Pan-African magmatism and sedimentation in the NW Himalaya

Correlation of early Palaeozoic, Pan-African (500 +/- 50 Ma) granites that intruded the Chail, Salkhala, Haimanta Formations in the Lesser Himalaya, Z anskar crystallines, and Lower Taglang La of Tso-Morari crystallines in the northwestern Himalaya, is based on the field relationship, tectonic settin g, mineralogical and geochemical characteristics, and isotope dating of the granites. These granite plutons exhibit identical petrographical and geoch emical character. The mineralogical composition of the granites is quite si milar, consisting of quartz, K-feldspar, plagioclase feldspar, biotite, mus covite, garnet, tourmaline, +/- cordierite, andalusite and sillimanite fibr olite. The granite which are massive and inequigranular in the core of the plutons, show strongly foliated character indicating development of ductile shear zone at the margins. These are peraluminous S-type granites having h igh A/CNK value (> 1). Presence of normative corundum, rounded shape of zir con,and high initial Sr ratio suggest crustal source of the granites. Mantl e normalized spider-diagram exhibits similar characters for all these grani toids. The intrusion of the Pan-African granites mark an abrupt end of the sedimentation that continued virtually uninterrupted from Palaeoproterozoic . The sudden break in sedimentation towards the terminal phases of the Lowe r Cambrian has been observed in almost all parts in Lesser as well as the T ethys Himalaya. Occurrences of large number of plutons along different tect onic belts of northwestern Himalaya are indicative of widespread tectono-th ermal event during early Palaeozoic (500 +/- 50 Ma). The bracketing of the two features like, the break in sedimentation during post-Late Cambrian and the intrusion of granites around 500 +/- 50 Ma, is considered to be the re sult of a strong diastrophic orogenic event correlatable to the late phases of the Pan-African Orogeny in Africa.