Role of strain-dependent weakening memory on the style of mantle convection and plate boundary stability

Abstract

How plate tectonic surface motions relate to the convecting mantle remains one of the major problems in geosciences. In particular, the cause and consequence of strain localization at plate boundaries remains debated, even though strain memory, i.e. the ability to preserve and reactivate tectonic inheritance over geological time, appears to be a critical feature in plate tectonics. Here, we analyze how a parameterized damage weakening rheology, strain-dependent weakening, affects the time-dependence of plate boundary formation, the transition between mobile and stagnant-lid, and the reorganization of plates in 2-D convection models. The strain-dependent weakening within our models allows for a self-consistent formation and preservation of lithospheric weak zones, which are formed as remnants of subduction zones due to large-scale compressional deformation in the trench region. Such inherited weak zones can be reactivated as intra-plate subduction zones, ridge adjacent subduction, or as spreading centers themselves. Due to the weakening along plate boundaries, the inherited weak zones, and partly the accumulated strain along spreading centers, which weakens the shallow parts of the lithosphere, the longevity of mobile-lid convection increases. Strain-dependent weakening also enhances strain localization along convergent plate boundaries which increases their stability and longevity. As a consequence, tectonic inheritance is an important contribution to understanding the time-dependence of plate reorganization. Strain-dependent weakening results in a shift of the mobile-stagnant lid transition to higher effective yield stresses, if the weak zones fully penetrate the lithosphere and are relatively weakened by at least 20 %.