Major and Trace Element Geochemistry of the Mafic Magmatic Rocks from the Betul Mobile Belt, Central Indian Tectonic Zone

Abstract:

Peninsular shield of India is composed of several Archaean cratons bordered by Proterozoic mobile belts which amalgamated the Archaean cratons and helped in the growth of the Indian subcontinent. The ENE-WSW trending Central Indian Tectonic Zone (CITZ) is one such important mobile belt which sutures the Bundelkhand and the Aravalli craton in the north and Bastar, Singhbhum and Dharwar cratons in the south.

The CITZ is a collection of lithotectonic terranes ranging in age from Archaean to recent and comprises supracrustal belts, granulite belts, shear zones and felsic-mafic magmatic rocks. The Betul belt is characterized by a litho-package of plutonic magmatic rocks, volcano-sedimentary rocks, bimodal volcanics and associated base metal sulphide mineralization. The petrological, geochemical and geochronological evolution of the mafic magmatic rocks has significance in our understanding of Proterozoic crustal evolution in central India.

Here we report major and trace element concentrations of 14 mafic samples (basaslts, gabbors, pyroxenites and dolerites) in an attempt to classify, characterise and suggest a spatial and temporal evolution of the mafic magmatic rocks of the Betul mobile belt vis-à-vis CITZ. Traditionally these rocks have been classified as being calc-alkaline rocks, related to arc volcanism and rift tectonics.

We have divided these rocks into those have a positive Europium anomaly and those having a negative Europium anomaly to better understand the source and the contaminant for these rocks. We find characterisitic difference specifically in the trace element ratios and concentrations of the rocks with +Eu anomaly [La=10.69ppm; La_N/Yb_N=3.65] and those with –Eu anomaly [La=27.59; La_N/Yb_N=8.86]. Based on these data we propose that the Betul mafic rocks may have been derived from an enriched mantle source that experienced contamination from the lower continental crust or sub-continental lithosphere prior to eruption.