Geochemical signatures and petrogenesis of intraplate dolerite dykes in the Salem block, Southern Granulite Terrane, India: Evidence of arc and MORB affinities

Abstract

This study provides geochemical signatures of dolerite dykes to unravel their tectonic settings and petrogenesis. The dykes were emplaced in the Southern Granulite Terrane, south India, which was accreted to the Dharwar craton. The Salem block has numerous mafic dykes, which are widespread within the high-grade rocks, in particular Salem dolerite dykes, which have four predominant orientations (NNW–SSE, NE–SW, NW–SE, N–S) located in the Attur, Mettur and Yercaud regions. Two geochemical groups of dolerite dykes are identified by their geochemical characteristics, which are (low to medium potassium content) tholeiitic in nature plotted in a sub-alkaline field consisting of basalt and basaltic andesite. The quartz normative basaltic composition of dolerites with Fe enrichment is found in the Attur region, while the Mg-rich basaltic andesitic composition of dolerites is found in the other two regions and one dyke in the Attur region. The fractionation of pyroxene and plagioclase can be inferred using the high-field-strength elements (HFSEs). The positive enrichment of Cs, U, K, Pb and Nd, and negative Nb, P, Zr, Ti and Y anomalies in a primitive normalized diagram and enriched light rare earth elements (LREEs)/large-ion lithophile elements (LILEs) and flat heavy rare earth elements (HREEs) with little or no anomalies of Eu values in the chondrite-normalized pattern resemble arc-related basalts, which represent potential contamination of crust resulting from partial melting of magma. The two distinguishable mafic emplacements in the study reveal two possible magmatic origins that may form in different periods in a regional stress intraplate extension caused by post-collisional arc and mid-ocean ridge basalt (MORB)-related tectonic settings. The petrogenetic models indicate that the dykes were intruded from the shallow part of the magma from the non-plume spinel-lherzolite field.