1420 Ma diabasic intrusives from the Mesoproterozoic Singhora Group, Chhattisgarh Supergroup, India: Implications towards non-plume intrusive activity

Abstract

Besides offering significant clues towards tracking the geochemical evolution of the mantle and architectural reconstruction of different ‘supercontinent’, geochronological and geochemical appraisal of igneous inputs are also important to bracket the depositional time frame of any lithopackage, particularly, the unfossiliferous sedimentary successions. The present study deals with diabasic intrusive within Mesoproterozoic Saraipalli Formation, which is an argillaceous constituent present at the basal part of nearly 400 m thick four-tiered unmetamorphosed but deformed sedimentary succession of Singhora Group, Chhattisgarh Supergroup, central India. The SE–NW trending intrusive comprises mainly of plagioclase and augite together with minor orthopyroxene, biotite and opaque minerals. Though some plagioclase laths are partially sericitized, the ophitic-to-subophitic texture of the rock is well preserved. Major and trace element geochemical data indicate that this intrusive is basalt-to-basaltic andesite in character and of subalkaline basalt affinity. Multi-element plot shows overall LILE-enrichment and enrichment of Pb and slight depletion of Nb and P, coupled with moderate La/Nb and Th/Nb ratios. Zr, Y and Nb ternary diagrams plot in the fields of within plate basalt. Selected HFSE ratios indicate a non-plume source with crustal assimilation/sediment mixing. Sm–Nd and Rb–Sr isotope data show that the intrusive has Srinitial and Ndinitial of 0.709377–0.706672 and 0.510919–0.510815, respectively. Positive ε t Nd [t = 1420 Ma] values (+0.3 to + 2.3) indicate depleted isotopic nature of their protolith. The calculated T DM age is 1.7–1.9 Ga. The mineral-whole rock isochron data (Sm–Nd systematics) of the intrusive implies an emplacement age of ca. 1420 Ma. Considering synchronous terrain boundary shear zone development in Bastar craton on the southeastern part of the Singhora basin, mafic magmatism in Eastern Ghats and large-scale basic intrusion in Sausar mobile belt, a major tectono-thermal event around 1400 Ma is surmised that affected eastern Indian craton. Moreover, geochronology of a bedded porcellanite unit (ca. 1500 Ma) at the base and a discordant basic intrusive (ca. 1420 Ma) allowed a unique opportunity to qualitatively offer an upper bound of time bracket for the deposition of Saraipalli Formation, i.e., ∼80 Ma.