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

• Published in: Geological Magazine
• Main Authors: KELLY, N. M., CLARKE, G. L., CARSON, C. J., WHITE, R. W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2000
• Subjects: Geology; East Antarctica; Rayner; Kemp Land; Oygarden; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1017/s0016756800004027; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800004027

Layered orthogneisses of the Oygarden Islands preserve evidence for four high-grade deformation events (D 1 to D 4 ). Archaean D 1 and D 2 structures are only patchily preserved due to extensive recrystallization during D 3 and D 4 , which represent effects of the c . 1000 Ma Rayner Structural Episode. Ductile thrusting at middle to lower crustal levels occurred during D 3 , 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 D 3 conditions of P =9 kbar and T =800–850 °C. The well-exposed D 3 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.