Can Subduction-Induced Mantle Flow Drive Backarc Extension?

Abstract

Backarc extension is a significant feature of subduction zones in nature, where seismological and geochemical studies evidence the occurrence of a 3-D mantle flow around the subducting slabs. Previous geodynamic models suggest that backarc extension is related to this type of subduction-induced mantle flow. There is, however, a lack of direct evidence to support this hypothesis. Using here three-dimensional dynamic laboratory models including an overriding plate, we show for the first time that the subduction-induced mantle flow can drive extension in the backarc region and overriding plate necking. By means of a stereoscopic Particle Image Velocimetry technique, we map the overriding plate deformation and the 3 components of subduction-induced mantle flow located underneath and around the overriding plate. We show that the strain field of the overriding plate is characterized by localization of an area of maximum extension, of which the position is correlated to the maximum horizontal velocity gradient of mantle flow located at 150km depth underneath the overriding plate. Furthermore, the direction of toroidal upper mantle flow mapped at the surface points to the necking deformation occurring at both edge sides of the overriding plate. Our results thus efficiently support the hypothesis that the backarc extension of the overriding plate is a consequence of the subduction-induced mantle flow horizontal velocity gradient generating a basal drag force.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015