Waveform tomography of the Antarctic Plate

SUMMARY We present a new seismic shear wave velocity model of the upper mantle of the Antarctic Plate region, AP2024. It includes the lithosphere and underlying mantle down to 660 km depth beneath both the continental and oceanic portions of the plate. To augment the limited seismic station coverage of Antarctica, we assemble very large regional and global data sets, comprising all publicly available broad-band seismic data. The model is built using 785 thousand seismograms from over 27 thousand events and 8.7 thousand stations. It is constrained by both body and Rayleigh surface waves, ensuring the dense data sampling of the entire upper mantle depth range. The tomographic inversion is global but focused on the Antarctic Plate, with the data sampling maximized in the Southern Hemisphere, with elaborate automated and manual outlier analysis and removal performed on the regional data, and with the regularization tuned for the region. The upper mantle of the Antarctic continent exhibits a bimodal nature. The sharp boundary along the trans-Antarctic mountains separates the cratonic eastern from tectonic western Antarctica and shows a shear-velocity contrast of up to 17 per cent at $\sim$100 km depth. The bimodal pattern is also seen in the oceanic part of the plate, with the older oceanic lithosphere beneath the Indian sector of the Southern Ocean showing higher shear velocities. The continental lithosphere in East Antarctica shows high velocity anomalies similar to those beneath stable cratons elsewhere around the world. It is laterally heterogeneous and exhibits significant thinning in the near-coastal parts of Dronning Maud Land and Wilkes Land. A low velocity channel is observed along the southern front of the West Antarctic Rift System and is probably related to Cenozoic rifting. High seismic velocity anomalies are detected beneath the Antarctic Peninsula and are likely to indicate fragments of the recently subducted Phoenix Plate Slab. Low velocity anomalies beneath Marie Byrd Land extend into the deep upper mantle and are consistent with a deep mantle upwelling feeding West Antarctica intraplate magmatism.