Abstract
Previous interpretations of a Jurassic subduction in Iran were based on trace element classification diagrams for granitoids, but their reliability is questionable, underscored by modern examples of continental break-up zones such as the Baja California. We present new field observations, bulk rock geochemistry, Sr and Nd isotope analyses and U–Pb zircon geochronology to assess the age and tectonic setting of previously undated intermediate to felsic magmatic rocks cropping out in the Precambrian basement of NW Iranian Azerbaijan. The geochronology revealed an uneven distribution in space and time: Late Jurassic (159–154 Ma) intrusions and dikes are alkaline to calc-alkaline. Their melt source is mantle dominated with a distinct continental contribution disclosed by radiogenic isotopes and abundant inherited zircon cores. Mid-Cretaceous (112–96 Ma) plutonic bodies and associated volcanic rocks occur only to the east of the major Siah Cheshmeh–Khoy Fault. They have geochemical signatures typical of a metasomatized mantle. In consistence with the sedimentation history of the area, our new interpretation attributes the Late Jurassic magmatism to thinning of a continental lithosphere in a rift-related setting. Mid-Cretaceous magmatism was produced by oceanic subduction beneath the Central Iran continent. We interpret the 40-Ma age gap between the two magmatic episodes as the time of opening of the oceanic basin witnessed by the Khoy ophiolite in the study area.
Highlights
The Khoy ophiolite complex is located to the northwest of the city of Khoy, between the Sanandaj–Sirjan zone and the Central Iranian block (Fig. 1; e.g. Hassanzadeh and Wernicke 2016)
Subduction along the northern margin of the Neo-Tethys below the Sanandaj–Sirjan zone is claimed to have started in latest Triassic to Early Jurassic forming a magmatic arc represented by Middle to Late Jurassic (150–175 Ma) intrusions (Fig. 1; Hassanzadeh and Wernicke 2016 and references therein)
Late Jurassic samples could be dated on both sides of the Siah Cheshmeh–Khoy right lateral strike-slip fault, suggesting an analogous tectono-magmatic evolution during this time for the two sides of the fault, i.e. western metamorphic unit (WMU) and EKOC + Central Iranian block (CIB)
Summary
The Khoy ophiolite complex is located to the northwest of the city of Khoy, between the Sanandaj–Sirjan zone and the Central Iranian block (Fig. 1; e.g. Hassanzadeh and Wernicke 2016). The Khoy ophiolite represents a former oceanic basin Khalatbari-Jafari et al 2003) whose opening and closure remain disputed. The setting of the Khoy ophiolite with respect to the other ophiolites of the Zagros fold belt (Fig. 1) remains debated. Beginning of collision took place between Late Eocene/Oligocene and Early Miocene Subduction along the northern margin of the Neo-Tethys below the Sanandaj–Sirjan zone is claimed to have started in latest Triassic to Early Jurassic forming a magmatic arc represented by Middle to Late Jurassic (150–175 Ma) intrusions (Fig. 1; Hassanzadeh and Wernicke 2016 and references therein)
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