M. Rahgoshay; J. Mehdipour Ghazi; H. Shafaii Moghadam
Abstract
Peridotites (Cpx-bearing harzburgites, lherzolites, wherlites and dunites) associated with pegmatite gabbros, gabbro impregnations, gabbroic-diabasic dikes, pyroxenites and websterites are the main constituents of the mantle sequence in the Nain ophioliote assemblage. Petrographic and geochemical studies ...
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Peridotites (Cpx-bearing harzburgites, lherzolites, wherlites and dunites) associated with pegmatite gabbros, gabbro impregnations, gabbroic-diabasic dikes, pyroxenites and websterites are the main constituents of the mantle sequence in the Nain ophioliote assemblage. Petrographic and geochemical studies indicate that peridotites in the Nain ophiolites are Cpx-bearing harzburgites with Al-rich spinels (Cr#=16.12-41.55) equilibrated at about 1000˚C. Pegmatite gabbros are found as small pockets within peridotites showing deformed clinopyroxenes and plagioclases. Gabbro-diabase dikes, mostly rodingitized, injected into the peridotites without chilled margins. These dikes are geochemically co-genetic with pillow lavas and micro-gabbros of the crustal sequence, but display variable degrees of partial melting. Based on the geochemistry of the mafic rocks and the peridotites, we suggest that Nain ophiolites were developed in a back arc spreading basin.
