Resolving the conundrum in origin of the Manipur Ophiolite Complex, Indo-Myanmar range: Constraints from Nd isotopic ratios and elemental concentrations in serpentinized peridotite

Major, trace and rare earth element (REE) abundances along with Nd isotopic ratios are measured in serpentinized peridotite samples from the Manipur Ophiolite Complex (MOC), Indo-Myanmar range (IMR). An attempt is made to resolve the conundrum caused by apparently contradictory petrogenetic models and tectonic settings reported in literature. Nd isotope ratios, reported for the first time, range from -7.6 to + 10.4 in epsilon units in the whole-rock samples of serpentinized harzburgite and lherzolite. Variation of La/Yb with (epsilon)Ndt is consistent with the progressive addition of a subduction derived fluid to a depleted mantle source. Literature data from the mafic extrusive, intrusive and ultramafic rocks together with new data generated during this study can be explained by a two stage petrogenetic model. Non-modal dynamic melting in the mantle-wedge subsequent to the mixing of fluids derived from the subducted slab explains the observed range of elemental abundances in the MOC mafic and ultramafic rocks. This model also explains the observed variability of Nb and Th in the mafic rocks without invoking different sources for the different types of rocks. Taking into account field, petrographic and geochemical evidences, we propose, that MOC comprises a buoyant fore-arc-mantle wedge system along with the subducted slab that was obducted during the terminal stage of subduction of the Neotethys below the Burmese plate.