Tectono-metamorphic evolution of the Karakoram Terrane: Constrained from P-T-t- uid history of garnet-bearing amphibolites from trans Himalaya, Ladakh, India

This study presents new data sets on the petrological, uid inclusion and U-Pb zircon geochronological aspects of the garnet-bearing amphibolites from the eastern Karakorum (Pangong-Tso), Ladakh. to delineate the P-T-t- uid evolution and its tectonic implications. The calculated phase equilibria in the model system NCKFMASHTO reveal that the peak metamorphism occurred at 8.5-9.5 kbar, 630-655 °C, and retrograde metamorphism crossed a stage at 5.5-5.7 kbar, 620-630 °C. Monophase primary and secondary carbonic and carbonic-aqueous uid inclusions occur in garnet and quartz. Trapping of the primary inclusion occurred at pressures lower than the estimated peak P-T condi- tions (5.8-6.1 kbar, 629-638 °C) indicative of partially re-equilibrated uid inclusions during exhumation. The primary inclusions were original as carbonic-aqueous uid derived from prograde decarbonation of the am- phibolite's protolith or adjacent carbonate-rich rocks and H2O leached out during deformation, leaving a pure CO2 uid. U-Pb dating of zircons yielded two age groups: (i) at 128 to 131 Ma interpreted as the age of detrital zircons of sedimentary derivation, and constrain the maximum depositional age of the sedimentary protolith at 131 Ma and (ii) at 114 ± 0.38 Ma is interpreted as the age of peak metamorphism remarkably similar to the meta- morphic age of the surrounding metapelites. This metamorphic stage corresponds to the well-known Cretaceous phase of crustal thickening and heating along the active continental margin of South Asia.