Insights into the P–T evolution path of Tso Morari eclogites of the north-western Himalayas: Constraints on the geodynamic evolution of the region

Abstract

The present study is on the Ultra High Pressure Metamorphic rocks of the Tso Morari Crystalline Complex of the northwestern Himalayas. Five different mineral associations representative of five stages of P–T (pressure–temperature) evolution of these rocks have been established based on metamorphic textures and mineral chemistry. The pre-UHP metamorphic association 1 of Na-Ca-amphibole + epidote ± paragonite ± rutile ± magnetite with T–P of ~ 500°C and 10 kbar. This is followed by UHP metamorphic regime marked by association 2 and association 3. Association 2 (Fe>Mg>Ca-garnet + omphacite + coesite + phengite + rutile ± ilmenite) marks the peak metamorphic conditions of atleast 33 kbar and ~ 750°C. Association 3 (Fe>Mg>Ca-garnet + Na-Ca amphibole + phengite ± paragonite ± calcite ± ilmenite ± titanite) yields a P–T condition of ~28 kbar and 700°C. The post-UHP metamorphic regime is defined by associations 4 and 5. Association 4 (Fe>Ca>Mg-garnet + Ca-amphibole + plagioclase (An05) + biotite + epidote ± phengite yields a P–T estimate of ~14 kbar and 800°C) and association 5 (Chlorite + plagioclase (An05) + quartz + phengite + Ca-amphibole ± epidote ± biotite ± rutile ± titanite ± ilmenite) yields a P–T value of ~7 kbar and 350°C.