Density, temperature and composition of Antarctica’s lithosphere and impact on geothermal heat flux and mantle viscosity

Abstract

A knowledge of Antarctica’s lithospheric properties is essential for understanding tectonic history and solid-earth influences on ice sheet dynamics. For example, the spatial variation of mantle temperature impacts both geothermal heat flow and mantle viscosity, which influence the ice sheet basal melt rate and glacial isostatic adjustment. Seismic tomography models can be used to constrain the mantle temperature. However, seismic velocity to temperature conversion is sensitive to variations in mantle composition, which are linked to changes in density that are also resolved in the gravity field.Here we model Antarctica’s density distribution using a 3D finite element gravity inversion approach based on the esys-escript model in python. We derived a correction to an initial density distribution based on a seismic tomography model (ANT-20). From the resulting density distribution and the initial seismic velocity distribution we estimated mantle temperature and composition and calculated the lithosphere thickness, mantle viscosity, and geothermal heat flow. The result shows that East Antarctica has a dense, thick (>150 km) and cold lithosphere, whereas West Antarctica has a thin (<100 km) hot lithosphere. The new heat flow model suggests a higher heat flow estimation than previous continental scale estimations.Our result highlights compositional heterogeneity within East Antarctica, with a highly depleted cratonic mantle in central East Antarctica. By considering compositional change, modelled mantle temperature increases up to 150 °C in depleted regions to accommodate lower density with fast seismic velocity. Higher modelled temperatures cause reduced lithospheric thickness up to 80 km compared with the initial model. In comparison to previous results in interior East Antarctica, a 5-10 mW/m2 higher heat flow is suggested by our model. In West Antarctica, large areas show heat flow of up to 110 mW/m2. Our result also suggests low mantle viscosity including Amundsen Sea Embayment, Marie Byrd Land and Antarctic Peninsula.