Magma Types and Source Characterization of the Early Deccan Magmatism, Kutch Region, NW India:Insights from Geochemistry of Igneous Intrusions

Abstract

The tholeiitic basalt intrusives as sills and dykes from the region have been classified into high Ti and low Ti categories. The high-Ti basalts display characters comparable to the shield lavas of the Reunion Island with OIB type signature. The incompatible trace element patterns and ratios as well as the Sr-Nd composition of the high Ti-basalts support their generation from mixing of melts derived from both the convecting asthenospheric mantle (plume?) as the dominant source and the SCLM with little contribution from the continental crust. The petrographic and chemical data indicate dominant clinopyroxene and plagioclase fractionation and small olivine fractionation. In contrast, the low-Ti basalts exhibit trace element characters and Sr and Nd isotopic systematics similar to MORB with relatively more contribution from the SCLM, and less from Reunion like source that has been modified by variable contribution from the crustal contaminants. The variable amount of crustal interaction further divide the low Ti basalts into two subtypes viz. low-Ti-high Pb and low Ti-low Pb. The geochemical characters of both the high Ti and Low Ti basalts as well as the lava flows from do not correlate well with any of their southwestern counterparts identified in the main Deccan province and most probably represent lower levels. It is essential to treat these basalts therefore as separate stratigraphic unit as Kutch Group in the Deccan stratigraphy.