Cooling history of subduction related granite from the Indus Suture Zone, Ladakh, India: Evidence from fluid inclusions

The P-T history of the subduction related Ladakh granite in northwestern Himalaya has been recorded from silicate-melt inclusions and other high temperature solid inclusions in the rock forming quartz. The silicate-melt inclusions show initial melting from 650 degrees C-705 degrees C. These inclusions have compositions similar to calc-alkaline granitic magma which is supported by the trace and major element chemistry of the granite. The earliest fluids (75 equiv. wt.% NaCl) circulated at subsolidus conditions from 625 degrees down to 425 degrees C, whereas invasion of dilute solution (< 8 equiv. wt.% NaCl) in the granite took place from 300 degrees C down to 165 degrees C. On the basis of the above observations it is inferred that the cooling history of the Ladakh granite started at 705 degrees C and continued up to 650 degrees C in the range of 1.2-2.8 kbar. This, therefore suggest a shallow emplacement of granitic magma. The hydrothermal processes involved during the cooling reveals simultaneous drop in temperature and pressure along with the introduction of dilute solution (very low saline) through microfractures.