Ophiolite of Manipur, NE India: An active continental margin ophiolite in the tectonic framework of the Indo-Myanmar ranges

Analysis of geological, structural and tectonic features of Manipur reveals good information about the tectonic framework of the Indo-Myanmar (Burma) Ranges (IMR) especially in terms of its deformation mechanism and evolutionary history. Manipur Hills, forming an integral part of the IMR, evolved as an accretionary prism due to subduction of the Indian plate below the Myanmar plate during the Alpine-Himalayan tectogenesis. Almost all the lithounits present in the region, therefore, lean one above the other in the form of an imbricate thrust system where older lithounits usually lie over the younger ones. Thus, oldest group of rocks expose in the eastern part while the youngest ones in the western part of the state. In the process of subduction, obducted oceanic crust (ophiolites) and pelagic sediments have intermingled with Disang and Barail sediments giving rise to a tectonic mélange belt possibly along an active continental margin.
The ophiolite of Manipur, which is predominantly composed of ultamafic (serpentinised peridotites) group of rocks, with minor basic dykes and spilitic pillow lavas associated with the ultramafics and sediments, has relatively rare gabbroic rocks. Although pre-rifting geology of the IMR is still very little known, possibly these rocks were formed during the rifting and stretching of the crustal layer that took place sometimes in the Upper Cretaceous. The mechanism of crustal stretching leading to the formation of a basin where the sediments of the IMR were deposited seems to be similar to the passive rifting of continental margin associated with formation of new oceanic crust. Petrographic and petrochemical studies as well as field setting of these volcanic and basic dykes, and the rare nature of gabbroic rocks in this ophiolite belt suggest that these rocks could have been formed in an active continental margin of a slow spreading center.
Key words: Manipur, Ophiolite, Indo-Myanmar Ranges, Active Continental Margin