Jurassic rifting at the Eurasian Tethys margin: Geochemical and geochronological constraints from granitoids of North Makran, southeastern Iran

Abstract

This study focuses on an east-west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern Dur Kan Complex, a continental slice outcropping to the north of the exposed Makran accretionary wedge in southeastern Iran. Field observations, petrographic descriptions, trace element, and isotope analyses combined with U-Pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks. Results document three magmatic episodes with different melt sources for (1) granites, (2) a diorite-trondhjemite-plagiogranite sequence, and (3) diabases and lavas. Granites, dated at 170-175 Ma, represent crystallized melt with a strong continental isotopic contribution. The diorite-trondhjemite-plagiogranite sequence is 165-153 Ma old and derives from a mantle magma source with minor continental contribution. East-west trending diabase dikes and bodies intruded the granitoids, which were eroded and then covered by Valanginian (140-133 Ma) alkaline lavas and sediments. Alkaline dikes and lavas have a mantle isotopic composition. Temporal correlation with plutonites of the Sanandaj-Sirjan Zone to the northwest defines a narrow, NW-SE striking and nearly 2000 km long belt of Jurassic intrusions. The increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling/decompression melting. Accordingly, the formation of the studied igneous rocks is related to the extension of the Iranian continental margin, which ultimately led to the formation of the Tethys-related North Makran Ophiolites.

The Neotethyan Sanandaj‐Sirjan zone of Iran as an archetype for passive margin‐arc transitions

“…First, after initiation of the arc, the plutonic belt occupied a strike length of at least 1200 km along the arc, from the Qorveh area (in the northwest) to the Jiroft area (in the southeast) during Early to Late Jurassic time (Figures and ). Jurassic plutonism also occurs in the southeastern tail of the SSA in the Makran [ Hunziker et al ., ]. This observation contrasts with a previous view that the Jurassic plutonic belt (i.e., Alvand‐like granitoids) is restricted to the northwestern half of the SSA (Figure ) [e.g., Eftekharnezhad , ; Mohajjel and Fergusson , ].…”

“…This relatively narrow definition overlooks one of the most significant discoveries of the East Iran Project in the 1970s, which is the continuation of the SSA as an east tapering wedge or “tail” in the accretionary prism of the Makran belt, well to the east of the syntaxis [ McCall and Kidd , ; McCall , , ]. The continuation of the Jurassic SSA southeast of the Strait of Hormuz into the Makran belt has more recently been confirmed with detailed field work and U/Pb geochronology on granitic and trondjemitic plutonic rocks from the Dur Kan complex, which yield ages of 175–163 Ma, with variable amounts of continental influence in the magmatic source regions [ Hunziker et al ., ]. Including the tail, the zone is more than 2000 km long (Figure ), longer in dimensions than the Late Cretaceous arc in the U.S. Cordillera between southern California and the Canadian border.…”

“…A broad range of K‐Ar and Rb‐Sr cooling ages, mostly ranging from Cretaceous to Paleocene, had previously been assumed to be crystallization ages for a number of these plutonic centers [e.g., Valizadeh and Cantagrel , ; Berberian and Berberian , ; Braud , ], but U‐Pb zircon ages published over the last decade show that the plutons dated thus far were emplaced almost entirely during Jurassic to Early Cretaceous time (circa 187 to 97 Ma) [ Ahmadi‐Khalaji et al ., ; Fazlnia et al ., , , ; Shahbazi et al ., ; Ahadnejad et al ., ; Mahmoudi et al ., ; Azizi et al ., ; Esna‐Ashari et al ., ; Hosseini et al ., ; Chiu et al ., ; Hunziker et al ., ]. Whole‐rock major and trace element compositions of many of these plutons have been presented in a number of recent publications and reveal calc‐alkaline affinity and arc‐related geochemical signatures [ Arvin et al ., ; Ahmadi‐Khalaji et al ., ; Fazlnia et al ., , ; Shahbazi et al ., ; Ahadnejad et al ., ; Mahmoudi et al ., ; Esna‐Ashari et al ., ; Hunziker et al ., ]. While the majority of the granitoids are I‐type, some A‐type examples have been identified throughout the zone [e.g., Sarjoughian et al ., , and references therein].…”

The Proto‐Zagros Foreland Basin in Lorestan, Western Iran: Insights From Multimineral Detrital Geothermochronometric and Trace Elemental Provenance Analysis

“…The only known significant magmatic body of this age in the Iranian Zagros include widespread granitic intrusions of the SSZ that formed due to subduction of the Neotethys ocean (Hunziker et al, 2015;Shahbazi et al, 2010). The only known significant magmatic body of this age in the Iranian Zagros include widespread granitic intrusions of the SSZ that formed due to subduction of the Neotethys ocean (Hunziker et al, 2015;Shahbazi et al, 2010).…”

Iranshahr blueschist: subduction of the inner Makran oceanic crust

“…Although different aspects of the geology of the Makran area including igneous activity (e.g. Hunziker et al ., ) and subduction and tectonic activity (e.g. Coleman, ; Glennie et al ., ,b; McCall, ; Hunziker et al ., ) have been studied, there is no published account on the low‐grade HP‐LT rocks of this area and their potential use in reconstructing the subduction and subsequent exhumation of the ophiolites and metamorphic rocks.…”