PETROGENESIS OF MANTLE ROCKS AND CHROMITE ORE, MANIPUR OPHIOLITE COMPLEX, INDIA

Abstract

The Manipur Ophiolite Complex (MOC) is the southern extension of Nagaland-Manipur Ophiolite (NMO) and an integral part of the Indo-Myanmar Orogenic Belt (IMOB), situated along the eastern margin of the Indian subcontinent. The MOC has a complex geological history and is relatively one of the less explored ophiolitic complexes in the globe. To date number of research publications, mainly covering petrogenesis and the tectonic evolutionary history of this ophiolite, are available. However, still, there is a difference of opinion regarding its origin. Both subduction and non-subduction related tectonic settings have been suggested. Similarly, the geochemical signatures of the volcanic rocks, studied by different researchers, indicate multiple sources of magma – mid-ocean ridge basalts (MORB), ocean island basalts (OIB) and island arc tholeiites (IAT). Until now the main problem remains, whether these rocks were derived from different magma sources at diverse tectonic settings or generated at different/single tectonic environments during the evolution of the MOC. Thus, the main objective of the thesis was to resolve the above-cited issues by providing new petrographical, mineralogical and geochemical data including Platinum Group of Elements (PGE) content from both ultramafic rocks (peridotite) and chromite ore. The present study concludes that the MOC, part of the NMO, is found to be a remnant of the Neo Tethyan Oceanic lithosphere and the ophiolite has a sequence of a different group of rocks, which were formed related to both subduction and non-subduction tectonic regimes, occurred during different geological times. The group of rocks, not related to the subduction process, in all likelihood, have formed at the time of the breakup of Gondwana during the Late Jurassic-Early Cretaceous times. On the other hand, the rocks, associated with the subduction process, are formed when the Indian plate started subducting beneath the Myanmar plate at a much later geological time, the Late Cretaceous period. Both the non-subduction and a subduction-related group of rocks of MOC were further tectonically deformed due to prolonged convergent movement of the Indian plate beneath the Myanmar plate and found as dismembered ophiolite section along the Indo-Myanmar orogenic belt (IMOB).