Multistage tectono‐magmatic evolution of the central Urumieh–Dokhtar magmatic arc, south Ardestan, Iran: Insights from zircon geochronology and geochemistry

Abstract

Combining high‐spatial resolution geochronology and geochemistry of zircon provides constraints on the geodynamic evolution of the Zagros orogen. This study underlines the significance of hitherto unknown magmatic/geological events in the central Urumieh–Dokhtar magmatic arc (UDMA) of Iran at ca. 35–22 and 10 Ma. Recently reported U–Pb zircon ages of 25–24 Ma for the granodioritic rocks from the south Ardestan area were interpreted to constrain the crystallization age. Newly determined U–Pb zircon ages of ca. 35 to 22 Ma from south Ardestan gabbroic to granitic rocks and related dikes indicate that the melt evolution continued from the Oligocene into Early Miocene time. In addition, a ca. 10 Ma U–Pb age for the zircons from a south Ardestan diorite provides evidence for a so far unknown, igneous episode. Representing the youngest magmatic stage recognized in the central part of the UDMA, the 10 Ma age is interpreted to document magmatic activity related to the Arabia–Eurasia collision, as recognized elsewhere in the Zagros orogen. South Ardestan zircons with geochemical signatures indicating continental affinity likely recrystallized in the course of a major event (asthenospheric mantle melt formation) that has affected crustal rocks. The significant lower LREEs of these zircons compared to hydrothermal zircons, moderate Th/U (>0.4), and high (Sm/La)N (>10) ratios associated with low [La] (<1 ppm) suggest that these crystals have an igneous origin and are not related to hydrothermal or metamorphic processes. These findings bear important implications for the geodynamic evolution of the Zagros orogen and support a model suggesting that magmatic activity still affected the UDMA in Late Miocene time.

A hidden crust beneath the central Urumieh‐Dokhtar Magmatic Arc revealed by inherited zircon ages, Tafresh, Iran

“…Late Neoproterozoic-Early Cambrian ages of inherited zircons (610.3 to 522.9 Ma) from the study area, and other regions in the Central UDMA (Babazadeh et al, 2019;Chiu et al, 2017;Shahsavari Alavijeh et al, 2019) indicate a basement for this zone. The crystalline basement of Iran that includes Late Neoproterozoic-Early Cambrian granodiorite, granitic gneisses, gabbro, and associated volcanics is considered as Iran's continental crust (Hassanzadeh et al, 2008;Jamshidi Badr et al, 2013;Karimpour et al, 2011;Ramezani & Tucker, 2003;Rossetti et al, 2015;Shakerardakani et al, 2015).…”

“…Late Neoproterozoic-Early Cambrian ages for the basement are reported from Central Iran (Ramezani & Tucker, 2003;Rossetti et al, 2015;Verdel et al, 2007), the Sanandaj-Sirjan Zone (Hassanzadeh et al, 2008), northeast Iran (Karimpour, Lang Farmer, Stern, & Salati, 2011;Shafaii Moghadam, Khademim et al, 2015;Shafaii Moghadam et al, 2016;Shafaii Moghadam, Griffin, et al, 2017), northwest Iran (Azizi, Chung, Tanaka, & Asahara, 2011;Hassanzadeh et al, 2008;Jamshidi Badr, Collins, Masoudi, Cox, & Mohajjel, 2013;Nutman, Mohajjel, Bennett, & Fergusson, 2014;Saki, 2010;Shahzeidi et al, 2016;Shakerardakani et al, 2015), and from the Urumieh-Dokhtar Magmatic Arc (UDMA; Babazadeh, Ghorbani, Cottle, & Bröcker, 2019;Chiu et al, 2017;Shahsavari Alavijeh, Rashidnejad-Omran, Toksoy-Köksal, Xu, & Ghalamghash, 2019; Figure 1).…”

“…The distribution of Paleoproterozoic, Late Neoproterozoic–Early Cambrian, and Cretaceous zircon ages in the central and south‐eastern UDMA with compilation of published age data (Babazadeh et al, ; Chiu et al, ; Hosseini, Hassanzadeh, Alirezaei, Sun, & Li, ; Shahsavari Alavijeh et al, ) [Colour figure can be viewed at wileyonlinelibrary.com]…”

Magma chamber evolution of the Ardestan pluton, Central Iran: evidence from mineral chemistry, zircon composition and crystal size distribution

“…Rossetti et al (2014) attributed an Eocene age to the transition from an extensional to a compressional plate margin along the Arabia–Eurasia convergence zone, which caused perturbation of the stress regime in the upper plate of the Neotethyan subduction system. The Urumieh-Dokhtar magmatic assemblage records abundant Tertiary magmatism, mainly related to continental arc (Berberian and Berberian, 1981; Moien-Vaziri, 1985; Babazadeh et al , 2017, 2019) or island-arc settings (Alavi, 1996; Shahabpour, 2007).

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“…The Ardestan plutonic bodies are associated with the NW–SE- and E–W-trending Marbin–Rangan and Marshenan Faults (Fig. 1), intruded volcanic rocks of Oligocene–Early Miocene age (Yeganehfar et al , 2013); available data for the age of these volcanic and plutonic rocks range from 35 to 10 Ma (Babazadeh et al , 2017, 2019).…”