Clinopyroxene compositions of the gabbros from Misho mountains in Northwestern Iran

The Misho Mts are located in the the East Azerbaijan province (NW Iran) and are bounded both in the north and the south by two dextral, oblique-strike slip Cenozoic fault systems that are responsible of the uplifting of the Precambrian to Triassic formations as a major positive flower structurehas. This mafic complex probably is a part of paleotethyan suture zone[1]. Field evidences indicate that the mafic plutonic rocks are intruded into the basement rocks of the infracambrian Kahar formation through sharp contacts. U-Pb method dating for gabbroes confirms Carboniferous age. They mainly consist of cumulate and isotropic gabbro with rare layers of dunite, pyroxenite, troctolite and anorthosite. In all magmatic varieties, the crystallization order is: (olivine) plagioclase - clinopyroxene - Fe-Ti-oxides. Gabbros display N-MORB normalized incompatible element pattern with elemental concentration decreasing from Th to Yb. The rocks show rather variable Mg#, most likely reflecting different, progressive degrees of fractionation. The pyroxenes in gabbros and diabases are mostly ca-clinopyroxene. The results of EMP analysese of clinoproxenes show that Pyroxens have diopside to augite compositions with subalkaline properties. The partial melting model of depleted MORB mantle (DMM) source[2] is shown for gabbros. Low Si, Ti, Al, Na and heigh Si in CPXs show these gabbros relation with MORBs. Low Ti and heigh Mg in CPXs are reasons for these gabbros source from pre- depleted oceanic lithosphere in within plate setting. The mantle melting originating all rock-types starts deep in the garnet-facies mantle and continues at shallow levels in the spinel-facies mantle. The Misho mafic complex is made of gabbros and sheeted dykes showing basically two magmatic affinities: N-MORB and P-MORB. The Misho mafic complex, together with the host continental rocks, represents a part of paleotethyan ocean.