GEOCHEMISTRY AND PETROGENESIS OF LOWER PALEOZOIC META-GRANITES OF LAHAUL-SPITI REGION, HIMACHAL-PRADESH, INDIA

In the Lahaul-Spiti region of Himachal Pradesh two meta-granite bodies (Jispa granite and Ratilaman granite) emplaced in the low grade Haima nta Formation which is tectonically overlying the Central Crystallines . Field, petrographical and geochemical features of these meta-granite s are compared with the orthogneisses of the Central Crystallines. Geo chemical signatures of these meta-granites and orthogneisses suggest t hat they are products of peraluminous melt generated by partial meltin g of older crustal rock, with high A/CNK values and higher normative c orundum. Decrease in Fe2O3, MgO, CaO, TiO2, Sr and Zr and enhancement in K2O, SiO2 and Rb as well as Rb/Sr ratios from melanocratic (margin) to leucocratic (core) portion of these bodies indicate that they are consistent with fractional crystallization processes. Decrease of tota l REE, moderate LREE/HREE ratios and more pronounced negative Eu anoma lies are also in accord with fractional crystallization. The heat sour ce for these lower Paleozoic granite magmas may be due to the lithosph eric extension which resulted in mantle melting beneath the crust whic h led to anomalous heat flow, and triggered crustal melting. Felsic ma gmas thus produced have intruded into shallow crustal levels.