Mantle rocks in East Antarctica

Abstract

AbstractOnly three localities of mantle xenoliths are known from all of East Antarctica, occurring at the Jetty Peninsula (Lambert–Amery Rift), Vestfold Hills and Gaussberg volcano. The latter two are spinel-facies peridotites, whereas the Jetty Peninsula rocks also include garnet-spinel lherzolites; all come from Indo-Antarctica. The mantle xenoliths of Jetty Peninsula and Vestfold Hills contain abundant geochemical and mineralogical evidence for multiple enrichment events that are attributed to infiltration of melts and their fluid products. Many of these episodes are spatially related to precursory activity along major trans-lithospheric structures that eventually led to the separation of India from Antarctica. Mantle rocks also occur at Schirmacher Oasis (Dronning Maud Land) and Haskard Highlands (Shackleton Ranges) as blocks tectonically emplaced in high-grade crustal rocks. These show varying degrees of alteration due to reaction with silicic crustal rocks or hydrous fluids: none correspond to unchanged mantle compositions. Geophysical surveys are our only information on the mantle lithosphere beneath the inland ice, and these can be used to infer the locations of thicker lithosphere probably related to cratons by southward extrapolation of coastal geological correlations. Intense local modification of the mantle lithosphere by melt infiltration and fluid movements may influence the large-scale images derived from geophysical data, and may be incorrectly interpreted as homogeneous compositions.