P-T-t-d evolution of Brattnevet Peninsula, Larsemann Hills, East Antarctica

Abstract

Brattnevet Peninsula, Larsemann Hills, comprises metamorphosed acidic rocks, sedimentary rocks and basic igneous suite belonging to timespan of 920-478 Ma and have experienced three phases of deformation and metamorphism. The first and second phase of deformation gave rise to moderately plunging isoclinal and open to closed folds, respectively and the third phase resulted into broad warping. M1 prograde (amphibolite) and M2 peak (granulite) and M3 retrograde (decompression) events have been inferred. In pyroxene granulite, inclusion assemblage of quartz, biotite, plagioclase and ilmenite in hornblende correspond to the relict M1 amphibolite grade event associated with D1-D2 deformation events (occurred at ~920 Ma; 538–692 °C at ~6kb). However, the presence of enstatite, diopside, quartz, biotite, ilmenite and plagioclase in pyroxene granulite and sillimanite, biotite and almandine garnet and plagioclase in metapelite indicates granulite facies during M2 event (~530 Ma; 868–920 °C at ~6.7 kb). The retrograde M3 event (500-480 Ma; ~620 °C at ~5kb) is largely depicted in pyroxene granulite and metapelite by coronal and symplectite cooling textures. The study shows a clockwise P-T path and suggests the crustal evolution of Larsemann Hills area have commenced at the wanning stages of Grenvillian Orogeny and imprinted by the Pan-African orogenic event in the terrane.