convective regime by thermal blanketing and stress focussing at the continental margins, which facilitates the formation of subduction zones by increasing convective stresses at the margins, which allows for plate tectonics at higher yield strength and leads to better agreement with the yield strength inferred from laboratory experiments. Depending on the lateral extent of the craton the critical strength can be increased by a factor of 2 compared to results with a homogeneous lithosphere. The resulting convective regime depends on the lateral extent of the craton and the thickness ratio of continental and oceanic lithosphere: for a given yield strength a larger ratio favours plate-like behaviour, while intermediate ratios tend towards an episodic and small ratios towards a stagnant lid regime.
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Two main hypotheses compete to explain the mid-Cretaceous global sea-level highstand: a massive pulse of oceanic crustal production that occurred during the Cretaceous Normal Superchron (CNS) and the "supercontinent breakup effect," which resulted in the creation of the mid-Atlantic and Indian ocean ridges at the expense of subducting old ocean floor in the Tethys and the Pacific. We have used global oceanic paleo-age grids, including now subducted ocean floor and two alternative time scales, to test these hypotheses. Our models show that a high average seafloor spreading rate of 92 mm/a in the Early Cretaceous that decreased to 60 mm/a during the Tertiary, with peaks of 86 mm/a and 70 mm/a at 105 Ma and 75 Ma ago, respectively, correspond to the two observed sea-level highstands in the Cretaceous. Calculations using GTS2004 produce lower seafloor spreading rates during the same period and diminish the mid-Cretaceous spreading pulse. Global ridge lengths increased in the earliest Cretaceous but stayed relatively constant through time. However, we find that the average age of the ocean basins through time is only weakly dependent on the choice of time scale. The expansive mid- and Late Cretaceous epicontinental seas, coupled with warm climates and oxygen-poor water masses, were ultimately driven by the younger average age of the Cretaceous seafloor and faster seafloor spreading rather than a vast increase in mid-ocean ridge length due to the breakup of Pangea or solely by higher seafloor spreading rates, as suggested previously.
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It is widely accepted that substantial relative motion has occurred between the Indo-Atlantic and Pacific hot spots since the Late Cretaceous. At the same time, a fixed Indo-Atlantic hot spot reference frame has been argued for and used since the advent of plate tectonics, implying relatively little motion between the hot spots in this domain since about 130 Ma. Most plumes purported to have caused these hot spots, while being advected in the global-scale mantle flow field, are assumed to move an order of magnitude more slowly than plates. However, the lifetime of a plume may be over ~100 Myr, and the integrated motion of a plume is expected to be significant over these times. The uncertainties inherent in hot spot reconstructions are of a magnitude similar to the expected plume motion, and so any differences between a fixed and moving frame of reference must be discernible beyond the level of these uncertainties. We present a method for constraining hot spot reconstruction uncertainties, similar to that in use for relative plate motion. We use a modified Hellinger criterion of fit for the hot spot problem, using track geometries and radiometric dating, and derive covariance matrices for our Indo-Atlantic rotations for the last 120 Myr. However, any given mantle convection model introduces additional uncertainties into such models, based on its model parameters and starting conditions (e.g., choice of global tomography model, viscosity profile, nature of mantle phase transitions). We use an interactive evolutionary approach, where we constrain the hot spot motion resulting from convection models to fit paleomagnetic constraints, and converge on an acceptable motion solution by varying unknowns over several generations of simulations. Our hot spot motion model shows large motion (5-10°) of the Indo-Atlantic hot spots for times >80 Ma, consistent with available paleomagnetic constraints. The differences between the fixed and moving hot spot reference frames are not discernible over the level of uncertainty in such rotations for times
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We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge-push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.
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Global plate motion models provide a spatial and temporal framework for geological data and have been effective tools for exploring processes occurring at the earth's surface. However, published models either have insufficient temporal coverage or fail to treat tectonic plates in a self-consistent manner. They usually consider the motions of selected features attached to tectonic plates, such as continents, but generally do not explicitly account for the continuous evolution of plate boundaries through time. In order to explore the coupling between the surface and mantle, plate models are required that extend over at least a few hundred million years and treat plates as dynamic features with dynamically evolving plate boundaries. We have constructed a new type of global plate motion model consisting of a set of continuously-closing topological plate polygons with associated plate boundaries and plate velocities since the break-up of the supercontinent Pangea. Our model is underpinned by plate motions derived from reconstructing the seafloor-spreading history of the ocean basins and motions of the continents and utilizes a hybrid absolute reference frame, based on a moving hotspot model for the last 100 Ma, and a true-polar wander corrected paleomagnetic model for 200 to 100 Ma. Detailed regional geological and geophysical observations constrain plate boundary inception or cessation, and time-dependent geometry. Although our plate model is primarily designed as a reference model for a new generation of geodynamic studies by providing the surface boundary conditions for the deep earth, it is also useful for studies in disparate fields when a framework is needed for analyzing and interpreting spatio-temporal data.
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1] We present four companion digital models of the age, age uncertainty, spreading rates, and spreading asymmetries of the world's ocean basins as geographic and Mercator grids with 2 arc min resolution. The grids include data from all the major ocean basins as well as detailed reconstructions of back-arc basins. The age, spreading rate, and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments. The age uncertainties for grid cells coinciding with marine magnetic anomaly identifications, observed or rotated to their conjugate ridge flanks, are based on the difference between gridded age and observed age. The uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities. Asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges, resulting in ridge jumps toward hot spots. We also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age-depth relationships. The new set of grids helps to investigate prominent negative depth anomalies, which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow. A combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems. Components: 10,219 words, 12 figures.
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Subduction zones on present-day Earth are strongly asymmetric features (Zhao 2004) composed of an overriding plate above a subducting plate that sinks into the mantle. While global self-consistent numerical models of mantle convection have reproduced some aspects of plate tectonics (e.g. Tackley 2000, van Heck & Tackley 2008), the assumptions behind these models do not allow for realistic single-sided subduction. Here we demonstrate that the asymmetry of subduction results from two major features of terrestrial plates: (1) the presence of a free deformable upper surface and (2) the presence of weak hydrated crust atop subducting slabs. We show that by implementing a free surface on the upper boundary of a global numerical model instead of the conventional free-slip condition, the dynamical behaviour at convergent plate boundaries changes from double-sided to single-sided. Including a weak crustal layer further improves the behaviour towards steady single-sided subduction by acting as lubricating layer between the sinking plate and overriding plate. For this study we perform experiments in 2-D and global 3-D spherical, fully dynamic mantle convection models with self-consistent plate tectonics. These are calculated using the finite volume multigrid code StagYY (Tackley 2008) with strongly temperature and pressure-dependent viscosity, ductile and/or brittle plastic yielding, and non-diffusive tracers tracking compositional variations (the 'air' and the weak crustal layer in this case). The free surface is implemented using a "sticky air" layer, which is proven to be a good approximation if its thickness and its viscosity are sufficiently high and low, respectively (Schmeling et al., 2008; Crameri et al., submitted). In conclusion, a free surface is the key ingredient to cause single-sided subduction, while a weak crustal layer does not cause single-sided subduction on its own, but helps to stabilise on-going subduction.
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Fundamental issues in our understanding of plate and mantle dynamics remain unresolved, including the rheology and state of stress of plates and slabs; the coupling between plates, slabs and mantle; and the flow around slabs. To address these questions, models of global mantle flow with plates are computed using adaptive finite elements, and compared to a variety of observational constraints. The dynamically consistent instantaneous models include a composite rheology with yielding, and incorporate details of the thermal buoyancy field. Around plate boundaries, the local resolution is 1 km, which allows us to study highly detailed features in a globally consistent framework. Models that best fit plateness criteria and plate motion data have strong slabs with high stresses. We find a strong dependence of global plate motions, trench rollback, net rotation, plateness, and strain rate on the stress exponent in the nonlinear viscosity; the yield stress is found to be important only if it is smaller than the ambient convective stress. Due to strong coupling between plates, slabs, and the surrounding mantle, the presence of lower mantle anomalies affect plate motions. The flow in and around slabs, microplate motion, and trench rollback are intimately linked to the amount of yielding in the subducting slab hinge, slab morphology, and the presence of high viscosity structures in the lower mantle beneath the slab.
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The Taylor (2006) hypothesis suggesting a common origin for the Ontong Java, Manihiki, and Hikurangi large igneous provinces provides an opportunity for a quantitative reconstruction and reassessment of the Ontong Java–Louisville hotspot connection. Our plate tectonic reconstructions of the three plateaus into Ontong Java Nui, or greater Ontong Java, combined with models for Pacific absolute plate motion (APM), allow an analysis of this connection. A new survey of the central Ellice Basin confirms easterly fracture zones, northerly abyssal hill fabric, as well as an area of sigmoidally-southeast-trending fracture zones associated with a late-stage spreading reorientation. From the fracture zone trends we derive new rotation poles for a two-stage model of Ellice Basin opening between the Ontong Java and Manihiki Plateaus. We use these and a single stage pole for separation of the Manihiki and Hikurangi Plateaus, together with three different Pacific APMs, to reconstruct the Ontong Java Nui super plateau back to 123 Ma and compare its predicted location with paleolatitude data obtained from the Ontong Java and Manihiki plateaus. Discrepancies between our Ontong Java Nui reconstructions and Ontong Java and Manihiki paleolatitudes are largest for the fixed Pacific hotspot APM. Assuming a Louisville hotspot source for Ontong Java Nui, remaining disparity between Ontong Java Nui's paleo-location at 123 Ma and published paleomagnetic latitudes for Ontong Java plateau imply that 8°–19° of Louisville hotspot drift or true polar wander may have occurred since the formation of Ontong Java Nui. However, the older portions of the Pacific APMs could easily be biased by a similar amount, making a firm identification of the dominant source of misfit difficult. Prior studies required a combined 26° of hotspot drift, octupole bias effects, and true polar wander just to link the Ontong Java Plateau to Louisville. Consequently, we suggest the super plateau hypothesis and our new reconstructions have considerably strengthened the case for a Louisville plume origin for Ontong Java Nui.
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One of the primary measures of plate tec- tonics is the history of production of new oceanic lithosphere. As shown by B. Par- sons, a direct estimate of the rate of plate creation can be derived from the area/age versus age distribution of the modern oce- anic lithosphere. Inversion of the most re- cent area versus age data (digital isochrons by R.D. Muller et al.) yields a result that the rate of oceanic plate production has not varied significantly since 180 Ma from a mean rate of 3.4 km 2 /yr. Reconstruction of the cumulative area of subducted litho- sphere over the past 90 m.y. is in excellent agreement with a fixed rate of ridge pro- duction. The conclusion that the rate of ridge production has not varied significant- ly contrasts markedly with most existing es- timates in which the rate is modeled as de- creasing by 50% or more since ca. 100 Ma. A constant rate of ridge production has im- portant implications for models of sea level and p(CO2), among other phenomena that have been linked to variations in global rates of seafloor spreading.
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The distribution of seafloor ages determines fundamental characteristics of Earth such as sea level, ocean chemistry, tectonic forces, and heat loss from the mantle. The present-day distribution suggests that subduction affects lithosphere of all ages, but this is at odds with the theory of thermal convection that predicts that subduction should happen once a critical age has been reached. We used spherical models of mantle convection to show that plate-like behavior and continents cause the seafloor area-age distribution to be representative of present-day Earth. The distribution varies in time with the creation and destruction of new plate boundaries. Our simulations suggest that the ocean floor production rate previously reached peaks that were twice the present-day value.
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The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work and fit the seismologically determined core density and inner-core boundary density jump. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection; the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.
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A new version of global and regional palaeogeographic maps is presented for two time intervals. These maps depict the plate tectonic configuration, palaeoenvironment and lithofacies during the Late Triassic (Carnian–Norian) and Early Jurassic (Hettangian–Toarcian) time. The individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the Absaroka sequence of Sloss. During Triassic time Pangaea began to stretch, initiating the rifting and future break-up of the supercontinent. The continued northward drift of the Cimmerian continent corresponded with the progressive closure and consumption of Palaeotethys oceanic crust, and the opening of the Neotethys Ocean. The most significant Late Triassic convergent event was the Indosinian orogeny, occurring as a result of the consolidation of South China and North China blocks. Also, Indochina and Indonesia were sutured to South China. At the same time the Qiangtang block approached the Eurasian margin. The consolidation of the North Chinese and Amurian blocks left open a large embayment of Panthalassa, between Amuria and Laurasia, the so-called Mongol-Okhotsk Ocean. Active subduction existed along the margin of this ocean, dipping cratonwards towards East Siberia. The last collisional events of the Uralian orogeny took place during the Triassic and Early Jurassic time. The conclusion of the Uralian orogeny was accompanied by uplift of the adjacent areas of Eastern Europe and Western Siberia. During the Early Jurassic the Palaeotethys Ocean was finally closed and the Cimmerian continent collided with Asia causing the Cimmerian orogeny. The time around the Triassic–Jurassic boundary marked an important biotic extinction event. Plate tectonic activity caused palaeogeographic and palaeoclimatic change, which may have contributed to the mass extinction. From the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction: 1) the closure of Palaeotethys and assembly of the Asian part of Pangaea; 2) the break-up of Pangaea in the future Central Atlantic area and transition from rifting to drifting; and 3) the very extensive basaltic volcanism of the Central Atlantic Magmatic Province.
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We developed a plate tectonic model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean spreading rates and major tectonic and magmatic events. Plates were constructed through time by adding/removing oceanic material, symbolized by synthetic isochrons, to major continents and terranes. Driving forces like slab pull and slab buoyancy were used to constrain the evolution of paleo-oceanic domains. This approach offers good control of sea-floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained, due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean–Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys–Atlantic domain versus the NeoTethys domain.
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1988.02 In this paper we present nine reconstructions for the Mesozoic and Cenozoic, based on previously published sea-floor spreading isochrons∗. The purpose of this study was 1.(1) to determine if the isochrons could be refitted to produce accurate plate tectonic reconstructions2.(2) to identify areas of apparent mismatch between magnetic isochrons as a focus for further investigations, and3.(3) to test the capabilities and accuracy of interactive computer graphic methods of plate tectonic reconstruction.In general, Tertiary and Late Cretaceous isochrons could be refitted with little overlap and few gaps; however, closure errors were apparent in the vicinity of the Bouvet and Macquarie triple junctions. It was not possible to produce Early Cretaceous reconstructions that were consistent with the previously published isochrons. In this paper we also propose that the Late Cretaceous and Early Tertiary plate reorganizations observed in the Indian Ocean were the result of the progressive subduction of an intra-Tethyan rift system.
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Oceanic plateaus are mafic igneous provinces commonly thought to derive from ascending mantle plumes. By far the largest, the Ontong Java Plateau (OJP) was emplaced ca. 120 Ma, with a much smaller magmatic pulse of ca. 90 Ma. Of similar age and composition, the Manihiki and Hikurangi Plateaus (MP and HP) are separated from the OJP by ocean basins formed during the Cretaceous long normal magnetic period. I present new seafloor fabric data that indicate the three plateaus formed as one (OJMHP). The data support previous interpretations that the Osbourn Trough is the relict of the spreading center that separated the MP and HP but they require a different interpretation than prevailing tectonic models for the Ellice Basin. Closely spaced, large offset, fracture zones in the Ellice Basin bound former right-stepping spreading segments that separated the OJP and MP. The MP was emplaced near the axis of the Pacific–Phoenix ridge and additional plateau fragments formerly bordered its eastern margins. Following OJMHP break-up, seafloor spreading removed these fragments to the east and SSE, together with the symmetric conjugates to the extant Phoenix magnetic lineations.
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Recent results from seismic tomography demonstrate that subducted oceanic lithosphere can be observed globally as slabs of relatively high seismic velocity in the upper as well as lower mantle(1,2). The Asian mantle is no exception, with high-velocity slabs being observed downwards from the west Pacific subduction zones under the Kurile Islands, Japan and farther south(3-5), as well as under Asia's ancient Tethyan margin. Here we present evidence for the presence of slab remnants of Jurassic age that were subducted when the Mongol-Okhotsk and Kular-Nera oceans closed between Siberia, the combined Mongolia-North China blocks and the Omolon block(6-8). We identify these proposed slab remnants in the lower mantle west of Lake Baikal down to depths of at least 2,500 km, where they join what has been interpreted as a 'graveyard'(9) of subducted lithosphere at the bottom of the mantle. Our interpretation implies that slab remnants in the mantle can still be recognized some 150 million years or more after they have been subducted and that such structures may be useful in associating geodynamic to surface-tectonic processes. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/62524/1/397246a0.pdf
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The motion of continents relative to the Earth's spin axis may be due either to rotation of the entire Earth relative to its spin axis--true polar wander--or to the motion of individual plates. In order to distinguish between these over the past 320 Myr (since the formation of the Pangaea supercontinent), we present here computations of the global average of continental motion and rotation through time in a palaeomagnetic reference frame. Two components are identified: a steady northward motion and, during certain time intervals, clockwise and anticlockwise rotations, interpreted as evidence for true polar wander. We find approximately 18 degrees anticlockwise rotation about 250-220 Myr ago and the same amount of clockwise rotation about 195-145 Myr ago. In both cases the rotation axis is located at about 10-20 degrees W, 0 degrees N, near the site that became the North American-South American-African triple junction at the break-up of Pangaea. This was followed by approximately 10 degrees clockwise rotation about 145-135 Myr ago, followed again by the same amount of anticlockwise rotation about 110-100 Myr ago, with a rotation axis in both cases approximately 25-50 degrees E in the reconstructed area of North Africa and Arabia. These rotation axes mark the maxima of the degree-two non-hydrostatic geoid during those time intervals, and the fact that the overall net rotation since 320 Myr ago is nearly zero is an indication of long-term stability of the degree-two geoid and related mantle structure. We propose a new reference frame, based on palaeomagnetism, but corrected for the true polar wander identified in this study, appropriate for relating surface to deep mantle processes from 320 Myr ago until hotspot tracks can be used (about 130 Myr ago).
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Our understanding of the dynamics of plate motions is based almost entirely upon modeling of present-day plate motions. A fuller understanding, however, can be derived from consideration of the history of plate motions. Here we investigate the kinematics of the last 120 Myr of plate motions and the dynamics of Cenozoic motions, paying special attention to changes in the character of plate motions and plate-driving forces. We analyze the partitioning of the observed surface velocity field into toroidal (transform/spin) and poloidal (spreading/subduction) motions. The present-day field is not equipartitioned in poloidal and toroidal components; toroidal motions account for only one third of the total. The toroidal/poloidal ratio has changed substantially in the last 120 Myr with poloidal motion decreasing significantly after 43 Ma while toroidal motion remains essentially constant; this result is not explained by changes in plate geometry alone. We develop a self-consistent model of plate motions by (1) constructing a straightforward model of mantle density heterogeneity based largely upon subduction history and then (2) calculating the induced plate motions for each stage of the Cenozoic. The “slab” heterogeneity model compares rather well with seismic heterogeneity models, especially away from the thermochemical boundary layers near the surface and core-mantle boundary. The slab model predicts the observed geoid extremely well, although comparison between predicted and observed dynamic topography is ambiguous. The midmantle heterogeneities that explain much of the observed seismic heterogeneity and geoid are derived largely from late Mesozoic and early Cenozoic subduction, when subduction rates were much higher than they are at present. The plate motion model itself successfully predicts Cenozoic plate motions (global correlations of 0.7–0.9) for mantle viscosity structures that are consistent with a variety of geophysical studies. We conclude that the main plate-driving forces come from subducted slabs (>90%), with forces due to lithospheric effects (e.g., oceanic plate thickening) providing a very minor component (<10%). For whole mantle convection, most of the slab buoyancy forces are derived from lower mantle slabs. Unfortunately, we cannot reproduce the toroidal/poloidal partitioning ratios observed for the Cenozoic, nor do our models explain apparently sudden plate motion changes that define stage boundaries. The most conspicuous failure is our inability to reproduce the westward jerk of the Pacific plate at 43 Ma implied by the great bend in the Hawaiian-Emperor seamount chain. Our model permits an interesting test of the hypothesis that the collision of India with Asia may have caused the Hawaiian-Emperor bend. However, we find that this collision has no effect on the motion of the Pacific plate, implying that important plate boundary effects are missing in our models. Future progress in understanding global plate motions requires (1) more complete plate reconstruction information, including, especially, uncertainty estimates for past plate boundaries, (2) better treatment of plate boundary fault mechanics in plate motion models, (3) application of numerical convection models, constrained by global plate motion histories, to replace ad hoc mantle heterogeneity models, (4) better calibration of these heterogeneity models with seismic heterogeneity constraints, and (5) more comprehensive comparison of global plate/mantle dynamics models with geologic data, especially indicators of intraplate stress and strain, and constraints on dynamic topography derived from the stratigraphic record of sea level change.
Article
The distribution of area of the ocean floor with age, t, is approximately described by dA/dt=C0(1-(t/tm)), where C0 is the rate of crustal generation and tm the maximum age. A linear differential area versus age relation can be explained by a balance between generation and consumption where consumption is uniformly distributed with age. The present distribution of consumption with age was estimated from the isochron map used to derive the area-age relation and a recently published set of angular velocity vectors describing present plate motions. The trenches appear to be distributed randomly with respect to age provinces in the oceans. Changes in the rate of plate generation and the distribution of consumption with age result in shifts in the area-age distribution. In turn, these shifts produce changes in the plate driving forces which act to restore the rate of plate generation and distribution of consumption to their initial states. This coupling between driving forces and the area-age distribution provides a feedback mechanism limiting the extent of any changes. A measure of the magnitude of shifts in the area-age distribution is given by global changes in sea level. The area-age relation can be combined with simple expressions for depth and heat flow versus age to obtain an empirical hypsometric distribution, parameterized in terms of age, and exact expressions for the heat loss from the ocean floor.-Author
A set of east-trending magnetic anomalies located in the western equatorial Pacific Ocean near the Phoenix Islands is Early Cretaceous in age. The use of magnetic reversal model studies shows that this lineated anomaly pattern correlates with one east of Japan that trends east, and with one west of Hawaii that trends northwest. These patterns were formed in their present relative positions, but about 40° (4,500 km) south of their present geographic locations. The configuration of these three contemporaneous sets of magnetic anomalies implies that the Late Mesozoic tectonic pattern consisted of five spreading centers joined at two triple points. In this interpretation, the oldest part of the Pacific Ocean lies just east of the Mariana Trench and is Early Jurassic in age. This Mesozoic system evolved into the Cenozoic spreading pattern recorded in the eastern Pacific Ocean. The details of this transition are open to speculation because it occurred during a period in the Late Cretaceous that lacked magnetic reversals. We propose a model that suggests the northern triple point jumped southeast about 2,000 km at 100 m.y. B.P., and that the Emperor Trough was a transform fault of large offset during the Late Cretaceous. The southern triple point migrated rapidly toward the south-southeast, approximately parallel to the Eltanin Fracture Zone-Louisville Ridge complex that we extend o t the westernmost of the Phoenix lineation fracture zones.