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Thrusting in the lower crust: evidence from the Oygarden Islands, Kemp Land, East Antarctica

N. M. KELLY^*,, G. L. CLARKE^*, C. J. CARSON^*, and R. W. WHITE

^* School of Geosciences, F05, University of Sydney, Sydney, NSW 2006, Australia
School of Earth Sciences, University of Melbourne, Parkville, VIC 3052, Australia

Author for correspondence: nkelly{at}mail.usyd.edu.au

Layered orthogneisses of the Oygarden Islands preserve evidence for four high-grade deformation events (D₁ to D₄). Archaean D₁ and D₂ structures are only patchily preserved due to extensive recrystallization during D₃ and D₄, which represent effects of the c. 1000 Ma Rayner Structural Episode. Ductile thrusting at middle to lower crustal levels occurred during D₃, which is separated into two mutually cross-cutting phases based on structural geometry; the two phases represent changes in finite strain that developed during progressive deformation. East-directed transport during D_3a developed subhorizontal thrusts that contain co-axial, east-trending F_3a folds and L_3a lineations. Buckling as a consequence of constriction in thrust duplexes developed upright F_3b folds coaxial to F_3a folds, and steeply south-dipping D_3b shear zones. Garnet–clinopyroxene- and garnet–orthopyroxene-bearing assemblages in mafic lithologies, and garnet–sillimanite-bearing assemblages in pelitic lithologies reflect D₃ conditions of P = 9 kbar and T = 800–850 °C. The well-exposed D₃ duplex structures indicate that shortening of the lower crust may be accommodated by extensive strain partitioning to develop contemporary kilometre-scale thrust stacking and ductile flow.

This article has been cited by other articles:

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