Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Supercontinents like Pangea impose a first-order control on Earth's evolution as they modulate global heat loss, sea level, climate and biodiversity. In a traditional view, supercontinents form and break-up in a regular, perhaps periodic, manner in a cycle lasting several 100Myr as reflected in the assembly times of Earth's major continental aggregations: Columbia, Rodinia and Pangea. However, modern views of the supercontinent cycle propose a more irregular evolution on thebasis of an improved understanding of the Precambrian geologic record. Here, we use fully dynamic spherical mantle convection models featuring plate-like behavior and continental drift to investigate supercontinent formation and break-up. We further dismiss the concept of regularity, but suggest a statistical cyclicity in which the supercontinent cycle may have a characteristic period imposed by mantle and lithosphere properties, but this is hidden in immense fluctuations between different cycles that arise from the chaotic nature of mantle flow.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... A number of authors used numerical modeling techniques to study the nonlinear influence of mantle convection on a supercontinent cycle. 2D models were used by Gurnis [11], Lowman and Jarvis [12], Lowman and Jarvis [13], Trubitsyn and Bobrov [14], Lowman and Jarvis [15], Honda et al. [16], Butler and Jarvis [17], Bobrov and Trubitsyn [18], Neil et al. [19], Heron and Lowman [20], Lobkovsky et al. [21], Rolf et al. [22], Trim and Lowman [23], Dal Zilio et al. [24], Kameyama and Harada [25], Bobrov and Baranov [26,27], Jain et al. [28], Mao et al. [29], and others. 3D mantle convection models were used to investigate the supercontinent cycle by Rykov and Trubitsyn [30], Lowman and Gable [31], Yoshida et al. [32], Honda et al. [16], Phillips and Bunge [33], Phillips and Bunge [34], Zhong et al. [35], Li and Zhong [36], Zhang et al. [37] , 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Yoshida [38], Yoshida [39], Heron and Lowman [20], Yoshida [40], Yoshida [41], Yoshida and Santosh [42], Lobkovsky and Kotelkin [43], Zhang et al. [44], Mao et al. [29], Yoshida [45] and others. ...
... Rolf et al. [22], Phillips and Bunge [34], and Bobrov and Baranov [27] demonstrated the existence of irregularities in the supercontinent cycle. For the supercontinent, typical shear stresses change in a wide range of 50e200 MPa. ...
... There is no substantial temperature difference between the subcontinental and suboceanic mantles (temperature anomaly max þ50 C under supercontinent). 21 Rolf et al. [22] Spherical annulus (2-D), spherical shell, Ra ¼ 2.05 Â 10 7 , selfconsistently generated oceanic plates. The continents are modelled as a compositionally buoyant tracers with weak continental margins. ...
Article
Full-text available
We investigate the evolution of stress fields during the supercontinent cycle using the 2D Cartesian geometry model of thermochemical convection with the non-Newtonian rheology in the presence of floating deformable continents. In the course of the simulation, the supercontinent cycle is implemented several times. The number of continents considered in our model as a function of time oscillates around 3. The lifetime of a supercontinent depends on its dimension. Our results suggest that immediately before a supercontinent breakup, the over-lithostatic horizontal stresses in it (referring to the mean value by the computational area) are tensile and can reach −250 MPa. At the same time, a vast area beneath a supercontinent with an upward flow exhibits clearly the over-lithostatic compressive horizontal stresses of 50–100 МРа. The reason for the difference in stresses in the supercontinent and the underlying mantle is a sharp difference in their viscosity. In large parts of the mantle, the over-lithostatic horizontal stresses are in the range of ±25 MPa, while the horizontal stresses along subduction zones and continental margins are significantly larger. During the process of continent-to-continent collisions, the compressive stresses can approximately reach 130 MPa, while within the subcontinental mantle, the tensile over-lithostatic stresses are about −50 MPa. The dynamic topography reflects the main features of the supercontinent cycle and correlates with real ones. Before the breakup and immediately after the disintegration of the supercontinent, continents experience maximum uplift. During the supercontinent cycle, topographic heights of continents typically vary within the interval of about ±1.5 km, relatively to a mean value. Topographic maxima of orogenic formations to about 2–4 km are detected along continent-to-continent collisions as well as when adjacent subduction zones interact with continental margins.
... In this study, we investigate the prerift, synrift, and postrift dynamics of continental extension using 2-D spherical annulus models of mantle convection with continents. Similar models have been previously used to study supercontinent cyclicity statistically (Rolf et al., 2014), but here we focus on the dynamics of rifting. In contrast to previous regional rift models, our simulations avoid the necessity to impose lateral boundary conditions so that rifting develops self-consistently as a response to the overall dynamics of the system. ...
... Decreasing the internal heating and thus increasing the strength of the plumes might result in plume-induced rifting (Koptev et al., 2015). Also, rifting might be facilitated by having weak continental margins (Rolf et al., 2014) while here we assume them to have the same rigidity as the continental interior. Timing of rifting is related to the mantle structures such as size of convective cells (Rolf et al., 2014) that are probably larger here compared to the Earth due to the lower convective vigor, which lead us to employ a transit time framework to scale the results and compare them to observations. ...
... Also, rifting might be facilitated by having weak continental margins (Rolf et al., 2014) while here we assume them to have the same rigidity as the continental interior. Timing of rifting is related to the mantle structures such as size of convective cells (Rolf et al., 2014) that are probably larger here compared to the Earth due to the lower convective vigor, which lead us to employ a transit time framework to scale the results and compare them to observations. Employing standard scaling using the diffusive time would result in ∼4 times lower rift velocities, while simultaneously leading to ∼4 times longer durations of each rift phase. ...
Preprint
Relative plate motions during continental rifting result from the interplay of local with far-field forces. Here, we study the dynamics of rifting and breakup using large-scale numerical simulations of mantle convection with self-consistent evolution of plate boundaries. We show that continental separation follows a characteristic evolution with four distinctive phases: (1) An initial slow rifting phase with low divergence velocities and maximum tensional stresses, (2) a syn-rift speed-up phase featuring an abrupt increase of extension rate with a simultaneous drop of tensional stress, (3) the breakup phase with inception of fast seafloor spreading and (4) a deceleration phase occurring in most but not all models where extensional velocities decrease. We find that the speed-up during rifting is compensated by subduction acceleration or subduction initiation even in distant localities. Our study illustrates new links between local rift dynamics, plate motions and subduction kinematics during times of continental separation.
... In this study, we investigate the pre-, syn-, and post-rift dynamics of continental extension using 2D spherical annulus models of mantle convection with continents. Similar models have been previously used to study supercontinent cyclicity statistically [Rolf et al., 2014] but here, we focus on the dynamics of rifting. In contrast to previous regional rift models, our simulations avoid the necessity to impose lateral boundary conditions so that rifting develops self-consistently as a response to the overall dynamics of the system. ...
... Decreasing the internal heating and thus increasing the strength of the plumes might result in plume-induced rifting [Koptev et al., 2015]. Also, rifting might be facilitated by having weak continental margins [Rolf et al., 2014] while here we assume them to have the same rigidity as the continental interior. Timing of rifting is related to the mantle structures such as size of convective cells [Rolf et al., 2014] These changes in plate motion are expected to be mirrored elsewhere either by enhanced convergence rates at an existing trench or through initiation of a new subduction zone. ...
... Also, rifting might be facilitated by having weak continental margins [Rolf et al., 2014] while here we assume them to have the same rigidity as the continental interior. Timing of rifting is related to the mantle structures such as size of convective cells [Rolf et al., 2014] These changes in plate motion are expected to be mirrored elsewhere either by enhanced convergence rates at an existing trench or through initiation of a new subduction zone. ...
Article
Full-text available
Relative plate motions during continental rifting result from the interplay of local with far-field forces. Here, we study the dynamics of rifting and breakup using large-scale numerical simulations of mantle convection with self-consistent evolution of plate boundaries. We show that continental separation follows a characteristic evolution with four distinctive phases: (1) An initial slow rifting phase with low divergence velocities and maximum tensional stresses, (2) a syn-rift speed-up phase featuring an abrupt increase of extension rate with a simultaneous drop of tensional stress, (3) the breakup phase with inception of fast seafloor spreading and (4) a deceleration phase occurring in most but not all models where extensional velocities decrease. We find that the speed-up during rifting is compensated by subduction acceleration or subduction initiation even in distant localities. Our study illustrates new links between local rift dynamics, plate motions and subduction kinematics during times of continental separation.
... Gurnis, 1988;Lowman and Gable, 1999;Lenardic et al., 2003;Phillips and Bunge, 2005;Zhong et al., 2007) are capable of revealing the feedback between continents, plates, and interior dynamics through space and time. Only recently, however, have such models reached a stage in which these components of the plate-mantle system are linked fully consistently in a time-dependent geodynamic framework (Yoshida, 2013;Yoshida and Santosh, 2014;Yoshida and Hamano, 2015;Rolf et al., 2012;Rolf et al., 2014). ...
... Numerical solutions of mantle convection with self-consistently generated plate-like behaviour and continental drift obtained with the code StagYY (Tackley, 2008) are used to investigate the interplay between continental drift and mantle-lithosphere rheology. The model is an advancement of previous versions, which are described in more detail elsewhere (Rolf et al., , 2014. The model reproduces the evolution of thermochemical mantle convection in a Table 1 List of reference parameters used to convert non-dimensional model parameters and results into dimensional units (see Appendix A). ...
... The former is defined by the viscosity ratio Dg C k of material k and the reference material at given temperature and depth. The latter is defined accordingly via the yield stress ratio Ds Y k (see Rolf et al., 2014). The effective temperature (T), depth (d), composition (C), and strain-rate (4) dependent viscosity g is given by ...
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.
... Global tectonics is a surface expression of mantle convection (Bercovici, 2003): the motions of continents and seafloor are generated by forces acting within the mantle and the lithosphere. For example, Ricard et al. (1989) and convection draws continents to aggregate (Zhong, 2001;Rolf et al., 2014). ...
... For almost a decade, 3-D spherical mantle convection models have shown the capability to self-consistently produce plate-like tectonics at their surface (Walzer & Hendel, 2008;Van Heck & Tackley, 2008;Yoshida, 2008;Foley & Becker, 2009). These models physically link surface tectonics comparable to that of the Earth to mantle convection processes (Coltice et al., 2012;Rolf et al., 2014;Mallard et al., 2016). In Bocher et al. (2016), we took advantage of this link to build a sequential data assimilation algorithm able to integrate plate reconstructions into a mantle convection code while taking into account the uncertainties on those plate tectonic reconstructions. ...
... Richards et al., 2001;Walzer & Hendel, 2008;Van Heck & Tackley, 2008;Yoshida, 2008;Foley & Becker, 2009). Further work has also involved the statistical comparison of the surface dynamics of this type of models with plate tectonics reconstructions (Coltice et al., 2012(Coltice et al., , 2013Rolf et al., 2014;Mallard et al., 2016). Finally, they have recently been used to reconstruct mantle circulation using the semi-empirical sequential method (Bello et al., 2015;Coltice, in prep). ...
Thesis
Full-text available
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.
... In addition, we consider the thermochemical convection only in a half of two-dimensional spherical annulus, not in a full annulus. We also employed a single continental lid, which is a crude assumption compared with sophisticated models of continental drift above the convecting mantle, which include multiple lids (e.g., [26][27][28]). ...
... Although our result highlights a crucial role of chemical heterogeneity in the deep mantle in the supercontinent cycle, several earlier studies obtained its occurrence in the numerical models without the effect of thermochemical convection (e.g., [26][27][28]50]). Among them, Zhong and coworkers proposed an idea called the "1-2-1 model" [1,32], which delineates the relations between the supercontinent cycle and the associated changes in the convective patterns in the mantle. ...
... The importance of chemical heterogeneities in the deep mantle on the supercontinent cycle also enables us to understand the reason why several earlier studies obtained its occurrence in the numerical models without the effect of thermochemical convection (e.g., [26][27][28]50]). These earlier models employed an abrupt change in viscosity at the 660-km discontinuity between the upper and lower mantle. ...
Article
Full-text available
In this study, we conduct numerical simulations of thermochemical mantle convection in a 2D spherical annulus with a highly viscous lid drifting along the top surface, in order to investigate the interrelation between the motion of the surface (super)continent and the behavior of chemical heterogeneities imposed in the lowermost mantle. Our calculations show that assembly and dispersal of supercontinents occur in a cyclic manner when a sufficient amount of chemically-distinct dense material resides in the base of the mantle against the convective mixing. The motion of surface continents is significantly driven by strong ascending plumes originating around the dense materials in the lowermost mantle. The hot dense materials horizontally move in response to the motion of continents at the top surface, which in turn horizontally move the ascending plumes leading to the breakup of newly-formed supercontinents. We also found that the motion of dense materials in the base of the mantle is driven toward the region beneath a newly-formed supercontinent largely by the horizontal flow induced by cold descending flows from the top surface occurring away from the (super)continent. Our findings imply that the dynamic behavior of cold descending plumes is the key to the understanding of the relationship between the supercontinent cycle on the Earth’s surface and the thermochemical structures in the lowermost mantle, through modulating not only the positions of chemically-dense materials, but also the occurrence of ascending plumes around them.
... Yoshida & Santosh, 2011). As an example it is worth mentioning the work of Rolf, Coltice & Tackley (2014) that, using 2D and 3D dynamic numerical models, dismissed the existence of regularity in the dispersion and aggregation of supercontinents, suggesting instead a statistical cyclicity with a characteristic period imposed by mantle and lithosphere properties (see also Section 8, Autocyclicity). According to these authors, such a characteristic period is hidden in the immense fluctuations between different cycles that arise from the chaotic nature of mantle convection. ...
... The same models showed that stronger or weaker plates promote longer supercycles: stronger plates by hampering supercontinent break-up and thus giving origin to longer periods of aggregation, and weaker plates by sustaining longer periods of dispersion. Rolf, Coltice & Tackley (2014) also showed statistically that a dispersed configuration can be maintained for up to 2 Ga and argued that this could be a consequence of the higher degrees of freedom in a dispersed configuration, as suggested by Gurnis (1988). However, such long cycles appear to be at odds with natural observations, suggesting the importance of other factors that might not have been tested in these models. ...
... It should be noted that our conceptual view implies that plate tectonics and mantle convection behave in some sort of autocyclic manner and that Wilson cycles and supercycles are the manifestation of a quasi-periodic variation in states of convergentness and divergentness. Rolf, Coltice & Tackley (2014) using global dynamic numerical models showed that a statistical cyclicity should exist in an Earth-like system with mantle convection, plate tectonics and continental drift. Several previous works suggested cycles with lifetimes of 500 to 1 Ga, or longer, depending on parameters such as the strength of the lithosphere, viscosity and temperature of the mantle, and number of continents, among several others factors. ...
Article
Full-text available
Subduction initiation is a cornerstone in the edifice of plate tectonics. It marks the turning point of the Earth’s Wilson cycles and ultimately the supercycles as well. In this paper, we explore the consequences of subduction zone invasion in the Atlantic Ocean, following recent discoveries at the SW Iberia margin.We discuss a buoyancy argument based on the premise that old oceanic lithosphere is unstable for supporting large basins, implying that it must be removed in subduction zones. As a consequence, we propose a new conceptual model in which both the Pacific and the Atlantic oceans close simultaneously, leading to the termination of the present Earth’s supercycle and to the formation of a new supercontinent, which we name Aurica. Our new conceptual model also provides insights into supercontinent formation and destruction (supercycles) proposed for past geological times (e.g. Pangaea, Rodinia, Columbia, Kenorland).
... The effects of varying convection simulation parameters are generally investigated a few at a time by running multiple simulations (e.g. Deschamps and Tackley, 2008;Lenardic and Crowley, 2012;Rolf et al., 2014). Conducted on a larger scale, this sampling can be used for sampling-based inversion. ...
... Moresi and Solomatov, 1998;Valencia et al., 2007;van Heck and Tackley, 2011;Lenardic and Crowley, 2012), and when continents are present, the strength is a factor in determining the wave-length of convective flow (e.g. Zhong et al., 2007;Rolf et al., 2014). ...
Article
Full-text available
The results of mantle convection simulations are fully determined by the input parameters and boundary conditions used. These input parameters can be for initialisation, such as initial mantle temperature, or can be constant values, such as viscosity exponents. However, knowledge of Earth-like values for many input parameters are very poorly constrained, introducing large uncertainties into the simulation of mantle flow. Convection is highly non-linear, therefore linearised inversion methods cannot be used to recover past configurations over more than very short periods of time, which makes finding both initial and constant simulation input parameters very difficult. In this paper, we demonstrate a new method for making inferences about simulation input parameters from observations of the mantle temperature field after billions of years of convection. The method is fully probabilistic. We use prior sampling to construct probability density functions for convection simulation input parameters, which are represented using neural networks. Assuming smoothness, we need relatively few samples to make inferences, making this approach much more computationally tractable than other probabilistic inversion methods. As a proof of concept, we show that our method can invert the amplitude spectra of temperature fields from 2D convection simulations, to constrain yield stress, surface reference viscosity and the initial thickness of primordial material at the CMB, for our synthetic test cases. The best constrained parameter is yield stress. The reference viscosity and initial thickness of primordial material can also be inferred reasonably well after several billion years of convection.
... Also, previous studies of full stress distribution in the continental lithosphere during supercontinent break-up were mainly limited to twodimensional (2D) models (e.g., Ulvrova et al., 2019). More importantly, the effects of preexisting orogens (or mobile belts, e.g., Nyblade & Robinson, 1994) in the supercontinent on stress distribution and timing of break-up have not been thoroughly addressed (Yoshida, 2013; 2014a; Rolf et al., 2014;Ulvrova et al., 2019). ...
... To analyze the relationship between changes in mantle thermal state and the supercontinent break-up (Rolf et al., 2014;Yoshida, 2013), we examine the evolution of subsupercontinent average temperature from the bottom of the supercontinent to the CMB (red curve in Fig. 3a) and more importantly, the average temperature in region right below the continental lithosphere (200-300 km depth; green curve in Fig. 3a). We find that the average temperature of the whole sub-supercontinent mantle starts to increase quickly after about one transit time, t0 (i.e., one transit time is the time it takes for a particle to travel from the surface to the CMB with the average surface horizontal velocity, or ~60 Ma in this study) with the first arrival of cold slabs on the CMB (Fig. 3c), similar to that in Zhong et al. (2007). ...
... 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
Full-text available
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.
... A third model proposed more recently is orthoversion, which involves closure of an ocean orthogonal to the original opening, within the downwelling of the previous supercontinents subduction girdle (Mitchell et al., 2012). An alternative method to understand the nature of supercontinent cyclicity involves self-consistent numerical modelling of a convecting Earth with platelike behaviour and continents (Rolf et al., 2014;Coltice and Shephard, 2017;Yoshida and Santosh, 2011). Models of this type are able to reproduce mantle structures that may cause degree-1 convection during supercontinent existence and also result in supercontinents forming through both intro-and extroversion (Yoshida and Santosh, 2014). ...
... This scenario is consistent with numerical models where supercontinents form from the closure of both internal and external oceans, accommodated by changes in plate motion and driven by heterogeneities introduced into the mantle via subduction (Yoshida and Santosh, 2014;Yoshida, 2016). Self-consistent numerical models with plate-like behaviour show that continental lithosphere does congregate and disperse over long time periods, but not necessarily with a regular periodicity (Rolf et al., 2014). Models also show that if enough continents congregate they can induce changes in mantle convection (e.g. ...
Article
The extent of continental rifts and subduction zones through deep geological time provides insights into the mechanisms behind supercontinent cycles and the long term evolution of the mantle. However, previous com- pilations have stopped short of mapping the locations of rifts and subduction zones continuously since the Neoproterozoic and within a self-consistent plate kinematic framework. Using recently published plate models with continuously closing boundaries for the Neoproterozoic and Phanerozoic, we estimate how rift and peri- continental subduction length vary from 1 Ga to present and test hypotheses pertaining to the supercontinent cycle and supercontinent breakup. We extract measures of continental perimeter-to-area ratio as a proxy for the existence of a supercontinent, where during times of supercontinent existence the perimeter-to-area ratio should be low, and during assembly and dispersal it should be high. The amalgamation of Gondwana is clearly re- presented by changes in the length of peri-continental subduction and the breakup of Rodinia and Pangea by changes in rift lengths. The assembly of Pangea is not clearly defined using plate boundary lengths, likely because its formation resulted from the collision of only two large continents. Instead the assembly of Gondwana (ca. 520 Ma) marks the most prominent change in arc length and perimeter-to-area ratio during the last billion years suggesting that Gondwana during the Early Palaeozoic could explicitly be considered part of a Phanerozoic supercontinent. Consequently, the traditional understanding of the supercontinent cycle, in terms of super- continent existence for short periods of time before dispersal and re-accretion, may be inadequate to fully de- scribe the cycle. Instead, either a two-stage supercontinent cycle could be a more appropriate concept, or al- ternatively the time period of 1 to 0 Ga has to be considered as being dominated by supercontinent existence, with brief periods of dispersal and amalgamation.
... Near-surface factors such as plate rheology have also been shown to influence the preferred large-scale pattern of convection (e.g. Yoshida, 2008;Rolf et al., 2014). This study does not attempt to simulate this; we do not impose surface or near-surface conditions to simulate plates. ...
... Conrad and Lithgow Bertelloni, 2006, and references therein). We note that full spherical models incorporating more detailed lithospheric rheologies are only just starting to appear (Van Heck and Tackley, 2008;Rolf et al., 2012Rolf et al., , 2014Yoshida and Santosh, 2014), and it is only through further advances in such models that a more quantitative assessment of this hypothesis will be achieved. ...
Article
Full-text available
Much debate has centred on whether continental break-up is predominantly caused by active upwelling in the mantle (e.g. plumes) or by long-range extensional stresses in the lithosphere. We propose the hypothesis that global supercontinent break-up events should always involve both. The fundamental principle involved is the conservation of mass within the spherical shell of the mantle, which requires a return flow for any major upwelling beneath a supercontinent. This shallow horizontal return flow away from the locus of upwelling produces extensional stress. We demonstrate this principle with numerical models, which simultaneously exhibit both upwellings and significant lateral flow in the upper mantle. For non-global break-up the impact of the finite geometry of the mantle will be less pronounced, weakening this process. This observation should motivate future studies of continental break-up to explicitly consider the global perspective, even when observations or models are of regional extent.
... Near-surface factors such as plate rheology have also been shown to influence the preferred large-scale pattern of convection (e.g. Yoshida, 2008;Rolf et al., 2014). This study does not attempt to simulate this; we do not impose surface or near-surface conditions to simulate plates. ...
... Conrad and Lithgow Bertelloni, 2006, and references therein). We note that full spherical models incorporating more detailed lithospheric rheologies are only just starting to appear (Van Heck and Tackley, 2008;Rolf et al., 2012Rolf et al., , 2014Yoshida and Santosh, 2014), and it is only through further advances in such models that a more quantitative assessment of this hypothesis will be achieved. ...
Article
Full-text available
Much debate has centred on whether continental break-up is predominantly caused by active upwelling in the mantle (e.g. plumes) or by long-range extensional stresses in the lithosphere. We propose the hypothesis that global supercontinent break-up events should always involve both. The fundamental principle involved is the conservation of mass within the spherical shell of the mantle, which requires a return flow for any major upwelling beneath a supercontinent. This shallow horizontal return flow away from the locus of upwelling produces extensional stress. We demonstrate this principle with numerical models, which simultaneously exhibit both upwellings and significant lateral flow in the upper mantle. For non-global break-up the geometry of the mantle will be less influential, weakening this process. This observation should motivate future studies of continental break-up to explicitly consider the global perspective, even when observations or models are of regional extent.
... When 2 continental rafts and plate-like behaviour are combined in 2-D spherical annulus geometry and 3-D spherical geometry, there is a range of values for the yield stress that produces a statistical cyclicity of aggregation and dispersal on times scales comparable to the observed timings on Earth (about 500-700 My for a cycle). When the yield stress is too low, convection is characterised by smaller scales, and continents do not aggregate frequently enough, while for a high yield stress convection is too large-scale, almost stuck to degree 1, to produce frequent supercontinent breakups ( Rolf et al., 2014). Consistently with this result, Yoshida (2014) shows that an intermediate yield stress in the range of those producing a plate-like behaviour, breaks up and disperses the pieces of a supercontinent with the shape of Pangea. ...
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?
... For almost a decade, 3-D spherical mantle convection models have shown the capability to self-consistently produce plate-like tectonics at their surface (Walzer and Hendel, 2008;Van Heck and Tackley, 2008;Yoshida, 2008;Foley and Becker, 2009). These models physically link surface tectonics comparable to that of the Earth to mantle convection processes (Coltice et al., 2012;Rolf et al., 2014;Mallard et al., 2016). In Bocher et al. (2016), we took advantage of this link to build a sequential data assimilation algorithm able to integrate plate reconstructions into a mantle convection code while taking into account the uncertainties in those plate tectonic reconstructions. ...
Article
Full-text available
Recent advances in mantle convection modeling led to the release of a new generation of convection codes, able to self-consistently generate plate-like tectonics at their surface. Those models physically link mantle dynamics to surface tectonics. Combined with plate tectonic reconstructions, they have the potential to produce a new generation of mantle circulation models that use data assimilation methods and where uncertainties in plate tectonic reconstructions are taken into account. We provided a proof of this concept by applying a suboptimal Kalman filter to the reconstruction of mantle circulation (Bocher et al., 2016). Here, we propose to go one step further and apply the ensemble Kalman filter (EnKF) to this problem. The EnKF is a sequential Monte Carlo method particularly adapted to solve high-dimensional data assimilation problems with nonlinear dynamics. We tested the EnKF using synthetic observations consisting of surface velocity and heat flow measurements on a 2-D-spherical annulus model and compared it with the method developed previously. The EnKF performs on average better and is more stable than the former method. Less than 300 ensemble members are sufficient to reconstruct an evolution. We use covariance adaptive inflation and localization to correct for sampling errors. We show that the EnKF results are robust over a wide range of covariance localization parameters. The reconstruction is associated with an estimation of the error, and provides valuable information on where the reconstruction is to be trusted or not.
... For example, Ricard et al. (1989) and Alisic et al. (2012) obtained a consistent description of surface kinematics by converting the long wavelength heterogeneities of seismic velocity into buoyancy forces. Mantle convection studies also attest to this link, showing for example that a downwelling in a context of large-scale convection draws continents to aggregate (Zhong 2001;Rolf et al. 2014). ...
Article
Full-text available
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.
... For almost a decade, 3-D spherical mantle convection models have shown the capability to self-consistently produce plate-like tectonics at their surface (Walzer and Hendel, 2008;Van Heck and Tackley, 2008;Yoshida, 2008;Foley and Becker, 2009). These models physically link surface tectonics comparable to that of the Earth to mantle convection processes (Coltice et al., 2012;Rolf et al., 2014;Mallard et al., 2016). In Bocher et al. (2016), we took advantage of this link to build a sequential data assimilation algorithm able to integrate plate reconstructions into a mantle convection code while taking into account the uncertainties on those plate tectonic reconstructions. ...
Article
Full-text available
Recent advances in mantle convection modelling led to the release of a new generation of convection codes, able to generate self-consistently plate-like tectonics at their surface. Those models physically link mantle dynamics to surface tectonics. Combined with plate tectonic reconstructions, they have the potential to produce a new generation of mantle circulation models that use data assimilation methods and where uncertainties on plate tectonic reconstructions are taken into account. We recently provided a proof of this concept by applying a suboptimal Kalman Filter to the reconstruction of mantle circulation (Bocher et al., 2016). Here, we propose to go one step further and apply the ensemble Kalman filter (EnKF) to this problem. The EnKF is a sequential Monte Carlo method particularly adapted to solve high dimensional data assimilation problems with nonlinear dynamics. We tested the EnKF using synthetic observations consisting of surface velocity and heat flow measurements, on a 2D-spherical annulus model and compared it with the method developed previously. The EnKF performs on average better and is more stable than the former method. Less than 300 ensemble members are sufficient to reconstruct an evolution. We use covariance adaptive inflation and localization to correct for sampling errors. We show that the EnKF results are robust over a wide range of covariance localization parameters. The reconstruction is associated with an estimation of the error, and provides valuable information on where the reconstruction is to be trusted or not.
... Progress in understanding the dynamics of the Earth mantle in the last hundreds of Myr ultimately requires a better description of plate motions in the framework of mantle convection. Promising research paths include conceptual developments such as the understanding of lithospheric damage (Bercovici and Ricard 2014) as well as an improved treatment of plate-like behavior in spherical simulations of mantle dynamics (Bello et al. 2014;Rolf et al. 2012Rolf et al. , 2014. In the meantime, improved reconstructions of plate velocities (Seton et al. 2012) can be prescribed to mantle convection models to investigate the role of specific ingredients such as mantle rheology, phase transitions and the nature of a possible dense basal layer. ...
Article
Full-text available
Mantle control on planetary dynamos is often studied by imposing heterogeneous core-mantle boundary (CMB) heat flux patterns on the outer boundary of numerical dynamo simulations. These patterns typically enter two main categories: Either they are proportional to seismic tomography models of Earth’s lowermost mantle to simulate realistic conditions, or they are represented by single spherical harmonics for fundamental physical understanding. However, in reality the dynamics in the lower mantle is much more complicated and these CMB heat flux models are most likely oversimplified. Here we term alternative any CMB heat flux pattern imposed on numerical dynamos that does not fall into these two categories, and instead attempts to account for additional complexity in the lower mantle. We review papers that attempted to explain various dynamo-related observations by imposing alternative CMB heat flux patterns on their dynamo models. For present-day Earth, the alternative patterns reflect non-thermal contributions to seismic anomalies or sharp features not resolved by global tomography models. Time-dependent mantle convection is invoked for capturing past conditions on Earth’s CMB. For Mars, alternative patterns account for localized heating by a giant impact or a mantle plume. Recovered geodynamo-related observations include persistent morphological features of present-day core convection and the geomagnetic field as well as the variability in the geomagnetic reversal frequency over the past several hundred Myr. On Mars the models aim at explaining the demise of the paleodynamo or the hemispheric crustal magnetic dichotomy. We report the main results of these studies, discuss their geophysical implications, and speculate on some future prospects.
... On the other hand, the episodic feature of geological records implies the cyclicity of Earth's evolution. Rolf et al. (2014) suggested the balance between regular and irregular processes in such a self-organized system might lead to the statistical cyclicity of supercontinent formation. As a matter of fact, a pronounced cyclicity of continental assembly with a period of 700-800 Ma is cursorily reflected by the proposed formation age of supercontinents: Kenoland (~2.6 Ga), Columbia (~1.8 Ga), Rodinia (~1.1 Ga), and Pangea (0.4 Ga) (see Nance et al., 2014, and references therein). ...
Article
Full-text available
Accessing the cyclicity and persistence of geological records with time series analysis deepens our understanding of Earth's long-term evolution. In this study, time series from recent global zircon U-Pb age and δ¹⁸O databases are analyzed using wavelet transform from a fractal perspective. Continuous wavelet transform of the local fractal sequences of both zircon records indicates a strong, persistent ~760 million year cycle over the 4.4 billion years of Earth's history. Wavelet coherence analysis shows that the U-Pb age and δ¹⁸O systems are coupled in significant in-phase coherence for a cycle of ~760 million year, implying synchronization between the two underlying processes. This study also demonstrates that the variation in the time series records manifests as 1/f β scaling behavior that persists β ~ 1.8 over the entire interval. This 1/f fractal scaling nature furnishes evidence for the conjecture that rather than being an equilibrium system, Earth's long-term evolution follows a self-organized pattern.
... Gondwana (c. 15% of Earth's surface) may be at the threshold of becoming a supercontinent, especially considering new insights into the statistical cyclicity of supercontinents (Rolf et al. 2014) and their putative effects on the lower mantle (e.g. Zhang et al. 2009). ...
Article
Full-text available
There is an emerging consensus that Earth's landmasses amalgamate quasi-periodically into supercontinents, interpreted to be rigid super-plates essentially lacking tectonically active inner boundaries and showing little internal lithosphere–mantle interactions. The formation and disruption of supercontinents have been linked to changes in sea-level, biogeochemical cycles, global climate change, continental margin sedimentation, large igneous provinces, deep mantle circulation, outer core dynamics and Earth's magnetic field. If these hypotheses are correct, long-term mantle dynamics and much of the geological record, including the distribution of natural resources, may be largely controlled by these cycles. Despite their potential importance, however, many of these proposed links are, to date, permissive rather than proven. Sufficient data are not yet available to verify or fully understand the implications of the supercontinent cycle. Recent advances in many fields of geoscience provide clear directions for investigating the supercontinent cycle hypothesis and its corollaries but they need to be vigorously pursued if these far-reaching ideas are to be substantiated.
... In our scenarios, these systems can split or merge, but the geometric constraints imposed by the Supercontinent cycle may force the Earth to be close to the two-convection-system mode. Further work should be pursued in order to understand the feedbacks between mantle convection and Supercontinent cycles (Rolf et al., 2014: Coltice et al. 2012Yoshida and Santosh, 2017). ...
Article
The theory of plate tectonics and the discovery of large scale, deep-time cycles, such as the Supercontinent cycle and Wilson cycle, has contributed to the identification of several supercontinents in Earth's history. Using the rules of plate tectonic theory, and the dynamics of subduction zones and mantle convection, it is possible to envisage scenarios for the formation of the next supercontinent, which is believed to occur around 200–300 Ma into the future. Here, we explore the four main proposed scenarios for the formation of the next supercontinent by constructing them, using GPlates, in a novel and standardised way. Each scenario undergoes different modes of Wilson and Supercontinent cycles (i.e., introversion, extroversion, orthoversion, and combination), illustrating that the relationship between them is not trivial and suggesting that these modes should be treated as end-members of a spectrum of possibilities. While modelling the future has limitations and assumptions, the construction of the four future supercontinents here has led to new insights into the mechanisms behind Wilson and Supercontinent cycles. For example, their relationship can be complex (in terms of being of the same or different order, or being in or out of phase with each other) and the different ways they can interact may led to different outcomes of large-scale mantle reorganization. This work, when combined with geodynamical reconstructions since the Mesozoic allows the simulation of the entire present-day Supercontinent cycle and the respectively involved Wilson cycles. This work has the potential to be used as the background for a number of studies, it was just recently used in tidal modelling experiments to test the existence of a Supertidal cycle associated with the Supercontinent cycle.
... 2D and 3S mantle models are used for investigating statistical cyclicity and timescales of the supercontinent cycle in Rolf et al. (2014). Here the continental materials are modelled by markers which differ from the mantle in terms of density and rheology. ...
Article
Full-text available
We employ 2D Cartesian geometry model of thermochemical convection with non-Newtonian rheology and phase transitions, in the presence of floating deformable continents. Using a mantle model with continental crust, lithosphere and the material of the oceanic crust that can be subjected to eclogitization we study the stages of supercontinent cycle: assembly, evolution of supercontinent, its breakup and divergence of continents. Our results show that cold downgoing flows aggregate continents into a supercontinent. After its formation, the convection pattern changes: the subduction zones at the edges of the supercontinent and typical relatively narrow mantle plumes in the subcontinental mantle arise. The lifetime of the supercontinent is about 550 Ma. Typical velocities for continents before collision are 3–10 cm/year, for supercontinent 0.5–1.5 cm/year and after the breakup 4–8 cm/year. Despite the small mobility of the supercontinent, there is no significant warming up of the subcontinental mantle. The temperature anomaly under supercontinent is less than + 50 K and the superplume does not arise. We obtain that the phase transitions at 410 km and 660 km and the eclogitization of the subducted oceanic crust affects the supercontinent cycle significantly. Our results demonstrate certain irregularity of supercontinent cycle. The typical shear stresses in the mantle are less than 30 MPa; in the subduction zones and on the continent borders they are 100–250 MPa. Before the breakup maximum shear stress generated in the supercontinent can reach 200 MPa.
... New theories link microscale physics at the size of grains to damage and healing of rocks that produce strain localization (Bercovici & Ricard, 2014), and including them in full 3-D spherical models is underway. Nonetheless, convection models with pseudo-plasticity produce several key emergent properties that closely match kinematic and tectonic observations: the ratio of toroidal to poloidal velocity at the surface (Van Heck & Tackley, 2008), seafloor age-area distribution (Coltice et al., 2012), supercontinent cycles (Rolf et al., 2014), plate area distribution (Mallard et al., 2016), continental versus oceanic plate velocities (Rolf et al., 2018), coexistence of multiple scales of convection , and topography (Arnould et al., 2018). ...
Article
Full-text available
Although plate tectonics has pushed the frontiers of geosciences in the past 50 years, it has legitimate limitations, and among them we focus on both the absence of dynamics in the theory and the difficulty of reconstructing tectonics when data are sparse. In this manuscript, we propose an anticipation experiment, proposing a singular outlook on plate tectonics in the digital era. We hypothesize that mantle convection models producing self‐consistently plate‐like behavior will capture the essence of the self‐organization of plate boundaries. Such models exist today in a preliminary fashion, and we use them here to build a database of mid‐ocean ridge and trench configurations. To extract knowledge from it, we develop a machine learning framework based on Generative Adversarial Networks (GANs) that learns the regularities of the self‐organization in order to fill gaps of observations when working on reconstructing a plate configuration. The user provides the distribution of known ridges and trenches, the location of the region where observations lack, and our digital architecture proposes a horizontal divergence map from which missing plate boundaries are extracted. Our framework is able to prolongate and interpolate plate boundaries within an unresolved region but fails to retrieve a plate boundary that would be completely contained inside of it. The attempt we make is certainly too early because geodynamic models need improvement and a larger amount of geodynamic model outputs, as independent as possible, is required. However, this work suggests applying such an approach to expand the capabilities of plate tectonics is within reach.
... The intermittent assembly of supercontinents punctuate an otherwise continuous redistribution of continental landmasses that has been an expression of Earth's mantle convective regime since at least 2 Ga (e.g., Bleeker, 2003;Hallam, 1987;Jacoby, 1981;Li et al., 2008Li et al., , 2013Meert, 2012;Pesonen et al., 2012;Rogers & Santosh, 2004;Rolf et al., 2014;Wegener, 1924;Zhang et al., 2012). These transient 300-to 500-million-year long events, which are expressed in plate reconstructions (e.g., Evans, 2009;Li et al., 2008Li et al., , 2013Merdith et al., 2019;Rogers & Santosh, 2004;Zhang et al., 2012) and emerge in three-dimensional geodynamic models (e.g., Höink et al., 2012;Li & Zhong, 2009) are inherent features of the punctuated character of mantle convective stirring and thermal mixing that define the highly time-dependent heat transfer properties of plate tectonics (Lenardic et al., 2016). ...
... The weak zones produced when continents collide are not implemented in this model, which strongly complicates breakup. In improved models with added weak zones at continental margins breakup of continental clusters seemed to be facilitated (Lenardic et al., 2003;Rolf et al., 2014;Yoshida, 2010), but though important for the evolution of Earth's continents, it is unknown whether this has any relevance for Venus' evolution since there is no evidence for any such behavior. ...
Article
Full-text available
Current Venus tectonics suggests a stagnant lid mode of mantle convection. However, the planet is debated to enter an episodic regime after long quiescent periods, driven by resurfacing due to rapid subduction and global crustal recycling. Tessera regions that cover approximately 10% of Venus’ surface appear to be strongly deformed, which suggests that they have survived at least the latest resurfacing event, although the composition and age of the tesserae are unknown. Based on mantle convection modelling, we studied the effects of anomalous crustal provinces (ACPs) on mantle dynamics and post‐overturn lithospheric survival. As a hypothesis, we assume ACPs to be thick, compositionally anomalous and rheologically strong units, similar to terrestrial cratons. We model Venus with a varying number of pre‐imposed ACP units and differing lithospheric yield stress in 2D and 3D spherical geometry. The impact of ACPs on mantle dynamics and the survival of lithosphere is investigated by examining the thermal evolution, crustal thickness and surface age distribution. We find that the number and timing of overturns are highly dependent on the yield stress and, to some degree, on the number and size of the pre‐imposed ACPs. ACPs in particular affect the wavelength of convection and may foster the survival of lithosphere even of those portions not being part of an ACP. However, ACPs do not seem to be a good analogue for tessera regions due to their exaggerated age and (likely) thickness, but – with appropriate density contrast – may be more useful representatives of Venus’ highland plateaus.
... If the supercontinent ''cycle" adapted at least partly to an already existing 400-Myr cycle, it soon became detached from this cycle, especially after 1 Ga. This agrees with the numerical models of Rolf et al. (2020), which suggest that any regularity in the timing of the supercontinent cycle is prevented by the chaotic nature of mantle convection. ...
Article
Of nine large age peaks in zircon and LIP time series < 2300 Ma (2150, 1850, 1450, 1400, 1050, 800, 600, 250 and 100 Ma), only four are geographically widespread (1850, 1400, 800 and 250 Ma). These peaks occur both before and after the onset of the supercontinent cycle, and during both assembly and breakup phases of supercontinents. During supercontinent breakup, LIP activity is followed by ocean-basin opening in some areas, but not in other areas. This suggests that mantle plumes are not necessary for ocean-basin opening, and that LIPs should not be used to predict the timing and location of supercontinent breakups. LIP events may be produced directly by mantle plumes or indirectly from subduction regimes that have inherited mantle-cycle signatures from plume activity. A combination of variable plume event intensity and multiple plume cyclicities best explains differences in LIP age peak amplitudes and irregularities. Peaks in orogen frequency at 1850, 1050, 600 Ma, which approximately coincide with major zircon and LIP age peaks, correspond to onsets of supercontinent assembly, and age peaks at 1450, 250 and 100 Ma correspond to supercontinent stasis or breakup. Although collisional orogens are more frequent during supercontinent assemblies, accretionary orogens have no preference for either breakup or assembly phases of supercontinents. A sparsity of orogens during Rodinia assembly may be related to incomplete breakup of Nuna as well as to the fact that some continental cratons never accreted to Rodinia. There are three groups of passive margins, each group showing a decrease in duration with time: Group 1 with onsets at 2.2-2.0 Ga correspond to the breakup of Neoarchean supercratons; Group 2 with onsets at 1.5-1.2 Ga correspond to the breakup of Nuna; and Group 3 with onsets at 1.5-0.1 Ga not corresponding to any particular supercontinent breakup. New paleogeographic reconstructions of supercontinents indicate that in the last 2 Gyr average angular plate speeds have not changed or have decreased with time, whereas the number of orogens has increased. A possible explanation for decreasing or steady plate speed is an increasing proportion of continental crust on plates as juvenile continental crust continued to be added in post-Archean accretionary orogens. Cycles of mantle events are now well established at 90 and 400 Myr. Significant age peaks in orogen frequency, average plate speed, LIPs and detrital zircons may be part of a 400-Myr mantle cycle, and major age peaks in the cycle occur near the onset of supercontinent assemblies. The 400-Myr cycle may have begun with a “big bang” at the 2700 Ma, although the LIP age spectrum suggests the cycle may go back to at least 3850 Ma. Large age peaks at 1850, 1050, 600 and 250 Ma may be related to slab avalanches from the mantle transition zone that occur in response to supercontinent breakups.
Article
Full-text available
The multitude of periodicities reported from detrital zircon and related geochemical time-series leads to questions about which cycles should be considered valid, which are byproducts of random noise, and the degree of uncertainty associated with the detected periodicities. To enhance understanding of detrital zircon periodicities, we review existing estimates by assessing both methodological reliability and reproducibility of results. Methods commonly employed include scalograms from wavelet analysis, periodograms from spectral analysis, and correlograms from cross-correlation analysis. This study analyzes possible zircon periodicities ranging from less than 1 million to 1 billion years. We systematically evaluate the capabilities of each approach, and then refine estimates in terms of their reproducibility using seven completely independent to partially independent UPb detrital zircon databases. Periodicities that are consistently found at high confidence levels are considered statistically significant, whereas those that cannot be replicated are considered as spurious. The comparative studies of detrital zircon ages reveal a dominant set of eight period-tripling cycles of ~0.373, 1.12, 3.35, 10.1, 30.2, 90.5, 272, and 815 myr (rounded to three digits). Additionally, a multitude of subordinate cycles are harmonically linked to the main period-tripling sequence. The detected periodicities often correspond to cycles found in large igneous province occurrence, seafloor spreading rates, million-year climatic cycles, mass extinctions, and other natural variation seemingly unrelated to geological processes. The commonality suggests a persistent episodic link between zircon production and other geological and non-geological processes throughout Earth's entire history. As a final step, we review a variety of hypotheses being explored to explain primary, secondary, and tertiary causes of cycles, and then propose tests that should soon be possible to either validate or falsify these diverse ideas.
Preprint
Earth’s climate variability over time scales greater than about one million years is modulated by a time-varying balance between volcanic sources for CO2 and surface and seafloor chemical weathering sinks. The characters and magnitudes of these sources and sinks depend on the continuously evolving planform of plate tectonics, as well as on the rate and global extent to which insulated and relatively warm subcontinental mantle is mixed globally by mantle convective overturning motions. Although lateral thermal mixing in the mantle is extensive over time scales of order 1 billion years, supercontinents can perturb this mixing to introduce lateral oceanic-continental mantle temperature variations that influence the major volcanic and weathering controls on Earth’s long-term carbon cycle for a few hundred million years. Here, we develop a thought experiment to investigate quantitatively how and to what extent supercontinental cycles have modulated Earth’s long-term climate change. We argue that the relatively warm and unchanging climate of the Precambrian Nuna supercontinental epoch (1.8-1.3 Ga) is a property of supercontinent formation and breakup where mantle thermal mixing is extensive and lateral oceanic-continental mantle temperature variations minimized. By contrast, we show that the extreme climate variability of the Neoproterozoic Rodinia episode (1-0.63 Ga), as well as the Jurassic cooling to Cretaceous warming characteristic of the Mesozoic Pangea cycle (0.3-0.05 Ga) can emerge as a result of a protracted thermal isolation of the mantles beneath insulating supercontinents from the more strongly-cooled oceanic mantle domains. Using calculations of a tectonically-modulated long-term inorganic carbon cycle along with a one-dimensional radiative energy balance climate model, we predict the form of Mesozoic climate evolution expressed in tropical sea-surface temperature and ice sheet proxy data, as well as a high likelihood for observed Ocean Anoxia Events. Applied to the Neoproterozoic, this tectonic control can drive Earth into, as well as out of, a continuous or intermittently pan-glacial climate. The character and intensity of this climate variability is influenced by the magnitude of a predicted abiotic methane production at mid-ocean ridges and on governed by the predominant mechanics and modes of chemical weathering. We identify conditions that would permit the occurrence of the Sturtian and shorter Marinoan global glaciations with an order 10 million year interlude. Our model also explains the abrupt termination of the Marinoan event and Earth’s entry into the relatively warm Ediacaran period. More generally, our results suggest that Earth‘s record of long-term climate variability can potentially provide rigorous constraints on the character and heat transfer properties of mantle convection.
Article
Full-text available
A supercontinent is generally considered to reflect the assembly of all, or most, of the Earth's continental lithosphere. Previous studies have used geological, atmospheric and biogenic ‘geomarkers’ to supplement supercontinent identification. However, there is no formal definition of how much continental material is required to be assembled, or indeed which geomarkers need to be present. Pannotia is a hypothesized landmass that existed in the interval c. 0.65–0.54 Ga and was comprised of Gondwana, Laurentia, Baltica and possibly Siberia. Although Pannotia was considerably smaller than Pangaea (and also fleeting in its existence), the presence of geomarkers in the geological record support its identification as a supercontinent. Using 3D mantle convection models, we simulate the evolution of the mantle in response to the convergence leading to amalgamation of Rodinia and Pangaea. We then compare this supercontinent ‘fingerprint’ to Pannotian activity. For the first time, we show that Pannotian continental convergence could have generated a mantle signature in keeping with that of a simulated supercontinent. As a result, we posit that any formal identification of a supercontinent must take into consideration the thermal evolution of the mantle associated with convergence leading to continental amalgamation, rather than simply the size of the connected continental landmass.
Article
We investigate the influence of tectonic mode on the thermo-chemical evolution of simulated mantle convection coupled to a parameterized core cooling model. The tectonic mode is controlled by varying the friction coefficient for brittle behavior, producing the three tectonic modes mobile lid (plate tectonics), stagnant lid and episodic lid. The resulting compositional structure of the deep mantle is strongly dependent on tectonic mode, with episodic lid resulting in a thick layer of subducted basalt in the deep mantle, whereas mobile lid produces only isolated piles and stagnant lid no basaltic layering. The tectonic mode is established early on, with subduction initiating at around 60 Myr from the initial state in mobile and episodic cases, triggered by the arrival of plumes at the base of the lithosphere. Crustal production assists subduction initiation, increasing the critical friction coefficient. The tectonic mode has a strong effect on core evolution via its influence on deep mantle structure; episodic cases in which a thick layer of basalt builds up experience less core heat flow and cooling and a failed geodynamo. Thus, a continuous mobile lid mode existing from early times matches Earth's mantle structure and core evolution better than an episodic mode characterized by large-scale flushing (overturn) events. This article is protected by copyright. All rights reserved.
Chapter
This chapter summarizes the key aspects of Precambrian geomagnetic field in three successive time intervals (pre-1880 Ma, 1190-1880 Ma, and post-1190 Ma) representing hypothesized supercontinents Kenorland, Nuna, and Rodinia. Our analyses of inclination frequency, reversal asymmetry, paleointensity, and paleosecular variation are generally in favor of Geocentric Axial Dipole as the time-averaged Precambrian geomagnetic field. However, in the Nuna supercontinent phase, the field was weaker, less reversing, and biased toward low inclinations, suggesting the presence of considerable (23%) octupole component or more likely that Nuna occupied shallow latitudes as evidenced by paleoclimate indicators. Another paradoxial result emerges from paleosecular variation data, which suggests a field with quadrupolar characteristics while the inclination analysis favors the presence of an octupolar field in the Mid-Proterozoic. Despite these exceptions, the existence of a stable dipole field gives us a solid ground for paleogeography studies beyond the Phanerozoic.
Chapter
Revealing Earth's paleogeography is important for understanding climate, sea-level, topography, orogeny, and magnetic field history. Quantitative constraints come from paleomagnetism, but are sparse for the Precambrian. As a consequence, the occurrence and formation scenarios of previous supercontinents remain enigmatic. Here, we shed light on this using 3D mantle convection models featuring self-consistent plate-like behavior and continental drift over a billion-year time scale. Our model suggests the need of a stable very long wavelength flow with large tectonic plates to assemble supercontinents with compact geometry; less compact and typically shorter-lived supercontinents can form with a somewhat smaller scale flow structure. A cycle with mostly compact supercontinents favors the extroversion scenario where the succeeding supercontinent forms in the opposite hemisphere of its predecessor. On a regional scale, ocean opening and closure between individual continents happens on top of this and becomes more relevant for less compact supercontinents. Compact supercontinent formation seems favored by a continent population with equal-sized units possibly due to geometric effects. Some continental blocks form coherent groups throughout most of the evolution, in line with paleomagnetic data; independently drifting blocks that take different positions in subsequent continental clusters occur less frequently. Without true polar wander, the continents need to sample latitudes for at least 1.5 Gyr to achieve close-to-uniform sampling, so that using the Precambrian record of magnetic inclinations to infer the persistence of a geocentric dipole-dominated magnetic field remains challenging. When extrapolated back in time to a hotter mantle, predicted continental motion is enhanced, but this feature likely suffers from the omission of magmatic processes in our model that likely caused a different geodynamic regime during the earlier periods of Earth’s evolution.
Article
Super-continents coalesce over subduction zone complexes and their subsequent dispersal is usually attributed to heating and upwelling of continent-insulated mantle. This dispersal mechanism, however, requires considerable mantle internal heating. Alternatively, the super-continent configuration may be mechanically unstable and disperse regardless of heating mode. In particular, increased drag on plates or subducting slabs (e.g., by accumulating continents) causes them to slow down and trenches to rollback. Once subcontinental slabs are slightly separated, resistance to their descent increases, inducing further trench migration. Slabs thus undergo a rollback instability, which disperses super-continents. A simple theoretical model illustrates this instability and shows there are two equilibrium states, one unstable super-continent state where slabs are conjoined, and one stable state where slabs are widely separated. Slab rollback from the unstable to stable states occurs at typical slow tectonic speeds, and over a period commensurate with the age of ocean basins and the Wilson cycle.
Article
Full-text available
The periodic assembly and dispersal of continental fragments, referred to as the supercontinent cycle, bear close relation to the evolution of mantle convection and plate tectonics. Supercontinent formation involves complex processes of “introversion” (closure of interior oceans), “extroversion” (closure of exterior oceans), or a combination of these processes in uniting dispersed continental fragments. Recent developments in numerical modeling and advancements in computation techniques enable us to simulate Earth's mantle convection with drifting continents under realistic convection vigor and rheology in Earth-like geometry (i.e., 3D spherical-shell). We report a numerical simulation of 3D mantle convection, incorporating drifting deformable continents, to evaluate supercontinent processes in a realistic mantle convection regime. Our results show that supercontinents are assembled by a combination of introversion and extroversion processes. Small-scale thermal heterogeneity dominates deep mantle convection during the supercontinent cycle, although large-scale upwelling plumes intermittently originate under the drifting continents and/or the supercontinent.
Article
Full-text available
Continental freeboard and eustasy, as gauged by the relative position of the world shelf break with respect to sea level, have varied by ± 250 m from today's ice-free shelf break depth of ∼ 200 m, during the past 600 Ma.Assuming constant or uniformly accreting continental crust and ocean water volume in an ice-free world, sea level fluctuations can be attributed to variation in the world ocean basin volume caused by changes in either its area or its depth relative to the world shelf break. An increase in volume and lowering of sea level occur as: (1) the world ocean floor ages, cools and subsides; (2) accreting continents collide, thicken and decrease in area; and (3) poorly conductive continental platforms become thermally elevated due to a size-induced stasis over the mantle. Conversely, a decrease in the age of the world ocean floor, attenuation of continental crust during rifting, and an increase in continent number and mobility, will reduce the world ocean basin volume and raise sea level.Theoretical sea level calculated from these principles correlates well with calibrated, first-order cycles of eustatic sea level change for the Phanerozoic. The record closely fits a simple model of retardation and acceleration of terrestrial heat loss during alternating periods of supercontinent accretion and fragmentation. Calibrated to sea-level highstands, successive first-order marine transgressions and orogenic “Pangea” regressions characterize a self-sustaining, ∼ 440 Ma plate tectonic cycle for the late Precambrian and Phanerozoic. The cycle can be recognized as far back as 2 Ga from the tectonic evidence of continental collision and rifting recorded in global orogenic peaks and mafic dike swarms, and may be related to major episodes of glaciation and evolutional biogenesis.
Article
Full-text available
The distribution of continents is thought to influence the temperature of the underlying mantle. Over geological timescales, insulation effects generate a build-up of heat that may cause increased magmatism1–4, such as flood basalt volcanism5,6, and ultimately rift the continents, causing them to break apart and new ocean basins to form. Here we use analyses of the major element geochemistry of lava samples collected from oceanic crust in the Atlantic and Pacific oceans to quantify the effect of continental insulation. The lavas formed at mid-ocean ridges following continental rifting and break up, and preserve a record of upper mantle temperatures over the past 170Myr. We find that samples from the Pacific Ocean—formed more than 2,000 km from the nearest continental margin—do not record raised mantle temperatures. In contrast, samples from the Atlantic Ocean that formed close to the margin of the rifted continent reveal an upper mantle temperature immediately after continental rifting that was up to 150 ◦ C higher than the present-day average; mantle temperatures remained high for 60–70Myr. We conclude that the Atlantic thermal anomaly was created by continental insulation, and persisted in the mantle beneath the Atlantic Ocean long after the continental fragments had dispersed.
Article
Full-text available
A theoretical basis for the regularity of supercontinent cycles is lacking. Here we show that periodic supercontinent cycles are unlikely if thermal instabilities originating at the core-mantle boundary are of sufficient strength. We couple multiple mobile continents with vigorous mantle convection in a spherical geometry. Regular supercontinent cycles lasting 400 ± 50 m.y. occur in idealized models with three continents and a mantle heated purely from within by radioactive decay. In a model incorporating six continents and strong mantle plumes, this regularity is broken and supercontinents form only sporadically. Our results suggest that periodic supercontinent cycles are unlikely to occur in realistic Earth models.
Article
Full-text available
The volume of Earth's continental crust depends on the rate of addition of continental crust from the mantle compared to the rate of continental loss back to the mantle, which at present is roughly balanced. Models for the growth rate of continental crust vary, with isotope data suggesting various episodes of increased growth rate throughout Earth's history; these episodes have been correlated with the supercontinent cycle, but may be a consequence of preferential preservation of continental crust during these cycles. The global balance between addition and loss of continental crust is controlled by: 1) the extent of internal orogens versus exterior orogens, with the latter favouring continental addition, and 2) the balance between exterior orogens in retreating mode versus those in advancing mode, with the latter favouring continental loss. A greater balance of continental addition versus loss should exist during supercontinent break-up, due to a high magmatic flux in retreating accretionary orogens, whereas the amalgamation of supercontinents should involve increased continental loss due to increased sediment subduction and tectonic erosion. Zircon U–Pb and Hf isotopes provide insight to models of crustal growth rate since they sample the continental crust at their time of formation. Using the distribution of data within εHf(t)-time space of a global zircon database, it is demonstrated that the data are in accord with the concept of increased continental loss during supercontinent amalgamation. Periods featuring increased continental addition relative to continental loss, and hence increased continental crust growth rate, occur at ~1.7–1.2Ga, ~0.85–0.75Ga, and ~0.45–0.35Ga, and follow the formation of the Columbia (Nuna), Rodinia and Gondwana supercontinents respectively. Distinct increases in continental loss compared to continental addition, i.e. decreased continental growth rate, occur at ~1.0–0.9Ga, and ~0.6–0.55Ga, correlating with the periods of Rodinia and Gondwana amalgamation respectively. Formation of Pangea by introversion rather than extroversion, means that continental addition in exterior orogens was concurrent with continental loss in interior orogens; a similar process may have been responsible for formation of the Columbia supercontinent. Peaks in the compilation of U–Pb zircon ages correlate with the timing of supercontinent amalgamation, and are likely to be a consequence of preferential preservation of continental crust during this part of the supercontinent cycle.
Article
Full-text available
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.
Article
Full-text available
In recent years, two end-member models for the formation of supercontinents have emerged. In the classical Wilson cycle, oceanic crust generated during supercontinent breakup (the interior ocean) is consumed during subsequent amalgamation so that the supercontinent turns ``inside in'' (introversion). Alternatively, following supercontinent breakup, the exterior margins of the dispersing continental fragments collide during reassembly so that the supercontinent turns ``outside in'' (extroversion). These end-member models can be distinguished by comparing the Sm-Nd crust-formation ages of accreted mafic complexes (e.g., ophiolites) in the collisional orogens formed during supercontinent assembly with the breakup age of the previous supercontinent. For supercontinents generated by introversion, these crust-formation ages postdate rifting of the previous supercontinent. For supercontinents generated by extroversion, the oceanic lithosphere consumed during reassembly predates breakup of the previous supercontinent, so that crust-formation ages of accreted mafic complexes are older than the age of rifting. In the Paleozoic Appalachian-Caledonide-Variscan orogen, a key collisional orogen in the assembly of Pangea, crust-formation ages of accretionary mafic complexes postdate the formation of the Iapetus Ocean (i.e., are younger than ca. 0.6 Ga), suggesting supercontinent reassembly by introversion. By contrast, the Neoproterozoic East African and Brasiliano orogens, which formed during the amalgamation of Gondwana, are characterized by mafic complexes with crust-formation ages (ca. 0.75 1.2 Ga) that predate the ca. 750 Ma breakup of Rodinia. Hence, these complexes must have formed from lithosphere in the exterior ocean that surrounded Rodinia, implying that this ocean was consumed during the amalgamation of Gondwana. These data indicate that Pangea and Gondwana were formed by introversion and extroversion, respectively, implying that supercontinents can be assembled by fundamentally distinct geodynamic processes.
Article
Full-text available
Atmospheric oxygen concentrations in the Earth's atmosphere rose from negligible levels in the Archaean Era to about 21% in the present day. This increase is thought to have occurred in six steps, 2.65, 2.45, 1.8, 0.6, 0.3 and 0.04 billion years ago, with a possible seventh event identified at 1.2 billion years ago. Here we show that the timing of these steps correlates with the amalgamation of Earth's land masses into supercontinents. We suggest that the continent–continent collisions required to form supercontinents produced supermountains. In our scenario, these supermountains eroded quickly and released large amounts of nutrients such as iron and phosphorus into the oceans, leading to an explosion of algae and cyanobacteria, and thus a marked increase in photosynthesis, and the photosynthetic production of O2. Enhanced sedimentation during these periods promoted the burial of a high fraction of organic carbon and pyrite, thus preventing their reaction with free oxygen, and leading to sustained increases in atmospheric oxygen.
Article
Full-text available
The Rheic Ocean is widely believed to have formed in the Late Cambrian-Early Ordovician as a result of the drift of peri-Gondwanan terranes, such as Avalonia and Carolina, from the northern margin of Gondwana, and to have been consumed in the Devonian Carboniferous by continent-continent collision during the formation of Pangea. Other peri-Gondwanan terranes (e.g., Armorica, Ossa-Morena, northwest Iberia, Saxo-Thuringia, Moldanubia) remained along the Gondwanan margin at the time of Rheic Ocean formation. Differences in the Neoproterozoic histories of these peri-Gondwanan terranes suggest the location of the Rheic Ocean rift may have been inherited from Neoproterozoic lithospheric structures formed by the accretion and dispersal of peri-Gondwanan terranes along the northern Gondwanan margin prior to Rheic Ocean opening. Avalonia and Carolina have Sm-Nd isotopic characteristics indicative of recycling of a juvenile ca. 1 Ga source, and they were accreted to the northern Gondwanan margin prior to voluminous late Neoproterozoic arc magmatism. In contrast, Sm-Nd isotopic characteristics of most other peri-Gondwanan terranes closely match those of Eburnian basement, suggesting they reflect recycling of ancient (2 Ga) West African crust. The basements of terranes initially rifted from Gondwana to form the Rheic Ocean were those that had previously accreted during Neoproterozoic orogenesis, suggesting the rift was located near the suture between the accreted terranes and cratonic northern Gondwana. Opening of the Rheic Ocean coincided with the onset of subduction beneath the Laurentian margin in its predecessor, the Iapetus Ocean, suggesting geodynamic linkages between the destruction of the Iapetus Ocean and the creation of the Rheic Ocean.
Article
Full-text available
1] Tracer methods are attractive for modeling compositional fields because they offer the potential of zero numerical diffusion. Composition is typically taken to be proportional to the absolute local concentration of tracers, but an increasingly popular method is to have ''dense'' and ''regular'' tracers with composition being equal to the local fraction of ''dense'' tracers. This paper tests this ''ratio'' method using established benchmarks and by comparing the performance of the two tracer methods and grid-based methods for simulating the long-term evolution of a convecting mantle with a thick, dense, stable layer. For this scenario the ratio method is found to have several advantages, giving sharp, stable long-term layering with no tracer settling, minimal statistical ''noise'' and low entrainment, even with only $5 tracers per cell. The method is equally applicable to finite volume and finite element treatments of the underlying flow. Entrainment in grid-based advection methods is heavily dependent on resolution and numerical details, and is reduced $1 order of magnitude by the filter proposed by A. Lenardic. Numerical determination of physically correct entrainment rates remains a challenging problem. Comparing tracer and grid based methods, the spatial pattern of the thermal and chemical fields appear to be converging on the finest grids; however the estimated entrainment differs significantly. Components: 6488 words, 11 figures, 1 table., Testing the tracer ratio method for modeling active compositional fields in mantle convection simulations, Geochem. Geophys. Geosyst., 4(4), 8302, doi:10.1029/2001GC000214, 2003.
Article
Full-text available
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.
Article
Full-text available
We show in this paper that mobile-lid mantle convection in a three-dimensional spherical shell with observationally constrained mantle viscosity structure, and realistic convective vigor and internal heating rate is characterized by either a spherical harmonic degree-1 planform with a major upwelling in one hemisphere and a major downwelling in the other hemisphere when continents are absent, or a degree-2 planform with two antipodal major upwellings when a supercontinent is present. We propose that due to modulation of continents, these two modes of mantle convection alternate within the Earth's mantle, causing the cyclic processes of assembly and breakup of supercontinents including Rodinia and Pangea in the last 1 Ga. Our model suggests that the largely degree-2 structure for the present-day mantle with the Africa and Pacific antipodal superplumes, is a natural consequence of this dynamic process of very long-wavelength mantle convection interacting with supercontinent Pangea. Our model explains the basic features of true polar wander (TPW) events for Rodinia and Pangea including their equatorial locations and large variability of TPW inferred from paleomagnetic studies. Our model also suggests that TPW is expected to be more variable and large during supercontinent assembly, but small after a supercontinent acquires its equatorial location and during its subsequent dispersal.
Article
Full-text available
The large-scale tectonics in the last billion years (Ga) are predominated by the assembly and breakup of supercontinents Rodinia and Pangea. The mechanisms controlling the assembly of supercontinents are not clear. Here, we investigate the assembly of a supercontinent with 1) stochastic models of randomly-moving continental blocks and 2) 3-D spherical models of mantle convection with continental blocks. For the stochastic models, we determined the time required for all the blocks to assemble into a single supercontinent on a spherical surface. We found that the assembly time from our stochastic models is significantly longer than inferred for Pangea and Rodinia. However, our study also suggests that the assembly time from stochastic models is sensitive to the rules for randomly assigning continental motion in the models. In our dynamic models of mantle convection, continental blocks are modeled as deformable and compositionally distinct materials from the mantle. We found that mantle convective planform has significant effects on supercontinent assembly. For models with moderately strong lithosphere and the lower mantle relative to the upper mantle that lead to degree-1 mantle convection, continental blocks always assemble to a supercontinent in ∼ 250 million years (Ma) and this assembly time is consistent with inferred for Pangea and Rodinia. However, for models with intrinsically small-scale mantle flows, we found that even when continental blocks merge to form a supercontinent, the assembly times are too long and the convective structures outside of supercontinent regions are of too small wavelengths, compared with observed.
Article
Earth as an Evolving Planetary System explores key topics and questions relating to the evolution of the Earth's crust and mantle over the last four billion years. This Second Edition features exciting new information on Earth and planetary evolution and examines how all subsystems in our planet-crust, mantle, core, atmosphere, oceans and life-have worked together and changed over time. Kent Condie synthesizes data from the fields of oceanography, geophysics, planetology, and geochemistry to address Earth's evolution. Two new chapters on the Supercontinent Cycle and on Great Events in Earth history New and updated sections on Earth's thermal history, planetary volcanism, planetary crusts, the onset of plate tectonics, changing composition of the oceans and atmosphere, and paleoclimatic regimes Also new in this Second Edition: the lower mantle and the role of the post-perovskite transition, the role of water in the mantle, new tomographic data tracking plume tails into the deep mantle, Euxinia in Proterozoic oceans, The Hadean, A crustal age gap at 2.4-2.2 Ga, and continental growth.
Article
[1] Several processes unfold during the supercontinent cycle, more than one of which might result in an elevation in subcontinental mantle temperatures, thus multiple interpretations of the concept of continental insulation exist. Although a consensus seems to have formed that sub-continental mantle upwellings appear below large continents extensively ringed by subduction zones, there are differing views on what role continental insulation plays in the production of elevated mantle temperatures. Here, we investigate how the heating mode of the mantle can change the influence of the ‘thermal blanket’ effect. We present 2D and 3D Cartesian geometry mantle convection simulations with thermally and mechanically distinct oceanic and continental plates. The evolution of mantle thermal structure is examined after continental accretion at subduction zones (e.g., the formation of Pangea) for a variety of different mantle heating modes. Our results show that in low Rayleigh number models the impact of the role of continental insulation on sub-continental temperatures increases, when compared to models with higher convective vigor. Broad, hot upper mantle features generated in low Rayleigh number models (due, in part, to the thermal blanket effect) are absent at higher Rayleigh numbers. We find that sub-continental heating in a high Rayleigh number flow occurs almost entirely as a consequence of the influence of subduction initiation at the continental margin, rather than the influence of continental insulation. In our models featuring Earth-like convective vigor, we find that it is difficult to obtain sub-continental temperatures in significant excess of sub-oceanic temperatures over timescales relevant to supercontinent aggregation.
Article
Continents slowly drift at the top of the mantle, sometimes colliding, splitting and aggregating. The evolutions of the continent configuration, as well as oceanic plate tectonics, are surface expressions of mantle convection and closely linked to the thermal state of the mantle; however, quantitative studies are so far lacking. In the present study we use 3D spherical numerical simulations with self-consistently generated plates and compositionally and rheologically distinct continents floating at the top of the mantle in order to investigate the feedbacks between continental drift, oceanic plate tectonics and the thermal state of the Earth's mantle, by using different continent configurations ranging from one supercontinent to six small continents. With the presence of a supercontinent we find a strong time-dependence of the oceanic surface heat flow and suboceanic mantle temperature, driven by the generation of new plate boundaries. Very large oceanic plates correlate with periods of hot suboceanic mantle, while the mantle below smaller oceanic plates tends to be colder. Temperature fluctuations of subcontinental mantle are significantly smaller than in oceanic regions and are caused by a time-variable efficiency of thermal insulation of the continental convection cell. With the presence of multiple continents the temperature below individual continents is generally lower than below supercontinent and is more time-dependent, with fluctuations as large as 15% that are caused by continental assembly and dispersal. The periods featuring a hot subcontinental mantle correlate with strong clustering of the continents and periods characterized by cold subcontinental mantle, at which it can even be colder than suboceanic mantle, with a more dispersed continent configuration. Our findings with multiple continents imply that periods of partial melting and strong magmatic activity inside the continents, which may contribute to continental rifting and pronounced growth of continental crust, might be episodic processes related to the supercontinent cycle. Finally, we observe an influence of continents on the wavelength of convection: for a given strength of the lithosphere we observe longer-wavelength flow components, when continents are present. This observation is regardless of the number of continents, but most pronounced for a single supercontinent.
Article
Geophysical evidence suggests the present day thermal field of the Earth is characterised by anomalously warm material beneath the African and Pacific plates. Continental insulation during the Mesozoic offers a possible explanation for why the mantle below the African plate, a former site of continental aggregation, is warmer than expected. We investigate the effect of continental insulation in 2D and 3D mantle convection models featuring mechanically and thermally distinct continental and oceanic plates to determine the significance of continental insulation. Supercontinental insulation is modelled by limiting continental surface heat flux relative to the heat flux through the isothermal surface of the oceanic plates. For 2D models, we vary continental insulation and width to assess the thermal response of the mantle to each parameter. Our findings indicate that subduction patterns determined by continental width play the dominant role in enabling the formation of subcontinental mantle upwellings. Extending our study to 3D calculations with supercontinental coverage of the mantle comparable to Pangea's, we again find that subcontinental plumes develop as a consequence of subduction patterns rather than continental thermal insulation properties. Moreover, we find that despite the presence of an overlying supercontinent with insulating properties appropriate for modelling terrestrial dynamics, averaged subcontinental mantle temperatures do not significantly exceed sub-oceanic temperatures on timescales relevant to super-continent assembly.
Article
To this day, there is a great amount of controversy about where, when and how the so-called supercontinents--Pangea, Godwana, Rodinia, and Columbia--were made and broken. Continents and Supercontinents frames that controversy by giving all the necessary background on how continental crust is formed, modified, and destroyed, and what forces move plates. It also discusses how these processes affect the composition of seawater, climate, and the evolution of life. Rogers and Santosh begin with a survey of plate tectonics, and go on to describe the composition, production, and destruction of continental and oceanic crust, and show that cratons or assemblies of cratons became the first true continents, approximately one billion years after the earliest continental crust evolved. The middle part of the book concentrates on supercontinents, beginning with a discussion of types of orogenic belts, distinguishing those that formed by closure of an ocean basin within the belt and those that formed by intracontinental deformation caused by stresses generated elsewhere. This information permits discrimination between models of supercontinent formation by accretion of numerous small terranes and by reorganization of large old continental blocks. This background leads to a description of the assembly and fragmentation of supercontinents throughout earth history. The record is most difficult to interpret for the oldest supercontinent, Columbia, and also controversial for Rodinia, the next youngest supercontinent. The configurations and pattern of breakup of Gondwana and Pangea are well known, but some aspects of their assembly are unclear. The book also briefly describes the histories of continents after the breakup of Pangea, and discusses how changes in the composition of seawater, climate, and life may have been affected by the sizes and locations of continents and supercontinents.
Article
LITHOSPHERIC plate motions at the Earth's surface result from thermal convection in the mantle1. Understanding mantle convection is made difficult by variations in the material properties of rocks as pressure and temperature increase from the surface to the core. The plates themselves result from high rock strength and brittle failure at low temperature near the surface. In the deeper mantle, elevated pressure may increase the effective viscosity by orders of magnitude2-5. The influence of depth-dependent viscosity on convection has been explored in two-dimensional numerical experiments6-8, but planforms must be studied in three dimensions. Although three-dimensional plan-forms can be elucidated by laboratory fluid dynamic experiments9,10, such experiments cannot simulate depth-dependent rheology. Here we use a three-dimensional spherical convection model11,12 to show that a modest increase in mantle viscosity with depth has a marked effect on the planform of convection, resulting in long, linear downwellings from the upper surface boundary layer and a surprisingly 'red' thermal heterogeneity spectrum, as observed for the Earth's mantle13. These effects of depth-dependent viscosity may be comparable to the effects of the plates themselves.
Article
Geologic secular trends are used to refine the timetable of supercontinent assembly, tenure, and breakup. The analysis rests on what is meant by the term supercontinent, which here is defined broadly as a grouping of formerly dispersed continents. To avoid the artificial pitfall of an all-or-nothing definition, quantitative measures of "supercontinentality" are presented: the number of continents, and the area of the largest continent, which both can be gleaned from global paleogeographic maps for the Phanerozoic. For the secular trends approach to be viable in the deep past when the very existence of supercontinents is debatable and reconstructions are fraught with problems, it must first be calibrated in the Phanerozoic against the well-constrained Pangea supercontinent cycle. The most informative geologic variables covering both the Phanerozoic and Precambrian are the abundances of passive margins and of detrital zircons. Both fluctuated with size of the largest continent during the Pangea supercontinent cycle and can be quantified back to the Neoarchean. The tenure of Pangea was a time represented in the rock record by few zircons and few passive margins. Thus, previously documented minima in the abundance of detrital zircons (and orogenic granites) during the Precambrian (Condie et al., 2009a, Gondwana Research 15, 228-242) now can be more confidently interpreted as marking the tenures of supercontinents. The occurrences of carbonatites, granulites, eclogites, and greenstone-belt deformation events also appear to bear the imprint of Precambrian supercontinent cyclicity. Together, these secular records are consistent with the following scenario. The Neoarchean continental assemblies of Superia and Sclavia broke up at ca. 2300 and ca. 2090 Ma, respectively. Some of their fragments collided to form Nuna by about 1750 Ma; Nuna then grew by lateral accretion of juvenile arcs during the Mesoproterozoic, and was involved in a series of collisions at ca. 1000 Ma to form Rodinia. Rodinia broke up in stages from ca. 1000 to ca. 520 Ma. Before Rodinia had completely come apart, some of its pieces had already been reassembled in a new configuration, Gondwana, which was completed by 530 Ma. Gondwana later collided with Laurentia, Baltica, and Siberia to form Pangea by about 300 Ma. Breakup of Pangea began at about 180 Ma (Early Jurassic) and continues today. In the suggested scenario, no supercontinent cycle in Earth history corresponded to the ideal, in which all the continents were gathered together, then broke apart, then reassembled in a new configuration. Nuna and Gondwana ended their tenures not by breakup but by collision and name change; Rodinia's assembly overlapped in time with its disassembly; and Pangea spalled Tethyan microcontinents throughout much of its tenure. Many other secular trends show a weak or uneven imprint of the supercontinent cycle, no imprint at all. Instead, these secular trends together reveal aspects of the shifting background against which the supercontinents came and went, making each cycle unique. Global heat production declined; plate tectonics sped up through the Proterozoic and slowed down through the Phanerozoic; the atmosphere and oceans became oxidized; life emerged as a major geochemical agent; some rock types went extinct or nearly so (BIF, massif-type anorthosite, komatiite); and other rock types came into existence or became common (blueschists, bioclastic limestone, coal).
Article
The goal of this study is to evaluate the global age distribution of granitoid magmatism and juvenile continental crust production with U/Pb isotopic ages from igneous and detrital zircons, and with Nd isotopic data. Granitoid age peaks, which are largely defined by TIMS data, are narrow and precise in contrast to detrital peaks that are often broad and hump-shaped due to the larger uncertainties of SHRIMP and LAM-ICPMS data. Granitic age peaks do not always have detrital counterparts and vice versa. Possible contributing factors to this mismatch are removal of crustal sources by erosion, inadequate sampling of granitoids because of cover by younger rocks, or small age peaks hidden by large age peaks in detrital spectra.Seven igneous peaks are found on five or more cratons or continents (3300, 2700, 2680, 2500, 2100, 1900 and 1100 Ma) and seven detrital peaks occur on three or more continents (2785, 2700, 2600, 2500, 1900, 1650 and 1200 Ma). Nd isotope distributions suggest important additions of juvenile continental crust at 2700, 2500, 2120, 1900, 1700, 1650, 800, 570 and 450 Ma. Tight clusters of craton ages occur for Superior–Karelia, Sao Francisco–Nain, and Kaapvaal–Siberia in the early Archean and for Wyoming–Kaapvaal–Slave, Superior–Nain, and West Africa–Amazonia in the late Archean. The global 2700-Ma peak is not a simple spike, but involves several peaks between 2760 and 2650 Ma. Events older than 3700 Ma are limited to the Yilgarn, Slave, Nain and North China cratons, and events between 2600 and 2500 Ma are widespread only in East Asia, Central and East Africa, and India.Single, short-lived mantle plume events at 2700 and 1900 Ga (or any other time) cannot easily account for prolonged episodes of granitoid magmatism during the Precambrian. The causes of geographically widespread and geographically restricted events are probably not the same.
Article
Supercontinents play an important role in Earth's history. The exact definition of what constitutes a super-continent is difficult to establish. Here the argument is made, using Pangaea as a model, that any superconti-nent should include ~ 75% of the preserved continental crust relevant to the time of maximum packing. As an example, Rodinia reached maximum packing at about 1.0 Ga and therefore should include 75% of all conti-nental crust older than 1.0 Ga. In attempting to 'name' any supercontinent, there is a clear precedent for models that provide a name along with a testable reconstruction within a reasonable temporal framework. Both Pangaea and Rodinia are near universally accepted names for the late Paleozoic and Neoproterozoic su-percontinent respectively; however, there is a recent push to change the Paleo-Mesoproterozoic superconti-nent
Article
The development of U-Th-Pb and Sm-Nd isotopic signatures in a convecting mantle is studied using a numerical convection model with melting-induced differentiation and tracking of major and trace elements. The models include secular cooling and the decay of heat-producing elements, a rudimentary "self-consistent" treatment of plate tectonics, and both olivine system and garnet-pyroxene system phase transitions. The system self-consistently evolves regions with a high μ(=U/Pb) (HIMU)-like Pb signature and regions with low 143Nd/ 144Nd. However, the isotopic "age" determined from the slope in (207Pb/204Pb)-(206Pb/204Pb) space is much larger than observed. Several hypotheses are examined to explain this discrepancy. Sampling length scale has a minimal effect on age. The extent of crustal settling above the core-mantle boundary makes some difference but not enough. More frequent remelting is a possible explanation but requires the rate of crustal production to have been much higher in the past. Not introducing HIMU into the mantle prior to 2.0-2.5 Gyr before present, because of a change in the surface oxidization environment or subduction zone processes, can account for the difference, but its effect on other isotope systems needs to be evaluated. Improved treatment of the stretching of heterogeneities, which reduces them to length scales at which they cease to be identifiable magma sources, greatly reduces the Pb-Pb age. The mantle develops substantial chemical stratification from a homogeneous start, including stratification around 660 km caused by the two-component phase transitions. A deep layer of subducted crust may provide storage for some of the "missing" heat-producing elements. Magmatic heat transport is important in the first 2 Gyr of model time.
Article
1] The formation of longest-wavelength mantle convection in the sluggish-lid regime is investigated using a three-dimensional spherical model. The bottom Rayleigh number is fixed at 10 7 . Considering temperature-dependent rheology, degree-one dominant thermal convection occurs for both purely basal heating and mixed (i.e., basal and internal) heating modes. For the purely basal heating mode, degree-one convection occurs when the viscosity contrast due to temperature-dependent rheology is 10 3 –10 4 in both Boussinesq and extended-Boussinesq fluids. However, with extended-Boussinesq fluid, degree-one convection may only occur in the basal heating mode: In the mixed heating mode, degree-one convection shifts to one with high-degree modes, presumably because of enhanced viscous dissipation in the highly viscous lid over up/ downwelling plumes. The geophysically relevant degree-two convection with sheet-like downwellings is not observed in this study. The inclusion of visco-plastic rheology in the top part of the mantle breaks down degree-one convection. Citation: Yoshida, M. (2008), Mantle convection with longest-wavelength thermal heterogeneity in a 3-D spherical model: Degree one or two?, Geophys. Res. Lett., 35, L23302, doi:10.1029/2008GL036059.
Chapter
First published in 1982, Don Turcotte and Jerry Schubert's Geodynamics became a classic textbook for several generations of students of geophysics and geology. The authors bring this text completely up-to-date in this second edition. Important additions include a chapter on chemical geodynamics, an updated coverage of comparative planetology based on recent planetary missions, and a variety of other new topics. Geodynamics provides the fundamentals necessary for an understanding of the workings of the solid earth, describing the mechanics of earthquakes, volcanic eruptions, and mountain building in the context of the role of mantle convection and plate tectonics. Observations such as the earth's gravity field, surface heat flow, distribution of earthquakes, surface stresses and strains, and distribution of elements are discussed.
Article
Understanding the formation of cratons and orogenic belts is critical to the modelling of supercontinental assemblies. Continental cratons began to assemble by 3000 Ma or possibly earlier. The oldest assembly, Ur, was followed by Arctica at ∼2500 Ma and Atlantica at ∼2000 Ma. These three continental blocks apparently remained coherent until the breakup of Pangea. Nearly all of earth's continental blocks were assembled into one large landmass during at least three times in earth history. The oldest assembly comparable in size to Pangea was probably Columbia, which formed at ∼1800 Ma and began to rift at ∼1500 Ma. Columbia was followed by Rodinia, which lasted from ∼1100 Ma to 700 Ma. East and West Gondwana combined to form Gondwana at ∼500 Ma, and it joined with Laurasia to form Pangea at ∼250 Ma.
Article
Many Archean cratons are surrounded by Proterozoic mobile belts that have experienced episodes of tectonic re-activation over their lifetimes. This suggests that mobile belt lithosphere may be associated with long lived, inherited weakness. It is proposed that the proximity of this weakness can increase the longevity of deep Archean lithosphere by buffering Archean cratons from mantle derived stresses. The physical plausibility of this idea is explored through numerical simulations of mantle convection that include continents and allow for material rheologies that model the combined brittle and ductile behavior of the lithosphere. Within the simulations, the longevity of deep cratonic lithosphere does increase if it is buffered by mobile belts that can fail at relatively low stress levels.
Article
The first time-dependent numerical simulations of continental aggregation and dispersal demonstrate a dynamic feedback between the motion of continental plates and mantle convection. Plate velocity is intrinsically episodic. Continental plates aggregate over cold downwellings and inhibit subduction and mantle cooling; the mantle overheats and fragments the continent under tension. Overall, the models are in agreement with the present geophysical state of the mantle and the geological record over the last 200 million years.
  • P Brandl
  • M Regelous
  • C Beler
  • K Haase
Brandl, P., M. Regelous, C. Beler, and K. Haase (2013), High mantle temperatures following rifting caused by continental insulation, Nat. Geosci., 6, 391–394.
  • B Phillips
  • H.-P Bunge
Phillips, B., and H.-P. Bunge (2007), Supercontinent cycles disrupted by strong mantle plumes, Geology, 35(9), 847–850.