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

• The Karakorum terrain is characterized by higher amphibolite facies of metamorphism. • The peak and retrograde conditions of metamorphism 8.5–9.5 kbar and 630–655 °C; 5.5–5.7 kbar and 620–630 °C. • A steep nearly isothermal decompression P-T path is constrained by fluid Inclusions textures. • The peak metamorphic stage occurred at 114 ± 0.38 Ma, and the age of the sedimentary protolith is 131 Ma. This study presents new data sets on the petrological, fluid 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-fluid 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 fluid inclusions occur in garnet and quartz. Trapping of the primary inclusion occurred at pressures lower than the estimated peak P-T conditions (5.8–6.1 kbar, 629–638 °C) indicative of partially re-equilibrated fluid inclusions during exhumation. The primary inclusions were original as carbonic-aqueous fluid derived from prograde decarbonation of the amphibolite's protolith or adjacent carbonate-rich rocks and H 2 O leached out during deformation, leaving a pure CO 2 fluid. 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 metamorphic 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. [ABSTRACT FROM AUTHOR]