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The Jurassic mafic to felsic magmatism affecting the older Ediacaran-to-Cambrian basement of the Sanandaj-Sirjan Zone of Iran has been traditionally interpreted as the product of arc and/or back-arc magmatism related to the early stages of Neo-Tethys subduction beneath Iran in the early Jurassic. Recent works and new compositional and geochronological data have started challenging this commonly accepted model in favor of scenarios involving continental rifting, mantle plume activity, and/or passive margin formation. In the Hamedan area of the central sector of the Sanandaj-Sirjan Zone, the Jurassic Cheshmeh-Ghasaban gabbro (ca. 165 Ma) is a key formation to better understand the tectono-magmatic framework of the whole area. Our new data, combined with the existing literature, suggest a transitional to alkaline OIB-like compositional character for this gabbro similar to the nearby but slightly younger (ca. 145 Ma) Panjeh and Ghalaylan basaltic complexes (in the Songhor-Ghorveh area). When integrated with the existing geochemical data of Jurassic mafic rocks from the central Sanandaj-Sirjan Zone, our results point to a scenario of intracontinental rifting, possibly involving the upwelling old metasomatized (by Proto-Tethys subduction?) mantle or mantle-plume activity. [Display omitted] • Jurassic OIB-like plume-type mafic magmatism in Central Sanandaj-Sirjan zone of Iran • Jurassic plume-influenced continental rifting affecting the Ediacaran-to-Cambrian crust of Iran • Rethinking the Mesozoic framework of SW Eurasia margin [ABSTRACT FROM AUTHOR]

Abstract: The Iran continental crust was metamorphosed, intruded by granitoid magmas, folded and faulted during the Late Precambrian by the Pan-African Orogeny. The basement complex in the Takab Complex (northwest Iran) consists of gneisses, amphibolites, pelitic schists, meta-ultramafic and calc-silicate rocks. Geochemically, the protoliths of the Takab gneisses are slightly peraluminous and medium to high-potassic with calc-alkaline affinity. These gneisses may have been emplaced in volcanic arc tectonic setting. Furthermore, the metapelitic protolith is shale deposited in an active continental margin setting. All these characteristics, and presence of paleo-suture zone and ophiolitic rocks (i.e. serpentines, meta-mafic and meta-ultramafic rocks) around the high grade metamorphic rocks suggest that a continental-margin magmatic arc (Andean-type) formed the Takab Precambrian basement. The basement complexes are extensively overprinted by the Pan-African Orogeny and younger igneous events; this supports the inference that Early Cambrian orogenesis in the Takab Complex region of northwest Iran marks one of the fundamental lithospheric boundaries within Gondwana which belonged to a greater Late Neoproterozoic–Early Paleozoic orogenic system that was active along the Proto-Tethyan margin of the Gondwana supercontinent, extending at least from its Arabian margin to the Himalayan margin of the Indian subcontinent. [Copyright &y& Elsevier]