Structure and timing of transpressional deformation in the Shackleton Glacier area, Ross orogen, Antarctica

Abstract

Basement of the Transantarctic Mountains comprises the Ross orogenic belt, a Neoproterozoic to Ordovician mobile belt located along the palaeo-Pacific margin of Gondwana. Our structural analysis of deformation in the Liv Group, a sequence of Cambrian volcanic, volcaniclastic, clastic and carbonate rocks, and nearby plutonic rocks indicates that the Shackleton Glacier area has a polyphase deformation history that includes development of both contractional and strike-slip structures. We describe evidence for synchronous contraction and strike-slip movement, and suggest that the structural suite in this area developed, at least in part, within a sinistral transpressive kinematic regime. Deformation in the Shackleton Glacier area is inferred to be at least in part younger than 505 Ma, based on the deformation of the well-dated Taylor Formation. New 40 Ar/ 39 Ar cooling ages from metamorphosed igneous and sedimentary rocks range from c. 500 to 470 Ma and are interpreted to date orogenic cooling. Based on our structural results, and on consideration of the tectonic environment represented by the Liv Group, we propose that shortening across a subduction-related volcanic arc system caused deformation of the Liv Group and associated plutonic rocks. Oblique convergence and thus, transpression, may have ultimately been related to left-oblique plate subduction.