Geoclub Seminar Series

The Himalayan Mountain Belt (HMB) is the youngest orogenic belt in the world and is the topographic expression of ongoing continent-collision between India and Asia. It hosts the most voluminous leucogranite belt in the world. Leucogranites (a light-colored granitic rock) in the HMB primarily occur in the Higher Himalayan Crystallines (HHC), which represents the metamorphic core of the HMB. Field, experimental, modelling and geochemical (including isotopic) studies have arrived at the consensus that the leucogranites were produced by partial melting of the metapelites of the HHC (fine-grained sediments of Indian continental margin) during the post-collisional high-grade metamorphism. These leucogranites serve as a chemical probe into an active continental collision providing a natural laboratory for evaluating crustal melting process and tectonic models.

Major points of contention in the HMB are: Given their derivation from compositionally similar source rocks, what caused the wide chemical diversity in the Himalayan leucogranites? What caused the extensive melting of the HHC? Did partial melting weakenthe crust and led to its exhumation? Or did "exhumation prompted decompression" caused partial melting? A more relevant question is how and when, along the burial and exhumationtrajectory, melt loss occur? Melt loss from a metapelite can increase the residuum strength by up to four (4) times, which would significantly affect its rheological property. Therefore, constraining the relative timing of melt loss may significantly influence the prevailing end-member tectonic models, critical taper versus channel flow, used to explain Himalayan exhumation.

I will present findings of phase equilibria modelling, rock textures and mineral chemical datain an attempt to address some of these questions.