Field and petrographic studies are carried out to characterize the interactions of mafic and felsic magmas from Pithora region of the northeastern part of the Bastar Craton. The MMEs, syn-plutonic mafic dykes, cuspate contacts, magmatic flow textures, mingling and hybridization suggest the coeval emplacement of end member magmas. Petrographic evidences such as disequilibrium assemblages, resorption textures, quartz ocelli, rapakivi and poikilitic textures suggest magma mingling and mixing phenomena. Such features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of mafic magmas into the felsic magmas before initiation of crystallization of the latter, results in hybrid magmas under the influence of thermal and chemical exchange. The mechanical exchange occurs between the coexisting magmas due to viscosity contrast, if the mafic magma enters slightly later into the magma chamber, then the felsic magma starts to crystallize. Blobs of mafic magma form as MMEs in the felsic magma and they scatter throughout the pluton due to convection. At a later stage, if mafic magma enters the system after partial crystallization of felsic phase, mechanical interaction between the magmas leads to the formation of fragmented dyke or syn-plutonic mafic dyke. All these features are well-documented in the study area. Field and petrographic evidences suggest that the textural variations from Pithora region of Bastar Craton are the outcome of magma mingling, mixing and hybridization processes.
Archean-Proterozoic boundary represents a significant transitional phase in the Earth's history. Bastar Craton is one of the major Archean cratons in the Indian subcontinent with voluminous granites, supracrustal rocks, and tectonic belts. Malanjkhand, Dongargarh, and Kanker are the three major granitic plutons emplaced during the Archean-Proterozoic transition in the Bastar Craton, and this study is confined to the granites of Kanker pluton. Based on geochemical systematics, the Kanker granites are classified into sanukitoids, biotite and two-mica granites, and hybrid granites. The compositional diversity of the Kanker granites is attributed to two end-member sources, i.e., the enriched mantle and an older felsic crust, and the interactions between them. The sanukitoids were derived from an enriched mantle source that was metasomatized by the subducted sediments. Heat supplied by the sanukitoid magmas induced the crustal melting to form the biotite and two-mica granites. The interaction between these two mutually end-member sources, i.e., the enriched mantle and an older felsic crust, resulted in the formation of hybrid granites. The evolution of the Kanker granites can be accounted for a transitional geodynamic environment, involving subduction, and collisional tectonics during the Archean-Proterozoic transition.
The interaction between the coeval mafic and felsic magmas result in mixing, mingling, and chemical exchanges between both the end‐member magmas. We document the features relevant to the magma chamber processes and quantify the extent of mixing by means of detailed field, petrographic, mineral, and whole‐rock geochemistry from one of the less known granitic plutons from the Pithora region that forms part of the Kanker granite, Bastar Craton. The study area is composed of granite, granodiorite (mixed zone), and quartz diorite microgranular enclaves (MEs). The occurrence of syn‐plutonic mafic dykes, cuspate contact, magmatic flow textures, and hybridization suggest the coeval emplacement of end‐member magmas. Petrographic evidence such as disequilibrium textures such as resorption, quartz ocelli, and spikes in plagioclase, acicular apatites, and mafic clots are formed by magma mixing. Plagioclase from MEs and the mixed region exhibit disequilibrium textures such as normal, reverse, and oscillatory zoning suggestive of magma mixing. Whole‐rock geochemical data indicates the metaluminous to peraluminous host granites and metaluminous ME. The broadly linear trend of geochemical variation diagrams for these granitoids and MEs showcase the hybridization of two end‐member magmas. The mineral chemistry of the biotites and hornblende show subduction affinity, being further constrained by whole‐rock trace elemental systematics. The granitoids of Pithora region were formed in a subduction setting where large‐scale mantle‐ and crustal‐derived magmas were generated and subsequently mixed at crustal emplacement level.
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