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U–Pb geochronology, Hf isotopes and trace-element chemistry of zircon grains from migmatite of the upper Sutlej valley (Leo Pargil), Northwest Himalaya, reveal a protracted geological evolution and constrain anatexis and tectonothermal processes in response to Himalayan orogenesis. U–Pb geochronology and ϵHf record separate clusters of ages on the concordia plots in the migmatite (1050–950 Ma, 850–790 Ma and 650–500 Ma). The 1050–950 Ma zircon population supports a provenance from magmatic units related to the assembly of Rodinia. A minor amount of Palaeoproterozoic grains were likely derived from the Indian craton. The potential source rock of the 930–800 Ma detrital zircons may be granitoid present in Greater Himalayan rocks themselves and the Aravalli Range, which has 870–800 Ma granitic rocks. The arc-type basement within the Himalayan–Tibet orogen recorded (900–600 Ma) igneous activity, which may depict a northeasterly extension of juvenile terranes in the Arabian–Nubian Shield. The granitoid of 800 Ma may be a potential source for 790 Ma detrital zircons owing to scatter in 206/238 dates. The 650–500 Ma zircon population suggests their derivation from the East African Orogen and Ross–Delamerian Orogen of Gondwana. The Cambrian–Ordovician magmatism during the Bhimphedian Orogeny and observed late Neoproterozoic to Ordovician detrital zircons have been derived to some extent from Greater Himalayan magmatic sources. We found no detrital zircon grains that cannot be explained as coming from local sources. One sample yielded a discordia lower intercept age of 15.6 ± 2.2 Ma, the age of melt crystallization. [ABSTRACT FROM AUTHOR]

This study presents new petrological and fluid inclusion datasets of migmatites from the Karakorum Shear Zone, Ladakh, India, to know the P–T–fluid evolution of mineral assemblages and the associated tectonic history. The presence of plagioclase, quartz, and biotite inclusions in the coarse-grained poikiloblastic pargasite (amphibole) is indicative of the hydration reaction b t + p l + qtz + H 2 O = prg + melt , which is consistent with diffusive H2O-fluxed melting. Phase equilibria calculations are consistent with migmatization at 0.85–1.02 GPa and 640–670 °C in water-saturated conditions (i.e., 0.7 wt% H2O). The monophase primary and secondary carbonic fluid inclusions present in quartz display eutectic temperatures between − 56.9 and − 56.6 °C, suggesting pure CO2 composition. The isochores of primary CO2 inclusions reveal that the post-peak migmatization event took place between 0.59–0.55 GPa and 550–670 °C, which occurred due to density reversal during the re-equilibration. The fluid inclusion microtextures preserved the signature of isothermal decompression, which is well corroborated with mineralogical P–T calculations. Primary inclusions were preserved initially as carbonic-aqueous fluids; however, the H2O phase diffused out subsequently and dissolved with the melt such that the inclusions became pure carbonic. Fluid infiltration along the Karakorum Shear Zone played a critical role in forming migmatites. The P–T path derived from thermodynamic modeling and fluid inclusion data are consistent with isothermal decompression during exhumation following crustal thickening of the Asian continent (or South Tibaten Crust) between 18 and 15 Ma. [ABSTRACT FROM AUTHOR]

Quartz-calcite veins in the Zildat ophiolitic mélange (ZOM) and Shergol ophiolitic mélange (SOM) of the Indus Suture Zone preserve a diversity of fluid activity in the late stages of ophiolitic mélange formation. This article presents fluid-inclusion and isotope geochemistry of these veins to understand their source and evolution in terms of pressure and temperature. The microstructures of quartz and calcite veins indicate deformation temperatures between 200° and 400°C. The δ13C and δ18O values of calcite veins from the ZOM and SOM are within the mixing hyperbolas of marine and primitive-mantle fields in the mixing model. The Sr and Pb isotopic values of calcite veins from the ZOM suggest a mid-ocean ridge basalt (MORB) fluid source of vein formation that was radiogenically enriched by metasomatism in a suprasubduction zone. For the SOM, fluids may have originated from the enriched-mantle (EM) and the depleted-MORB-mantle rocks. It is inferred that the carbonic fluids were derived from ultramafic lithologies and oceanic crust that formed the ophiolitic mélange rocks, which also host these veins. These source rocks have EM and MORB geochemical signatures that are also obtained in the quartz-calcite veins, as characterized by their C-O-Sr-Pb isotopic ratios. The magmatic saline fluid is inferred to have formed in the early stages of vein formation and to have been subsequently diluted, as exemplified by the presence of low-saline secondary aqueous inclusions. The microthermometry fluid pressure-temperature estimation of veins from the studied sections suggests that the maximum depth of emplacement of veining fluid was about 24.5 MPa (corresponding to ∼2.5 km) at 336°C. The vein-forming fluids (calcareous and siliceous) were introduced into the fractures that developed in the host as a result of deformation. [ABSTRACT FROM AUTHOR]