Tectonic Environment of Basalts Emplacement on the basis of Petrography & Major Element Geochemistry, Sindh Pakistan.

Basaltic flow exposures are reported from Ranikot, Bara Nai and Rehman Dhoro of Sindh province, Pakistan, interbedded with the sedimentary rocks of cretaceous–Paleocene age from Laki Range. The flows are confined to Pab sandstone of late cretaceous age, Khadro Formation of early Paleocene age and the Bara formation of middle Paleocene age. The rocks from Ranikot (Bara Formation) and Rehman Dhoro (Khadro Formation & Pab Sandstone) are classified as amygdaloidal Thoeliitic Basalt. Texturally fine to very fine grained, intergranular and ophitic to subophitic, occasionally glomeroporphyritic and composed of plagioclase (LabrodoriteByotonite: where possibly measured) and pyroxene (Pigeonite). Vesicles are occupied mostly by spherulitic calcite occasionally limonite and zeolite. The basalts from all three formations are similar; however samples from Pab Sandstone are relatively coarser. The major element geochemical studies of all three localities reflect that basalts are thoeliitic in composition and belong to continental flood basalt. It is depicted by various binary and ternary plots that all the samples fall in the thoeliitic field. For comparison binary TAS and ternary AFM diagrams of Deccan Basalt, western ghats (after Sheth, H last updated 2006) are given showing that both are falling in the similar fields i.e; thoeliitic however samples from our study area are richer in iron (Fe). The CIPW norms calculated on the basis of chemical composition yield normative hypersthene and quartz indicative of thoeliitic nature.