Tracing multiple sources of sediments using trace element and Nd isotope geochemistry: provenance of the Mesozoic succession in the Kutch Basin, western India

Abstract

An integrated approach involving Sr–Nd isotope, trace and rare earth element analyses tracks multiple sources of the Mesozoic sediments of the Kutch Basin at the western continental margin of India. High ( ⁸⁷Sr/ ⁸⁶Sr) _t (ratio at time of deposition), negative ε _Nd and high concentrations of large-ion lithophile elements (LILEs) indicate the upper continental source. Ratios of Nb/Ta and Zr/Hf suggest sedimentary and felsic igneous sources of sediments. The moderate to high concentration of La, Th and Sc, light rare earth elements (LREE-) enrichment, weak negative Eu anomalies and the relationship between ε _Nd(0) and Th/Sc indicate the dominantly felsic composition of source rocks. However, low contents of Th, low values of ( ⁸⁷Sr/ ⁸⁶Sr) _t and depleted mantle model age T _DM < 1600 Ma indicate input from a younger mafic source. Increasing concentrations of Zr, Hf and Nd isotopes and a gradual increase in mean T _DM from the older to the younger formations indicate erosional unroofing at the source terrain. The increasing ( ⁸⁷Sr/ ⁸⁶Sr) _t through time relates to increased weathering of the source rock. The overwhelmingly southwesterly palaeocurrent direction of current-generated sedimentary structures, and the mean T _DM ages trace suggest source areas of the Kutch Basin to Precambrian rocks in the north and NE of this basin. The T _DM ages highlight the dominance of late Palaeoproterozoic source rocks. Nd isotope composition indicates that Proterozoic rocks of Marwar Supergroup and Erinpura Granite, in particular, served as main sediment contributors for the Mesozoic sediments in Kutch. We therefore conclude that the Mesozoic sediments in the Kutch Basin are predominantly of late Palaeoproterozoic age with lesser inputs from rocks of early Mesoproterozoic and early Palaeoproterozoic age.