SHRIMP geochronology for the 1450 Ma Lakhna dyke swarm: Its implication for the presence of Eoarchaean crust in the Bastar Craton and 1450–517 Ma depositional age for Purana basin (Khariar), Eastern Indian Peninsula

Zircon U–Pb ages of the Mesoproterozoic dyke swarms (Lakhna dyke swarm) at the interface between the Eastern Ghats Mobile Belt and Bastar Craton of the Indian Peninsula are reported here to decipher the tectonic evolution of the region. The dyke swarm, which is dominantly N–S in orientation, has intruded the Bastar Craton at ca. 1450 Ma. The dykes vary in composition from dolerite to trachyte and rhyolite and have been emplaced in a continental anorogenic setting. The above age puts a lower time constraint on the sedimentary sequences of the Purana basin (Khariar basin) that have been deposited unconformably over the Bastar Craton. The shale member of the Khariar basin shows evidence of synsedimentary shearing suggesting that the sedimentation probably continued up to 517 Ma, the age of shearing and overthrusting of the granulite nappes of the Eastern Ghats Mobile Belt on the Craton. Further, the compression accompanying thrusting of the nappes, uplifted the Purana basins during inversion.