Tectonic significance of Proterozoic ductile shortening and translation along the Antarctic margin of Gondwana

The central Transantarctic Mountains of Antarctica are divided into distinct lithotectonic packages of variable age, deformation style and metamorphic character. In the Miller Range (83°S, 155°E), the boundary between two such lithotectonic units is a low-angle, thrust-type ductile shear zone that carried high-grade gneisses of the East Antarctic craton to the southeast over a lower-grade metasedimentary sequence. Broad constraints limit the age of ductile deformation as late Early Proterozoic to Late Cambrian. In addition to a reverse component of movement, this zone also records along-strike motions in a direction subparallel to the present orientation of dominant Beardmore- and Ross-age orogenic trends. We postulate that major pre-Ordovician crustal shortening which occurred along this part of the Gondwana continental margin began in the Middle to Late Proterozoic as an early phase of long-lived convergence. Furthermore, orogen-parallel displacements indicate that oblique plate interactions may have played an important role in the early evolution of this active margin.