Thermal softening induced subduction initiation at a passive margin

Daniel Kiss (1) , Lorenzo Candioti (1) , Thibault Duretz (2) , Stefan M Schmalholz (1)

1 UNIL - Université de Lausanne = University of Lausanne
2 GR - Géosciences Rennes

We present 2-D numerical simulations of convergence at a hyperextended passive margin with exhumed subcontinental mantle. We consider viscoelasto-plastic deformation, heat transfer and thermomechanical coupling by shear heating and associated thermal softening due to temperature dependent viscosity. The simulations show subduction initiation for convergence velocities of 2 cm yr−1, initial Moho temperatures of 525 °C and maximal deviatoric stresses of ca. 800 MPa, around the Moho, prior to localization. Subduction initiates in the region with thinned continental crust and is controlled by a thermally activated ductile shear zone in the mantle lithosphere. The shear zone temperature can be predicted with a recently published analytical expression. The criterion for subduction initiation is a temperature difference of at least 225 °C between predicted temperature and initial Moho temperature. The modelled forced subduction broadly agrees with geological data and reconstructions of subduction during closure of the Piemont-Liguria basin, caused by convergence of the European and Adriatic plates during the Alpine orogeny.

Mots clés: Subduction initiation; thermal softening; shear heating; numerical mod- 20 elling; thermo-mechanics

Domaines: Tectonique

Daniel Kiss, Lorenzo Candioti, Thibault Duretz, Stefan M Schmalholz. Thermal softening induced subduction initiation at a passive margin. Geophysical Journal International, 2020, 220 (3), pp.2068-2073. ⟨10.1093/gji/ggz572⟩. ⟨insu-02462658⟩