Talk Description
Pb SHRIMP ages have been determined from the sandstone of Par Formation of Gwalior Basin having conformable contact with the basement granite and sandstone unit of the Bhopal Basin. These basins respectively occur along the north-western and south-eastern margins of the Bundelkhand Craton in north-central India. Based on the geochemistry and discrimination diagrams, the basement rocks of the Gwalior basin are classified as A2-type granites. Rift-induced passive margin settings are determined for the deposition of the sandstones of Gwalior and Bhopal Basins. The magmatic zircon grains from the basement granite of the Gwalior Basin yield a 207Pb/206Pb average age of 2538±2 Ma (MSWD = 1.44). The detrital zircons from the sandstone of Par Formation yielded two distinct age groups at ~ 2564±24 Ma and ~ 2044±2 Ma. In contrast, the detrital zircons from the Bhopal basin yield three distinct populations with a weighted average mean ages of 2511±5 Ma, 1694±6 Ma, and 1355±9 Ma, respectively. These three zircon populations also yield concordia ages of 2541±5 Ma, 1675±8 Ma and 1384±7 Ma respectively. Presence of ~2564 Ma detrital zircons with magmatic features in the sandstone of Gwalior Basin construe the maximum deposition age (MDA) of the clastic rocks and initiation of Gwalior Basin due to rifting. Prevalence of extensional tectonics during the same period is also evidenced from emplacement of A2-type basement granite in the basin and additionally in the Bundelkhand Craton. The younger weighted mean age ~2044 Ma obtained from the rims of zircons from the sandstone sample of the Gwalior Basin constrain the second phase of zircon growth. This event is correlated with the intrusions of mafic dykes along the northern margin of the Bundelkhand Craton between 2100-2000 Ma. Similarly, the youngest age population of ~1384-1355 Ma from the sandstone of Bhopal Basin constrains the MDA for the unit. This event is correlated with extensional tectonics leading to emplacement of A-type granitoids along the Chotanagpur Gneissic Complex in eastern segment of Central Indian Tectonic Zone along the southern margin of Bundelkhand Craton. The 2500 Ma ages from the Gwalior granites are thus linked to global magmatic activity leading to the stabilization of extended Ur at ~2500 Ma. The 2048 Ma and 1355 Ma ages from the Gwalior and Bhopal Basins, respectively, are correlated with the breakup of extended Ur and Columbia respectively.