Imaging the Antarctic mantle using adaptively parameterized P-wave tomography: Evidence for heterogeneous structure beneath West Antarctica

Previously developed continental-scale surface wave models for Antarctica provide only broad interpretations of the mantle structure, and the best resolved features in recent regional-scale seismic models are restricted above ~300-400 km depth. We have developed the first continental-scale P-wave velocity model beneath Antarctica using an adaptively parameterized tomography approach that includes data from many new seismic networks. Our model shows considerable, previously unrecognized mantle heterogeneity, especially beneath West Antarctica. A pronounced slow velocity anomaly extends between Ross Island and Victoria Land, further grid south than previous studies indicate. However, at least for mantle depths ≥~200 km, this anomaly does not extend grid north along the Transantarctic Mountains (TAMs) and beneath the West Antarctic Rift System. The boundary between these slow velocities and fast velocities underlying East Antarctica is ~100-150 km beneath the front of the TAMs, consistent with flexural uplift models. The lateral extent of the low velocity anomaly is best explained by focused, rift-related decompression melting. In West Antarctica, Marie Byrd Land is underlain by a deep (~800 km) low velocity anomaly. Synthetic tests illustrate that the low velocities also extend laterally below the transition zone, consistent with a mantle plume ponded below the 660 km discontinuity. The slow anomalies beneath Ross Island and Marie Byrd Land are separate features, highlighting the heterogeneous upper mantle of West Antarctica.