Petrology and geochemistry of a boninite dyke from the western Bastar craton of central India

Abstract

The Dongargarh Supergroup along with the basal Amgaon Gneissic Complex constitutes the northwestern part of the central Indian Bastar craton. In the present study, we report a new finding of a boninite dyke intruded in the Amgaon gneisses of this area. The dyke composed of mainly pyroxenes, amphiboles and subordinate amount of plagioclase. The higher contents of \(\hbox {SiO}_{2}\) (51–54 wt.%), MgO (12–14 wt.%), Ni (375–473 ppm), Cr (1416–1580 ppm) and very low \(\hbox {TiO}_{2}\) (0.2–0.4 wt.%) are consistent with the boninite nature of the dyke as well as the unevolved primary nature of the source magma. The extraordinarily high CaO content (15.97–17.7 wt.%) with higher \(\hbox {CaO/Al}_{2}\hbox {O}_{3}\) (3.13–3.96) ratios classifies it as high-Ca boninite. The trace element ratios including Zr/Ti, Ti/V, Ti/Sc and Ti/Yb further show its geochemical similarity with the Archaean boninite. The dyke also shows negative high-field strength element (Nb, Ta and Ti) anomalies which are the characteristics of the boninite rocks reported elsewhere and along with the enriched light rare earth element pattern, it shows more affinity particularly with the northern Bastar boninite dyke. The mineralogical and geochemical similarities of the boninite dykes from the Bastar craton indicate a widespread boninitic event during the Palaeoproterozoic having a similar origin. These boninite dykes indicate the preservation of subduction-related signatures in the lithospheric mantle beneath the Bastar craton at the time of its evolution or may be during the convergence of the Bastar and Bundelkhand cratons.