GEODYNAMIC SETTING AND MINERALIZATION IN THE WESTERN NEO-TETHYS

Abstract

The southern section of the Neo-Tethys Ocean was located between the Arabian shield and the Sanandaj-Sirjan Zone. To understand the mineral exploration potential in this area, a new database including 420 U-Pb and 1147 lithogeochemical samples, 1552 Lu-Hf, and 353 Sm-Nd isotopic composition results were constructed from published articles. This research is the first attempt to provide quantitative constraints on the development of the Western Neo-Tethys by utilizing the available published geochronological and geochemical data on the Mesozoic evolution of the Neo-Tethys. The collected dataset potentially provides insights into the relationship between tectono-magmatic environments and geochemical signatures in the overall study area. The geodynamic evolution of the Neo-Tethys in Iran started potentially as a rift by the Late Permian. Thus, igneous and metamorphic rocks older than Permian has been considered as basement and crustal blocks. The calculated εHf and εNd values distinguish five large crustal blocks in the western Neo-Tethys. However, the isotopic composition in the central and northwest of the Urumieh-Dokhtar Magmatic Arc confirms the rifting and seafloor spreading of Neo-Tethys during the Permian–Triassic times. Contrary to previous studies, the GPlates-based reconstructions showed that the closure of Paleo-Tethys occurred in the Late Jurassic, not in the Permian–Triassic period. Moreover, based on this paleo-plate reconstruction, the opening of the Neo-Tethys was formed in the Late Triassic - Early Jurassic period and the initiation of subduction has occurred during the Middle Jurassic - Late Jurassic. Furthermore, the GPlates reconstructions, indicate that the initiation of collision between Arabia and Eurasia occurred between the upper Miocene to Pliocene (10-5 Ma). The geodynamic evolution of the southern Neo-Tethys Ocean involved a significant flare-up of arc magmatism affecting a large part of Iran and western Neo-Tethys from Cretaceous until the mid-Tertiary. The peak of magmatism occurred between 55 and 35Ma. This flare-up has formed two parallel arc regions, the Sanandaj-Sirjan Zone in the fore-arc and Urumieh-Dokhtar Magmatic Arc in the back-arc. These two parallel domains are believed to be the result of the NE-dipping subduction of the Neo-Tethys in the Western Neo-Tethys. The geochemical features and adakitic signatures in these areas are interpreted similarly to the Andean-type magmatism. The mineralization in this realm is linked to the intrusion-related porphyry copper system of the Urumieh-Dokhtar Magmatic Arc. This area is significantly dominated by substantial volcanic activity. Alternatively, volcanic massive sulfide deposit formation is related to the evolution of an extensional continental margin in a back-arc environment that affected the Central Iranian Microcontinent. This study has shown that no adakitic signatures are observed in Western Neo-Tethys rocks until the Early Jurassic. The first signs of adakitic magmatism appeared during the Middle to Late Jurassic period for the Ghorveh area in the northwest of Sanandaj-Sirjan Zone. However, the subduction of the Neo-Tethys oceanic crust under the Central Iranian Microcontinent has continued from Jurassic to Paleogene time, and adakitic magmatism has occurred in some segments along Western Neo-Tethys.