Revealing the sub-ice geology: crustal composition determined by seismic networks in Antarctica

Knowing the crustal architecture, including its thickness, layering, fine structure and chemical composition of Antarctica benefits our understanding of its geological history and effects on potential climate change. For instance, quantitative measurements of chemical composition of the crust provide key information of its tectonic history, in that the direct geological samplings are only sparsely available by its limited surface rock exposure as the 99% of the continent is covered by thick ice-sheet. Silica, one of the most abundant oxides, plays an important role in chemical composition measurements since it not only constitutes the weakest mineral quartz but also are compatible with heat generating elements. In this presentation, we show an effort trying to quantify the silica content of the crust by studying its seismic properties using data recorded by seismic networks in Antarctica, based on the fact that the silica content can be quantified by a combination of two seismic properties together, shear velocities (Vs) and ratios between P velocities and shear velocities (Vp/Vs). Particularly, we used body wave seismograms with magnitude > 5.5 at about 100 stations for the last 15 years. Receiver functions are calculated and a multi-layer (ice/sediment and crystalline crust) H-κ(layer thickness and Vp/Vs) stacking method is applied to them. Combining the resulting crystalline crust Vp/Vs with an existing Vs model (Shen et al. 2018), we construct local crustal silica content models through a Monte Carlo approach and meaningful error estimations are also made. This resulting model provides unique insights into the geological and thermal properties in Antarctica as well as its tectonic history, showing a distinct difference in chemical composition between the tectonically active West Antarctica and more stable East Antarctica, with variations within each region also recovered.