Polyphase Metamorphism in UHP Eclogite from Tso Morari, Northwest India.
Monday, 15 December 2014: 1:55 PM
Garnet in high- to ultrahigh-pressure (HP/UHP) mafic eclogite at Tso Morari, Ladakh Himalaya, India, records multiple growth stages. Grain cores in eclogite from the centre of the Tso Morari dome are grossular-rich and pyrope poor in comparison to grain mantles and rims. The two garnet domains are separated by a layer of spessartine-rich garnet, which reflects a period of partial grain resorption. Grain cores have inclusion assemblages involving paragonite, ilmenite, rutile, actinolite and quartz, whereas grain mantle and rim inclusions involve omphacite, talc, rutile and quartz. The two garnet domains also have distinct REE compositions: REE content in grain cores defines a common trend of element enrichment increasing with atomic mass whereas grain mantles and rims are enriched in MREE and comparatively depletion in HREE. Eclogite from towards the dome margin is metasomatised in comparison with samples taken from the dome core, and is extensively recrystallized to a third assemblage rich in barroisite, paragonite and phengite. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analysis of in situ zircon grains from the matrix and garnet rims yield maximum ages of c. 53 Ma. Zircon grains from garnet mantles and cores yield older, mixed ages having a possible Panjal Traps origin. In situ age constraints of UHP Tso Morari eclogites provide a minimum earliest Eocene age for the high-P metamorphic event.