Constraining the upper plate surface deformation across coupled subduction-collision systems

Abstract:

The relationships between subduction dynamics, continental collision, surface erosion, upper mantle flow and the tectonic history recorded in the continental crust have attracted significant interest. Major results confirmed that mantle convection is a valuable mechanism behind much of the observed dynamic topography and plate motion. However, the degree to which mantle flow controls surface deformation and how this is modulated by erosion are major open questions. Geodetic measurements, coupled with geological observations, enable to achieve a fairly good understanding of the evolution of active features, but the long-term dynamic origins of this kinematics are still controversial. For example, mantle flow is proposed as a driver of plate tectonics, but lithospheric processes such as slab rollback are also known to affect mantle flow. In addition, surface erosion affects crustal deformation, but the interactions between surface mass transfer, crustal strain and deeper dynamics are still widely unknown. More definitive conclusions, especially regarding how the dynamical mantle flow associated to slab tearing and rollback and the mass transfer by surface erosion affect crustal strain, require the investigation of the 3D relationships between the lithosphere and mantle, from the topmost crustal layers to the asthenosphere.

We present new high-resolution 3D thermo-mechanical numerical joint models of continental collision, oceanic subduction and slab tearing which allow self-consistent reproduction of first order Tethyan tectonic structures such as back-arc rifting and large scale strike-slip faults accommodating continental escape. We compare these numerical outcomes with observations from the Aegean-Anatolian and eastern Indian-Eurasian margins. We show that the dynamical mantle flow due to slab rollback and tearing can modulate surface deformation by locally enhancing trench retreat and actively dragging the upper plate from below. Further investigations will include surface processes and allow us to assess the role of erosion. However, the similarities between modeled and natural surface kinematics suggest that horizontal to sub-horizontal mantle flow due to slab rollback and tearing codetermined the surface strain across the Aegean-Anatolian and eastern Indian-Eurasian domains.