PRESSURE-TEMPERATURE-TIME CONSTRAINTS FOR UHP TSO MORARI ECLOGITE, NW INDIA

Petrochronology on Tso Morari eclogites supports a single, protracted UHP event across the orogen from ca. 47 Ma to 43 Ma, consistent with the initiation of the Indian subduction at ca. 51Ma. Pressure-temperature data adds constraints, and the resultant P-T-t path of the eclogites can provide significant insight into the collision event and subsequent exhumation. The eclogite occur as rare boudins in felsic, Indian supracrustal rocks. The samples contain garnet, omphacite, phengite, rutile, quartz, amphiboles, zoisite, sodic augite-plagioclase symplectite, zircon, pyrite, and titanite. The rock is largely granoblastic, and approximately 25% of the garnet porphyorblasts display atoll texture. The pale-red, inclusion-rich cores are prograde, and likely underwent selective replacement with matrix minerals from metamorphic reactions at peak conditions. Colorless, inclusion-poor rims record peak conditions. While it is likely that the unit reached coesite stability field, no evidence of coesite has been observed in these samples. P-T estimations were calculated using published thermobarometers and THERMOCALC. To minimize stoichiometric error from Fe²⁺/Fe³⁺ estimations in omphacite, net-transfer equilibria were used in place of exchange equilibria by use of the garnet-omphacite-phegite thermometer instead of the traditional garnet-pyroxene thermometer. Analyses suggest a clockwise P-T path. A prograde stage is preserved in garnet cores and yields conditions of 23.2 ± 2.6 kbar and 411 ± 67°C; U/Pb zircon data suggest the eclogite facies initiated at ca. 51 Ma. Garnet rims yield peak metamorphic conditions of 27 ± 4 kbar and 743 ± 149°C which occurred from ca. 47 to 43 Ma. Temperature estimations from Ti-in-peak phengite is consistent with the P-T-t path, as is preliminary petrochronology of rutile and titanite. The P-T path is also in broad agreement with published paths from both Kaghan Valley and Tso Morari, further suggesting the synchronous suturing of India and the Kohistan Ladakh Arc in the NW Himalaya.