Phanerozoic history of the Mahanadi region, India

Abstract

The Mahanadi Basin is a NW-SE stretching Gondwana basin perpendicular to the east coast of India. The metamorphic basement to the basin mainly comprises rocks of the Eastern Ghats Mobile Belt (EGMB) which experienced a complex thermotectonic evolution involving several episodes of deformation and magmatism. It can be inferred from 40Ar/39Ar ages on hornblende (845 Ma) and biotite (622 and 593 Ma) from basement rocks that the last high-grade metamorphism in the western part of the EGMB (i.e., the Western Khondalite Zone) occurred during the late Grenvillian, with any Pan-African overprint only reaching anchimetamorphic conditions. Only pseudotachylite intrusions and their related thermal imprint with ages around 515 Ma display a direct Pan-African signature. Fission track analyses on nine zircon (419-313 Ma) and 49 apatite (443-119 Ma) samples indicate a rift-related formation of the Mahanadi Basin as an asymmetrical half graben in two stages during the Permo-Carboniferous and the Middle Triassic. Moreover, the Gondwana breakup in eastern India is signified by dyke intrusions and the thermal overprint of thrusts and faults in the Mahanadi region and the onset of ocean floor production in the Mahanadi offshore basin at around 120 Ma.