Crustal exhumation during ongoing compression in the Variscan Maures-Tanneron Massif, France : geological and thermo-mechanical aspects - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Tectonophysics Année : 2018

Crustal exhumation during ongoing compression in the Variscan Maures-Tanneron Massif, France : geological and thermo-mechanical aspects

Muriel Gerbault
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Julie Schneider
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A. Reverso-Peila
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Michel Corsini

Résumé

The Maures-Tanneron Massif (MTM), together with Corsica and Sardinia, represent the Southeastern branch of the huge European Variscan belt. A continuous evolution from continental collision to exhumation is described from ca. 350 Ma to ca. 320 Ma, based on an extended compilation of available geological and geochronological data. This geological compilation is complemented with thermo-mechanical modelling that tests the conditions under which deep-seated HP units can melt and exhume massively during continued convergence. We simulate in two-dimensions the development of gravitational instabilities in a partially melting crust, depending on rhe-ological layering and heat sources, and accounting for temperature dependent elasto-visco-plastic rheologies. In order to reproduce PT exhumation patterns in the MTM, over the appropriate timescale (N 20 My) and spatial extent (N100 km), a best fit was obtained with a convergence rate of 0.5 cm/yr and moderate diffusive surface processes. The contribution of radiogenic heating in the pre-stacked felsic crustal units is crucial. A lateral alternation with mafic units is also required in order to prevent lateral spreading of the orogen. A low viscosity partially molten crust (10 20 Pa·s, thus rather felsic) accompanies crustal exhumation in a decoupled mode from the deeper mantle. A shallow asthenosphere below the orogen (LAB at ~70 km depth, e.g. shallow slab break-off) produces too warm and sudden exhumation as opposed to a competent mantle lithosphere (120 km depth LAB) that restrains it. The MTM witnesses the typical competition between far-field plate convergence and internal body forces, and our study pleads for a progressive evolution of transpression towards perpendicular extension from ca. 320 Ma.
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Dates et versions

hal-01745102 , version 1 (30-03-2018)

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Muriel Gerbault, Julie Schneider, A. Reverso-Peila, Michel Corsini. Crustal exhumation during ongoing compression in the Variscan Maures-Tanneron Massif, France : geological and thermo-mechanical aspects. Tectonophysics, In press, ⟨10.1016/j.tecto.2016.12.019⟩. ⟨hal-01745102⟩
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