Exhumation of west Sundaland: A record of the path of India?

Abstract

The Indian Plate commenced its northward migration towards Eurasia in the Early Cretaceous. The lateral effect of this migration on the western edge of the Sunda Plate in Southeast Asia still remains equivocal. In order to assess this effect, we evaluate several key sectors characterized by deep crustal exhumation along a N-S transect from the southern Malay Peninsula to the East Himalayan Syntaxis. The evaluation is aided by a structural analysis of vertical movements and basin development. Five major metamorphic domes with similar geodynamic evolution, maximum P-T burial conditions and exhumation are studied. Exhumation of these domes migrated with time between Late Cretaceous in the Stong Complex (north Malaysia) in the south and Late Miocene in the Gaoligong Shear Zone (south China) in the north, as documented by published work and our new fission track data presented herein. Deformation is characterized by a N-S oriented extension that followed the more regional E-W oriented plate tectonic shortening, creating local core-complexes and syn-kinematic magmatism in the footwall of crustal-scale detachments, which displays a consistent temporal northward migration. The N-S extension was associated with the onset of hanging-wall deposition in the sedimentary basins of western Sundaland (e.g. Malay, Sumatra, and Thai Basins) during continuous exhumation of the footwall to upper brittle levels. Our multifaceted analysis of structural and thermochronological data shows a similar succession of tectonic, thermal and sedimentary events in west Sundaland that was driven by the gradual northward migration of India starting from Cretaceous times. We infer that the principal mechanism was driven by the subduction of an excess topography of Greater India rifted continental margin during its underplating, resulting in uplift, thermal anomalies, extensional exhumation and associated subsidence.