On the relation between lithospheric strength and ridge push transmission in the Nazca plate

Abstract

The ridge push force and the total lithospheric strength of the Nazca plate are compared along an East-West transect from the East Pacific Rise to the Peru–Chile trench at latitude 12°S. The thermal structure of the plate is estimated from the plate cooling model and constrained by heat flow, bathymetry, and geoid height data. The best fitting thermal model has a basal temperature of ∼1600 K and an asymptotic plate thickness (not reached because of the relatively young age of the plate at the trench) of ∼101 km. The ridge push force, also determined from the plate cooling model, is of the order of 1.5 TN m −1 at the trench. The total lithospheric strength as a function of age is estimated for a possible range of conditions (compressional/extensional intraplate tectonic regime, wet/dry rheology). A comparison of ridge push force with lithospheric strength, extended beyond the Nazca plate by considering different spreading rates and ages, shows that oceanic plates with dry rheology have strengths higher than the ridge push force at any age if the tectonic regime is compressional, and comparable if the regime is extensional. On the other hand, oceanic plates with wet rheology have strengths lower than the ridge push force, especially if the tectonic regime is extensional. Therefore, if the rheology is wet and mantle drag at the base of the plate is sufficiently strong, the ridge push force may result in intraplate deformation and be partly dissipated within the plate.