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 c an be identified. Metamorphic rocks derived from India occur structura lly below the suture, in the core of a regional antiform. Isotopic and fission track dating are consistent with the geological interpretatio n. 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 t hermal softening of a thickened continental lithosphere. However, in t he Eastern Himalayas, we argue that exhumation is caused by c. 10 mm y r(-1) erosion coeval with crustal scale folding. The general history o f this syntaxis resembles the evolution of the western Himalayas synta xis in Pakistan. (C) 1998 Elsevier Science Ltd. All rights reserved.