Metamorphism in the Ross orogen and its bearing on Gondwana margin tectonics

The Ross orogen of Antarctica is one of Earth’s great Phanerozoic mountain belts. It is thought from igneous geochemistry, deformation patterns, and sedimentation history to be the result of late Neoproterozoic and early Paleozoic plate-margin convergence between paleo-Pacifi c oceanic lithosphere and continental lithosphere represented by the composite East Antarctic shield. Convergence along this margin is contemporaneous with, and tectonically linked to, amalgamation of the Gondwana supercontinent following collapse of former ocean basins and collision along the East African orogen. Although there is general agreement about the large-scale tectonic framework of the Ross orogen, there is a great deal of remaining uncertainty regarding crustal province correlation, deformation kinematics, precise timing, and platemargin paleogeography. Our uncertainty stems from (1) a fragmentary record left by younger tectonic events that have modifi ed and, in some cases, removed parts of the orogen, and (2) extensive ice cover. Because the basement geology of the Ross orogen is composed largely of metamorphic rocks, however, study of the metamorphic roots of the orogen should help to constrain tectonic setting, thermal structure, tectonic displacements, cooling history, and timing. Evidence in the metamorphic domains refl ects 60–100 million years of continental-margin subduction, which is characterized by primary magmatic crustal accretion and low-P/T magmatic-arc meta morphism, crustal thickening and high-P/T metamorphism due to convergence and oceanic-arc collision, and high-P/T metamorphism associated with seaward growth of a platemargin accretionary system.