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ABSTRACT: Extrusion Collusion and Rotational Confusion in SE Asian Tectonic Models

Longley, Ian M. , Woodside Energy Ltd, Perth, Australia

Extrusion Tectonics has been proposed as the driving mechanism for the Tertiary evolution of SE Asia (Tapponier et al., 1982) even though seismic data throughout the region suggests that in the Paleogene the area experienced an extensional rift phase with no material element of transtensional or transpressional tectonism. Extrusion Tectonics also fails to explain the origin of the backarc basins of Sumatra and Java, the Malay Basin, the oceanic spreading history of the South China Sea and the collision of rifted blocks along the margin of NW Borneo. The alternative model presented (modified after Longley, 1997) relates the Paleogene evolution of the region principally to a regional (Indian, Southern and Pacific Ocean) middle Eocene plate re-organisation cause by the Indian-Eurasia plate collision. Extrusion tectonics is presented as a Neogene modifier to the basins formed by the Paleogene event.

Other models suggest that Borneo has rotated anticlockwise, even though it's connection with the remainder of the Sundaland platform makes such a rotation direction geometrically implausible, and similarly other models have Sumatra rotating anticlockwise even though the variable Neogene inversion in the back-basins of Sumatra strongly suggest a clockwise rotation. The presented model suggest all Tertiary rotations in SE Asia are clockwise due initially due to the opening of the South China Sea and later due to the effects of extrusion tectonics.

Longley, I.M., 1997. The Tectonostratigraphic Evolution of SE Asia. In; Fraser, A.J., Matthews, S.J. & Murphy, R.W. (eds): The Petroleum Geology of SE Asia. Geol. Soc. Spec. Publ., 126, 311-339.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia