Tectonic setting of plagiogranites and gabbros in the Shahre-Babak ophiolitic sequence (Nain-Baft belt), Iran

摘要

Plagiogranite intrusive rocks crop out in the gabbroic section of an ophiolite southeast of Shahre-Babak.Petrographically, the rocks are comprised of tonalite, trondhjemite and leucogabbro.The plagiogranites have inequigranular, hypidiomorphic and granophyric textures, and consist of plagioclase, quartz and sodium feldspars with less than 10％ amphibole ± pyroxene and opaques.The gabbros consist primarily of augite, plagioclase and amphibole.Geochemical studies show that the parent magma was sub-alkaline (calc-alkaline series) and metaluminous, typical of volcanic arc granite (VAG) and MORB or I-type granites.Chondrite-normalized REE patterns of the Shahre-Babak plagiogranites and gabbros show weak light REE enrichment with fiat HREE sections, consistent with formation in a supra-subduction zone environment.It seems probable that the parental magma of the plagiogranites formed by partial melting of mafic rocks, such as gabbro, in a spreading basin associated with a subduction zone.