Surgeon island granite SHRIMP zircon ages: a clue for cambrian tectonic setting and evolution of the Palaeopacific margin of Gondwana (northern Victoria Land, Antartica).

In northern Victoria Land (NVL), Antarctica, the palaeopacific margin of Gondwana is made up of the inboard Wilson (WT) and the two outboard Bowers (BT) and Robertson Bay (RBT) terranes. The occurrence of a Cambro-Ordovician magmatic arc in the WT argues for a southwestward subduction leading to the final configuration of this margin during the Ross-Delamerian Orogeny. A U-Pb SHRIMP crystallization age (511.7 ± 2.9 Ma) obtained on the Surgeon Island Granite (SIG), located at the eastern end of the RBT, indicates that the SIG also belongs to the Ross cycle, and provides evidence for multiple subduction zones during the Ross Orogeny. Structural observations show that the SIG and its country rocks are basement to the RBT turbidites. SIG inherited zircon ages indicate the occurrence of Proterozoic crust east of the RBT and constrains the location of the Proterozoic-Palaeozoic boundary in Cambrian Gondwana.