Geochemistry of Cambrian volcanics of the Bowers Supergroup and implications for the Early Palaeozoic tectonic evolution of northern Victoria Land, Antarctica

Abstract

Rocks of the Bowers Supergroup include volcanics of the Middle Cambrian Glasgow Formation and form a narrow, fault-bounded belt running 350 km across northern Victoria Land from the Southern Ocean to the Ross Sea. The volcanics, which interdigitate with marine volcaniclastic sediments in a 3.5-km-thick succession, comprise pillow lavas and breccias of basalt and andesite with subordinate dacite-rhyolite. Basic rocks are notably depleted in Ti Zr Y and high in Mg Cr Ni, and are interpreted as primitive island are tholeiites. Southwest of the Bowers belt lie high-grade metamorphic rocks of the Precambrian Wilson Group, cut by Cambro-Ordovician S-type granitoids. To the northeast are low-grade metasediments of the Late Precambrian or Early Palaeozoic Robertson Bay Group. Geological relationships between the Bowers Supergroup and the Wilson and Robertson Bay Groups are enigmatic and controversial. A number of tectonic models for the Lower Palaeozoic of northern Victoria Land are advanced. It seems likely that major strike-slip faulting was significant in the Early Palaeozoic evolution of this sector of the Gondwana margin, and that some currently adjacent terranes have allochthonous relationships.