Upper mantle seismic anisotropy beneath the Northern Transantarctic Mountains inferred from peridotite xenoliths near Mt. Melbourne, northern Victoria Land, Antarctica

Abstract

Microstructural investigations of mantle xenoliths from the Mt. Melbourne area were undertaken to reveal the origin of S-wave splitting beneath northern Victoria Land, Antarctica. The six analyzed peridotites contain various deformation features. The rotated olivine maxima of [100] and [010] into horizontal and vertical orientations, respectively, are classified into five samples with a D-type crystallographic preferred orientation (CPO) and one sample as an A-type CPO. The D-type olivine fabric can be explained by multiple slip systems of {0kl}[100] at low-temperature and high-stress conditions; therefore, both compressional and extensional regimes during subduction and rifting, respectively, could be applied in this study. With an assumption that olivine a-axes are aligned along the direction of mantle flow to form maximum S-wave splitting, the observed delay time of 0.9？1.3 s beneath northern Victoria Land can be partially explained by the anisotropy in the mantle peridotites. The remaining seismic anisotropy can be explained by the presence of melt pockets trapped along tectonic faults that developed perpendicular to the fast S-wave splitting direction. This study therefore demonstrates that the NE？SW-trending S-wave splitting beneath northern Victoria Land, Antarctica, results from the existence of both mantle peridotites as well as melt pockets trapped along the tectonic faults.