Structural constraints on the Proterozoic reworking of Archaean crust in the Rayner Complex, Macrobertson and Kemp Land coast, East Antarctica

Abstract

The high-grade metamorphic rocks exposed along the MacRobertson and east Kemp Land coasts consist of, in the west, Archaean gneisses reworked during a ductile mid-Proterozoic deformation, and in the east, foliated Proterozoic charnockite gneiss containing large remnants of gneiss of probable Archaean age. Evidence for three folding events is recognized in the reworked gneisses. An early recumbent terrain is deformed by two upright events possessing near-vertical axial surfaces. The charnockite gneiss preserves evidence of only the final event. These three events comprise the Rayner Structural Episode, which was a consequence of the ductile thrusting of Archaean gneiss westward toward a stable Archaean block, the Napier Complex. Kinematic indicators are consistent with formation of the Proterozoic recumbent terrain by dominantly shear deformation. Dissection of both the Rayner and Napier Complexes by retrograde shear zones and mylonite-pseudotachylite zones was a consequence of the northward thrusting of the two complexes during the Cambrian.