Fluid evolution of Indus basin, Ladakh North-West Himalaya, India: constraint from fluid inclusion and oxygen isotope thermometry

Abstract

Fluid inclusions and oxygen isotope thermometry were carried out on quartz–calcite veins of the Indus Basin in Indus Suture Zone (ISZ) of northwest Ladakh Himalaya to constrain fluid evolution history of the basin. Three types of veins are identified as fault fill, network, and sigmoidal in the study area. The fault fill veins microstructures of calcite and quartz suggest the deformation temperature of veins between 250 and 400 °C and oxygen isotope thermometry provide the range between 192 and 359 °C. The network type veins microstructures of calcite revel deformation temperature in the range of 170—250 °C, and oxygen isotope thermometry indicate vein temperature range between 144 and 276 °C. Stable isotopic values of sigmoidal, and network type veins suggest the magmatic source of fluid. The fault fill veins display magmatic to the marine fluid signature. Microstructures and isotope data set advocate the formation of veins from the wall rocks by leaching processes. Fluid Inclusion Microthermometric dataset indicates that veins were formed at a maximum depth of 20 km at 700 °C. The CO2 fluids were trapped below 6.2 kbar at 700 °C. CH4 fluid was trapped at a shallower depth, between 4.2 kbar, 650 °C and 2.3 kbar, 381 °C. The primary aqueous fluids were trapped below 3.0 kbar up to 2.3 kbar at 594 to 382 °C and secondary aqueous fluids were trapped between 2.9 and 1.5 kbar at 359 to 197 °C. The P–T path for the entrapment defines an initial isothermal decompression (ITD). ITD is also supported by decrepitated and stretched inclusions texture as well as ‘C’ shaped or hook-like fluid inclusions morphology, which collectively points towards fast basin uplift.