a1 GNS Science, Private Bag 1930, Dunedin, New Zealand
a2 Department of Geology, University of Otago, PO Box 56, Dunedin, New Zealand
a3 Department of Geology and Geophysics, University of Minnesota, Minneapolis MN 55455, USA
a4 IFM-GEOMAR Leibniz Institute for Marine Sciences, Wischhofstrasse 1–3, D-24148 Kiel, Germany
The Ross Sea is bordered by the Late Precambrian–Cambrian Ross–Delamerian Orogen of East Antarctica and the more Pacific-ward Ordovician–Silurian Lachlan–Tuhua–Robertson Bay–Swanson Orogen. A calcsilicate gneiss from Deep Sea Drilling Project 270 drill hole in the central Ross Sea, Antarctica, gives a U-Pb titanite age of 437 ± 6 Ma (2σ). This age of high-grade metamorphism is too young for typical Ross Orogen. Based on this age, and on lithology, we propose a provisional correlation with the Early Palaeozoic Lachlan–Tuhua–Robertson Bay–Swanson Orogen, and possibly the Bowers Terrane of northern Victoria Land. A metamorphosed porphyritic rhyolite dredged from the Iselin Bank, northern Ross Sea, gives a U-Pb zircon age of 545 ± 32 Ma (2σ). The U-Pb age, petrochemistry, Ar-Ar K-feldspar dating, and Sr and Nd isotopic ratios indicate a correlation with Late Proterozoic–Cambrian igneous protoliths of the Ross Orogen. If the Iselin Bank rhyolite is not ice-rafted debris, then it represents a further intriguing occurrence of Ross basement found outside the main Ross–Delamerian Orogen.
(Received August 30 2010)
(Accepted November 04 2010)
(Online publication February 08 2011)