Cenozoic Geodynamic Evolution of the Burma-Andaman Platelet

Rangin, Claude
EGERIE, CNRS, Aix en Provence, France.

The Burma Andaman platelet is a complex shear zone extending from the northern tip of Sumatra to the Assam belt developed during the Cenozoic along the India-Sundaland plate boundary. Into the west, the India sub continent attached to the rigid and undeformed Bengal oceanic basin and plateau is brushing the western margin of Sundaland. Two GPS networks were measured both in central and northern Myanmar and have revealed the main Sagaing-Shan fault has a constant instantaneous strain rate (1,8 cm/yr) in both areas. This fault absorbs half of the estimated active motion between India and Sundaland (3,5 cm/yr). The Andaman sea spreading center and the connected Sagaing-Shan fault in the north, and the the Semangko fault in Sumatra, absorbs the same rate of motion (2 cm/yr) since the early Pliocene. Remained motion was localized along subsidiary right lateral faults present within the Indo-Burma wedge, but also southwards along the East Andaman fault. The central Myanmar basins filled by up to 10 km of dominantly clastic sediments deposited from the Eocene to the late Miocene, has en echelon right pull apart basin pattern inverted during the last 10 Ma. The Indo-Burma ranges and its southern extension along the Andaman Nicobar islands and northern Sumatra, reveal obliquely accreted volcanic ridges, (90°E,92°E...) associated with exotic continental terranes (Kampetlet schist, Triassic Chin flysch..) all drifted from Antarctica during the northern motion of India. The Yadana gas field is located on one of these scalped and partially accreted ridges topped by cenozoic neritic carbonates transfered to the accretionary wedge. Along the eastern flank of the Indo-Burma wedge, melanges including blue-schist, early cretaceous ophiolite outline the wedge of the Tethys Mesozoic subduction zone, extending north of great India This Kabaw suture zone is disconformably sealed by Maastrichtian clastics, the basal formation of overlying Central Myanmar basins. In northern Burma the Eastern Tibet plateau crustal flow affects the northern motion of the Platelet since 10 Ma, inducing large gravity sliding in the northern Bengal basin. This evolution of the Burma-Andaman platelet illustrates the complexity of an hyper oblique convergent zone, present along the 2200 km long India Sundaland plate boundary.

This work was conducted in cooperation with Myanmar universities and Myanmar Oil and Gas Enterprise, sponsored by Total

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012