The Himalayan Collisional Orogeny: A Metamorphic Perspective

Abstract

This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core. The Himalayan orogeny was divided into three stages. Stage 60-40 Ma: The Himalayan crust thickened to similar to 40 km through Barrovian-type metamorphism (15-25 degrees C/km), and the Himalaya rose from <0 to similar to 1000 m. Stage 40-16 Ma: The crust gradually thickened to 60-70 km, resulting in abundant high-grade metamorphism and anatexis (peak-P, 15-25 degrees C/km; peak-T, >30 degrees C/km). The three sub-sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo-Himalayan thrust, High Himalayan thrust, and Main Central thrust, and the Himalaya rose to >= 5,000 m. Stage 16-0 Ma: the mountain roots underwent localized delamination, causing asthenospheric upwelling and overprinting of the lower crust by ultra-high-temperature metamorphism (30-50 degrees C/km), and the Himalaya reached the present elevation of similar to 6,000 m. Underplating and imbricate thrusting dominated the Himalaya' growth and topographic rise, conforming to the critical taper wedge model. Localized delamination of mountain roots facilitated further topographic rise. Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events, contact metamorphism and rare metal mineralization, metamorphic decarbonation and the carbon cycle in collisional belts.