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Abstract:
Spatial heterogeneities of density, temperature, and composition in the Antarctic lithosphere are crucial for controlling its geodynamic evolution and ice sheet dynamics. Mantle density and temperature can be estimated from seismic tomography models with a given or assumed mantle composition. However, this conversion is non-unique, as the mantle composition cannot be determined from seismic tomography alone.Here, we used gravity inversion along with a seismic tomography model to constrain the composition of Antarctic lithosphere. We modelled lithospheric 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) with an initial uniform mantle composition. From the resulting density distribution and the initial seismic velocity distribution, we updated mantle temperature and composition and calculated the lithosphere thickness, mantle viscosity, and geothermal heat flow.Our result highlights the compositional effect is essential to constraining the mantle temperature in East Antarctica, where our model suggests a highly depleted cratonic mantle in central East Antarctica. When compositional variations are considered, modelled mantle temperature increases in depleted regions by up to 150 °C to accommodate lower density and fast seismic velocity. Sensitivity tests suggest anelasticity effects dominate the uncertainty in resolving mantle temperature in slow seismic velocity regions (for example, West Antarctica). Future work requires constraining the seismic anelasticity to reduce the uncertainties in estimating lithosphere properties in West Antarctica.
