Tectonothermal evolution of the northernmost crustal segment of the Eastern Ghats Belt, India, and its linkage to Columbia and Rodinia assembly

The Eastern Ghats Belt (EGB), along the eastern coast of the Indian peninsula, forms a key crustal element in reconstructing the Palaeoproterozoic and Neoproterozoic supercontinents, Columbia (~1.9-1.6 Ga) and Rodinia (~1.1-0.9 Ga), respectively. The connection of the south-eastern segment of the EGB with east Antarctica, Australia, and Laurentia in an accretionary orogeny during the assembly of the Columbia has been established. Additionally, the central and western segments of the EGB are believed to have accreted to the Rayner Complex of Western Australia and East Antarctica during the assembly of the Rodinia supercontinent.

            In this contribution, we constrain the Proterozoic tectonothermal events recorded from the khondalites and granitoids occurring within the northernmost crustal segment of the EGB, as the major lithodemic units. In-situ monazite analysis from poly-metamorphosed garnet-sillimanite-biotite-quartz-feldspar bearing khondalites helps to establish two major metamorphic events: M_1KH and M_2KH. The earliest anatectic event (M_1KH) was recorded at 1.1 Ga leading to the formation of peritectic garnet, potash felspar, and melt. A collisional tectonic setting is implied by a clockwise P-T path constrained for the mid-crustal partial melting event (M_1KH; ~8-9 kbar, >760°C). The second metamorphic event (M_2KH) occurred in a melt-absent solid-state condition (~7.8 Kbar, 675°C). The M_2KH event occurred along an anticlockwise P-T trajectory with isobaric cooling. The monazite age ranges from 922±17 Ma and 909±8 Ma correlating with the isobaric cooling of the khondalites.

The granitoid bodies associated with the khondalites preserve evidence of multiple phases of deformation. Some of these granitoids are migmatites.  Zircons from one of the samples of the undeformed granitoids yield a crystallization age of ca. 1700 Ma. The monazite ages yielded from the granitoids show crystallization ages between ~1041-997 Ma. Monazites from granitoids produce a second peak at ~934-884 Ma, indicating the litho units experienced a partial melting event which is correlated with Rodinia supercontinent formation when the belt was a part of the Rayner Complex. The creation of the extensional Mahanadi Shear Zone is linked to the third monazite population within the granitoids, which yields ages ranging from approximately 750 to 740 Ma.

The present study implies that signatures of both Columbia and Rodinia ages are stronger in the northernmost segment of the EGB. The Imprint of a 1700 Ma event significantly impacts our comprehension of the crustal domains of the EGB that formed during the accretionary orogeny as part of the Columbia assembly. A linkage of significant accretionary belts around preexisting cratons involving Laurentia, Antarctica, South Africa, and Australia can be established with the 1700 Ma events in the northern EGB. The entire EGB from the north to south thus can be added to a hypothetical correlation of orogenic belts in several continents that underwent orogenesis between 1800 and 1700 Ma, reflecting Columbia's expansion. The findings in this study further imply that all the crustal domains of the EGB were unequivocally part of the accretionary orogenies leading to the assembly of the Rodinia.