Two Types of Plagiogranite from Mesozoic Ashin Ophiolite (Central Iran): a Mark of Tectonic Setting Change from Jurassic to Cretaceous


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The Ashin ophiolite is situated in the western part of Central Iran and presents two stages of Jurassic and Cretaceous spreading. The Ashin ophiolite represents fragments of the Neo-Tethys oceanic lithosphere. Plagiogranite intrusions of this ophiolite have good exposures. Plagiogranites of Cretaceous are more fresh than the metamorphosed samples of Jurassic. The main minerals of plagiogranites from the Ashin ophiolite are plagioclase, quartz and amphibole. Plagiogranites of the Jurassic have tholeitic nature with higher amounts of amphibole, \({\text{F}}{{{\text{e}}}_{2}}{\text{O}}_{3}^{*},\) TiO2, Co and lower values of Mg#, Th and Sr than the Cretaceous calc-alkaline plagiogranites. The chondrite-normalized REE patterns of these plagiogranites are characterized by higher values of REEs and negative Eu anomalies for the Jurassic samples and low values of REEs and positive Eu anomalies for the Cretaceous ones. Very low values of HREEs in the Cretaceous plagiogranites indicates a non-peridotitic source rock. We suggest that the Jurassic plagiogranites are formed by fractional crystallization of a low-K tholeitic magma; and the adakitic Cretaceous plagiogranites are formed by partial melting of an amphibolite in the subducting slab. Geochemical criteria of the Ashin plagiogranites indicate changing the Ashin ophiolite tectonic setting from a mid-ocean ridge system in the Jurassic to a supra-subduction zone in the Cretaceous.

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G. Torabi

University of Isfahan, Department of Geology

编辑信件的主要联系方式.
Email: Torabighodrat@sci.ui.ac.ir
伊朗伊斯兰共和国, Isfahan, P.C. 8174673441

T. Morishita

Kanazawa University-School of Natural System, College of Science and Engineering

Email: Torabighodrat@sci.ui.ac.ir
日本, Kanazawa, P.C. 920‒1192

S. Arai

Kanazawa University-Institute of Liberal Arts and Science

Email: Torabighodrat@sci.ui.ac.ir
日本, Kanazawa, 920‒1192

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