ABSTRACT: Tomographic constraints on the tectonic evolution of SE Asia

Spakman, Wim¹, Claude Rangin², and Harmen Bijwaard¹
(1) Utrecht University, Utrecht, Netherlands 
(2) Ecole Normale Superieure, 75005 Paris, France

We discuss a new 3-D image of P-wave seismic velocity heterogeneity of the lithosphere and mantle of Southeast Asia (SEA). Subducted oceanic slab is found below most of the Sunda arc but with varying depth penetration. A 500 km long slab under Burma is separated from the Andaman-Sumatra slab (~700 km deep) by a 300-400 km wide gap spatially associated with the Andaman Basin. The central Sunda slab penetrates the lower mantle to a depth of 1500 km, but subduction below the Banda arc is confined to the upper mantle (700 km). No clear slab is imaged below west New Guinea whereas a long and north dipping slab is found under east New Guinea. The eastern margin of Sundaland is characterized by a complex system of subduction zones: Sangihe subduction to the NW (down to 1500 km) is directly opposed by ESE Molucca sea subduction (down to 900 km). To the north of this system the Philippine Sea plate is subducting westward below the southern Philippines. This system is truncated by eastward subduction of the South China Sea below the northern Philippines (Luzon) and the Manila trench. Below the South China Sea at depths between 500 and 700 km a flat-lying anomalous structure is possibly related to the destroyed proto-South China Sea basin.

This detailed image of mantle structure places important constraints on the temporal and spatial tectonic evolution of the region. In particular imaged slab lengths impose new constraints on plate tectonic reconstructions.

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