Geochemical evidence for the Paleoproterozoic arc – Back arc basin association and its importance in understanding the evolution of the Central Indian Tectonic Zone

Abstract

The Central Indian Tectonic Zone (CITZ) is considered to be one sector in a series of Paleoproterozoic orogens that stitched together the supercontinent Columbia. The Paleoproterozoic Mahakoshal belt forms the foundation of the CITZ. Metabasalts and metaclastic rocks of the Mahakoshal belt have been studied for major elements and trace elements, including the rare earth elements (REE).Metabasalts of the lower Saleemanabad Formation are grouped into two types. However, both types of metabasalt depict a back arc basalt character by showing enrichments in large ion lithophile elements (LILEs like K, Rb, Cs and Ba) and light rare earth elements (LREEs) but show depletions in high field strength elements (HFSEs like Nb, Ta, Y, and Ti) and HREE (heavy rare earth elements) in comparison to the N-MORB. This is further supported by some key elemental ratios like Ba/Nb, Nb/Ta, La/Nb, Eu/Eu*, Nb/Nb*, and REE patterns. The geochemistry of the metaclastic rocks of the lower Saleemanabad, middle Parsoi, and upper Dudhmaniya Formations of the Mahakoshal belt show an arc signature rather than the cratonic signature in the Bundlekhand TTG and N-MORB normalised diagrams. The arc signature (calc-alkaline series) of metaclastic rocks is further supported by various tectonic discrimination diagrams.The overall study indicates that the Mahakoshal belt was formed as a back arc rift basin very close to continental arcs on the hinterland of the Bundelkhand craton at the initial stage of subduction as a result of trench rollback followed by thermal relaxation and basin inversion. The sediment supply started from the continental arcs lying south of the Mahakoshal basin. Furthermore, the present study strengthens the mechanism of subduction-related outgrowth of Columbia along its continental margins and implies that the CITZ is a major Precambrian crustal boundary that began as a Mahakoshal back arc rift by northward subduction.