Neoproterozoic extension and decompression in the northern Eastern Ghats Province, India: Mid-crustal signature of Rodinia break-up?

Abstract

The Eastern Ghats Province (EGP) of India is considered to have been a part of the supercontinents Rodinia and Gondwana at c. 1.0 Ga and 500 Ma, respectively. A range of ages spanning much of the Neoproterozoic have been periodically reported from parts of the EGP, indicating that the terrane remained tectonically active in the interval between Rodinia and Gondwana amalgamation, although the nature of the associated events remains uncertain. In this study conducted on the northern EGP, we constrain these enigmatic events from structural (field, microstructural and Electron Backscatter Diffraction studies), metamorphic (pseudosection modelling and geothermobarometry) and geochronological (monazite chemical dating) evidence. The area is multiply deformed, with the D1 and D2 shortening deformation accompanying granulite facies metamorphism that peaked at temperatures in excess of 900 °C, at ~955 ± 28 Ma. Following hydrous fluid infiltration at ~808 ± 10 Ma, the entire northern EGP was affected by an extensional deformation event D3 that reoriented all earlier fabrics into an E-W trending, northerly dipping orientation. Deformation microstructures and results of geothermobarometry indicate that D3 operated at around 600 °C at ~711 ± 18 Ma. Dextral strike-slip deformation (D4) along the Mahanadi Shear Zone operated under greenschist facies conditions and did not reset monazite isotope systematics in the region. The signature of mid-crustal extension during D3 is likely to be associated with the break-up of Rodinia. The lack of corresponding evidence for mid-Neoproterozoic extension in the adjacent Indian cratons suggests relative uplift of the EGP following Gondwana amalgamation.