Re-using terrane boundaries in supercontinent cycles –evaluating an Indo-Antarctica contact in Rodinia and Gondwanaland

Abstract:

The Eastern Ghats Province (EGP) of India is a granulite belt that was continuous with the Rayner Province in East Antarctica in the supercontinent Rodinia. An E-W trending lineament, now known to be a strike-slip shear zone, separates the EGP from the Archaean Indian craton to the north which is characterised by penetrative 2.8 Ga granulite foliation. In contrast, the penetrative granulite foliation in the EGP is 1.0 Ga in age; in places along the contact zone, both granulite foliations are overprinted by a greenschist facies mylonitic fabric related to a later dextral strike-slip motion along the lineament. Identification of a sub-surface, sub-vertical structural discontinuity along the lineament through field gravity-magnetic studies further confirms that craton-mobile belt boundary continues in the sub-surface. The northern side of the lineament shows no overprint of the 1 Ga fabric on the 2.8 Ga fabric, implying that the presently juxtaposed 2.8 Ga and 1 Ga terranes in the Indian shield may not have been juxtaposed during the 1 Ga event. Kinematic analysis of the contact shear zone by using strain gradients across the width of the domain, confirms that a dominantly strike-slip deformation brought the terranes together. ⁴⁰Ar-³⁹Ar ages of ~490-470 Ma have been reported from deformed micas within the shear zone, and this is suggested to correspond to the age of this mobilization. This lineament can be traced into the Rauer Group in East Antarctica that separates similarly aged domains, suggesting that it represents a site preferred for terrane amalgamation during assembly of temporally disparate supercontinents. Whether the lineament developed during the last dextral strike-slip movement or it is a reactivated 1.0 Ga, 2.8 Ga or even older discontinuity, remains unclear.