Global mantle convection models produce transform offsets along divergent plate boundaries

AbstractThe presence of offsets, appearing at intervals ranging from 10s to 100s of kilometres, is a distinct characteristic of constructive tectonic plate margins. By comparison, boundaries associated with subduction exhibit uninterrupted continuity. Here, we present global mantle convection calculations that result in a mobile lithosphere featuring dynamically derived plate boundaries exhibiting a contrasting superficial structure which distinguishes convergence and divergence. Implementing a yield-stress that governs the viscosity in the lithosphere, spreading boundaries at the top of a vigorously convecting mantle form as divergent linear segments regularly offset by similar length zones that correlate with a large degree of shear but comparatively minimal divergence. Analogous offset segments do not emerge in the boundaries associated with surface convergence. Comparing the similarity in the morphologies of the model plate margins to the Earth’s plate boundaries demonstrates that transform-like offsets are a result of stress induced weakness in the lithosphere owing to passive rupturing.

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Tectonic regime variety and stability in mantle convection with strain-induced weakening

10.5194/egusphere-egu21-540 ◽

2021 ◽

Author(s):

Tobias Rolf ◽

Maëlis Arnould

Keyword(s):

Yield Stress ◽

Stress Reduction ◽

Mantle Convection ◽

Critical Strain ◽

Global Scale ◽

Plate Boundaries ◽

Mantle Dynamics ◽

Tectonic Regime ◽

Surface Mobility ◽

Critical Yield

Earth's tectonic evolution and its link to global mantle dynamics are controlled by the pre-existing structure of the lithosphere which guides how strain localizes and causes the necessary weakness to (re-)activate plate boundaries. Recent models of global-scale mantle convection have self-consistently reproduced Earth-like tectonic regimes, consistent with several aspects of today&#8217;s observed tectonics. In many cases these models ignore the memory on pre-existing deformation though. Here, a mantle convection model is advanced to include the associated rheological inheritance via a parameterization of strain-induced plastic (brittle) weakening. Based on more than 180 simulations in a wide 2D cartesian box, the control of strain-induced weakening on the resulting tectonic regime is demonstrated. Strain-induced brittle weakening impacts the stability fields of the different tectonic regimes observed, but to first order it does not generate new tectonic regimes or change the dynamics of a given regime (e.g., its characteristic surface mobility). A time-dependent plate-like regime similar to Earth's becomes more feasible with decreasing critical strain at (and above) which maximum weakening is observed. It is less feasible with increasing temperature-dependence of the healing rate, but remains a possibility at small critical strain. While the critical yield stress that still allows for plate-like behavior is apparently larger with strain-induced weakening considered, the effective shift (incorporating the yield stress reduction due to strain weakening) is relatively small and only about 10% under the tested conditions. Strain accumulation in stable continental lithosphere is generally small because of the necessity of high rheological strength. This holds true even for continental collision events, although at least some strain is accumulated and preserved following such events in the immediate proximity of the colliding continental margins.<div>&#160;</div>

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Earthquake Engineering in Areas Away from Tectonic Plate Boundaries

Lecture Notes in Civil Engineering - Recent Advances in Computational Mechanics and Simulations ◽

10.1007/978-981-15-8138-0_29 ◽

2020 ◽

pp. 367-380

Author(s):

Nelson Lam

Keyword(s):

Earthquake Engineering ◽

Plate Boundaries ◽

Tectonic Plate

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Lithospheric deformation and mantle convection, a geological approach

10.5194/egusphere-egu21-594 ◽

2021 ◽

Author(s):

Laurent Jolivet

Keyword(s):

Numerical Modelling ◽

Crustal Deformation ◽

Mantle Convection ◽

Numerical Models ◽

Plate Boundaries ◽

Long Distance ◽

Data Set ◽

Lithospheric Deformation ◽

Sequence Of Events ◽

History Of

<div>Whether the deformation of continents is entirely caused by stresses transmitted from plate boundaries horizontally through the lithospheric stress-guide or also by viscous coupling with the asthenosphere flowing underneath, which was part of Arthur Holmes&#8217; early vision, &#160;is a long-standing question. An increasing amount of observations suggests an efficient coupling between mantle flow and crustal deformation far from plate boundaries, tipping the scale toward the second option. Modern seismic reflection profiles probing the entire crust down to the Moho show asymmetrical features implying simple shear at crustal scale in compressional (mountain belts) and extensional (rifts and passive margins) contexts. Comparison of crustal-scale strain field with seismic anisotropy in strongly extended regions shows homoaxiality of crustal and mantle deformation in continental rifts and back-arc regions. 2-D and 3-D numerical models show that the flow of mantle underneath these regions is faster than in the crust and drives crustal deformation. Beside seismic tomography that images ancient slabs preserved as velocity anomalies in the deep mantle but does not provide any information on the timing, the geological history of basins and orogens, although indirectly, is the only record of past mantle convection. Looking for evidence of coupling between the tectonic history of wide regions and mantle convection in parallel with numerical modelling can provide clues on how convection drives crustal deformation. The recent evolution of numerical modelling, with high-resolution 3-D experiments, can now match the first order of regional models based on geological observations, including the timing and the sequence of events, which are both crucial elements of geological models. This will allow testing complex conceptual models that have been discussed for long. In this lecture, I review different contexts where these questions are debated. Among these contexts complex in 3-D where the geological data set is abundant, the Mediterranean and the Middle East allow discussing the respective contributions of whole-mantle convection involving large plumes vs more local convection in the upper mantle due to slab dynamics in crustal deformation. Studying the dynamics of the India-Asia collision, and the respective roles of lithospheric-scale indentation on the one hand and asthenospheric flow due to slab retreat on the Pacific rim and to large-scale plumes, on the other hand, is also likely to bring interesting insights on how deformation propagates within continents at long distance from plate boundaries.</div>

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Plate tectonic modelling: review and perspectives

Geological Magazine ◽

10.1017/s0016756817001030 ◽

2018 ◽

Vol 156 (2) ◽

pp. 208-241 ◽

Cited By ~ 2

Author(s):

CHRISTIAN VÉRARD

Keyword(s):

Plate Boundaries ◽

Dual Control ◽

Plate Tectonic ◽

Joint Effort ◽

Tectonic Plate ◽

Deep Time ◽

Tectonic Plates ◽

Control Approach ◽

New Frontier ◽

Tectonic Boundaries

AbstractSince the 1970s, numerous global plate tectonic models have been proposed to reconstruct the Earth's evolution through deep time. The reconstructions have proven immensely useful for the scientific community. However, we are now at a time when plate tectonic models must take a new step forward. There are two types of reconstructions: those using a ‘single control’ approach and those with a ‘dual control’ approach. Models using the ‘single control’ approach compile quantitative and/or semi-quantitative data from the present-day world and transfer them to the chosen time slices back in time. The reconstructions focus therefore on the position of tectonic elements but may ignore (partially or entirely) tectonic plates and in particular closed tectonic plate boundaries. For the readers, continents seem to float on the Earth's surface. Hence, the resulting maps look closer to what Alfred Wegener did in the early twentieth century and confuse many people, particularly the general public. With the ‘dual control’ approach, not only are data from the present-day world transferred back to the chosen time slices, but closed plate tectonic boundaries are defined iteratively from one reconstruction to the next. Thus, reconstructions benefit from the wealth of the plate tectonic theory. They are physically coherent and are suited to the new frontier of global reconstruction: the coupling of plate tectonic models with other global models. A joint effort of the whole community of geosciences will surely be necessary to develop the next generation of plate tectonic models.

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Effects of strain weakening in self-consistent models of mantle convection with plate-like behavior and continental drift

10.5194/egusphere-egu2020-5118 ◽

2020 ◽

Author(s):

Tobias Rolf ◽

Maëlis Arnould

Keyword(s):

Mantle Convection ◽

Previous History ◽

Plate Boundary ◽

Continental Drift ◽

Rheological Parameters ◽

Plate Boundaries ◽

The Earth ◽

Cumulative Strain ◽

First Results ◽

Long Time

It is now well-established that the Earth&#8217;s mantle and lithosphere form an integrated, dynamically self-regulating system. Numerical convection models that self-consistently generate plate-like behavior are a powerful tool to investigate this system, but have only recently reached a level at which they can be linked to the geodynamics of the Earth. Strongly temperature-dependent and viscoplastic rheology is known to be a key ingredient for these models to be successful. Such rheologies, however, are typically time-independent and lack a memory on the previous history of deformation. Yet, it is known that the Earth&#8217;s geodynamic evolution is somewhat guided by structures of pre-existing weakness, which was initiated a potentially long time before.As a step forward we implement a simple form of rheological memory in the mantle convection code StagYY: strain weakening [Fuchs & Becker, 2019, Role of strain-dependent weakening memory on the style of mantle convection and plate boundary stability, Geophys. J. Int., 218, 601-618]. We present calculations in 2D cases with and without continents, and also selected 3D cases. By varying the governing parameters for plate-like behavior as well as the rates of rheological damage and healing, we examine how strain weakening modifies the generation of plate-like behavior and its time dependence as well as the drift of continents.First results indicate the importance of the balance of weakening (via the critical strain) and thermal healing. The averaged cumulative strain (effectively the degree of lithospheric weakening) is lower when healing is more effective, so that plastic failure of the lithospheric and the formation of new plate boundaries is complicated, as expected. In initial models with strong, long-living continents, accumulated strain is very small within the continents and seems insufficient to induce substantial weakening, even if the memory on previous deformation is infinite (i.e. no healing with continents). Further models with weaker continents and different rheological parameters will be presented.

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Theoretical deficiencies of isostatic schemes in modeling the crustal thickness along the convergent continental tectonic plate boundaries

Journal of Earth Science ◽

10.1007/s12583-015-0608-x ◽

2016 ◽

Vol 27 (6) ◽

pp. 1045-1053 ◽

Cited By ~ 2

Author(s):

Robert Tenzer ◽

Mohammad Bagherbandi

Keyword(s):

Crustal Thickness ◽

Plate Boundaries ◽

Tectonic Plate

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Fluid mechanical representation of plate boundaries in mantle convection modeling

Physics of The Earth and Planetary Interiors ◽

10.1016/j.pepi.2007.10.003 ◽

2008 ◽

Vol 166 (1-2) ◽

pp. 44-56 ◽

Cited By ~ 2

Author(s):

Masao Takaku ◽

Yoshio Fukao

Keyword(s):

Mantle Convection ◽

Plate Boundaries

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Interior dynamics of tidally-locked super-Earths: the case of LHS 3844b

10.5194/egusphere-egu2020-10961 ◽

2020 ◽

Author(s):

Tobias G. Meier ◽

Dan J. Bower ◽

Tim Lichtenberg ◽

Paul J. Tackley

Keyword(s):

Yield Stress ◽

Mantle Convection ◽

Plate Tectonics ◽

High Yield ◽

Large Temperature ◽

Return Flow ◽

Plastic Yielding ◽

Near Surface ◽

First Case ◽

Stress Criteria

The vigour and style of mantle convection in tidally-locked super-Earths may be substantially different from Earth's regime. Earth's surface temperature is spatially uniform at 300 K, which is sufficiently cold to drive strong downwellings into the interior (i.e. subduction). In contrast, a tidally-locked super-Earth can have a large temperature contrast between the dayside and nightside, which we infer could lead to a dichotomy of the interior dynamics. We therefore use constraints from astrophysical observations to infer the possible pattern of flow in the interior of a tidally-locked super-Earth, using super-Earth LHS 3844b as a case study.&#160;We run mantle convection models using the code StagYY with two-dimensional spherical annulus geometry and parameters from the literature that are appropriate for LHS 3844b. The majority of the mantle is either perovskite or post-perovskite with the phase transition occurring around 1700 km depth (the total mantle depth is 3757 km). An upper and lower bound for the viscosity of post-perovskite is provided by previous theoretical calculations. We include plastic yielding to model the brittle nature of the lithosphere; plastic yielding occurs when the local stress state exceeds a prescribed yielding criteria and is commonly applied in studies of Earth to produce surface behaviour similar to plate tectonics.For a low yield stress criteria (promoting a weak lithosphere), we find that plumes are generally evenly distributed between the dayside and nightside, albeit strong downwellings form on the nightside.&#160;Plumes on the nightside have less lateral mobility than on the dayside because they are confined by downwellings either side. In contrast, for a high yield stress criteria, the interior dynamics are mostly driven by a prominent downwelling on the dayside which flushes hot material from the lower thermal boundary layer around the CMB towards the nightside where plumes preferentially arise. This, in turn, leads to a return flow of colder material from the near surface of the nightside towards the dayside. This seemingly counterintuitive pattern of flow is a consequence of weak lithosphere (due to temperature) on the dayside that is able to deform and thereby subduct, whereas lithosphere on the nightside is too stiff to subduct.Our models therefore show that the vigour of convection and the distribution of upwellings and downwellings of tidally locked super-Earths are sensitive to the strength of the lithosphere: plumes can either be equally distributed around the planet or preferentially occur on the nightside. In the first case, the cold downwellings are also equally distributed but more prominent on the nightside, whereas in the second case they are preferentially on the dayside. Somewhat unexpected, we do not observe a preference for hot plumes to congregate on the dayside. Our results have implications for space missions such as TESS, CHEOPS, JWST, PLATO and ARIEL that will discover and characterise super-Earths, thereby potentially probing for signals of volatile outgassing and volcanism.

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