Article

# Linking continental drift, plate tectonics and the thermal state of the Earth's mantle

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## Abstract

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.

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... Many previous studies of supercontinent dynamics explored the roles of dynamically self-consistently-generated mantle plumes under a supercontinent (Gurnis, 1988;Lowman & Jarvis, 1995;Zhong & Gurnis, 1995;Phillips & Bunge, 2007;Zhong et al., 2007;Li & Zhong, 2009;Zhang et al., 2009;Rolf et al., 2012;Yoshida, 2014b;Zhang et al., 2018). These studies commonly emphasized the importance of plume-push force during the break-up of the supercontinent. ...
... This plasticity formulation is widely used in mantle convection simulations (e.g., Tackley, 2000;Foley & Becker, 2009;Rolf et al., 2012;Yoshida, 2014a). ...
... Here  c is set to be 100 times of the viscosity of oceanic lithosphere (Zhang et al., 2009;Yoshida, 2014a). The  c is set to be -50 kg/m 3 (Poudjom Djomani et al., 2001;Yoshida, 2013;Rolf et al., 2012). ...
... Previous studies of supercontinent and global mantle dynamics (Zhong et al., 2007;Yoshida, 2008;Li and Zhong, 2009;Zhang et al., 2009Zhang et al., , 2010Rolf and Tackley, 2011;Rolf et al., 2012;Yoshida, 2014Yoshida, , 2016) established a good framework for investigating the force balance during supercontinent breakup. The dynamic effects of continental suture zones, rheology and strength have been carefully investigated in Rolf and Tackley (2011), Rolf et al. (2012), and Yoshida (2014). ...
... Previous studies of supercontinent and global mantle dynamics (Zhong et al., 2007;Yoshida, 2008;Li and Zhong, 2009;Zhang et al., 2009Zhang et al., , 2010Rolf and Tackley, 2011;Rolf et al., 2012;Yoshida, 2014Yoshida, , 2016) established a good framework for investigating the force balance during supercontinent breakup. The dynamic effects of continental suture zones, rheology and strength have been carefully investigated in Rolf and Tackley (2011), Rolf et al. (2012), and Yoshida (2014). These studies emphasized the importance of continental size, yield stress, or a weak zone within a supercontinent in destabilizing the supercontinent. ...
... . This plasticity formulation is commonly used in previous studies (e.g., Tackley, 2000;Foley and Becker, 2009;Rolf et al., 2012;Yoshida, 2014). ...
Article
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Understanding the dominant force responsible for supercontinent breakup is crucial for establishing Earth’s geodynamic evolution that includes supercontinent cycles and plate tectonics. Conventionally, two forces have been considered: the push by mantle plumes from the sub-continental mantle which is called the active force for breakup, and the dragging force from oceanic subduction retreat which is called the passive force for breakup. However, the relative importance of these two forces is unclear. Here we model the supercontinent breakup coupled with global mantle convection in order to address this question. Our global model features a spherical harmonic degree-2 structure, which includes a major subduction girdle and two large upwelling (superplume) systems. Based on this global mantle structure, we examine the distribution of extensional stress applied to the supercontinent by both sub-supercontinent mantle upwellings and subduction retreat at the supercontinent peripheral. Our results show that: (1) at the center half of the supercontinent, plume push stress is ∼3 times larger than the stress induced by subduction retreat; (2) an average hot anomaly of no higher than 50 K beneath the supercontinent can produce a push force strong enough to cause the initialization of supercontinent breakup; (3) the extensional stress induced by subduction retreat concentrates on a ∼600 km wide zone on the boundary of the supercontinent, but has far less impact to the interior of the supercontinent. We therefore conclude that although circum-supercontinent subduction retreat assists supercontinent breakup, sub-supercontinent mantle upwelling is the essential force.
... A long-standing challenge for such models is their ability to incorporate self-consistently Earth's continents (Gurnis, 1988;Zhong & Gurnis, 1993, 1995Tackley, 1998Tackley, , 2000aTackley, , 2000bLenardic et al., 2005;Heron & Lowman, 2010Rolf & Tackley, 2011;Rolf et al., 2012;Yoshida, 2013;Jellinek & Jackson, 2015), which are believed to affect the Earth's evolution substantially (Grigné & Labrosse, 2001;Korenaga, 2008). With the notable exception of Cooper et al. (2006), these studies have however neglected the enrichment of continents in long-lived radioactive isotopes. ...
... Rheology is a long-standing issue in models of planetary mantles. Traditionally, Newtonian rheologies with temperature and pressure dependent viscosity is considered for the bulk mantle, while rheology with plastic yielding have been used at the surface to mimic plate-like behaviour (Rolf & Tackley, 2011;Rolf et al., 2012;Yoshida, 2013). ...
... This observation has led some authors to model continents by prescribing an insulator layer at the top surface (Heron & Lowman, 2010. Alternatively, other authors prescribed a large viscosity jump within continents (Gurnis, 1988;Zhong & Gurnis, 1993;Lenardic et al., 2005Lenardic et al., , 2011Rolf & Tackley, 2011;Rolf et al., 2012;Cooper et al., 2013) inducing a thicker thermal boundary layer, in agreement with the higher thickness of the continental lithosphere compared to the oceanic lithosphere, which in turn causes an insulation effect. These models, however, do not include the enrichment in heat producing elements within continents. ...
Preprint
Earth's continents are characterized by a strong enrichment in long-lived radioactive isotopes. Recent estimates suggest that they contribute to 33\% of the heat released at the surface of the Earth, while occupying less than 1\% of the mantle. This distinctive feature has profound implications for the underlying mantle by impacting its thermal structure and heat transfer. However, the effects of a continental crust enriched in heat-producing elements on the underlying mantle have not yet been systematically investigated. Here, we conduct a preliminary investigation by considering a simplified convective system consisting in a mixed heated fluid where all the internal heating is concentrated in a top layer of thickness $d_{HL}$ (referred to as "heat-blanketed convection"). We perform 24 numerical simulations in 3D Cartesian geometry for four specific set-ups and various values of $d_{HL}$. Our results suggest that the effects of the heated layer strongly depend on its thickness relative to the thickness of the thermal boundary layer ($\delta_{TBL}$) in the homogeneous heating case ($d_{HL} = 1.0$). More specifically, for $d_{HL} > \delta_{TBL}$, the effects induced by the heated layer are quite modest, while, for $d_{HL} < \delta_{TBL}$, the properties of the convective system are strongly altered as $d_{HL}$ decreases. In particular, the surface heat flux and convective vigour are significantly enhanced for very thin heated layers compared to the case $d_{HL} = 1.0$. The vertical distribution of heat producing elements may therefore play a key role on mantle dynamics. For Earth, the presence of continents should however not affect significantly the surface heat flux, and thus the Earth's cooling rate.
... The conductivities of the olivine aggregates with various ilmenite contents can be applied to invert the magnetotelluric (MT) profiles, and further research electrical structures of the Earth's upper mantle. Combining with the electrical conductivities of olivine-ilmenite systems and the thermal models of the Earth's continental upper mantle and oceanic upper mantle (Rolf et al., 2012), the electrical conductivity-depth profiles of the olivine aggregates with various ilmenite contents in the continental and oceanic upper mantles were constructed in detail ( Figures 11A-C). Q12 Figure 12, the conductivities of dry olivine aggregates with a certain content of ilmenites at the same depth beneath the (Rolf et al., 2012), which were used to construct electrical conductivity-depth profiles for olivine aggregates with various ilmenite contents in the Earth's oceanic upper mantle (B) and continental upper mantle (C). ...
... Combining with the electrical conductivities of olivine-ilmenite systems and the thermal models of the Earth's continental upper mantle and oceanic upper mantle (Rolf et al., 2012), the electrical conductivity-depth profiles of the olivine aggregates with various ilmenite contents in the continental and oceanic upper mantles were constructed in detail ( Figures 11A-C). Q12 Figure 12, the conductivities of dry olivine aggregates with a certain content of ilmenites at the same depth beneath the (Rolf et al., 2012), which were used to construct electrical conductivity-depth profiles for olivine aggregates with various ilmenite contents in the Earth's oceanic upper mantle (B) and continental upper mantle (C). Electrical conductivities of olivine aggregates were calculated based on the thermodynamic parameters of the Arrhenius (Continued ) FIGURE 12 | relation (Dai et al., 2019), and the conductivities of the olivine-ilmenite systems and ilmenite aggregates were calculated based on the thermodynamic parameters in this study. ...
Article
Full-text available
Ilmenite is a common metallic oxide distributed in the mafic rocks from the Earth’s upper mantle, and thus the effect of ilmenite contents on the electrical structures of the Earth’s upper mantle should be investigated in detail. Electrical conductivities of the olivine–ilmenite systems with various contents of ilmenite (VIlm = 4, 7, 10, 11 and 15 vol%) and pure ilmenite aggregates were measured using a complex impedance spectroscopic technique at 1.0–3.0 GPa and 773–1273 K. Electrical conductivities of the olivine–ilmenite systems increased with increasing temperatures in different degrees, conforming to the Arrhenius law. With the rise of pressure, the conductivities of the olivine–ilmenite systems slightly increased. According to the significant change of the conductivities, the percolation threshold of ilmenite grains in the olivine–ilmenite systems was proposed to be ∼ 11 vol%. Isolated ilmenites moderately influence the conductivities of olivine aggregates, but the interconnected ilmenites dramatically enhanced the conductivities of the olivine–ilmenite systems. The conductivities of the olivine aggregates with 11 vol% ilmenites were about 1.5–3 orders magnitude higher than those of 10 vol% ilmenites-bearing olivine aggregates. Small polarons were proposed to be the dominant charge carriers for olivine aggregates with isolated ilmenites (activation enthalpies: 0.62–0.89 eV) and interconnected ilmenites (activation enthalpies: 0.15–0.20 eV). Furthermore, the conductivity–depth profiles of olivine–ilmenite systems in the Earth’s upper mantle were constructed, providing an important constraint on the electrical structures of the Earth’s interior.
... In addition, a large geoid high similar to that over presentday Africa would be generated sub-supercontinent as a result of the thermal expansion caused by the continental insulation. Subsequent numerical (e.g., Zhong and Gurnis, 1993;Jarvis, 1993, 1999;Yoshida et al., 1999;Lenardic et al., 2005;Phillips and Bunge, 2005;Coltice et al., 2007Coltice et al., , 2009Phillips et al., 2009;Phillips and Coltice, 2010;Yoshida, 2010; Lenardic et al., 2011;Rolf et al., 2012) and geochemical (Brandl et al., 2013;Brown and Johnson, 2018) studies suggest an important role for continental insulation in producing increased sub-continental mantle temperatures. ...
... Despite generating very similar trends to this study for Pangaean heat flux with and without thermo-chemical piles,Zhang and Zhong (2011) highlighted the fluctuating heat flux between 100 Ma and the present-day as being marks a first step in the classification of periods of continental convergence and amalgamation over geologic time through identifying mantle thermal responses to the convergence, assembly and dispersal stages of supercontinents. We do not model continental material which, in itself, has an impact on mantle dynamics through modifying the wavelength of mantle flow(Gringé et al., 2007;Phillips et al., 2009;Rolf et al., 2012) and the initiation and polarity of subduction (e.g.,Crameri and Tackley, 2014), alongside topographic and sea-level influences. However, we do prescribe surface velocities from plate reconstructionsMerdith et al., 2017) that may help to artificially capture some aspects of these mantle dynamics. ...
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.
... A genetic relationship between large-scale mantle flow and the dynamics of the supercontinent cycle is commonly assumed 64,74,76,86,164 , although deciphering the evolution of such convective models throughout Earth history has remained elusive. Numerical simulations of mantle convection 74 , particularly those including the influence of continents 164,165 , starting with random flow (Fig. 3a), arrive at degree 1 structures, as smaller downwellings (or upwellings) gradually merge together until only one of each remain (superdownwelling and superupwelling, respectively) and are antipodal (Fig. 3b). ...
... A genetic relationship between large-scale mantle flow and the dynamics of the supercontinent cycle is commonly assumed 64,74,76,86,164 , although deciphering the evolution of such convective models throughout Earth history has remained elusive. Numerical simulations of mantle convection 74 , particularly those including the influence of continents 164,165 , starting with random flow (Fig. 3a), arrive at degree 1 structures, as smaller downwellings (or upwellings) gradually merge together until only one of each remain (superdownwelling and superupwelling, respectively) and are antipodal (Fig. 3b). Supercontinent formation is a likely, if not inevitable, outcome of degree 1 flow, as continents would converge towards and then aggregate over the developing mantle superdownwelling 74,76,86 , although subduction zone initiation elsewhere can modify such a degree 1 planform 166 . ...
Article
Full-text available
Supercontinents signify self-organization in plate tectonics. Over the past ~2 63 billion years, 3 major supercontinents have been identified, with increasing age: Pangaea, 64 Rodinia, and Columbia. In a prototypal form, a cyclic pattern of continental assembly and 65 breakup likely extends back to ~3 billion years ago, albeit on the smaller scale of Archaean 66 supercratons which, unlike global supercontinents, were tectonically segregated. The 67 emergence of supercontinents provides a firm minimum age for the onset of the modern 68 global plate tectonic network, whereas supercratons might reflect an earlier geodynamic and 69 nascent tectonic regime. The assembly and breakup of Pangaea attests that the supercontinent 70 cycle is intimately linked with whole mantle convection. In this Review, the supercontinent 71 cycle is interpreted both as an effect and a cause of mantle convection, emphasizing the 72 importance of both top-down and bottom-up geodynamics and the coupling between them. 73 However, the nature of this coupling and how it has evolved remains highly controversial, 74 resulting in strikingly contrasting models of supercontinent formation. Conceptual models 75 can be tested by quantitative geodynamic modeling and geochemical proxies. Specifically, 76 which oceans close to create a supercontinent, and how such predictions are linked to mantle 77 convection, are directions for future research. 78 79
... Many numerical studies have shown that the combination of supercontinent coverage and insulation can generate sub-supercontinental temperatures higher than sub-oceanic mantle material, suggesting that continental insulation acts as the main driver for supercontinent break-up (e.g. Gurnis 1988;Zhong & Gurnis 1993;Lowman & Jarvis 1993, 1999Bobrov et al. 1999;Yoshida et al. 1999;Phillips & Bunge 2005;Coltice et al. 2007;Trubitsyn et al. 2008;Coltice et al. 2009;Phillips et al. 2009;Phillips & Coltice 2010;Yoshida 2010;Rolf et al. 2012). A geochemical study into ancient lava samples from the Atlantic Ocean indicates increased mantle temperatures relative to Pacific Ocean samples during the dispersal of the supercontinent Pangaea (Brandl et al. 2013). ...
... Although many studies have shown the importance of continental insulation (e.g. Gurnis 1988;Zhong & Gurnis 1993;Lowman & Jarvis 1993, 1999Bobrov et al. 1999;Yoshida et al. 1999;Phillips & Bunge 2005;Coltice et al. 2007;Trubitsyn et al. 2008;Coltice et al. 2009;Phillips et al. 2009;Phillips & Coltice 2010;Yoshida 2010;Rolf et al. 2012), other studies have indicated a lesser impact on mantle dynamics (Heron & Lowman 2011;Yoshida 2013;Heron & Lowman 2014), alongside cases where continental insulation would, in fact, promote cooling of the mantle (Lenardic et al. 2005). In threedimensional numerical simulations of mantle convection, Yoshida (2013) showed the difficulty in obtaining sub-continental temperatures in excess of sub-oceanic temperatures on timescales relevant to supercontinent episodes for Earth-like Rayleigh numbers, despite the thermal blanket effect of an insulating continent and the formation of sub-continental plumes. ...
Article
Full-text available
This review discusses the thermal evolution of the mantle following large-scale tectonic activities such as continental collision and continental rifting. About 300 myr ago, continental material amalgamated through the large-scale subduction of oceanic seafloor, marking the termination of one or more oceanic basins (e.g. Wilson cycles) and the formation of the supercontinent Pangaea. The present day location of the continents is due to the rifting apart of Pangaea, with the dispersal of the supercontinent being characterized by increased volcanic activity linked to the generation of deep mantle plumes. The discussion presented here investigates theories regarding the thermal evolution of the mantle (e.g. mantle temperatures and sub-continental plumes) following the formation of a supercontinent. Rifting, orogenesis and mass eruptions from large igneous provinces change the landscape of the lithosphere, whereas processes related to the initiation and termination of oceanic subduction have a profound impact on deep mantle reservoirs and thermal upwelling through the modification of mantle flow. Upwelling and downwelling in mantle convection are dynamically linked and can influence processes from the crust to the core, placing the Wilson cycle and the evolution of oceans at the forefront of our dynamic Earth.
... 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). ...
... g d describes the depth-dependence, characterised by a viscosity jump Dg R at 660 km depth. Here, 1 ≤ Dg R ≤ 100 is variable (while it was fixed at Dg R = 1 in Rolf et al., 2012Rolf et al., , 2014. However, in order to keep the globally averaged viscosity unchanged, the condition Rs Rc g d dV = 1 is enforced. ...
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.
... In this paper we draw on the results of extensive theoretical, numerical, and laboratory studies of the mechanical and insulating effects of continents on mantle convection (Coltice et al., 2009;Grigné et al., 2007;Korenaga, 2007;Lenardic et al., 2005Lenardic et al., , 2011O'Neill et al., 2009;Phillips & Coltice, 2010;Rolf et al., 2012) to investigate a hypothesis that the temporal cold-warm climate pattern characteristic of the Pangean and Rodinian climates and the absence of any significant climate change related to the Nuna epoch are primarily consequences of differing effects of the formation and breakup of supercontinents on the structure and heat transfer properties of Earth's mantle convective regime. A more general motivation for this paper is the question of the extent to which Earth's record of long-term climate variability can rigorously constrain key features of Earth's current plate tectonic mode of mantle convection. ...
... Whether this extensive magmatism reflects an increased mantle heatflow related to effects of the Nuna supercontinent on the structure and planform of upwelling motions in a thermally well-stirred mantle (Hoffman, 1989) or requires enhanced subcontinental mantle temperatures and melting more characteristic of mantle thermal isolation is unclear on petrologic grounds (e.g., Longhi, 2005;Morse, 1982;Taylor et al., 1984)Enhanced mantle temperatures are, for example, not required by statistical reconstructions of the MgO contents of mafic melts and of the extent of mantle melting during this period (Keller & Schoene, 2012). However, a marked feature of simulations with extensive (or assumed extensive) mantle thermal mixing is that mantle upwelling flows can become reorganized and focused beneath a growing or well-established supercontinent (e.g., Coltice et al., 2009;Grigné et al., 2007;Holmes, 1931;Lenardic et al., 2011;Li & Zhong, 2009;O'Neill et al., 2009;Pekeris, 1935;Rolf et al., 2012). Thus, an absence of significant ice sheets and the extensive occurrence of anorthosite massifs and related granitic and granodioritic plutonic bodies are not unexpected. ...
... Many numerical studies have shown that the combination of supercontinent coverage and insulation can generate sub-supercontinental temperatures higher than sub-oceanic mantle material, suggesting that continental insulation acts as the main driver for supercontinent break-up (e.g. Gurnis 1988;Zhong & Gurnis 1993;Lowman & Jarvis 1993, 1999Bobrov et al. 1999;Yoshida et al. 1999;Phillips & Bunge 2005;Coltice et al. 2007;Trubitsyn et al. 2008;Coltice et al. 2009;Phillips et al. 2009;Phillips & Coltice 2010;Yoshida 2010;Rolf et al. 2012). A geochemical study into ancient lava samples from the Atlantic Ocean indicates increased mantle temperatures relative to Pacific Ocean samples during the dispersal of the supercontinent Pangaea (Brandl et al. 2013). ...
... Although many studies have shown the importance of continental insulation (e.g. Gurnis 1988;Zhong & Gurnis 1993;Lowman & Jarvis 1993, 1999Bobrov et al. 1999;Yoshida et al. 1999;Phillips & Bunge 2005;Coltice et al. 2007;Trubitsyn et al. 2008;Coltice et al. 2009;Phillips et al. 2009;Phillips & Coltice 2010;Yoshida 2010;Rolf et al. 2012), other studies have indicated a lesser impact on mantle dynamics (Heron & Lowman 2011;Yoshida 2013;Heron & Lowman 2014), alongside cases where continental insulation would, in fact, promote cooling of the mantle (Lenardic et al. 2005). In threedimensional numerical simulations of mantle convection, Yoshida (2013) showed the difficulty in obtaining sub-continental temperatures in excess of sub-oceanic temperatures on timescales relevant to supercontinent episodes for Earth-like Rayleigh numbers, despite the thermal blanket effect of an insulating continent and the formation of sub-continental plumes. ...
... On Earth, however, one runs the risk of being mistaken because of the many complicating factors involved, which include the presence of continents or multiple mantle phase changes (e.g. Gurnis 1988;Guillou & Jaupart 1995;Tackley 1998b;Stixrude & Lithgow-Bertelloni 2011;Rolf, Coltice & Tackley 2012). Thus, whether all the available observations form a self-consistent set, such that they can all be accounted for by the workings of a single convective system, is an important issue. ...
Article
Motions in the solid mantle of silicate planets are predominantly driven by internal heat sources and occur in laminar regimes that have not been systematically investigated. Using high-resolution numerical simulations conducted in three dimensions for a large range of Rayleigh–Roberts numbers ( $5\times 10^{3}\leqslant Ra_{H}\leqslant 10^{9}$ ), we have determined the characteristics of flow in internally heated fluid layers with both rigid and free slip boundaries. Superficial planforms evolve with increasing $Ra_{H}$ from a steady-state tessellation of hexagonal cells with axial downwellings to time-dependent clusters of thin linear downwellings within large areas of nearly isothermal fluid. The transition between the two types of planforms occurs as a remarkable flow polarity reversal over a small $Ra_{H}$ range, such that downwellings go from isolated cylindrical structures encircled by upwellings to thin interconnected linear segments outlining polygonal cells. In time-dependent regimes at large values of $Ra_{H}$ , linear downwellings dominate the flow field at shallow depth but split and merge at intermediate depths into nearly cylindrical plume-like structures that go through the whole layer. With increasing $Ra_{H}$ , the number of plumes per unit area and their velocities increase whilst the amplitude of thermal anomalies decreases. Scaling laws for the main flow characteristics are derived for $Ra_{H}$ values in a $10^{6}$ – $10^{9}$ range. For given $Ra_{H}$ , plumes are significantly colder, narrower and wider apart beneath free boundaries than beneath rigid ones. From the perspective of planetary studies, these results alert to the dramatic changes of convective planform that can occur along secular cooling.
... The hypothesis has been tested through numerical modelling with contrasting results; several authors have found that the formation of supercontinents would cause sufficient thermal insulation of the mantle to raise temperatures enough to produce melting (e.g. Coltice et al. 2009;Rolf et al. 2012), whereas others have found that this is not the case and that the formation of LIPs after supercontinent amalgamation is likely to be a response to subducting slabs surrounding the supercontinent (e.g. Heron & Lowman 2010;Heron et al. 2015). ...
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.
... The divergent flow of the thermally insulated hotter mantle beneath a newly forming rift zone gives rise to additional stress, without which it is difficult to get the passive margin to collapse, implying an important role of the continents in our model. Other studies have also demonstrated the effect of the continental cover on mantle dynamics, continental drift and break-up of supercontinents through rifting (e.g., Coltice et al., 2009;Heron and Lowman, 2011;Rolf et al., 2012). In addition to the mantle drag resulting from the thermal blanketing, the continents act to increase the stress acting on the passive margins by inducing edge-driven flow in the underlying mantle (King and Anderson, 1998). ...
Article
The collapse of passive margins has been proposed as a possible mechanism for the spontaneous initiation of subduction. In order for a new trench to form at the junction between oceanic and continental plates, the cold and stiff oceanic lithosphere must be weakened sufficiently to deform at tectonic rates. Such rates are especially hard to attain in the cold ductile portion of the lithosphere, at which the mantle lithosphere reaches peak strength. The amount of weakening required for the lithosphere to deform in this tectonic setting is dictated by the available stress. Stress in a cooling passive margin increases with time (e.g., due to ridge push), and is augmented by stresses present in the lithosphere at the onset of rifting (e.g., due to drag from underlying mantle flow). Increasing stress has the potential to weaken the ductile portion of the lithosphere by dislocation creep, or by decreasing grain size in conjunction with a grain-size sensitive rheology like diffusion creep. While the increasing stress acts to weaken the lithosphere, the decreasing temperature acts to stiffen it, and the dominance of one effect or the other determines whether the margin might weaken and collapse. Here, we present a model of the thermal and mechanical evolution of a passive margin, wherein we predict formation of a weak shear zone that spans a significant depth-range of the ductile portion of the lithosphere. Stiffening due to cooling is offset by weakening due to grain size reduction, driven by the combination of imposed stresses and grain damage. Weakening via grain damage is modest when ridge push is the only source of stress in the lithosphere, making the collapse of a passive margin unlikely in this scenario. However, adding even a small stress-contribution from mantle drag results in damage and weakening of a significantly larger portion of the lithosphere. We posit that rapid grain size reduction in the ductile portion of the lithosphere can enable, or at least significantly facilitate, the collapse of a passive margin and initiate a new subduction zone. We use this model to estimate the conditions for passive margin collapse for modern and ancient Earth, as well as for Venus.
... However, it is stable in the initial stage without imposed plate motions and in the stage with imposed plate motions (see the next subsection). Hence, the typical non-dimensional viscosity 18 N. Coltice and G.E. Shephard in the upper mantle (except in slabs) is around 10 −1 as seen from Fig. 2. We consider a stress dependence of the viscosity through a pseudo-plastic approximation in order to produce plate boundaries surrounding strong plate interiors (see, for instance Rolf et al. 2012). This choice leads to stiff slabs and one-sided subduction with imposed plate kinematics, as described by Bello et al. (2015). ...
Article
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Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough for an accurate prediction of instantaneous flow, but not for a prediction after 10 My of evolution. Therefore, inverse methods (sequential or data assimilation methods) using short-term fully dynamic evolution that predict surface kinematics are promising tools for a better understanding of the state of the Earth's mantle.
... 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. ...
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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.
... glossopterisové flóry zachované v Indii, Jižní Africe a Antarktidě, ale i výskyty charnockitů a doleritů; viz např. Torsvik et al. 2010, Rolf et al. 2012, Rundić 2012. ...
... Since the 1990s, numerical convection models of mantle convection can generate self-consistent plate-like behavior [Moresi and Solomatov, 1998;Trompert and Hansen, 1998;Tackley, 2000Tackley, , 2008. These calculations have allowed to uncover that the plates layout depends on the models parameterizations [Stein et al., 2004;Van Heck and Tackley, 2008;Foley and Becker, 2009], and have helped to better understand dynamic feedbacks between mantle convection and the strength of the lithosphere [Rolf et al., 2012;Mallard et al., 2016]. ...
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Mantle convection models with plate-like behavior produce surface structures comparable to Earth's plate boundaries. However, analyzing those structures is a difficult task, since convection models produce, as on Earth, diffuse deformation and elusive plate boundaries. Therefore we present here and share a quantitative tool to identify plate boundaries and produce plate polygon layouts from results of numerical models of convection: Automatic Detection Of Plate Tectonics (ADOPT). This digital tool operates within the free open-source visualization software Paraview. It is based on image segmentation techniques to detect objects. The fundamental algorithm used in ADOPT is the watershed transform. We transform the output of convection models into a topographic map, the crest lines being the regions of deformation (plate boundaries) and the catchment basins being the plate interiors. We propose two generic protocols (the field and the distance methods) that we test against an independent visual detection of plate polygons. We show that ADOPT is effective to identify the smaller plates and to close plate polygons in areas where boundaries are diffuse or elusive. ADOPT allows the export of plate polygons in the standard OGR-GMT format for visualization, modification and analysis under generic softwares like GMT or GPlates.
... We use a stress dependence of the viscosity through a pseudo-plastic approximation in order to produce plate boundaries surrounding strong plate interiors [see for instance Rolf et al., 2012]. This choice leads to stiff slabs as described by Bello et al. [2015]. ...
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The existence of undulations of the geoid, gravity and bathymetry in ocean basins, as well as anomalies in heat flow, point to the existence of small scale convection beneath tectonic plates. The instabilities that could develop at the base of the lithosphere are sufficiently small scale ( <500 km) that they remain mostly elusive from seismic detection. We take advantage of 3D spherical numerical geodynamic models displaying plate-like behavior to study the interaction between large-scale flow and small-scale convection. We find that finger-shaped instabilities develop at seafloor ages >60 Ma. They form networks that are shaped by the plate evolution, slabs, plumes and the geometry of continental boundaries. Plumes impacting the boundary layer from below have a particular influence through rejuvenating the thermal lithosphere. They create a wake in which new instabilities form downstream. These wakes form channels that are about 1000 km wide, and thus are possibly detectable by seismic tomography. Beneath fast plates, cold sinking instabilities are tilted in the direction opposite to plate motion, while they sink vertically for slow plates. These instabilities are too small to be detected by usual seismic methods, since they are about 200 km in lateral scale. However, this preferred orientation of instabilities below fast plates could produce a pattern of large-scale azimuthal anisotropy consistent with both plate motions and the large scale organisation of azimuthal anisotropy obtained from recent surface wave models.
... The ability of the networks to find yield stress is probably also enhanced by the low temperature dependence of viscosity used in my simulations. This re- duces the variations in viscous stress that would be caused by the near-surface temperature variations resulting from blanketing by the crust (e.g Rolf et al., 2012;Heron and Lowman, 2014). The lithosphere has the same strength through- out my simulations. ...
... High Ra produces smaller convective features, which have greater relative difficulty breaking through the phase change (Peltier, 1996). When running models at Ra lower than Earth-like (~ 10 8 , Weeraratne and Manga, 1998) the modelled Clapeyron slope must be more negative to obtain Earth-like behaviour. ...
Article
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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.
... Yoneda et al. (2009) measured a thermal conductivity (k) of 5.00 W/(m • K) for perovskite, although we varied the thermal conductivity of the mantle between runs, with the best results obtained using k = 5.00 W/(m • K). It is important to note that our model can include both stable continents and plate tectonics, similar to the models of Lenardic et al. (2004), , Yoshida and Santosh (2011), Rolf et al. (2012), and Yoshida (2012). We also emphasise that our model continents were not artificially imposed on the convection model. ...
Article
Oceanic plateaus develop by decompression melting of mantle plumes and have contributed to the growth of the continental crust throughout Earth's evolution. Occasional large-scale partial melting events of parts of the asthenosphere during the Archean produced large domains of precursor crustal material. The fractionation of arc-related crust during the Proterozoic and Phanerozoic contributed to the growth of continental crust. However, it remains unclear whether the continents or their precursors formed during episodic events or whether the gaps in zircon age records are a function of varying preservation potential. This study demonstrates that the formation of the continental crust was intrinsically tied to the thermoconvective evolution of the Earth's mantle. Our numerical solutions for the full set of physical balance equations of convection in a spherical shell mantle, combined with simplified equations of chemical continent–mantle differentiation, demonstrate that the actual rate of continental growth is not uniform through time. The kinetic energy of solid-state mantle creep (Ekin) slowly decreases with superposed episodic but not periodic maxima. In addition, laterally averaged surface heat flow (qob) behaves similarly but shows peaks that lag by 15–30 Ma compared with the Ekin peaks. Peak values of continental growth are delayed by 75–100 Ma relative to the qob maxima. The calculated present-day qob and total continental mass values agree well with observed values. Each episode of continental growth is separated from the next by an interval of quiescence that is not the result of variations in mantle creep velocity but instead reflects the fact that the peridotite solidus is not only a function of pressure but also of local water abundance. A period of differentiation results in a reduction in regional water concentrations, thereby increasing the temperature of the peridotite solidus and the regional viscosity of the mantle. By plausibly varying the parameters in our model, we were able to reproduce the intervals of the observed frequency peaks of zircon age determinations without essentially changing any of the other results. The results yield a calculated integrated continental growth curve that resembles the curves of GLAM, Begg et al. (2009), Belousova et al. (2010), and Dhuime et al. (2012), although our curve is less smooth and contains distinct variations that are not evident in these other curves.
... However, our estimated Al-in-olivine eruption temperatures are independent of traditional petrologic methods for estimating magma temperatures based on olivine-liquid equilibrium and are not subject to the source mantle compositions and magma water contents (i.e., even if the mantle source of the ELIP contains pyroxenite/eclogite or volatiles, the calculated maximum crystallisation temperature remains~1440°C). Therefore, we provide strong evidence indicating that the temperature of the mantle source region of ELIP is substantially higher than that beneath the mid-ocean ridges, which supports either the standard mantle plume model (Coogan et al., 2014) or the continental insulation/supercontinent assembly-induced internal mantle heating model (Coltice et al., 2007(Coltice et al., , 2009Rolf et al., 2012) for the origin of the ELIP; the existing data are insufficient for discriminating between the two models. However, the mantle global warming model predicts a subcontinental increase in temperature only as large as 100°C (Coltice et al., 2007), while the calculated maximum temperature of ELIP (1440°C) is significantly (~250°C) higher than that of MORB. ...
Article
The Emeishan large igneous province (ELIP) is renowned for its world-class Ni–Cu-(PGE) deposits and its link with the Capitanian mass extinction. The ELIP is generally thought to be associated with a deep mantle plume; however, evidence for such a model has been challenged through geology, geophysics and geochemistry. In many large igneous province settings, olivine-melt equilibrium thermometry has been used to argue for or against the existence of plumes. However, this method involves large uncertainties such as assumptions regarding melt compositions and crystallisation pressures. The Al-in-olivine thermometer avoids these uncertainties and is used here to estimate the temperatures of picrites in the ELIP. The calculated maximum temperature (1440 °C) is significantly (~250 °C) higher than the Al-in-olivine temperature estimated for the average MORB, thus providing compelling evidence for the existence of thermal mantle plumes in the ELIP.
... There is a strong possibility that the strength of the lithosphere exerts a stronger control on the long wavelength structure of the flow, than continental rafts at the surface. However continents enhance fluctuations of the thermal structure ( Rolf et al., 2012). 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). ...
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?
... A well-documented corollary of continental drift is the supercontinent cycle, characterized by the alternating assembly and dispersal of the majority of the Earth's continental cratons. Modeling studies show that supercontinents influence the mantle's thermal evolution due to their influence on subduction zone positioning and suggest feedback between continental drift and the deep mantle [e.g., Gurnis, 1988;Lowman and Gable, 1999;Li and Zhong, 2009;O'Neill et al., 2009;Heron and Lowman, 2011;Lenardic et al., 2011;Rolf et al., 2012;Heron et al., 2015]. ...
Article
Shear-wave travel times in the Earth's deep mantle reveal broad steep-sided seismologically distinct provinces lying on the Core-Mantle Boundary (CMB). The longevity and permanence of the two large principal provinces, located below the sites of present-day Africa and the Pacific Ocean, have become a matter of great interest. Examination of the flood basalt record and kimberlite eruption dating suggests the presence of these provinces may disclose a deep mantle component with a compositionally distinct origin that plays a role in the generation of mantle plumes at preferred locations. By extension, the presence of these provinces may affect the supercontinent cycle. Implementing a mantle convection model featuring distinct continental lithosphere and a Compositionally Anomalous and Intrinsically Dense (CAID) component, we study the distribution and mobility of naturally forming compositionally distinct provinces and their impact on model supercontinent assembly. We employ 2D Cartesian geometry calculations of thermo-chemical convection with extremely low compositional diffusion to model Earth-like convective vigor on a global scale and find that an intrinsically dense mantle component generally aggregates into one or two broad provinces. The positions of the provinces are time-dependent but in many of our calculations the province locations are characterized by periods of fixity that reach several hundred million years. Eras of province and associated plume fixity are punctuated by periods of relatively rapid migration. A correlation between supercontinent position and the locations of CAID provinces is not supported by our findings. However, we find the frequency of supercontinent assemblies increases when CAID provinces are present.
... [23]). Secular cooling impacts on mantle viscosity, which along with increasing rigidity of the lithospheric lid [200,201], will lead to an increase in the wavelength of mantle convection, which in turn feeds back into the mechanism of heat transfer [202]. Plate tectonics is associated with mantle convection of wide aspect ratios [203], whereas Figure 9. Schematic temporal evolution of the lithosphere associated with decreasing mantle temperature. ...
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Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780-2710 Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700-2440 Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.
... Although it has been argued that supercontinents influence deep mantle flow (Gurnis, 1988;Phillips and Bunge, 2007), numerical modelling suggests that the thermal state of the convecting upper mantle is only insignificantly affected by "stagnant lid" effects (Lenardic et al., 2005;O'Neill et al., 2009;Rolf et al., 2012). These results show that the ambient thermal conditions beneath thick continental lithosphere within a stable supercontinent assembly are not hot enough to enable major melting such as the generation of flood basalt magmas . ...
... Continental breakup is shown in Figure 1c: we consider that continents have an insulating effect (e.g., Coltice et al., 2007;Grigné et al., 2007;Guillou & Jaupart, 1995;Gurnis, 1988;Rolf et al., 2012;Whitehead & Behn, 2015), which in turn enhances convective vigor in the upper mantle (e.g., Lenardic et al., 2005;Samuel et al., 2011). We derive a parameterization of the warming rate and subsequent advective motion in a shallow layer below a continent as a function of its width and of the radiogenic heating rate in the mantle. ...
Article
Geochemical constraints on mantle temperature indicate a regular decrease by around 250 K since 3 Ga. However, models of Earth’s cooling that rely on scaling laws for thermal convection without strong plates are facing a thermal runaway backwards in time, due to the power-law dependence of heat loss on temperature. To explore the effect of surface dynamics on Earth’s cooling rate, we build a 2D temperature-dependent model of plate tectonics that relies on a force balance for each plate and on Earth- like parameterized behaviors for the motion, creation and disappearance of plate boundaries. While our model predicts the expected thermal runaway if plate boundaries are fixed, we obtain an average cooling rate consistent with geochemical estimates if the geometry of plate tectonics evolves through time. For a warmer mantle in the past, plates are faster but also larger (and less numerous) so that the average seafloor age and resulting heat flux always remain moderate. The predicted decrease in the number of plates backwards in time is in good agreement with recent plate reconstructions over the last 400 Myr. Our model also gives plate speed and subduction area flux consistent with these reconstructions. We finally compare the effect of parameters controlling mantle viscosity and individual plate speeds to the effect of localized surface processes, such as oceanization and subduction initiation. We infer that studies of Earth’s thermal history should focus on surface processes as they appear to be key control parameters.
... Generally, they have high zircon generation rates. In contrast, the epochs of supercontinent breakup are characterized by mantle upwellings (e.g., Arndt and Davaille, 2013;Rolf et al., 2012;Yoshida and Santosh, 2011;Li and Zhong, 2009), resulting in the addition of a large volume of mantle-derived materials into the crust, dominated by basaltic magmatism (exemplified by flood basalts), and rocks from this phase are relatively depleted in zircon. ...
Article
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The evolution of continental crust can be directly linked to the first-order supercontinentsuperplume cycles. We demonstrate that: (1) a mantle-like oxygen isotopic signature is not a diagnostic feature for distinguishing crustal addition from the reworking of pre-existing continental crust; (2) juvenile continental crust shows a wide range of whole-rock Hf isotopic compositions throughout Earth’s history; and (3) detrital zircon Hf model ages cannot reliably determine the growth of continental crust. Thus, the wide use of zircon Hf model ages, based on zircon grains with mantle-like oxygen isotopes, is inappropriate for estimating the timing of continental crustal generation. Based on an analysis of global Hf and O isotope and zircon age databases, we argue that the actual U-Pb crystallization ages of juvenile zircon grains provide the best opportunity to unravel crustal growth through time and to test its relationship with supercontinent-superplume cycles. Furthermore, when the Hf isotopes of these juvenile grains plot within the field of juvenile continental crust, they correlate well with times of global mantle depletion as recorded by Os and He isotopes, plume activity as recorded by LIP events, and periods of crustal growth and the breakup of supercontinents. In contrast, zircon grains crystallized from magmas that were produced by partial melting of pre-existing continental crust show U-Pb age peaks that correspond mainly to times of supercontinent assembly and crustal reworking. Detailed analysis shows the key role played by recycling of mafic crustal components in the generation of juvenile continental crust.
... Guillou and Jaupart, 1995) and influence heat loss out of the system as they act as thermal insulators (e.g. Lenardic and Moresi, 1999;Phillips and Coltice, 2010;Rolf et al., 2012). Importantly, numerical simulations and laboratory experiments suggest that continents change the lithospheric stress distribution and facilitate subduction initiation (e.g. ...
Article
The thermo-mechanical evolution of the Earth's mantle is largely controlled by the dynamics of subduction zones, which connect the surface tectonic plates with the interior. However, little is known about the systematics of where subduction initiates and ceases within the framework of global plate motions and evolving continental configurations. Here, we investigate where new subduction zones preferentially form, and where they endure and cease using statistical analysis of large-scale simulations of mantle convection that feature self-consistent plate-like lithospheric behaviour and continental drift in the spherical annulus geometry. We juxtapose the results of numerical modelling with subduction histories retrieved from plate tectonic reconstruction models and from seismic tomography. Numerical models show that subduction initiation is largely controlled by the strength of the lithosphere and by the length of continental margins (for 2D models, the number of continental margins). Strong lithosphere favours subduction inception in the vicinity of the continents while for weak lithosphere the distribution of subduction initiation follows a random process distribution. Reconstructions suggest that subduction initiation and cessation on Earth is also not randomly distributed within the oceans, and more subduction zones cease in the vicinity of continental margins compared to subduction initiation. Our model results also suggest that intra-oceanic subduction initiation is more prevalent during times of supercontinent assembly (e.g. Pangea) compared to more recent continental dispersal, consistent with recent interpretations of relict slabs in seismic tomography.
... We selected nondimensional parameters for the models at low convective vigor following the studies of Rolf et al. (46) and Mallard et al. (20). Within their proposed range of yield stress values, and allowing for little increase with depth, convection models produce plate-like behavior and plate size distributions with both large and small plates. ...
Article
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Does Earth's mantle drive plates, or do plates drive mantle flow? This long-standing question may be ill posed, however, as both the lithosphere and mantle belong to a single self-organizing system. Alternatively, this question is better recast as follows: Does the dynamic balance between plates and mantle change over long-term tectonic reorganizations, and at what spatial wavelengths are those processes operating? A hurdle in answering this question is in designing dynamic models of mantle convection with realistic tectonic behavior evolving over supercontinent cycles. By devising these models, we find that slabs pull plates at rapid rates and tear continents apart, with keels of continents only slowing down their drift when they are not attached to a subducting plate. Our models show that the tectonic tessellation varies at a higher degree than mantle flow, which partly unlocks the conceptualization of plate tectonics and mantle convection as a unique, self-consistent system.
... However, geologic reconstructions indicate supercontinents during approximately 900-750 and 1550-1400 Ma, which have been named Rodinia and Nuna, respectively (Li et al., 2019), and geoscientists have predicted various future supercontinents based on different extrapolations of current tectonic motions (Davies et al., 2018). Such cycles of supercontinent assembly and dispersal, which are often referred to as "Wilson Cycles," are governed by changes to the distribution of heat within the Earth's mantle (Rolf et al., 2012), with supercontinents trapping heat beneath them until this heat is released by onset of ridge spreading within the supercontinent. The supercontinent cycle can thus be thought of as a mode of planetary convection (section "The Uniqueness of Plate Tectonics"), although the dynamics of this interaction between surface tectonics and mantle convection are not fully understood and remain a topic of ongoing research. ...
Chapter
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... Geodynamic modeling is particularly useful for constraining the likely effects of secular cooling of the mantle (cf. Section 1.3), which impacts on its viscosity and the rigidity of the lithospheric lid (Rolf et al., 2012). Mantle viscosity also directly controls the wavelength of mantle convectionwith increases as mantle T P decreasesand so feeds back on the mechanism of heat transfer (Bunge et al., 1996). ...
Article
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The Earth as a planetary system has experienced significant change since its formation c. 4.54 Gyr ago. Some of these changes have been gradual, such as secular cooling of the mantle, and some have been abrupt, such as the rapid increase in free oxygen in the atmosphere at the Archean-Proterozoic transition. Many of these changes have directly affected tectonic processes on Earth and are manifest by temporal trends within the sedimentary, igneous, and metamorphic rock record. Indeed, the timing of global onset of mobile-lid (subduction-driven) plate tectonics on our planet remains one of the fundamental points of debate within the geosciences today, and constraining the age and cause of this transition has profound implications for understanding our own planet's long-term evolution, and that for other rocky bodies in our solar system. Interpretations based on various sources of evidence have led different authors to propose a very wide range of ages for the onset of subduction-driven tectonics, which span almost all of Earth history from the Hadean to the Neoproterozoic, with this uncertainty stemming from the varying reliability of different proxies. Here, we review evidence for paleo-subduction preserved within the geological record, with a focus on metamorphic rocks and the geodynamic information that can be derived from them. First, we describe the different types of tectonic/geodynamic regimes that may occur on Earth or any other silicate body, and then review different models for the thermal evolution of the Earth and the geodynamic conditions necessary for plate tectonics to stabilize on a rocky planet. The community's current understanding of the petrology and structure of Archean and Proterozoic oceanic and continental crust is then discussed in comparison with modern-day equivalents, including how and why they differ. We then summarize evidence for the operation of subduction through time, including petrological (metamorphic), tectonic, and geochemical/isotopic data, and the results of petrological and geodynamical modeling. The styles of metamorphism in the Archean are then examined and we discuss how the secular distribution of metamorphic rock types can inform the type of geodynamic regime that operated at any point in time. In conclusion, we argue that most independent observations from the geological record and results of lithospheric-scale geodynamic modeling support a global-scale initiation of plate tectonics no later than c. 3 Ga, just preceding the Archean-Proterozoic transition. Evidence for subduction in Early Archean terranes is likely accounted for by localized occurrences of plume-induced subduction initiation, although these did not develop into a stable, globally connected network of plate boundaries until later in Earth history. Finally, we provide a discussion of major unresolved questions related to this review's theme and provide suggested directions for future research.
... In this context, it has been proposed that continents can act as thermal insulators by inhibiting heat loss, thereby increasing mantle temperatures regionally (e.g., Ballard and Pollack, 1987;Lenardic et al., 2005). For instance, Rolf et al. (2012) predicted a temperature increase of ∼140 K underneath continental regions relative to the sub-oceanic mantle, based on internally heated 3-D mantle convection simulations with various continental configurations. However, the influence of the insulating effect of continents on present-day mantle thermal state remains uncertain (cf. ...
Article
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Earth's thermo-chemical structure exerts a fundamental control on mantle convection, plate tectonics, and surface volcanism. There are indications that mantle convection occurs as an intermittent-stage process between layered and whole mantle convection in interaction with a compositional stratification at 660 km depth. However, the presence and possible role of any compositional layering in the mantle remains to be ascertained and understood. By interfacing inversion of a novel global seismic data set with petrologic phase equilibrium calculations, we show that a compositional boundary is not required to explain short- and long-period seismic data sensitive to the upper mantle and transition zone beneath stable continental regions; yet, radial enrichment in basaltic material reproduces part of the complexity present in the data recorded near subduction zones and volcanically active regions. Our findings further indicate that: 1) cratonic regions are characterized by low mantle potential temperatures and significant lateral variability in mantle composition; and 2) chemical equilibration seems more difficult to achieve beneath stable cratonic regions. These findings suggest that the lithologic integrity of the subducted basalt and harzburgite may be better preserved for geologically significant times underneath cratonic regions.
... • Mantle convection models with prescribed weak zones as plate boundaries (Davies, 1989;Puster et al., 1995;Zhong and Gurnis, 1995;Zhong SJ et al., 2000). iv) Internally driven forcing with self-nucleated shear zone • Passive margin collapse: triggered by hydrous upwelling (van der Lee et al., 2008), or by sedimentary loading (Fyfe and Leonardos, 1977;Cloetingh et al., 1989;Regenauer-Lieb et al., 2001); • Plume injection (Ueda et al., 2008;Burov and Cloetingh, 2010;Gerya et al., 2015;Davaille et al., 2017); • Plume induced mantle traction (Lu et al., 2015); • Suction from sinking slab (Baes et al., 2018); • Continent push (Marques et al., 2013;Rey et al., 2014); • Small-scale convection (Solomatov, 2004); • Transient mantle flow with damage and inheritance (Bercovici and Ricard, 2014); • Initiation of global network of rifts due to thermal expansiondriven fracturing (Tang et al., 2020); • Mantle convection models with self-organized plate behavior (e.g., Tackley, 2000a, b, c;Zhong SJ et al., 2007;Rolf and Tackley, 2011;Coltice et al., 2012;Rolf et al., 2012Rolf et al., , 2018Tackley, 2014, 2016;Lourenço et al., 2016;Ballmer et al., 2017;Nakagawa and Iwamori, 2017), some of which have shown self-consistent subduction polarity reversal (Crameri and Tackley, 2014) and plate reorganization (Mallard et al., 2016;Coltice et al., 2019). ...
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Key Points: We raise a "paradox of the first SI", a situation that appears to require existing subduction before the start of the first subduction, and review state-of-the-art SI models with a focus on evaluating their suitability in explaining the onset of plate tectonics. q We re-investigate plate driving mechanisms and conclude that mantle drag may be more important than previously thought, which may be the missing driving force that can resolve the "paradox of the first SI". q We propose a composite driving mechanism, one that is compatible with present-day Earth and may also be applicable to broader geodynamic settings. q Citation: Lu, G., Zhao, L., Chen, L., Wan, B. and Wu, F. Y. (2021). Reviewing subduction initiation and the origin of plate tectonics: What do we learn from present-day Earth?. Earth Planet. Phys., 5(2), 1-18. http://doi. Abstract: The theory of plate tectonics came together in the 1960s, achieving wide acceptance after 1968. Since then it has been the most successful framework for investigations of Earth's evolution. Subduction of the oceanic lithosphere, as the engine that drives plate tectonics, has played a key role in the theory. However, one of the biggest unanswered questions in Earth science is how the first subduction was initiated, and hence how plate tectonics began. The main challenge is how the strong lithosphere could break and bend if plate tectonics-related weakness and slab-pull force were both absent. In this work we review state-of-the-art subduction initiation (SI) models with a focus on their prerequisites and related driving mechanisms. We note that the plume-lithosphere-interaction and mantle-convection models do not rely on the operation of existing plate tectonics and thus may be capable of explaining the first SI. Re-investigation of plate-driving mechanisms reveals that mantle drag may be the missing driving force for surface plates, capable of triggering initiation of the first subduction. We propose a composite driving mechanism, suggesting that plate tectonics may be driven by both subducting slabs and convection currents in the mantle. We also discuss and try to answer the following question: Why has plate tectonics been observed only on Earth?
... Generally, they have high zircon generation rates. In contrast, the epochs of supercontinent breakup are characterized by mantle upwellings (e.g., Arndt and Davaille, 2013;Rolf et al., 2012;Yoshida and Santosh, 2011;Li and Zhong, 2009), resulting in the addition of a large volume of mantle-derived materials into the crust, dominated by basaltic magmatism (exemplified by flood basalts), and rocks from this phase are relatively depleted in zircon. ...
... In addition to this thermal effect, the presence of ACPs changes the mantle flow pattern, the number of convection cells, and the positioning of plumes (Figures 2d-2f). One large ACP decreases the number of convection cells from four to two and increases the dominant wavelength of mantle flow as previously indicated by numerical studies with terrestrial continents (see, e.g., Phillips & Coltice, 2010;Rolf et al., 2012) as well as in laboratory experiments of partially insulated convection (Guillou & Jaupart, 1995). The insulation underneath the ACP causes upward flow in this area, which is forced to the sides at the base of the ACP. ...
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... This observation has led some authors to model continents by prescribing an insulator layer at the top surface (Heron & Lowman, 2010. Alternatively, other authors prescribed a large viscosity jump within continents (Cooper et al., 2013;Gurnis, 1988;Lenardic et al., 2011Lenardic et al., , 2005Rolf & Tackley, 2011;Rolf et al., 2012;Zhong & Gurnis, 1993) inducing a thicker thermal boundary layer, in agreement with the higher thickness of the continental lithosphere compared to the oceanic lithosphere, which in turn causes an insulation effect. These models, however, do not include the enrichment in heat producing elements within the continental crust. ...
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... This plasticity formulation has been commonly used in previous studies [67][68][69] , and the approach approximates the effect of strain-related softening 70,71 . ...
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Technical Report
1991.11 Superseded by: Scotese, C.R., 1991. Jurassic and Cretaceous Plate Tectonic Reconstructions, Palaeogeography, Palaeoecology, and Palaeoclimatology, v. 87, p. 493-501.
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Distinct rigidly moving oceanic and continental plates of finite thickness are incorporated into a two-dimensional numerical model of mantle convection. We investigate upper mantle convection in models having aspect ratios as great as 24 and compare our findings with the results of earlier studies which were limited to aspect ratio 4 models. In addition, we implement models of whole mantle flow by specifying high Rayleigh number convection and thinner nondimensional plates. We are thus able to compare the results of continental collision models which include similarly sized continents in the cases of upper and whole mantle convection. For each case considered we model a pair of identical continents being carried toward a site of plate convergence by underlying counterrotating mantle convection cells. Upon collision, the continents form a motionless, rigid, model supercontinent, while oceanic plate material continues to recycle through the mantle. Following the continental collision, our models of upper mantle convection exhibit a reorganization of the convective planform below the model supercontinent into a smaller wavelength mode which is unable to generate the net stress needed to break apart the continent; alternating compressive and tensile deviatoric stress associated with the small scale flow results in a low integrated stress. In contrast the large scale of whole mantle convection enables flow reversals to produce shear stresses acting in a common direction over extensive areas of the base of a continent, the integrated effect of which is capable of causing continental rifting. The conventional view of the role of thermal blanketing in continental rifting does not apply in the whole mantle convection scenario.
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After thirty years of plate-tectonic theory, the reasons why supercontinents disintegrate and disperse to form smaller continental plates remain enigmatic. Possible causes range from abnormally hot mantle upwellings, or plumes, to changes in plate-boundary driving forces. The breakup of the Gondwanaland super-continent, which started about 180 million years ago, provides an excellent case history against which to test models.
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Evidence indicating that the mantle below Pangea was characterized by elevated temperatures supports the widely held view that a supercontinent insulates the underlying mantle. Implementing a D model of mantle convection featuring distinct oceanic and continental plates, we explore different effects of supercontinent formation on mantle evolution. We find that a halt in subduction along the margins of the site of the continental collision is sufficient to enable the formation of mantle plumes below a composite super-plate'' and that the addition of continental properties that contribute to insulation have little effect on sub-continental temperature. Our findings show that the mean temperature below a supercontinent surpasses that below the oceanic plates when the former is a perfect insulator but that continental thermal insulation plays only a minor role in the growth of sub-supercontinent mantle plumes. We suggest that the growth of a super-oceanic plate can equally encourage the appearance of underlying upwellings.
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Relative motions poles describing the displacement histories between the Pacific plate and once adjacent oceanic plates (Farallon, Kula, Izanagi I, Izanagi II, and Phoenix) were derived for the late Mesozoic and Cenozoic eras. Because fracture zone and magnetic anomaly data are generally available from the Pacific plate but not from adjacent plates, a new method of analysis for onesided data was required. This analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions. Magnetic anomaly numbers and their assigned ages are both given in the text and in tables of finite rotation stage poles. Errors in the timing of stage boundaries are estimated to be 3-5 m. y. , reflecting uncertainty in the ages of the magnetic lineations and possible errors in identifying anomalies.
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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.
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a b s t r a c t a r t i c l e i n f o The assembly of supercontinents should impact mantle ! ow " elds signi" cantly, affecting the distribution of subduction, upwelling plumes, lower mantle chemical heterogeneities, and thus plausibly contributing to voluminous volcanism that is often associated with their breakup. Alternative explanations for this volcanism include insulation by the continent and thus elevated subcontinental mantle temperatures. Here we model the thermal and dynamic impact of supercontinents on Earth-like mobile-lid convecting systems. We con" rm that insulating supercontinents (over 3000 km extent) can impact mantle temperatures, but show the scale of temperature anomaly is signi" cantly less for systems with strongly temperature-dependent viscosities and mobile continents. Additionally, for continents over 8000 km, mantle temperatures are modulated by the development of small-scale convecting systems under the continent, which arise due to inef" cient lateral convection of heat at these scales. We demonstrate a statistically robust association between rising plumes supercontinental interiors for a variety of continental con" gurations, driven largely by the tendency of subducting slabs to lock onto continental margins. The distribution of slabs also affects the spatial positioning of deep mantle thermochemical anomalies, which demonstrate stable con" gurations in either the sub-supercontinent or intraoceanic domains. We " nd externally forced rifting scenarios unable to generate signi" cant melt rates, and thus the ultimate cause of supercontinent breakup related volcanism is probably related to dynamic continental rifting in response to mantle recon" guration events.
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By analyzing convection characteristics and surface and basal heat flux we investigate the influence on mantle convection of finite thickness plates with dynamically determined velocities and mobile boundaries. Our 6 × 6 × 1 Cartesian geometry numerical model features periodic sidewall boundary conditions, a lower mantle that increases in viscosity and a Rayleigh number of 5 × 106 (based on the uniform viscosity upper mantle). A calculation with 9 plates and fixed plate boundaries is compared with a second calculation incorporating evolving plate boundaries. The number of plates in the latter case fluctuates between 6 and 9. We find that mean heat flux output decreases during periods characterized by the presence of larger plates and that evolving plate boundaries cause surface (and basal) heat flux output to vary much more than the heat flux observed with either fixed plate boundaries or a free-slip surface.