ABSTRACT

In the Lahaul-Spiti region of Himachal Pradesh two meta-granite bodies (Jispa granite and Ratilaman granite) emplaced in the low grade Haimanta Formation which is tectonically overlying the Central Crystallines. Field, petrographical and geochemical features of these meta-granites are compared with the orthogneisses of the Central Crystallines. Geochemical signatures of these meta-granites and orthogneisses suggest that they are products of peraluminous melt generated by partial melting of older crustal rock, with high A/CNK values and higher normative corundum. 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 total REE, moderate LREE/HREE ratios and more pronounced negative Eu anomalies are also in accord with fractional crystallization. The heat source for these lower Paleozoic granite magmas may be due to the lithospheric extension which resulted in mantle melting beneath the crust which led to anomalous heat flow, and triggered crustal melting. Felsic magmas thus produced have intruded into shallow crustal levels.