Geochemistry and petrogenesis of acidic volcanics from Betul–Chhindwara Belt, Central Indian Tectonic Zone (CITZ), central India

Abstract

Betul–Chhindwara belt is part of Central Indian Tectonic Zone (CITZ) that includes Proterozoic basalt, rhyolite, quartzite, mafic–ultramafic rocks, volcano sediments and banded iron formation (BIF). Studied rhyolites and leuco-micro granites are deformed due to shearing and includes quartz, K-feldspar (microcline), muscovite, biotite and epidote. In some samples, feldspar has been sericitized due to interaction with hydrothermal fluids. The major element geochemistry of volcanic rocks clearly indicates acidic nature and falls in the rhyolite field. Rhyolites show difference in the enrichment of REEs and major element composition which help us divide them into two groups and also indicate heterogenous source. The rhyolites show very strong negative Eu anomaly, which indicates fractionation of feldspar. Positive anomalies of U–Th–Zr for the rhyolites indicate crustal involvement. The εNdt (t=1500) for the Group I rhyolites vary from –1.42 to –0.19 and for the Group II rhyolites vary from –5.81 to +0.14 and DM model ages for Group I rhyolites vary from 2284 to 2464 Ma and for Group II vary from 2174 to 2863 Ma. It is suggested that contemporary mafic magma of the Betul–Chhindwara belt while ascending from mantle sources interacted with the continental crust at different levels, supplying heat and fluids which reduced the melting points of the crustal source rocks, producing felsic melt of varying compositions. Tectonic discriminant diagrams and geochemical data indicate subduction zone tectonic environment for the genesis of the Betul–Chhindwara acidic volcanism. The acidic volcanics of Betul–Chindwara, Sakoli and the Bijli rhyolites from the adjoining areas display similarity in terms of the total alkali vs. silica diagram and many of the major and trace elements, including rare earth element characteristics. Compared to Betul Rhyolite, Sakoli Rhyolites are derived from less enriched source with less involvement of crust and/or the latter represents high degree of partial melting of similar source. They are considered contemporaneous to Betul Rhyolite based on geochronological data. Contrastingly, Bijli Rhyolite show highly fractionated patterns with high LREE enrichment indicating considerable crustal involvement which is very obvious for within plate magmatism, assigned for the Bijli rhyolites.