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What is the influence of the overriding plate rheology on the convergence zones?

Abstract : Most of deformation at the surface of the Earth is localized at tectonic plate boundaries. This deformation is accommodated in very different ways depending on the tectonic setting. In convergence zones, oceanic or continental subduction/collision can form contrasted structures in terms of unit size, morphology and metamorphism (e.g., the Andes vs., the Alps). Moreover, some convergent zones with apparently similar tectonic settings (e.g., continent-continent convergence) show very different deformation styles, either very localized (e.g., in the Alps) or, at the opposite, distributed over thousands of kilometers (such as in the Himalaya/Tibet). Finally, other convergent zones seem to show similar structures (e.g., Tibetan and Altiplano/Puma plateaus) beside their different tectonic settings. Hence, although the mechanism of plate convergence appears to be the same in each case, the structures obtained at the surface seem to be unique. Rheology of both the lower subducting plate and of the plate interface is known to influence the convergence zones dynamics. However, the influence of the overriding plate rheology on the convergence zones dynamics and deformation style at plate boundaries remains poorly understood. In this study, we present 3D thermo-mechanical numerical models, for oceanic and continental subduction/collision settings where the rheological properties of the overriding plate are tested. For this, we modified the overriding lithosphere geotherm in order to control the thicknesses of the thermal plate ranging from 40 km (corresponding to a "weak" overriding plate) to 150 km (corresponding to a "strong" overriding plate). Our first results show that the overriding plate rheology (which highly depends on the initially imposed temperature profile) has a high impact on the convergence zone dynamics: - First, some noticeable geometrical differences appear in cross section view. In the case of a "strong" overriding plate, the slab dip, the coupling at the subduction interface and the topography are higher. The slab folds on itself, the crustal material seems less involved in the subduction interface and the asthenospheric flow appear to be more heterogeneous than with a "weak" overriding plate. In plan view, the trench location and shape are strongly linked to the overriding plate rheology. The trench is more mobile and its final retreat on the edges is more important (673km vs., 147km) with a "weak" overriding plate. - Our models also show some kinematic differences. Trench motions are faster for the "weak" model whereas the timing of slab break-off is delayed (35Ma vs., 14Ma) and its impact on the asthenospheric flow is observable over a longer period of time for the "strong" overriding plate. - Finally, the strength of the overriding plate controls the distribution of its own deformation. The location and the amount of strain differ between the two end-members. The "weak" model shows a diffuse deformation in the whole overriding plate while in the "strong" model the deformation is much more localised at the trench. This study question the classical vision of the convergence zones. Our results lead to reconsider the convergence zone dynamic as a whole, i.e., considering also the overriding plate and its influence and not only the subducting plate.
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-01717281
Contributor : Isabelle Dubigeon <>
Submitted on : Monday, February 26, 2018 - 10:44:24 AM
Last modification on : Tuesday, February 18, 2020 - 2:08:17 PM

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  • HAL Id : insu-01717281, version 1

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Solenn Hertgen, Philippe Yamato, Benjamin Guillaume, Nicholas Schliffke, Valentina Magni, et al.. What is the influence of the overriding plate rheology on the convergence zones?. NetherMod, Aug 2017, Putten, Netherlands. ⟨insu-01717281⟩

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