THE STRUCTURAL EVOLUTION OF THE RAUER GROUP, EAST ANTARCTICA - MAFIC DYKES AS PASSIVE MARKERS IN A COMPOSITE PROTEROZOIC TERRAIN

Archaean gneisses in the Rauer Group of islands, East Antarctica, reco rd a prolonged history of high-grade deformational episodes, many of w hich predate that identified in mid-Proterozoic gneisses. Eleven gener ations of mafic dykes, belonging to discrete chemical suites, have bee n used as relative time markers to constrain this deformational histor y. Based on the timing of intrusion with respect to structures, dykes in the Rauer Group have been correlated with largely undeformed and da ted dyke suites in the adjacent Vestfold Hills. This has allowed absol ute ages to be inferred for the early to mid-Proterozoic mafic dyke su ites in the Rauer Group, and a correlation of the interspersed structu ral events. Most structures in the Rauer Group, however, developed in response to high-grade progressive deformation at approximately 1000 M a. During this deformational episode, strains were repeatedly partitio ned into sub-vertical, noncoaxial, high-strain zones recording NW-dire cted sinistral transpression, that separated zones of lower strain dom inated by coaxial folding with axes parallel to the shear direction. T hree additional mafic dyke suites intruded during this deformation whi ch was followed by three stages of brittle-ductile deformation and a f inal suite of lamprophyre dykes. Due to the numerous intrusive time ma rkers, the Rauer Group serves as an excellent illustration of how comp licated gneiss terrains may be.