Role of axial and transverse drainages in sedimentation of the Permo-Triassic rift basins at the eastern continental margin of India: Implications for East-Gondwana reconstruction

The Permo-Triassic Gondwana rift basins of Eastern India formed after the East Gondwana amalgamation, resulting from the collision of India, East Antarctica, and Australia. This study investigates the roles of longitudinal and transverse drainages in supplying Permo-Triassic sediments and delineates the sources that contributed towards sedimentation. Paleocurrent data, petrography of sandstones, heavy mineral chemistry, and monazite geochronology track the axial drainage to the Shillong-Meghalaya Complex, southwest Australia, and transverse drainage to the Chhotanagpur Gneissic Complex, East Antarctica, and Eastern Ghat Metamorphic Belt. Modal analysis of sandstones, along with the mineral chemistry of detrital rutile, tourmaline, and garnet, suggests that granitoids and metamorphic rocks are the primary sources of sediment. The detrital garnet of almandine variety exhibits maximum similarity with that of the Shillong-Meghalaya Complex, East Antarctica, and southwest Australia. The detrital tourmalines of the dravite variety show compositional similarity with the Chhotanagpur Gneissic Complex. The detrital monazites give four age populations: 500-400 Ma, 700-600 Ma, 900-800 Ma, and 1100-1000 Ma. The 900-800 Ma age population is dominant and occurs in all the formations. The 1100-1000 Ma and 500-400 Ma age populations are the second most abundant and show considerable variation in appearance. The age populations of detrital monazite from 500-400 Ma and 1100-900 Ma, as well as the similarity in garnet chemistry with the Shillong Meghalaya Granite Complex in East Antarctica and southwestern Australia, indicate that the sediment supply was dominated by longitudinal drainage during the early Permian Barakar Formation. The absence of 500-400 Ma age groups in the overlying middle Permian Barren Measures Formations suggests that supply from longitudinal drainage became subordinate. The late Permian Raniganj Formation, with the reappearance of Cambrian ages, indicates axial drainage became active again. The Triassic Panchet Formation, with age groups of 500-400 Ma, 700-600 Ma, and 1100-900 Ma, suggests that supply came from both proximal and distal sources actively. This study, therefore, establishes that the interplay of axial and transverse drainages brought sediments into the Permo-Triassic Gondwana Basins of Eastern India from a unified East Gondwana.