Deformation Microstructures and Geochemistry of the Mylonitic Augen Gneisses in the Chail Thrust Zone in Satluj Valley of Himachal Pradesh

Microstructural and geochemical analysis have been carried out on the mylonitic augen gneisses of the Chail thrust zone, in the Satluj valley of Himachal Pradesh. The microstructural features of K-feldspar, plagioclase, quartz and mica indicate that these gneisses have undergone an early deep level ductile deformation followed by a high level brittle deformation. The mylonites and blastomylonites represent ductile deformation products and the cataclasite represents brittle deformation product. The mylonitization is related to thrusting events during the Himalayan Orogeny.

Available geochronological data with high initial strontium ratio suggests that the protoliths of the mylonitic augen gneisses (Svtype granitoid) intruded the Chait formation during Precambrian times. The major element chemistry, with the absense of normative corundum values and low Al-index values indicate a mantle origin.