Neoproterozoic-Cambrian basement-involved orogenesis within the Antarctic margin of Gondwana

High-grade metamorphic tectonites of the Nimrod Group in the central Transantarctic Mountains compose a major ductile shear zone that formed within the paleo-Pacific margin of Gondwana. Four intrusive units with incipient to well-developed ductile fabrics yield U-Pb zircon ages of 541-521 Ma, and a nondeformed pegmatite has a U-Pb zircon age of ~515 Ma. These data show that early Paleozoic Ross magmatism was compositionally, texturally, and temporally more heterogeneous than previously recognized. Fabrics in the igneous rocks are concordant with those in their host tectonites, indicating that Nimrod tectonism was in part synchronous with plutonism. The timing provides compelling evidence for transcurrent basement involvement in oblique plate convergence along the Neoproterozoic to Early Cambrian Antarctic margin of Gondwana. -from Authors