IMAGING MANTLE STRUCTURE AND GEODYNAMIC PROCESSES BENEATH ANTARCTICA USING ADAPTIVELY PARAMETERIZED P-WAVE TOMOGRAPHY

Due to an historic paucity of data, the mantle structure beneath Antarctica is much less resolved than beneath other continents, leading to a relative lack in understanding of its geologic history and ongoing processes. Present continental-scale models for Antarctica provide only broad interpretations of the mantle structure, and the best resolved features in recent regional-scale 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 highlights considerably more mantle heterogeneity than previous continental-scale models and provides higher resolution imaging at deeper mantle depths. Beneath East Antarctica, fast mantle velocities are consistent with Archean or Proterozoic cratonic lithosphere, but slower velocities beneath the Polar Subglacial Basin may reflect a Precambrian lithospheric suture. The upper-mantle boundary between fast velocities in East Antarctica and slow velocities in West Antarctica is found ~100-150 km beneath the Transantarctic Mountains front. A pronounced ~200-250 km deep slow anomaly underlies Ross Island, which may be associated with rift-related processes. In West Antarctica, Marie Byrd Land is underlain by a deep (~800 km) low velocity anomaly. Synthetic tests show that these low velocities must extend laterally beneath the transition zone, and we interpret this structure as a mantle plume ponded below the 660 km discontinuity. These results provide new insight on the deep geodynamic processes of Antarctica.