Ar-40/Ar-39 geochronolgy and Neoproterozoic tectonics along the northern margin of the Eastern Ghats Belt in north Orissa, India

The post-1100-950 Ma cooling history of the northern margin of the high-gra de Eastern Ghats Belt is determined from Ar-40/Ar-39 data collected from sc hist and gneiss samples. The data define two groups of dates with distinct cooling histories between ca. 700 and 420 Ma. The oldest group of ages defi ne a slow apparent cooling path, whereas a younger group of Ar-40/Ar-39 dat es from the west and north margin of the Eastern Ghats Belt and along the s outhern margin of the Rengali Province define a more rapid cooling path. Th e younger Ar-40/Ar-39 dates are interpreted to reflect a variable and local ly intense thermal event at ca. 550-500 Ma associated with reactivation of major shear zones. Final exhumation to current exposed levels occurred by c a. 300 Ma as constrained by unconformable Permo-Triassic coal-bearing sedim ents overlying the northern Eastern Ghats Belt and northwestern Rengali Pro vince. Dextral-reverse reactivation after ca. 950 Ma and possibly prior to ca. 700 Ma along the Kerajang and Barakot Fault Zones, was associated with regional shortening within the Eastern Ghats Belt and Rengali Province. Fur ther reactivation of major shear zones within the same shortening regime at ca. 550-500 Ma is indicated by the Ar-40/Ar-39 data. Resetting of the K/Ar system was locally more intense along the Eastern Ghats Boundary Fault and Kerajang Fault Zones and was associated with ingress of high-temperature f luids. The resulting post-Grenvillian tectonic framework for northern Oriss a provides insight into the character of intra-cratonic Pan-African tectoni sm within East Gondwanaland. (C) 2001 Elsevier Science B.V. All rights rese rved.