High-Al chromian spinel in peridotites of Manipur Ophiolite Complex, Indo-Myanmar Orogenic Belt: implication for petrogenesis and geotectonic setting

摘要

Chromian spinels (Cr-spinels) in peridotites of the Manipur Ophiolite Complex occur as euhedral to subhedral inclusions in olivine, opx, cpx and sepentine. Rarely they are highly corroded and exhibit irregular shape; altered to ferritchromite or magnesioferrite along the cracks and boundaries. Cr-spinels are characterized by low values of Cr# (10.75-26.37), and high Al# (72.71-88.36) and Mg# (70.00-73.43) are identified as Al-rich Cr-spinels. Chemical discontinuity between the Cr-spinel core and rim (ferrochromites/magnesioferrite) was observed in the analysed grains. Mineral chemistry of these Al-rich Cr-spinels suggests that host peridotites have an affinity to abyssal and alpine-type peridotites. It also suggests that these peridotites might have been derived from tholeiitic melt, i.e. MORB at low degree of partial melt.