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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.

Basic-intermediate volcanic rocks from the Karaj-Danesfahan area in the Neotethyan magmatic belt of Iran show typical island arc geochemical signatures. The rocks demonstrate calcalkaline affinity with low abundances of "high field strength elements" (HFSE) such as Nb, Ta, Hf and Ti, and highly distinctive spiked trace element patterns at "large ion lithophile elements" (LILE) such as Ba, K, and Sr. Comparing the geochemical characteristics of two sets of the volcanic rocks sampled from two parts of the study area 100 km apart, however, indicate subtle but significant geochemical differences which bear important petrogenetic implications. One set of the volcanic rocks is abnormally enriched in Pb and shows consistently higher abundances of HFSE, particularly Ti, than the other set. These two series are called HTL series (after high titanium and lead) and LTL series (after low titanium and lead), respectively. HTL series volcanic rocks are further from the subduction axis, so they should have had a deeper descending slab contributing to their mantle wedge magmatism. To be able to release Pb-enriched fluids, the subducting slab should not have undergone earlier dehydration. It is because Pb is highly incompatible. It appears that in the early stage, subduction proceeded at a higher rate (cold slab), so slab-dehydration occurred at greater depths triggering HTL series magmatism. Subsequently the subduction rate decreased which in turn raised isotherms and promoted partial melting at shallower depths leading to LTL series magmatism.

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Geochemical and mineralogical characteristics of the Eocene volcanic succession in Tafresh area of the Urumieh-Dokhtar Magmatic Assemblage (UDMA) are unique in the 2000-kmlength assemblage. Demonstrating rather steep rare earth element (REE) patterns and the widespread presence of amphibole (+biotite) phenocrysts are two distinct characters that dominate the Eocene volcanic succession of mainly andesitic composition. Coincidence of the geochemical and mineralogical characteristics of the whole volcanic succession with adakites, rather amphibole-(+biotite) rich dacitic (with 61-64 wt% SiO 2) stocks and dykes, is considered as the key in unraveling the role of 'slab-derived melt contribution' in petrogenesis of the volcanic succession. Slab-derived melting has been an ongoing process that metasomatized some parts of the mantle wedge from which hybrid rocks (andesites) are derived. Basalts with distinct signatures of slab melt metasomatism are yet another support for the occurrence of slab melting. Interlayering of normal, island-arctype calc-alkaline volcanic rocks with the slab-melt metasomatized basalts and hybrid andesites suggests that the slab melting has been motivated by the subduction. Formation of the Tafresh Caldera, the likely consequence of an explosive eruption, is compatible with the volatile-bearing nature of the adakitic volcanism in the study area. It is indicated by the ubiquitous presence of the hydrous minerals. Beneath the Tafresh area, in Eocene time, the subducting slab seems to have reached a critical high depth that is enough for the development of amphibolite-eclogite. The slab deformation, motivated by the geometry of subduction and/or the underlying mantle's steeper geotherms, is suggested to have resulted in the slab melting that helped develop a rock assemblage unique to the UDMA.

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