scholarly journals The dependence of planetary tectonics on mantle thermal state: applications to early Earth evolution

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170409 ◽  
Author(s):  
Bradford J. Foley
Keyword(s):  
Grain Size ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Thermal State ◽  
Plate Boundary ◽  
Thermal Conditions ◽  
Size Reduction ◽  
Early Earth ◽  
Plate Boundaries ◽  
Boundary Formation

For plate tectonics to operate on a planet, mantle convective forces must be capable of forming weak, localized shear zones in the lithosphere that act as plate boundaries. Otherwise, a planet's mantle will convect in a stagnant lid regime, where subduction and plate motions are absent. Thus, when and how plate tectonics initiated on the Earth is intrinsically tied to the ability of mantle convection to form plate boundaries; however, the physics behind this process are still uncertain. Most mantle convection models have employed a simple pseudoplastic model of the lithosphere, where the lithosphere ‘fails’ and develops a mobile lid when stresses in the lithosphere reach the prescribed yield stress. With pseudoplasticity high mantle temperatures and high rates of internal heating, conditions relevant for the early Earth, impede plate boundary formation by decreasing lithospheric stresses, and hence favour a stagnant lid for the early Earth. However, when a model for shear zone formation based on grain size reduction is used, early Earth thermal conditions do not favour a stagnant lid. While lithosphere stress drops with increasing mantle temperature or heat production rate, the deformational work, which drives grain size reduction, increases. Thus, the ability of convection to form weak plate boundaries is not impeded by early Earth thermal conditions. However, mantle thermal state does change the style of subduction and lithosphere mobility; high mantle temperatures lead to a more sluggish, drip-like style of subduction. This ‘sluggish lid’ convection may be able to explain many of the key observations of early Earth crust formation processes preserved in the geologic record. Moreover, this work highlights the importance of understanding the microphysics of plate boundary formation for assessing early Earth tectonics, as different plate boundary formation mechanisms are influenced by mantle thermal state in fundamentally different ways.This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

Great Earthquakes on Plate Boundaries

2016 ◽  
Author(s):  
Thorne Lay
Keyword(s):  
Elastic Wave ◽  
Elastic Strain ◽  
Slip Velocity ◽  
Plate Tectonics ◽  
Plate Boundary ◽  
Plate Boundaries ◽  
Seismic Slip ◽  
Sliding Motion ◽  
Great Earthquakes ◽  
Elastic Wave Energy

Earthquakes involve sudden shear sliding motion between large rock masses across internal contact surfaces called faults. The slip on the fault releases strain energy previously stored in the surrounding rock that accumulated due to frictional resistance to sliding. Most earthquakes are directly caused by plate tectonics, and locate in the cool, brittle rock near Earth’s surface. Events with seismic magnitude measured 8.0 or greater are called great earthquakes and involve slip of from several to tens of meters across faults with lengths from 100 to more than 1,000 kilometers. These huge ruptures tend to occur on or near plate boundaries; the largest are on shallow-dipping plate boundary faults (megathrusts) found in compressional regions called subduction zones, where one tectonic plate is thrusting under another. Some great earthquakes occur within bending or detaching plates as they deform seaward of or below a subduction zone. Yet others occur on plate boundary strike-slip faults where two plates are shearing horizontally past one another, or within deforming plate interiors. Elastic wave energy released during the fault sliding is recorded and studied by seismologists to determine the fault location, orientation and sense of sliding motion, amount of radiated elastic wave energy, and distribution of slip on the fault during the event (co-seismic slip). Geodetic methods measure elastic strain accumulation prior to an earthquake, co-seismic slip, and afterslip on the fault that occurs without earthquakes, along with viscous deformation of the mantle as it responds to the fault offset. Great earthquakes commonly locate under the ocean, and the sudden motion of the seafloor generates tsunami—gravitational water waves that can be recorded with ocean floor pressure sensors (these waves are also used to determine co-seismic slip). As seismic, geodetic. and tsunami modeling methods have progressed over the past 50 years, our understanding of great earthquake rupture processes and earthquake interactions has advanced steadily in the context of plate tectonics and improved understanding of rock friction. All faults have heterogeneous frictional properties inferred from non-uniform sliding during each event, with areas of large slip instabilities called asperities having slip-velocity weakening friction and other areas having slip-velocity strengthening friction that results in stable sliding. The seismic wave shaking and tsunami waves can cause great devastation for humanity, so efforts are made to anticipate future earthquake hazards. As plate tectonics steadily move Earth’s plates, elastic strain around plate boundary faults accumulates and releases in a repeated stick-slip sliding process that causes a limited degree of regularity of faulting. Given the history of prior earthquakes on a given fault, we can identify seismic gaps where future slip events are likely to occur. With geodesy we can also now measure locations of accumulating slip deficit relative to plate motions, as well as variation in seismic coupling, which characterizes the fraction of plate motion accounted for by earthquake failure.

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

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

<p>It is now well-established that the Earth’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’s geodynamic evolution is somewhat guided by structures of pre-existing weakness, which was initiated a potentially long time before.</p><p>As a step forward we implement a simple form of rheological memory in the mantle convection code <em>StagYY</em>: strain weakening [<em>Fuchs & Becker, 2019,</em> <em>Role of strain-dependent weakening memory on the style of mantle convection and plate boundary stability</em>, <em>Geophys. J. Int., 218, 601-618</em>]. 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.</p><p>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.</p>

scholarly journals Geodynamic diagnostics, scientific visualisation and StagLab 3.0

2018 ◽  
Author(s):  
Fabio Crameri
Keyword(s):  
Software Package ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
State Of The Art ◽  
Plate Boundary ◽  
Plate Bending ◽  
Scientific Software ◽  
Mantle Dynamics ◽  
Geodynamic Models ◽  
Visual Error

Abstract. Today's Geodynamic models can, often do, and sometimes have to become very complex. Their underlying, increasingly elaborate numerical codes produce a growing amount of raw data. Post-processing such data becomes therefore more and more challenging and time consuming. In addition, visualising processed data and results has, in times of coloured figures and a wealth of half-scientific software, become one of the weakest pillars of science, widely mistreated and ignored. Efficient and automated Geodynamic diagnostics and sensible, scientific visualisation, preventing common pitfalls, is thus more important than ever. Here, a collection of numerous diagnostics for plate tectonics and mantle dynamics is provided and a case for truly scientific visualisation is made. Amongst other diagnostics are a most accurate and robust plate-boundary identification, slab-polarity recognition, plate-bending derivation, surface-topography component splitting and mantle-plume detection. Thanks to powerful image processing tools and other elaborate algorithms, these and many other insightful diagnostics are conveniently derived from only a subset of the most basic parameter fields. A brand-new set of scientifically proof, perceptually uniform colour maps including "devon", "davos", "oslo" and "broc" is introduced and made freely available. These novel colour maps bring a significant advantage over misleading, non-scientific colour maps like "rainbow"', which is shown to introduce a visual error to the underlying data of up to 7.5 %. Finally, StagLab (http://www.fabiocrameri.ch/software) is introduced, a software package that incorporates the whole suite of automated Geodynamic diagnostics and, on top of that, applies state-of-the-art, scientific visualisation to produce publication-ready figures and movies, all in a blink of an eye, all fully reproducible. StagLab, a simple, flexible, efficient and reliable tool, made freely available to everyone, is written in MatLab and adjustable for use with Geodynamic mantle-convection codes.

scholarly journals Beyond Plate Tectonics: Looking at Plate Deformation with Space Geodesy

1988 ◽  
Vol 129 ◽  
pp. 341-350
Author(s):  
Thomas H. Jordan ◽  
J. Bernard Minster
Keyword(s):  
Plate Tectonics ◽  
Plate Boundary ◽  
Point Of View ◽  
Space Geodesy ◽  
Plate Motion ◽  
Plate Boundaries ◽  
Measurement Systems ◽  
Motion Models ◽  
Plate Deformation ◽  
Continental Plate

We address the requirements that must be met by space-geodetic systems to place useful, new constraints on horizontal secular motions associated with the geological deformation of the earth's surface. Plate motions with characteristic speeds of about 50 mm/yr give rise to displacements that are easily observed by space geodesy. However, in order to improve the existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of < 3 mm/yr. Because motions considered small from a geodetic point of view have rather dramatic geological effects, especially when taken up as compression or extension of continental crust, detecting plate deformation by space-geodetic methods at a level that is geologically unresolvable places rather stringent requirements on the precision of the measurement systems: the tangential components on intraplate baselines must be observed with an accuracy of < 1 mm/yr. Among the measurements of horizontal secular motions that can be made by space geodesy, those pertaining to the rates within the broad zones of deformation characterizing the active continental plate boundaries are the most difficult to obtain by conventional ground-based geodetic and geological techniques. Measuring the velocities between crustal blocks to ± 5 mm/yr on 100-km to 1000-km length scales can yield geologically significant constraints on the integrated deformation rates across continental plate-boundary zones such as the western United States. However, baseline measurements in geologically complicated zones of deformation are useful only to the extent that the endpoints can be fixed in a local kinematical frame that includes major crustal blocks. For this purpose, the establishment of local geodetic networks around major VLBI and SLR sites in active areas should receive high priority.

Reconciling thermal regimes and tectonics of the early Earth

Geology ◽  
2019 ◽  
Vol 47 (10) ◽  
pp. 923-927 ◽  
Author(s):  
F.A. Capitanio ◽  
O. Nebel ◽  
P.A. Cawood ◽  
R.F. Weinberg ◽  
P. Chowdhury
Keyword(s):  
High Pressure ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Early Earth ◽  
Plate Tectonic ◽  
Metamorphic Belt ◽  
Thermal Regimes ◽  
Tectonic Environments

Abstract Thermomechanical models of mantle convection and melting in an inferred hotter Archean Earth show the emergence of pressure-temperature (P-T) regimes that resemble present-day plate tectonic environments yet developed within a non–plate tectonics regime. The models’ P-T gradients are compatible with those inferred from evolving tonalite-trondhjemite-granodiorite series rocks and the paired metamorphic belt record, supporting the feasibility of divergent and convergent tectonics within a mobilized, yet laterally continuous, lithospheric lid. “Hot” P-T gradients of 10–20 °C km–1 form along asymmetric lithospheric drips, then migrate to areas of deep lithospheric downwelling within ∼300–500 m.y., where they are overprinted by high-pressure warm and, later, cold geothermal signatures, up to ∼8 °C km–1. Comparisons with the crustal production and reworking record suggest that this regime emerged in the Hadean.

Modern plate tectonic cycles are inherited from Hadean mantle convection

2020 ◽  
Author(s):  
Ross N. Mitchell ◽  
Christopher J. Spencer ◽  
Uwe Kirscher ◽  
Simon A. Wilde
Keyword(s):  
Time Series ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
The Other ◽  
Early Earth ◽  
Plate Tectonic ◽  
Hafnium Isotopes ◽  
Planetary Evolution ◽  
Secular Changes ◽  
Jack Hills

&lt;p&gt;&lt;strong&gt;Earth&amp;#8217;s oldest preserved crustal archive, the Jack Hills zircon of Western Australia, has been controversial to interpret in terms of the onset of plate tectonics. Here we conduct time series analysis on hafnium isotopes of the Jack Hills zircon and reveal an array of statistically significant cycles that are reminiscent of plate tectonics, i.e., subduction. At face value, such cycles may suggest early Earth conditions similar to today&amp;#8212;the uniformitarian &amp;#8220;day one&amp;#8221; hypothesis. On the other hand, in the context of expected secular changes due to planetary evolution and geological observations, the cycles could instead imply that modern plate tectonic subduction inherited convective harmonics already facilitated by an early phase of stagnant-lid delamination&amp;#8212;the &amp;#8220;lid-to-plates&amp;#8221; hypothesis. Either way, any model for the initiation of plate tectonics must begin in Hadean time.&lt;/strong&gt;&lt;/p&gt;

Experimental constraints on mylonite formation

2020 ◽  
Author(s):  
Philip Skemer ◽  
Caroline Bollinger ◽  
Andrew Cross ◽  
Helene Couvy
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Plate Tectonics ◽  
Microstructural Analysis ◽  
Ex Situ ◽  
Plate Boundaries ◽  
Localized Deformation ◽  
Phase Mixing ◽  
Viscosity Contrast ◽  
Shear Strains

&lt;p&gt;Mylonites are ubiquitous structural features of dynamic plate boundaries, and are widely assumed to represent the product of localized deformation at high pressure and temperature. There are two features of mylonites that distinguish them from typical host rocks: grain-sizes that may be reduced by orders of magnitude and mineral phases that generally well-mixed.&amp;#160; Together, these microstructural characteristics are thought to promote rheological weakening over long geologic intervals, an essential feature of Earth-like plate tectonics.&amp;#160; In this contribution we describe experiments that seek to reproduce deformation processes and resulting microstructures that occur during mylonitization. Experiments were conducted at high pressure (1-2 GPa) and temperature (500-750 C) on dense synthetic composites of calcite (Ca) and quartz (Qz), anhydrite (An), or fluorite (Fl).&amp;#160; These composites were selected to investigate the influence of viscosity contrast on the phase mixing process. Shear strains of &amp;#947; &gt; 50 were produced using the Large Volume Torsion Apparatus (LVT) at Washington University in St. Louis.&amp;#160; Ex situ microstructural analysis was performed with optical microscopy, SEM, EBSD, and TEM. Experiments are interpreted to have deformed by either viscoplastic (Ca+Fl and Ca+An) or semi-brittle mechanisms (Ca+Qz). We show that the evolution of the protolith towards recrystallized and well-mixed microstructures occurs over a large range of shear strains. The critical strain depends on the mechanism of mixing, the viscosity contrast between the two phases, and the microstructure of the starting material. Phase mixing is determined to be the product of several independent mechanisms, the relative importance of which depends on pressure, stress, strain, composition, viscosity contrast, and the ratio of the initial grain-size to the recrystallized grain size.&lt;/p&gt;

Plate tectonics and Earth System Science

2021 ◽  
Author(s):  
Dietmar Müller
Keyword(s):  
Plate Tectonics ◽  
Plate Boundary ◽  
Plate Motion ◽  
Plate Boundaries ◽  
Earth System ◽  
Dynamic Topography ◽  
Lithospheric Deformation ◽  
The Earth ◽  
Plate Models ◽  
Reconstruction Software

&lt;p&gt;Over the last 25 years the theory of plate tectonics and a growing set of geo-databases have been used to develop global plate models with increasing sophistication, enabled by open-source plate reconstruction software, particularly GPlates. Today&amp;#8217;s editable open-access community models include networks of evolving plate boundaries and deforming regions, reflecting the fact that tectonic plates are not always rigid. The theory of plate tectonics was originally developed primarily based on magnetic anomaly and fracture zone data from the ocean basins. As a consequence there has been a focus on applying plate tectonics to modelling the Jurassic to present-day evolution of the Earth based on the record of preserved seafloor, or only modelling the motions of continents at earlier times. Modern plate models are addressing this shortcoming with recently developed technologies built upon the pyGPlates python library, utilising evolving plate boundary topologies to reconstruct entirely destroyed seafloor for the entire Phanerozoic. Uncertainties in these reconstructions are large and can represented with end-member scenarios. These models are paving the way for a multitude of applications aimed at better understanding Earth system evolution, connecting surface processes with the Earth&amp;#8217;s mantle via plate tectonics. These models allow us to address questions such as: What are the causes of major perturbations in the interplay between tectonic plate motion and Earth&amp;#8217;s deep interior? How do lithospheric deformation, mantle convection driven dynamic topography and climate change together drive regional changes in erosion and sedimentation? How are major perturbations of the plate-mantle system connected to environmental change, biological extinctions and species radiation?&lt;/p&gt;

scholarly journals Geodynamic diagnostics, scientific visualisation and StagLab 3.0

2018 ◽  
Vol 11 (6) ◽  
pp. 2541-2562 ◽  
Author(s):  
Fabio Crameri
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
State Of The Art ◽  
Plate Boundary ◽  
Scientific Quality ◽  
Plate Bending ◽  
Scientific Software ◽  
Mantle Dynamics ◽  
Geodynamic Models ◽  
Visual Error

Abstract. Today's geodynamic models can, often do and sometimes have to become very complex. Their underlying, increasingly elaborate numerical codes produce a growing amount of raw data. Post-processing such data is therefore becoming more and more important, but also more challenging and time-consuming. In addition, visualising processed data and results has, in times of coloured figures and a wealth of half-scientific software, become one of the weakest pillars of science, widely mistreated and ignored. Efficient and automated geodynamic diagnostics and sensible scientific visualisation preventing common pitfalls is thus more important than ever. Here, a collection of numerous diagnostics for plate tectonics and mantle dynamics is provided and a case for truly scientific visualisation is made. Amongst other diagnostics are a most accurate and robust plate-boundary identification, slab-polarity recognition, plate-bending derivation, surface-topography component splitting and mantle-plume detection. Thanks to powerful image processing tools and other elaborate algorithms, these and many other insightful diagnostics are conveniently derived from only a subset of the most basic parameter fields. A brand new set of scientific quality, perceptually uniform colour maps including devon, davos, oslo and broc is introduced and made freely available (http://www.fabiocrameri.ch/colourmaps, last access: 25 June 2018). These novel colour maps bring a significant advantage over misleading, non-scientific colour maps like rainbow, which is shown to introduce a visual error to the underlying data of up to 7.5 %. Finally, StagLab (http://www.fabiocrameri.ch/StagLab, last access: 25 June 2018) is introduced, a software package that incorporates the whole suite of automated geodynamic diagnostics and, on top of that, applies state-of-the-art scientific visualisation to produce publication-ready figures and movies, all in the blink of an eye and all fully reproducible. StagLab, a simple, flexible, efficient and reliable tool made freely available to everyone, is written in MATLAB and adjustable for use with geodynamic mantle convection codes.

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