The Lithospheric Density Structure of the Antarctic Continent from Integrated 3D Gravity and Petrological Modelling

Abstract

Numerous
unresolved issues exist regarding the Antarctic lithosphere, especially in
terms of density, temperature, and compositional structure. For example,
contemporary estimates of the Moho depth from different geophysical methods
show significant discrepancies of 10-20 km in large areas of the continent.
While seismological methods suffer from a limited station coverage and ice
reverberation, potential field methods, such as gravity studies, are inherently
non-unique. By modelling densities and seismic velocities in a consistent way
and accounting for thermodynamically stable mineral phases of rocks under
in-situ pressure and temperature conditions, we are able to compensate for the
sparseness of data in Antarctica and reduce inconsistencies and ambiguities of
separate geophysical methods to a large extent. Gravity gradient data from ESA’
s satellite mission ‘GOCE’ are used to constrain the density distribution
within the lithosphere in an integrated 3D model of the Antarctic continent,
whereas independent seismic estimates serve as a benchmark for the robustness
of the results. Intra-crustal density variations are inverted from airborne
gravity data and evaluated against thermodynamic modelling results of potential
upper crustal rock compositions. As a main outcome, we present a new crustal thickness map of Antarctica. It
includes varying density contrast at the Moho and exhibits detailed thickness
changes in East Antarctica, also in regions with sparse or absent seismic
station coverage. At locations where compositions of xenoliths from deeper
sources are available, we analyse the model’s sensitivity to introduction of
such regional information. As an example of the applicability of our model for
further studies, we demonstrate how its deep thermal field is used to derive
upper mantle viscosities for glacial isostatic adjustment (GIA) modelling.