The Namche Barwa syntaxis: evidence for exhumation related to compressional crustal folding

Geological observation in the eastern end of the Himalayas shows that the Asia/India suture is folded and continues southward into India and Burma where the continuation of the Transhimalayan plutonic complex can be identified. Metamorphic rocks derived from India occur structurally below the suture, in the core of a regional antiform. Isotopic and fission track dating are consistent with the geological interpretation. In addition, they establish cooling exhumation of rocks from c. 30 km depth within the last 4 Ma. Rapid exhumation of deep crustal levels in mountain systems is generally related to extension subsequent to thermal softening of a thickened continental lithosphere. However, in the Eastern Himalayas, we argue that exhumation is caused by c. 10 mm yr(-1) erosion coeval with crustal scale folding. The general history of this syntaxis resembles the evolution of the western Himalayas syntaxis in Pakistan. (C) 1998 Elsevier Science Ltd. All rights reserved.