ABSTRACT: Reconstructing SE Asia and the SW Pacific

Hall, Robert , London University SE Asia Research Group, Egham, Surrey, United Kingdom

In SE Asia and the SW Pacific many oceans opened and closed during the Cenozoic, and the configuration of the region changed significantly. Present plate motions have only slight relevance to understanding the long-term kinematic development. Any useful plate tectonic models must depend on interpretation of all geological information. An animated plate tectonic model for the Cenozoic development of the region shows the importance of subduction in driving tectonics, of extension within a convergent setting, and of rapid changes in plate boundaries and motions, particularly at about 45 Ma, 25 Ma and 5 Ma.

Indentation by India modified Eurasia but this was not the driving force of tectonics in SE Asia. About 25 Ma saw the most important Cenozoic plate boundary reorganisation. The New Guinea passive margin collided with the Philippines-Halmahera-New Guinea arc. The Bird's Head continental margin was close to collision with the Eurasian margin in Sulawesi. The Ontong Java plateau collided with the Melanesian arc. Since 25 Ma tectonic events east of Eurasia have been driven by motion of the Pacific plate. Further west, the northward movement of Australia has caused rotations of blocks and accretion of microcontinental fragments to SE Asia.

Most new Cenozoic subduction systems were initiated close to the boundary between thick and thin crust after collision events or plate reorganisations. Slab rollback since 25 Ma was accompanied by significant arc volcanism and in most cases by marginal basin formation. In contrast, periods of subduction hinge advance were marked by reduction of volcanic activity.

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