Origin, evolution, and emplacement of the Nagaland–Manipur ophiolites, Indo–Myanmar orogenic belt, Northeast India

The Nagaland–Manipur Ophiolites (NMO) characterize the Neo-Tethyan ophiolites of the Indo-Myanmar Orogenic Belt (IMOB), which lie along the southern extension of the Indus–Tsangpo Suture Zone. The NMO represents both the mantle section and crustal section. The geochemical characteristics of mafic rocks are affine to Mid-ocean ridge basalt and Ocean island basalt. Such geochemical variations can not simply be explained by fractional crystallization or variable degrees of partial melting of a single source but rather signify derivation from different tectonic settings of subduction and non-subduction magma factories. The mantle sequence has a wide range of chemical compositions. Lherzolites represent the residual product of a fertile mantle that underwent low-degree partial melting (< 10%) in a divergent Mid-ocean ridge (MOR) tectonic setting. Conversely, harzburgites and dunites were derived from a highly depleted mantle source, which experienced a higher degree of partial melting (> 17%). The occurrences of MOR and SSZ melting regime types specify the IMOB ophiolites formed at two significant stages of the pre-subduction and subduction events, respectively. The metamorphic records from the NMO also establish intra-oceanic subduction with the Neo-Tethys starting from subduction infancy, characterized by a warmer subduction channel (recorded by hornblende eclogite facies) to a more mature-colder stage of subduction (recorded by lawsonite/epidote blueschist) culminating in final collision of India plate and Myanmar microplate.