Mineralogy of the Manipur Ophiolite Belt, North East India:Implications for Mid-Oceanic Ridge and Supra-Subduction Zone Origin

Abstract

Mineralogical studies on the mantle and crustal sections of the Manipur Ophiolite Belt (MOB) lead to important findings pertaining to its genesis and controlling tectonic milieu. The wide compositional gap in the Cr# and Mg# content of spinel in the mantle peridotites of MOB implies upper mantle melting in two different tectonic settings. The tectonic discrimination diagrams based on spinel chemistry indicate a midoceanic ridge (MOR) origin for the high-Al spinel peridotites and a supra-subduction zone origin for the high-Cr spinel peridotites. The pyroxenite mantle dyke, ultramafic cumulate and pillow-basalt record temperature in the range of 600-1030°C, 600-800°C and 700-1005°C respectively. Plotting of clinopyroxene composition of pillow-basalt in the TiO 2 -Na 2 O-SiO 2 /100 (wt%) tectonic discrimination diagram, implies a subduction-related origin of the basalts. Experimental studies on the serpentine stability indicate that it was dominantly affected by high temperature-low deformation setting.