GEOCHEMISTRY, PETROGENESIS AND CRUSTAL CONTAMINATION OF HOTSPOT RELATED VOLCANISM ON THE NORTH WESTERN MARGIN OF INDIAN CONTINENT AND ITS IMPLICATIONS FOR PALEOSEDIMENTARY ENVIRONMENTS

Abstract

The Bibai volcanics of a proposed hotspot origin occur in the Suleman and Kirthar Ranges of Pakistan and are intermittently exposed near Waziristan, Zhob, Loralai, Muslim Bagh, Quetta, Khuzdar, Bela and Karachi areas in a zone more than 1200 km long and up to 2 km wide. The volcanics are mainly alkali basalts but occasionally picro-basalt (MgO 17.57 wt %), trachybasalt, basanite, tephrite, hawaiite and trachyandesite are also found. Major and trace element chemistry confirm their alkaline affinity and within plate (hotspot) signatures. Major elements show enrichment in K2O, TiO2 and Al2O3 and depletion in CaO and MgO as compared to N-MORB. Their LILE and LREE enriched patterns and marked positive Nb and Ba anomalies are consistent with an enriched mantle source. The lower Mg # (41-61), REE, Zr - Zr/Y, La-Cr and Cr-Yb- study show that the parent magma for the Bibai volcanics was