Geochemistry of Volcanic Rocks Recovered from Bransfield Strait, Antarctica

Abstract

Bransfield Strait (BFS) is a rifting system located between South Shetland Islands and Antarctic Peninsula. The strait is unique in that because the rifting was occurred in continental crust. There are volcanic features including Hook Ridge, Orca Volcano (Viehoff Seamount) and Three sisters along the axis of BFS. In 2004 and 2005, KOPRI geochemical team conducted dredging on these volcanic features to characterize the mantle source, melting and magmatic process in BFS during a cruise onboard R/V Yuhzmogeoloya. Here, we present major and trace elements composition of the rock samples from the volcanic features in the axis of BFS. The lavas from the various volcanic features show a large compositional variation, ranging from basalt to rhyolite, and belong to tholeiitic and low K-series, but it appears that they fall in the single fractional crystallization trends. Such finding indicates that the primary magma compositions of each volcanic feature are similar to one another, suggesting that melting beneath the each volcanic feature were occurred in similar conditions. However, it is worth to noting that there are large gaps between groups of the lavas from region by region and/or single region in fractional crystallization trends. Such finding raises the possibility that the magma eruptions in the volcanic features were not occurred continuously, but episodically in different magmatic fractionation stage. REEs patterns of the BFS lavas also support the above possibility. Incompatible elements patterns of the lavas indicate that sub-BFS mantle is heterogeneous. The enrichment of Pb and LILE (large ion lithophile elements) relative to HFSE (high field strength elements) in the lavas from the volcanic features suggests that sub-BFS mantle was contaminated by subduction environment. In addition, influence of sub-continental lithosphere should be considered to understand the geochemistry of the BFS lavas.