ONE DIMENSIONAL BACKSTRIPPING RESULTS FROM IODP EXPEDITION 318, SITE U1356: TECTONIC IMPLICATIONS FOR THE WILKES LAND MARGIN OF ANTARCTICA

Wilkes Land is the conjugate margin of the Great Australian Bight, which underwent extension, thinning and rifting from ~160 Ma until breakup at ~83 Ma. Both Wilkes Land and the Great Australian Bight are considered passive margins, and were thought to be tectonically inactive since breakup at 83 Ma. We have backstripped the U1356 Core recovered from the continental rise off Wilkes Land, Antarctica by IODP Expedition 318. Backstripping input included lithological and sedimentary analysis, paleo-environmental indicators, combined paleomagnetic and biostratigraphic chronologies, and physical properties measurements. Tectonic subsidence shows a major event between 50 and 33.6 Ma, a time represented by a hiatus in the U1356 core. The magnitude of subsidence requires it to be tectonic in origin, and the timing matches with a reorganization of plate motions that represents the transition from slow spreading to fast spreading between Antarctica and Australia, which occurred at approximately 43 Ma. Coupled with a regional seismic framework, and using other Expedition 318 site analyses, the Wilkes Land margin is shown to be far more complex then the simple passive margin currently assumed. We explore several possible causes for the subsidence observed. One clue might be the tertiary episodic volcanism of Southeast Australia, which is suggested to be driven by lithospheric edge effect convection in the asthenosphere.

Additional co-authors: A. Klaus, A. Fehr, T. Williams, J. Bendle, P. Bijl, S. Bohaty, S. Carr, R. Dunbar, M. Iwai, F. Jimenez-Espejo, K. Katsuki, G. Kong, R. McKay, M. Nakai, M. Olney, S. Passchier, S. Pekar, S. Sugisaki, L. Tauxe, S. Tuo, C. van de Flierdt, K. Welsh, M. Yamane, J. Pross, C. Riesselman, U. Röhl, T. Sakai, P. Shrivastava, C. Stickley, the Expedition 318 Scientific Participants.