Variation in dip-angle of the Indian plate subducting beneath the Burma plate and its tectonic implications

摘要

The paper presents and analysis of the dip-angle of the Benioff zone trajectory, infers the state of stress of the descending Indian plate and the overriding Burma plate, and proposes three-stage episodic development of the descending Indian lithosphere and the Burma plate along the strike of the Indoburman are. The first stage aceounts for the late Oligocene-early Miocene east-west stretching of back-are region, which divided the central lowland of Burma into western and eastern troughs along the volcanic line. The dip-angle of Benioff zone trajectory in sector II (ca. 24.0° to 25.5°N), the late Oligocene-early Miocene westward transcurrent displacement of blocks, and the east-west splitting of late Cretaceous-early Eocene ophiolites are evidences of this stretching. The effect of stretching probably lasted through till when post-middle Miocene causing north-northeastward motion of the hanging Indian lithosphere together with the Burma plate through the asthenosphere. This may have been the cause of the westward offset between the main Irrawaddy River and the Chindwin River in the second stage. North-south varying degree of decoupling between the descending Indian plate and overriding plate may account for the interplay betwwen the Indoburman are and the northward moving Indian plate. The stress and north-south shallow level seismicity observed in the present study may be evidences for a slow subduction of the Indian plate in the recent or third stage of development.