Grain size assisted thermal runaway as a nucleation mechanism for continental mantle earthquakes: Impact of complex rheologies

Thielmann, Marcel

doi:10.1016/j.tecto.2017.08.038

Cited by 37 publications

(48 citation statements)

References 68 publications

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“…The idea that strain rate is an important factor in understanding deep earthquakes is not new, but it has been largely ignored or forgotten in the literature relating potential failure mechanisms to the physical state of the slab. The mechanism of shear instability explicitly relies on having a high enough strain rate (and stress) to cause shear heating ( 3 ); however, localized grain size reduction is likely necessary to reach sufficient strain rates for this mechanism to be viable ( 5 ). Transformational faulting of olivine also requires a sufficient strain rate, and the strain rate affects the window of temperatures at which this mechanism occurs in the laboratory [see Figure 4 in ( 6 )].…”

Section: Discussionmentioning

confidence: 99%

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Deep slab seismicity limited by rate of deformation in the transition zone

Billen

2020

Sci. Adv.

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Deep earthquakes within subducting tectonic plates (slabs) are enigmatic because they appear similar to shallow earthquakes but must occur by a different mechanism. Previous attempts to explain the depth distribution of deep earthquakes in terms of the temperature at which possible triggering mechanisms are viable, fail to explain the spatial variability in seismicity. In addition to thermal constraints, proposed failure mechanisms for deep earthquakes all require that sufficient strain accumulates in the slab at a relatively high stress. Here, I show that simulations of subduction with nonlinear rheology and compositionally dependent phase transitions exhibit strongly variable strain rates in space and time, which is similar to observed seismicity. Therefore, in addition to temperature, variations in strain rate may explain why there are large gaps in deep seismicity (low strain rate), and variable peaks in seismicity (bending regions), and, possibly, why there is an abrupt cessation of seismicity below 660 km.

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Section: Discussionmentioning

confidence: 99%

“…Second, regional differences in b values suggest that rupture may occur by a combination of mechanisms including transformational faulting and thermal shear instability for deep earthquakes (15). Third, recent studies suggest that shear instability is also a viable mechanism for intermediate-depth earthquakes (4,5,16).…”

Section: Introductionmentioning

confidence: 99%

Deep slab seismicity limited by rate of deformation in the transition zone

Billen

2020

Sci. Adv.

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“…§3a), so this effect of neglecting dislocation creep is also unlikely to significantly influence the results. I also note that in the shallow lithosphere, additional creep mechanisms, such as low-temperature plasticity, can become important [62,[107][108][109]. However, as explained above, diffusion creep is the dominant deformation mechanism in shear zones that have undergone significant grain size reduction.…”

Section: Background Theory and Model Set-up (A) Grain Damage Theorymentioning

confidence: 99%

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

Foley

2018

Phil. Trans. R. Soc. A.

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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’.

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“…Three hypotheses have been proposed to induce mechanical instability within the normally ductile regime. The first is a thermal runaway process where a self-amplifying mechanical instability arises from the combination of shear localization and grain size reduction within a visco-plastic material (Kelemen and Hirth, 2007;Thielmann, 2018). Crucial issue here is the conditions under which shear localizations nucleate and self-amplify, leading to failure (John et al, 2009).…”

Section: Possible Mechanisms Of Intermediate-depth Seismicity Under Smentioning

confidence: 99%

“…A recent study shows that at pressures corresponding to depths up to 100 km, shear-banding and localized heating may develop in deforming olivine, resulting in seismogenic faulting (Ohuchi et al, 2017). Numerical modeling also shows that as deformation mechanisms change (either due to temperature or stress), shear localization may develop and may cause potential adiabatic heating, inducing mechanical instability (Thielmann, 2018). From these viewpoints, sub-Moho seismicity under southern Tibet may be interpreted as shear-localization induced instability triggered by stress heterogeneities produced through strong mechanical coupling between the crust and upper mantle.…”

Section: Possible Mechanisms Of Intermediate-depth Seismicity Under Smentioning

confidence: 99%

The Indo–Eurasia convergent margin and earthquakes in and around Tibetan Plateau

Wang

Deng

Shi

et al. 2020

Journal of Mineralogical and Petrological Sciences

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After a brief review on tectonic settings of the Himalayas and Tibetan Plateau, we survey the literature on characteristics of earthquakes occurring in Tibetan Plateau and the surrounding regions. Shallow events (focal depths <50 km) show remarkable correlation with surface fault systems in both spatial locations and focal mechanisms. Some shallow events appear to be triggered by remote earthquakes and seasonal variations of ground water storage, suggesting stress levels nearing critical threshold. Intermediate-depth earthquakes (IDEQs; i.e., earthquakes with focal depths between 50 and 300 km) are concentrated beneath southern Tibet, the Hindu Kush-Pamir region, and the Burmese subductions zones. Underneath southern Tibet, the subducted Indian plate extends northward to at least the Bangong-Nujiang suture zone, with IDEQs occurring in the lower crust and the adjacent upper mantle. Possible mechanisms for IDEQs are also reviewed.

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Grain size assisted thermal runaway as a nucleation mechanism for continental mantle earthquakes: Impact of complex rheologies

Cited by 37 publications

References 68 publications

Deep slab seismicity limited by rate of deformation in the transition zone

Deep slab seismicity limited by rate of deformation in the transition zone

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

The Indo–Eurasia convergent margin and earthquakes in and around Tibetan Plateau

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