Results for the Mantle Transition Zone Beneath the Transantarctic Mountains From Receiver Functions

There is a significant geologic contrast between the East Antarctica Craton (EAC) and the accreted terranes that make up West Antarctica. The boundary between these two provinces is marked by the Transantarctic Mountains (TAM) that parallel the West Antarctica Rift System (WARS). The TAM are the largest non- compressional mountain chain in the world, but their origin is not fully understood. Also not well explained is the anomalously high topography of the EAC. A potential cause for both is a thermal upwelling, either a very broad (>500 km wide) anomaly or a narrower one (~100-200 km wide). To investigate these two unique tectonic features of the Antarctic continent, receiver-function stacking was conducted with broadband seismic data collected by the 2000-2003 Transantarctic Mountain Seismic Experiment (TAMSEIS) to image topography on the 410 and 660 km discontinuities and the thickness of the transition zone. A deep-seated mantle thermal anomaly would evidence itself by creating topography on the 410 and/or 660 km discontinuities. After generating the receiver functions using a frequency-domain deconvolution with water-level stabilization, a geographical binning technique has been applied to better resolve lateral variations in structure. Stacking was performed with a 3D velocity model to correct for heterogeneity in the upper mantle. Results demonstrate that the transition zone is thicker than the global average even in the region of Ross Island and the WARS. Although there is a clear change in the relative depths of the 410 and 660 between the EAC and the TAM/Ross Island area, the average thickness of the transition zone is consistent throughout the study area.