The impact of brittle and ductile weakening mechanisms on strain localization and the stabilization of transform fault zones

Abstract

Rheological weakening mechanisms play a crucial role in plate tectonics by locally dropping lithospheric strength and leading to the formation of new plate boundaries, including new subduction zones or transform boundaries. Despite the abundance and persistence of large-offset oceanic transform faults, understanding their formation, the role of their preceding continental rifting history and their preservation is less understood. Furthermore, the role of different rheological weakening mechanisms is still debated.In this study, we aim to better understand the contribution of different rheological weakening mechanisms, including both brittle and ductile processes, to the development of rifts and transform fault zones. To achieve this, we are running a comprehensive series of high-resolution 3D petrological-thermomechanical models (i3ELVIS). These models include elasto-visco-plastic rheology with strain-rate induced weakening, partial mantle melting, oceanic crustal growth, thermal contraction and mantle grain size evolution. To investigate the influence of weakening processes, we compare model evolutions that include strain-induced and strain-rate induced plastic weakening parameters. A particular focus is made on the evolution of locally high plastic strain rate values during the evolution and stabilization of transform faults following rifting and during oceanic spreading. New insight from this study can then be applied on a natural example such as the Romanche Transform Fault Zone located in the equatorial Atlantic.