Geochemistry of distinct mafic intrusive rocks from Darba-kukanar and kerlapal-sukma-mokhpal areas, Southern Bastar craton: further data on the early precambrian mafic magmatism of Central India

Abstract

Geochemistry of mafic igneous rocks of early Precambrian age of the southern Bastar craton in and around Darba-Kukanar and Kerlapal-Sukma-Mokhpal areas are presented. Most of these mafic rocks occur as NW-SE trending dykes intruded into the Archaean granite/granite-gneiss and over metamorphic rocks. Few intrusives also occur as sills or plutonic bodies. On the basis of field relationships between mafic rocks and other exposed rock types and also between the mafic rocks, available geochronological data, petrological and geochemical characteristics, the studied mafic rocks are classified into three main types: (i) Group 1 (BD1): Mesoarchaean mafic rocks, metamorphosed under mid-amphibolite facies conditions, showing concentration of high-field strength element (HFSE) higher than the Group 3 (boninite-norite) mafic rocks, and lower than the Group 2 (BD2: dolerite-diorite),(ii) Group 2 (BD2):Paleoproterozoic mafic rocks of dolerite-diorite composition, characterized by higher concentration of HFSE than the other two types, and (iii) Group 3 (BN: boninite-norite): Neoarchaean mafic rocks, metamorphosed under greenschist-amphibolite transitional conditions, characteristically showing high-Mg and Si, very low-Ti, and HFSE composition close to boninite. These observations are very similar to the previously studied mafic rocks from the other parts of the southern Bastar craton. It is suggested that the BD1 mafic rocks are derived from depleted sub-alkaline basaltic magma, whereas enriched sub-alkaline basaltic magma was responsible for the BD2 mafic rocks. High-Mg boninite-norite (BN) mafic rocks were probably derived from a primary boninitic magma originated from a refractory lherzolitic mantle source. These observations clearly suggest heterogeneous mantle source beneath the Bastar craton during the early Precambrian.