SUB-GLACIAL GEOLOGY OF PRINCESS ELIZABETH LAND, EAST ANTARCTICA- A PRELIMINARY INVESTIGATION AND RESULTS: ITS TECTONIC IMPLICATION

Antarctica is covered by ice. There are only about 2% bedrocks cropping out. Our knowledge of the geology of Antarctica is based upon them and various tectonic models were drawn from them. However we often face the fact that there is too little exposed rock to develop robust models of basement geological evolution. To understand the sub-glacial geology of Antarctica, we present our recent investigation and preliminary results of erratic rocks in the Grove Mountains and the Vestfold Hills. The Grove Mountains, a high-grade terrane that underwent a single high-temperature granulite facies tectonic event at 530-550 Ma, which is the southern continuation of the Pan-African age Prydz belt. However direct evidence is still wanted for the assembly model to support collision between different Grenville-age blocks in East Antarctica, e.g., slices of ophiolite suite and/or high pressure metamorphism. To search for the suture zone inland Antarctica, we examined erratic rocks in morainal deposits and obtained four high pressure mafic granulite erratic rocks, which give peak metamorphism at 12.9-15.8 kb and 810-910°C around 545-542 Ma by a conventional thermometer and barometer with SHRIMP U-Pb zircon dating. It is the first report of a Pan-African high-pressure granulite facies record inland Antarctica, which is key evidence for a Pan-African suture beneath ice sheet near the Grove Mountains in the upper reaches of ice flows. We also investigated morainal deposits along the Sorsdal Glacier. We observed, at the southeastern Vestfold Hills, not only gneisses but also low-grade rocks, including greenschist, quartzite and phyllite, which are much different from autochthonous rocks and are considered brought out beneath upper reaches of Antarctic ice sheet. Statistics of erratic rocks at ten localities shows that low-grade rocks are in the majority at least at four localities. Analyses of zircon grains from the erratic rocks gives U-Pb age clustering around 3530 Ma or arranging from over 3.4Ga to ca. 2.4Ga, which enrich our knowledge of the sub-glacial geology of Princess Elizabeth Land, East Antarctica and have better understanding Pan-African assembly of East Antarctic Craton. In this way we can, combined with glacier dynamics, sub-glacier morphology and geophysics, improve our knowledge on the sub-glacial geology of Antarctica.