Comparative petrogenesis and tectonics of Paleoproterozoic Malanjkhand and Dongargarh granitoids, Central India

Abstract

The Malanjkhand granitoid (MG) and two units of Dongargarh granitoids (DGs) represent contemporaneous episodes of Paleoproterozoic felsic magmatism in the Bastar Craton, Central India. A comparative geochemical study is carried out between the mineralized Malanjkhand granitoid (MG) and barren Dongargarh granitoids (DGs) that occur adjacent to each other separated by the Dongargarh Group of rocks. Major element oxides geochemistry reveals that MG is granite–granodiorite whereas DG is strictly granite in composition and both plutons show calc-alkaline affinity. Geochemical discrimination indicates that MG is an I-type, whereas an A-type affinity can only be suspected in case of DG and both can be labeled as ‘peraluminous’.Trace element data from these Paleoproterozoic granitoids indicate that they evolved in a tectonic environment similar to continental rift setting. HFSE ratios suggest variable degree of fractionation of highly differentiated granitic magma was a very complex crystallization process results in the formation of these two granitoids by common mechanism, possibly fluid separation might be involved. Highly fractionated REE and depleted MREE patterns with Eu-anomaly absent in MG and negative in DG, inferred that the parental magma derived by low-degree partial melting of heterogeneous mafic source probably amphibolitic in nature, followed by progressive differentiation.Zircon saturation temperature and Zr content reveals that MG crystallized from wet melt whereas DG crystallized from relatively dry melt but both are classify as hot-granites. Thermobarometric calculations indicates that MG has emplaced at upper level whereas DG at relatively deeper or middle-upper level in the continental crust. The origin of Palaeoproterozoic granitoids in Central India has attributed to the magma mixing process between crustal derived felsic and mafic magma contributed by basaltic underplating in a continental rift environment.