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Quartzitic pelites forms a part of Higher Himalayan Crystalline of higher geotectonic zone in Garhwal Himalaya. Quartzitic pelites (locally known as Pandukeshwar Quartzite) in Garhwal Himalaya is sandwiched between high grade metamorphic rocks of Central Crystallines and Badrinath Formation. Fluid inclusion studies are carried out on the detrital, and recrystallized quartz grains of quartzitic pelites to know about the fluid phases present during recrystallization processes at the time of maximum depth of burial. The quartzitic pelite (Pandukeshwar Quartzite) essentially consists of recrystallised quartz with accessory minerals like mica and feldspar. Fluid microthermometry study reveals the presence of three types of fluids: (i) high-salinity brine, (ii) CO 2-H 2O and (iii) H 2O-NaCl. These fluids were trapped during the development of grain and recrystallization processes. The high saline brine inclusions and CO 2-H 2O fluid with the density of 0.90 to 0.97 gm/cm 3 are remnants of provenance area. CO 2 density in detrital quartz grains characterise the protolith of the sandstone as granite or metamorphic rock. The H 2O-NaCl fluids involved in the recrystallization processes at temperature-pressure of 430-350°C; 4.8 to 0.5 Kbars as constrained by fluid isochores of CO 2-H 2O and H 2O-NaCl inclusions and bulging and subgrain development during recrystallization processes. The re-equilibration of the primary fluid due to elevated internal and confining pressure is evident from features like ‘C’ shaped cavities, stretching of the inclusions, their migration and decrepitation clusters. The observed inclusion morphology revealed that the rocks were exhumed along an isothermal decompression path. [ABSTRACT FROM AUTHOR]

Abstract: The Greater Himalayan Sequence in the Garhwal Region of India is a 14–20km thick succession of various pelitic and psammitic metasediments which contain individual units that are traceable for at least 250km along the strike of the Himalayan range in northwestern India. Bulk rock geochemical analyses show a chemical index of alteration (CIA) values of 57–93 with an average of 67, average (La/Yb) N =18.6, average (La/Sm) N =3.7, Cr/Th range between 0.2 and 214.5, and Th/Sc range between 0.2 and 10.3. The various geochemical tectonic indicators reveal a signature akin to an active continental margin. A low degree of weathering and high concentrations of incompatible/compatible element ratios respectively point to a proximal and primarily a silicic source region. The occurrence of three-phase halite bearing primary fluid inclusions in the quartz grains of metasediments indicate their provenance from a magmatic terrain. Potential source regions of the Greater Himalayan Sequence are the East African Orogeny, the East Antarctic Orogeny, and/or the Bhimpedian Orogeny of Northern India. Fluid inclusions in the Greater Himalayan Sequence (three-phase halite bearing inclusions, moderately high temperature bi-aqueous inclusions, and carbonic-aqueous inclusions) estimate maximum salinity at ∼33wt.% NaCl. This occurrence of fluid inclusions is also consistent with a magmatic terrain. [Copyright &y& Elsevier]