Silicate and Sulphide Mineralogy, and Conditions of Equilibration of Ultramafic Rocks of the Indo-Myanmar Ophiolite Belt between Tusom, Manipur and Shomra Village, Myanmar

Abstract

The northeast-India ophiolite complex is exposed in many parts of Nagaland and Manipur, with particularly well-preserved mantle-sequence peridotite present in its southern section in Manipur state. We present the results of an investigation into the petrology and constituent mineral chemistry of this peridotite, which is associated with the Indo-Myanmar ophiolite located between Tusom, Ukhrul District (Manipur) and Shomra village (Myanmar). Mineral compositions indicate that it is an abyssal peridotite that has undergone minimal partial melting (1-5%). Equilibration probably occurred in the upper mantle at a temperature of 1080-1240°C, a pressure of 23- 24 kbar, and an oxygen fugacity between 0.303 and 0.580 log units above the FMQ buffer. Primary and secondary sulphide phases in the studied peridotites have also been analysed. Pentlandite ((Fe,Ni) 9 S 8 ) was found to be the primary sulphide mineral, which occurred in association with orthopyroxene and awaruite (Ni 3 Fe). Cu-rich alloys and magnetite occur as secondary minerals that developed during later serpentinization.