Petrology and geochemistry of Abyssal Peridotites from the Manipur Ophiolite Complex, Indo-Myanmar Orogenic Belt, Northeast India: Implication for melt generation in mid-oceanic ridge environment

Abstract

The Manipur Ophiolite Complex (MOC) located in the Indo-Myanmar Orogenic Belt (IMOB) of Northeast India forms a section of the Tethyan Ophiolite Belt of the Alpine–Himalayan orogenic system. Whole rock compositions and mineral chemistry of mantle peridotites from the MOC show an affinity to the abyssal peridotites, characterized by high contents of Al2O3 (1.28–3.30anhydrouswt.%); low Cr# of Cr-spinel (0.11–0.27); low Mg# of olivine (∼Fo90) and high Al2O3 in pyroxenes (3.71–6.35wt.%). They have very low REE concentrations (∑REE=0.48–2.14ppb). Lherzolites display LREE-depleted patterns (LaN/SmN=0.14–0.45) with a flat to slightly fractionated HREE segments (SmN/YbN=0.30–0.65) whereas Cpx-harburgites have flat to upward-inflected LREE patterns (LaN/SmN=0.13–1.23) with more fractionated HREE patterns (SmN/YbN=0.13–0.65) than the lherzolite samples. Their platinum group elements (PGE) contents (<50ppb) and distinct mantle-normalised PGE patterns with the Pd/Ir values (1.8–11.9) and Pt/Pt* values (0.2–1.1) show an affinity to the characteristic of the residual mantle material. Evaluation of mineralogical and petrological characteristics of these peridotites suggests that they represent the residues remaining after low degree of partial melting (∼2–12%) in the spinel stability field of a mid-oceanic ridge environment. The well-preserved mid-oceanic ridge characteristics of these peridotites further suggest that the mantle section was subsequently trapped in the forearc region of the subduction zone without undergoing significant modification in their chemistry by later subduction-related tectonic and petrological processes before its emplacement to the present crustal level.