Abstract
In northwestern Iran, magmatic activity occurred during three main intervals: The Cretaceous, Eocene, and Miocene-Quaternary. The first two phases of magmatic activity are more consistent with arc-type magmatism on an active continental margin; whereas the last phase, which has calc-alkaline and alkaline affinities, shows more similarity to postcollisional magmatism. Magmatic belts are mostly situated in the northern and eastern parts of the Oshnavieh–Salmas–Khoy ophiolite belt (OSK-Ophiolite) in northwestern Iran. The OSK-Ophiolite is known as the Neotethys, an ocean remnant in northwestern Iran, and extends to eastern Turkey and surrounds the Van area. This configuration shows that the Van microplate and surrounding ocean have played an important role in the evolution of magmatic activity in northwestern Iran, eastern Turkey, and the Caucasus since the Cretaceous. The Van microplate is situated among the Arabian plate to the south, northwestern Iran to the east, and Armenia to the north. The subduction of the northern branch of the Neotethys oceanic lithosphere beneath southern Eurasia has been critical in flare-up magmatism in the southern Caucasus since the Late Cretaceous. Considering the Van area as a new microplate makes understanding the geodynamic evolution of this area easier than in the many tectonic models that have been suggested before. When regarding the Van microplate, the main suture zone, which is known as the Bitlis–Zagros zone, should be changed to the Zagros–Khoy–Sevan–Akera suture zone, which extends to the eastern and northern Van microplate and western Iran.
Highlights
Most crust in Iran and Turkey is part of the Alpine–Himalaya orogenic belt, which is situated at the junction of Gondwana and the Eurasian plate (Dewey et al, 1973; An and Harrison, 2000; Göncüoglu, 2010; Prelevicand Seghedi, 2013; Tian et al, 2017)
Published research has confirmed that the initiation of Neotethys subduction beneath the Sanandaj–Sirjan zone (SaSZ) (Azizi and Stern, 2019) occurred in the Cretaceous Period, and the collision of the Arabian plate and Van microplate in northwestern Iran occurred in the late Eocene epoch (Azizi et al, 2019)
In line with our suggestion, the new OSK zone shows that northwestern Iran-eastern Turkey magmatism was mainly controlled by Neotethys oceanic subduction, which was situated on the northern side of the Van microplate (Figures 2, 3)
Summary
Most crust in Iran and Turkey is part of the Alpine–Himalaya orogenic belt, which is situated at the junction of Gondwana (in the south) and the Eurasian plate (in the north) (Dewey et al, 1973; An and Harrison, 2000; Göncüoglu, 2010; Prelevicand Seghedi, 2013; Tian et al, 2017). Cu–Mo–Au deposits and Fe mineralization (Azizi et al, 2009; Siani et al, 2015; Mehrabi et al, 2016; Rabiee et al, 2019) occurred during magmatic activity in the western and southern areas of the Caspian Sea. Late Miocene-Quaternary Rocks This group of rocks is distributed along the rim of the Van microplate, and they are classified into two main groups. The variation in the Ta/Yb vs Th/Yb ratios (Pearce, 1982) shows a wide range for the Eocene and Cretaceous intermediate-to-acidic magmatic rocks and more affinity with the upper Miocene-Quaternary for the withinplate granite field (Figure 9C). Depleted mantle, oceanic-island basalt (OIB), source-like, and enriched mantle (EM2) contributed to the genesis of Eocene and upper Miocene-Quaternary magmatic activity, with less contribution from continental crust for the upper MioceneQuaternary rocks
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