Urumieh Dokhtar Research Articles

What controls structural variations along the Zagros Collision Zone? Insights from geophysical observations and thermo-mechanical modelling

The Zagros Collision Zone is a complex tectonic region formed as a consequence of the collision between Arabia and Eurasia after the subduction of the Neo-Tethys ocean. The NW-SE striking Zagros orogen consists of the following parallel tectonic units (from SW to NE): Zagros Fold and Thrust Belt (ZFTB), Sanandaj–Sirjan Metamorphic Zone (SSZ), and Urumieh–Dokhtar Magmatic Arc (UDMA). In this study, we perform a combined analysis of recent geophysical data, revealing pronounced differences in the crustal and lithospheric structure along the Zagros Mountains. The northwestern sector shows a fairly uniform crustal thickening across the broad symmetric orogen from the ZFTB to the UDMA. In contrast, in the central Zagros, the transition from a relatively narrow zone of high elevations and high-frequency relief in the ZFTB to a smoother surface topography of the SSZ and UDMA occurs with an abrupt increase in Moho depth below the SSZ. The last observation has recently been interpreted as a result of “relamination” process, where the felsic upper crust of the Arabian plate underthrust the mafic crust of the Iranian plate. We present geodynamic numerical models of crustal relamination during continental collision and compute static gravity field of the resulting structures. We show that oblique closure of the Neo-Tethys affects lateral variations in the style and extent of crustal relamination, which control the observed along-strike changes in crustal configuration and orogen altitude. In particular, a narrow and higher orogen (as in the central Zagros) develops in the experiments with a young and wide oceanic plate, whereas an old and narrow subducting plate tends to form a broad and lower topography (as in the northwestern Zagros). This is geometrically consistent with the progressive closure of the Neo-Tethys from NW to SE during the oblique continental collision between Arabia and Eurasia.

Mineral Chemistry, Trace Elements, Isotopic Analysis and Zircon U‐Pb Dating in the Hesar Pluton, Northern UDMA, Iran: Implications for Pre‐Collisional Magma Mixing

AbstractThe Hesar pluton in the northern Urumieh–Dokhtar magmatic arc hosts numerous mafic‐microgranular enclaves (MMEs). Whole rock geochemistry, mineral chemistry, zircon U‐Pb and Sr‐Nd isotopes were measured. It is suggested that the rocks are metaluminous (A/CNK = 1.32–1.45), subduction‐related I‐type calc‐alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures. The host rocks yielded an U‐Pb crystallization age of 37.3 ± 0.4 Ma for gabbro‐diorite. MMEs have relatively low SiO2 contents (52.9–56.6 wt%) and high Mg# (49.8–58.7), probably reflecting a mantle‐derived origin. Chondrite‐ and mantle‐normalized trace element patterns are characterized by LREE and LILE enrichment, HREE and HFSE depletion with slight negative Eu anomalies (Eu/Eu* = 0.86–1.03). The host rocks yield (87Sr/86Sr)i ratios of 0.70492–0.70510, positive εNd(t) values of +1.55–+2.06 and TDM2 of 707–736 Ma, which is consistent with the associated mafic microgranular enclaves ((87Sr/86Sr)i = 0.705014, εNd(t) = +1.75, TDM2 = 729 Ma). All data suggest magma‐mixing for enclave and host rock formation, showing a complete equilibration between mixed‐mafic and felsic magmas, followed by rapid diffusion. The TDM1(Nd) and TDM2(Nd) model ages and U‐Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantle‐derived magmas in a pre‐collisional setting of Arabian–Eurasian plates. Clinopyroxene composition indicates a crystallization temperature of ∼1000°C and a depth of ∼9 km.

Genesis of the Mahour Base Metal Deposit, Iran: Constraints from Fluid Inclusions and Sulfur Isotopes

The Mahour base metal deposit is located northeast of Badroud in the middle of the Urumieh–Dokhtar magmatic arc in the Isfahan province of Iran. The main host rocks to the ores are Eocene volcanic and volcaniclastic rocks. Hypogene ore minerals constituting the main ore body are galena, sphalerite, pyrite, and chalcopyrite. In addition to gangue quartz, a variety of supergene minerals comprising gypsum, goethite, hematite, “limonite”, malachite, azurite, covellite, and chalcocite are also present; gangue minerals are quartz, barite, calcite, sericite, and chlorite. Silicification, intermediate argillic, and propylitic are the main wall-rock alteration types. The presence of fluid inclusions with different vapor/liquid ratios in quartz and sphalerite could indicate a boiling process. The primary liquid-rich fluid inclusions suggest that the homogenization temperature was between 107 and 298 °C from fluids with salinities from 1.5 to 13.7 wt.% NaCl equiv. These data suggest that the ore-forming fluids were magmatic with a contribution from meteoric waters. The δ34S values of sulfides range from 1.9 to 3.4‰, those of barite range from 12.1 to 13.2‰, and those of gypsum range from 4.3 to 5.6‰. These data suggest that sulfur was mostly of magmatic origin with a minor contribution from sedimentary rocks. Our data suggest that the boiling of fluids formed an intermediate-sulfidation style of epithermal mineralization for the Mahour deposit.

Arc magmatism associated with continental convergence in the SE segment of the UDMA, Iran: Insights from zircon geochronology and Hf–Sr–Nd–Fe isotopes

Magmatic suites provide the keys to evaluate the growth and reworking of continental crust. Late Cretaceous to Pleistocene convergence in the Urumieh–Dokhtar magmatic arc (UDMA) of Iran produced continental-arc magmatism that traces the transition from subduction to collision. The extent and origin of some magmatic segments in the SE UDMA remain poorly understood. The Oligocene (31 to 25 Ma) Jiroft plutonic rocks here investigated encompass the compositional spectrum from gabbro to granodiorite. Zircon εHf(t) (−1.3 to +8.1), whole rock εNd(t) (+0.8 to +3) and δ56Fe (0.07‰ to 0.16‰) are intermediate between values of depleted mantle and arc-related magmas, and indicate low degrees of oxidization of metasomatized mantle. Modelling indicates that the trace element patterns of Jiroft parental melts can be closely replicated by 4% partial melting (i.e., F = 4%) of a mantle source which was metasomatized by 2% of sediment melt. The parental melt fits well with a model pattern of ∼97% batch melt (i.e., 98% DM + 2% sediment at F = 4%) and contaminated with ∼3% upper crustal components. The 31–25 Ma magmas of the SE UDMA formed before the main collision event (< 20 Ma) between Arabia and Iran, in conjunction with changing tectonic regime from extensional to compressional. Compilation of the Cenozoic magmatic front (i.e., UDMA) and rear-arc (NE Iran and Alborz–Azerbaijan) data reveals variable degrees of crustal cannibalization during the flare-up episodes. We find that individual segments of the UDMA experienced different geodynamics conditions, further documenting the diachronous collision and correspondingly non-uniform crustal thickening across the UDMA.

Cu isotope patterns of whole rocks in the Kerman porphyry copper belt, southeastern Urumieh Dokhtar magmatic arc, Iran

This study presents copper isotope compositions of mineralized whole-rock samples from the Kerman porphyry copper belt (KPCB) southeast of the Urumieh Dokhtar magmatic arc. Samples for this study were specifically collected from the Sar Cheshmeh, Meiduk, Iju, SarKuh, Darreh Zar, Bagh Khoshk, and Jebal Barez deposits and investigated to study the application of Cu isotopes to mineral exploration. While in the leached cap zone of the deposits, δ65Cu values range between −3.41 to 5.82 ‰ (avg. 0.42 ‰), in the supergene enriched zone of these deposits the relatively higher δ65Cu content ranges from 5.18 to 8.71 ‰ (avg. 7.17 ‰), and in the hypogene zone, the intermediate δ65Cu values range from 1.49 to 7.31 ‰ (avg: 4.36 ‰). Most measured δ65Cu values in these investigated porphyry copper deposit are positive, which indicates the presence of a Cu − enriched zone. In the enriched leached cap zones, the δ65Cu of the Darreh Zar and Sar Cheshmeh deposits are overall higher relative to the Iju, Meiduk, SarKuh, and Bagh Khoshk deposits, and these higher δ65Cu values are associated with the highest Cu grade and tonnage in the Sar Cheshmeh and Darreh Zar deposits. It is therefore plausible to conclude that the higher δ65Cu value in the leached areas are diagnostic of the high concentration of copper.These findings are complemented by the presence of Cu(II) carbonates, silicates, and Fe − oxides in each sample that has resulted in the enrichment of 65Cu, relative to the remnant sulfides with a wider copper isotope range. In addition, there is a general shift toward higher δ65Cu isotope values relative to the inferred precursor minerals. The overall apparent weathering and oxidative dissolution is likely to have generated isotopically heavier fluids and lighter residual minerals. The elevated δ65Cu of the bulk samples from porphyry Cu deposits in KPCB is consistent with a preferential loss of 63Cu into fluids during the segregation of aqueous fluid–melt. This is best explained by several pulses of hypogene magmatic fluid which led to repeated enrichment in 65Cu in the magmatic system. It is plausible to conclude that copper isotope values in these mineralized samples can be used as an effective exploration tool to identify buried porphyry Cu systems.

Gold metallogeny in Iran; implications for gold exploration and conceptual modelling

Significant progress in the classification, definition and understanding of the main Au deposit types could significantly aid improvements in Au exploration. Because of the wide occurrence of Au in the central part of the Tethyan Eurasian Metallogenic Belt, Iranian structures composed of more than 17 zones (arcs and blocks) are considered as having one of the largest Au reserves in the Middle East. Without attempts at understanding the tectono-magmatic evolution of Iran and the geodynamic settings of Au deposition, the establishment of a reliable predictive exploration model for Au-type deposits in Iran and other parts of the world will be unsuccessful. By considering a total of 33 Au deposits and prospects in Iran, a mineralization sequence is revealed from orogenic and volcanogenic massive sulfide (VMS), orogenic, Carlin-type, epithermal/porphyry Cu–Au/skarn, epithermal/iron oxide–copper–gold (IOCG). The trend of deposition gradually changes in the SW–NE axis to intrusion-related, epithermal and porphyry Cu–Au deposits at the Urumieh–Dokhtar Magmatic Arc (UDMA) and post-arc magmatism. VMS deposits occur adjacent to the NE Zagros Fold and Thrust Belt, at the Sanandaj–Sirjan Zone. The Zagros Orogeny and associated post-collisional magmatism at UDMA host many porphyry, epithermal and intrusion-related Au deposits, with a major magmatism peak in the Miocene. This work reveals that orogenic and Carlin-type Au mineralization are linked genetically. After each associated subduction for Palaeotethys (286–215 Ma) and Neotethys (210–68 Ma) in Iran, VMS and orogenic Au-deposits are formed in the border of the subduction (±obduction) zone. The porphyry, intrusion-related, epithermal and IOCG mineralization are emplaced in appropriate formations and structures during collision and post-collision processes.

Magnetite chemistry of the Sarkuh Porphyry Cu deposit, Urumieh–Dokhtar Magmatic Arc (UDMA), Iran: A record of deviation from the path sulfide mineralization in the porphyry copper systems

The Miocene Sarkuh porphyry Cu deposit is located in the southwestern part of Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. Compared with the neighboring giant Sarcheshmeh porphyry Cu deposit, this is a low-grade sub-economic porphyry Cu system (110 million tons @ 0.26 % Cu) characterized by an unusual abundance of magnetite. The present work tried to answer the question of whether or not there are differences in the hydrothermal system of Sarkuh, resulting in the lack of considerable mineralization. In this way, the mineral associations and EMPA data of magnetite were considered to distinguish the different stages of magnetite crystallization reflecting the magmatic-hydrothermal evolution of the Sarkuh deposit. They include (1) magmatic stage magnetite, including magnetite inclusions within primary silicate minerals (i.e., plagioclase and biotite), (2) pre-ore stage magnetite associated with potassic alteration assemblages, (3) main ore stage magnetite tightly associated with sulfide mineralization, and (4) late stage magnetite forming overgrowths on the sulfides. The results of EPMA analysis confirm that magnetite of these four stages differ in Mn, Fe, Ti, Mg, Al, Cr, and V concentrations. Higher V concentrations are found in the magmatic and pre-ore stages, whereas Al and Si reach the highest in the ore and late stages. Our data show that increasing fluid-rock interaction and changes in the oxygen fugacity, especially during the main ore stage extending to the late stage, are key factors controlling the trace element partitioning of magnetite. Most of ore stage magnetite formed at temperatures >500 °C and high temperatures prevailed during it. Magnetite crystallization after the main stage of sulfide mineralization accompanied by (partial) martitization indicate the increase of oxygen fugacity towards the late hydrothermal stage. This could explain why the ore and late stage magnetites show chemical similarities to those from sulfur-poor iron oxide copper‑gold (IOCG) deposits rather than porphyry deposits.

The coherence function and lithospheric elastic thickness of the Zagros fold and thrust belt

SUMMARY This study derives the spatial variation of the elastic thickness (Te) and its implications for understanding the structure, geodynamic and seismicity of the lithosphere for the Zagros fold and thrust belt region of the Arabia–Eurasia collision zone. Te is calculated using the coherence function in the fan wavelet domain based on recent terrestrial Bouguer gravity and topography data as input signals. Utilizing the load deconvolution method and Brent's method of 1-D minimization, the final Te for the survey region is estimated for each grid node of the studied area. To illustrate the mass distribution in the studied area, the subsurface loading fraction (F) is calculated simultaneously with Te in the inversion. The crust thickness and density from three different global crustal models are tested and the results obtained for these input models do not yield substantially different Te patterns. The final results are in accord with the global Te models as well as previous rheological, geodynamical and flexural studies, however, this study establishes much more detailed regional information. The calculations yield a mean value of Te of 61 km for the Zagros, with a mean estimated error of about 5 km. The high-Te values (&amp;gt;70 km) are observed in the southeast of the studied area (some parts of the Sanandaj–Sirjan zone, Urumieh–Dokhtar magmatic arc and most of the Central Iranian blocks); while over most of the northwest of the studied area, the value of Te is about 58 km. The Te results are consistent with the lithospheric structure of the study area and also support the idea of the crust–mantle decoupling. Further, there is a positive and negative correlation between the surface wave velocity and surface heat flow, respectively. The mean value estimated for the internal loading friction (F) of 0.4 means in most of the studied areas we may consider that the surface loading is dominant, or at least the ratio of the surface and subsurface loading can be assumed equal. Based on earthquake distribution in the period 1900–2020, seismicity is more likely to occur in areas with a relatively low value of Te.

Spatial distribution of porphyry copper deposits in Kerman Belt, Iran

The Kerman Cenozoic Magmatic Arc (KCMA, or Kerman Belt) in the southeastern part of the Urumieh–Dokhtar Magmatic Belt (UDMB) is considered as the most prospective geological province for porphyry copper deposits in Iran. Distance-based point pattern analysis methods, fractal analysis and Fry analysis are applied to porphyry copper deposits in order to gain insights into the geological controls over mineralization in the belt and suggest strategies for future exploration targeting. The results confirmed a significant structural control of strike-slip faults over the spatial distribution of deposits at the regional scale as previous structural studies defined it. The emplacement of porphyries in the Kerman Belt is likely controlled by extensional fault duplexes. The analyses further confirmed that there are two distinctly different sectors of porphyry copper mineralization in the Kerman Belt, namely, Sarduieh–Dahaj sector in the northwest and Jebal-e-Barez sector in the southeast as previous geological studies had demonstrated it. It is found that intrusive rock units, which form the permissive tracts for porphyry copper deposits in the Kerman Belt, are clustered, while the copper deposits within the permissive tracts generally show random distribution. It is recommended that predictive prospectivity modeling can be used to target mineralized intrusive bodies in the Kerman Belt; however direct detection techniques should be used to identify mineral deposits within the intrusive bodies.

Latest Oligocene adakitic rocks in western Iran: implications for early crustal thickening and tectonic evolution of the Iran Block

Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic evolution and geodynamics of orogenic belts. We investigated latest Oligocene (23.5–22.5 Ma) quartz monzonites and granites from the western segment of the Urumieh–Dokhtar magmatic belt in Iran, which are likely to have formed in response to the early stages of Arabia–Eurasia collision. The studied rocks have the geochemical characteristics of typical adakites, such as high SiO 2 (60.18–68.82 wt%) and Sr (499–793 ppm) contents, low Y (8.90–17.1 ppm) and Yb (0.88–1.58 ppm) contents, and high Sr/Y (26.1‒67.8) and (La/Yb) N (21.9‒32.9) ratios. They have variable K 2 O (3.88–5.09 wt%), MgO (0.44–2.74 wt%; Mg# = 33.7–52.5), Cr (4.27–40.59 ppm), Ni (4.28–35.68 ppm) and Th (9.56–59.59 ppm) contents, and relatively depleted Sr–Nd isotopic compositions [( 87 Sr/ 86 Sr) i = 0.70450–0.70516; ε Nd ( t ) = 2.1–2.7]. These characteristics indicate that the quartz monzonites were derived from the partial melting of delaminated lower crust that interacted with mantle peridotite with high MgO, Cr and Ni contents and depleted Sr–Nd isotopic compositions and suggest that the granites were formed by the fractional crystallization of quartz monzonitic magma. The geochemical features of the studied adakitic rocks could therefore have been affected by magmatic processes (e.g. fractional crystallization), which might be misleading in interpretations of their petrogenesis and related tectonic settings. The geochemical features of the studied rocks indicate that the crust of the western segment of the Urumieh–Dokhtar magmatic belt was thickened to c. 50 ± 4.43 km during the latest Oligocene ( c. 23.5 Ma) as a result of Arabia–Eurasia collision. Supplementary material: Whole rock geochemical and Sr–Nd isotopic compositions, and zircon U–Pb and Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.6188328

Petrogenesis and tectonic implications of Cenozoic mafic volcanic rocks in the Kahak area of central Urumieh–Dokhtar magmatic arc, Iran

• Mafic volcanic rocks in the Kahak area were erupted at ∼ 60–55 Ma and ∼ 21 Ma. • The Kahak basaltic rocks are divided into two groups of low and high Nb/Ta ratios. • The petrogenesis of the Kahak basaltic rocks involved slab dehydration and melting. • Slab rollback and mantle metasomatism occurred during the Paleocene–Eocene and Miocene . Cenozoic volcanic rocks are widely distributed in the Urumieh–Dokhtar magmatic arc (UDMA), Iran, but their petrogenesis and tectonic implications remain enigmatic. The volcanic rocks in the Kahak area of the central UDMA are mostly basalt and basaltic andesite. They show enrichment in light rare earth elements and large ion lithophile elements and depletion in the high-field-strength elements (Nb, Ta, and Ti), corroborating a subduction-related origin. U–Pb ages of zircon from these volcanic rocks demonstrate two episodes of magmatism during the Paleocene–Eocene (∼60–55 Ma) and Miocene (∼21.9–21.4 Ma). These rocks have 87 Sr/ 86 Sri values from 0.70485 to 0.70577, ɛ Nd (t) values from +2.0 to +5.0, and zircon Hf isotopes ε Hf (t) values from +8.3 to +10.2. These features with isotopic modeling support derivation from partial melting of an asthenospheric mantle wedge in an extensional intracontinental-arc basin. This mantle source was previously metasomatized by subducted slab components of the Neotethys Ocean. The mafic melts underwent fractional crystallization and minor crustal contamination during magma evolution. The Paleocene–Eocene basaltic rocks have subchondritic Nb/Ta ratios, indicating that the magma source was affected by fluids with low-Nb/Ta ratios, which were released during shallow metamorphism of a subducted slab. However, the Miocene basaltic rocks have unusual superchondritic Nb/Ta ratios, indicating slab melt involvement. Geochemical data and field relationship indicate that mafic volcanism in the Kahak area occurred in an extensional setting associated with the Paleogene shallowing of the northeastward-subducting Neotethyan oceanic lithosphere followed by Late Paleogene and Neogene slab rollback and eventual partial melting of a deeply subducted oceanic slab.

Two-Dimensional Attenuation and Velocity Tomography of Iran

Seismic bulletin data collected by the Iranian Seismological Center are used to image crust and mantle seismic attenuation, group velocity, and phase velocities for Lg, Pg, Sn, and Pn phases. This is possible because the peak amplitude time is picked, and amplitude measurements can be associated with the phase based on travel time plots. The group velocity is the apparent velocity of the maximum amplitude arrival and represents the combined effect of phase velocity and seismic scattering. Thus, it can be used in combination with the attenuation to identify where scattering attenuation is dominant. The Arabian–Iranian plate boundary separates low-velocity Zagros sediments from central Iran; however, in the mantle, it separates a high-velocity Arabian shield from central Iran. Scattering attenuation is low within the Arabian mantle and crust, and the Zagros sediments do not cause Lg or Pg attenuation. The Eocene Urumieh Dokhtar Magmatic Arc has high attenuation within both the crust and mantle, and while there is no partial melting in the crust, there may be some in the mantle. The northern Eocene Sistan Suture Zone shows particularly high attenuation that is accompanied by high scattering. It represents an incompletely closed ocean basin that has undergone intense alteration. The Alborz Mountains have high attenuation with some scattering.

Geochronology and petrogenesis of granitoids and associated mafic enclaves from Ghohroud in the Urumieh–Dokhtar Magmatic Arc (Iran): Evidence for magma mixing during the closure of the Neotethyan Ocean

The Ghohroud granitoids (GG), containing mafic microgranular enclaves (MMEs) are located in the central part of the Urumieh‐Dokhtar Magmatic Arc (UDMA) in central Iran. They are associated with the subduction‐related magmatism in the Alpine‐Himalayan orogenic belt. The GG are comprised of a variety of intermediate and felsic rocks, including tonalite, granodiorite, granite, diorite porphyry and monzodiorite. The MMEs are gabbroic diorite and tonalite in composition and characterized by a fine‐grained hypidiomorphic microgranular texture with occasional chilled margins. They show rounded, sharp or irregular contact with the host granitoids. The occurrences of quartz, K‐feldspar and corroded plagioclase indicate that MMEs are the products of mixing between mantle and crust‐derived magmas. New ages of zircon U–Pb dating reveal that the GG in the Kashan area emplaced at ca. 19–17 Ma (Burdigalian). All the samples of MMEs and granitoid host rocks in this study are metaluminous and calc‐alkaline with I‐type affinities. They are enriched in light rare earth elements (LREEs) and show slight negative Eu anomalies (Eu/Eu* = 0.36–0.95). These features in a combination with the relative depletion in Nb, Ta, Ti and P, indicate the granitoids and MMEs are closely associated with subduction‐related magmas at an active continental margin. The host rocks yield relatively homogeneous isotopic compositions of initial 87Sr/86Sr ratios ranging from 0.706036 to 0.707055, εNd(t) values varying from −2.25 to 0.8, and the Nd model ages (TDM) vary in a limited range of 0.70–0.96 Ga. The MMEs show similar initial 87Sr/86Sr ratios (0.706420–0.707366), εNd(t) values (−1.32 to −0.27), TDM (0.68–1.09 Ga) and Pb isotopic compositions with host granitoids, which imply they attained isotopic equilibration during magma mingling and mixing. In combination with the petrographic, chemical and isotopic results, we suggest that the origin of MMEs and their host rocks were related to the interaction between crust‐derived melts and mantle‐derived mafic magmas. The magma‐mixing event possibly occurred during the transition from subduction to collision in the UDMA along with the closure of the Neotethyan ocean.

Foraminiferal biozonation, biostratigraphy and trans-basinal correlation of the Oligo-Miocene Qom Formation, Iran (northeastern margin of the Tethyan Seaway)

During the Rupelian–Burdigalian (early Oligocene–early Miocene), the Qom Formation was deposited along the northeastern margin of the Tethyan Seaway in the Sanandaj–Sirjan, Urumieh–Dokhtar, and Central Iran basins. The biostratigraphic data from a total of 1152 thin sections from 10 outcrop sections along over 1000 km of the Tethyan Seaway margin are presented. A larger benthic foraminiferal (LBF) biozonation, consisting of five biozones, is proposed for dating the Rupelian–Burdigalian Qom Formation. It is correlated with global planktonic zones, LBF zones, southeastern Asian “Letter Stages”, shallow benthic foraminiferal zones (SB-zones) of southern European basins, and newly revised zones of the Asmari Formation in southwestern Iran. This biozonation subdivides the Rupelian stage into “early Rupelian” and “late Rupelian”, based on the first appearances of lepidocyclinids in the latter one. The early Rupelian strata are characterized by the presence of Nummulites without lepidocyclinids which are reported merely from southwestern and southern Kashan, where the thickest Rupelian deposits of the Qom Formation are recorded. The basal layers of the Qom Formation in southeasternmost outcrops (northwestern Jazmurian Lake) are late Rupelian in age based on the co-occurrence of lepidocyclinids and Nummulites spp. By comparison of the well-documented transgression of the Tethyan Seaway over the Iranian plate (from southeast to northwest) and the limitation of all reported early Rupelian strata of the Qom Formation to southwestern and southern Kashan, the following scenarios can be supposed: 1) the oldest deposits could be deposited in southeastern Iran, but they have not been reported, yet; 2) during early Rupelian, there was a transgression from the Zagros Basin to southwestern and southern Kashan areas, then the transgression progressed both northwestward and southeastward.

Juvenile crust and mantle sources for the Nasrand intrusive rocks, the central Urumieh–Dokhtar magmatic arc, Iran: Insights from elemental and isotopic geochemistry

The Oligocene Nasrand intrusive rocks (NIRs), located in the central part of the Urumieh–Dokhtar magmatic arc, are mainly composed of granite and subordinate diorite and gabbro. These rocks are characterized by the enrichment of light rare earth elements (LREEs), Nb‐Ta negative anomalies, and high LILE/HFSE, suggesting a subduction‐related origin. The felsic rocks with granite compositions have high SiO2 content (69.77–77.88 wt.%), low Mg# (0.02–0.43), low Nb/Ta, and Zr/Hf (Avg: 12.53, and 33.08, respectively). The initial 87Sr/86Sr ratio and εNd(t) values in felsic rocks range from 0.70577 to 0.70576 and 0.4 to −0.3, respectively. These data suggest that these felsic rocks originated from juvenile crust by heat rising from basaltic magmas in an orogenic setting. The mafic‐intermediate rocks and dikes are gabbro, gabbroic diorite, and monzodiorite, with low SiO2 content (48.08–56.11 wt.%) and high Mg# (0.37–0.68), with average ratios of Nb/Ta and Zr/Hf are 27.88 and 39.84, respectively. The initial 87Sr/86Sr ratio and εNd(t) values for mafic‐intermediate rocks and dikes are 0.70583 to 0.70476 and −0.1 to +2.6, respectively. These characteristics indicate magma from a mantle source that had undergone minor mixing with juvenile crust. It seems mantle‐derived juvenile magma underplating played an important role in the crustal growth in the Urumieh–Dokhtar magmatic belt during the Ediacaran to Early Cambrian, relative to other time frames.

Comparative analysis of exploration potential within the Urumieh Dokhtar Magmatic Arc, Iran, with a detailed example from mineral chemistry of the Marshenan intrusion

The Early Miocene Marshenan intrusion, in the central part of the Urumieh-Dokhtar magmatic arc (UDMA), central Iran, includes granodiorite-granite and diorite; it is a classic example of a CuAu barren intrusive system. Zircon U-Pb dating indicates that the diorite display an age of 20.32 ± 0.36 Ma, coeval with granodiorite rocks (20.5 ± 0.8 Ma). These rocks are composed of feldspar, quartz, amphibole, biotite, titanite, and magnetite. In the granodiorites, the plagioclase composition ranges from oligoclase to bytownite, the amphiboles are magnesio-hornblende and biotites is Mg rich, related to calc-alkaline orogenic suites in the region. Plagioclase phenocrysts exhibits oscillatory zoning and marked changes in the abundance of elements, such as Ba, Sr, and Fe, suggesting magma mixing/mingling may have had a role in generating these parental magmas. The average calculated P–T conditions of the granodiorite and diorite rocks are about 730 °C and 2.1 kbar and 733 °C and 1.7 kbar, respectively, corresponding to near solidus conditions equal to emplacement depths of ~7 to 8 km. Magmatic H2O contents and ƒO2 calculated from crystallized amphiboles indicate that the Marshenan granodiorite had initial magmatic H2O contents ~5 wt% and relatively high ƒO2 (ΔNNO; ave. 1.3) and the diorite had initial magmatic H2O contents ~4.7 wt% and relatively high ƒO2 (ΔNNO; ave. 1.5), both consistent with the presence of phases, such as hornblende, biotite, magnetite, and titanite. In comparison with other intrusions in the UDMA, the Marshenan intrusion formed via the same physico-chemical mechanisms like other barren intrusions, whereas the fertile intrusions exhibit slightly higher temperatures, pressures, ƒO2, and H2O values than the barren intrusions. These compiled data suggest that, in spite of the high magmatic H2O and ƒO2 contents, the Marshenan and other barren intrusions in the UDMA will not produce porphyry Cu mineralization, unlike the giant Kerman deposit, probably due to magma source, magmatic evolution processes, timing of volatile exsolution, pre-existing crustal-scale fractures, coeval volcanism, and extended duration of volatile saturated crystallization to subsolidus conditions.

Biotite compositions and geochemistry of porphyry-related systems from the central Urumieh Dokhtar Magmatic Belt, western Yazd, Iran: Insights into mineralization potential

Commonly biotite occurs as a minor rock-forming mineral in a wide range of felsic to intermediate intrusive rocks. It can record the physicochemical conditions of the parent magma due to its complex crystal structure that allows multiple site substitutions of a wide range of elements. Geochemical studies of whole rocks and biotite (using EPMA and LA-ICP-MS methods) with petrographic analysis of biotite provide distinction between barren and fertile granitoids in western Yazd. Fertile suites are characterized by Si- and Mg-rich (3.47–4.35, ave. 3.75 a.p.f.u.) and total REE-poor biotite. In contrast, Fe (2.66–3.15, ave. 3.08 a.p.f.u.), Al, Ti, and REEs (in particular HREE+Y) increase in barren rocks. On the basis of biotite geobarometry, the fertile rocks (Darezereshk Porphyry Copper Deposit (PCD)) solidified at low pressure (ca. 0.6 kb, i.e., subvolcanic); in contrast, the barren rocks (Galvic and Shirkouh granodiorites) crystallized at higher pressures (1.1 to 3.6 kb). The temperature of the fertile granitoids is inferred to be about 750 °C, whereas T's of 625–675 °C for barren granitoids. The fertile suites have redox characteristic near the Ni-NiO buffer, whereas the barren suites are more reduced, near the quartz-fayalite-magnetite (QFM) buffer. Therefore, biotite major-element compositions, fertile magma bodies are emplaced at higher temperature and redox to lower pressures (subvolcanically) than the barren intrusive bodies. The whole-rock geochemical signatures show that both barren and fertile suites are represented by peraluminous to metaluminous granite to diorite that have calc-alkaline characteristics with an I-type volcanic arc (VAG) tectonic setting. However, fertile suites originated from the mantle-crust mixed magma exhibiting calc-alkaline affinity, whereas the barren suites are derived predominantly from recycling of continental crust.

Late cenozoic exhumation of the Nodoushan plutonic complex constrained by low-temperature thermochronology: evidence for Arabia–Eurasia collision in the southeastern Iranian Plateau

ABSTRACT The Nodoushan plutonic complex in the central part of the Urumieh–Dokhtar Magmatic Belt developed mainly in the Cenozoic in response to the final stages of subduction-related magmatism that preceded the post-Oligocene collision between the Arabian and Eurasian Plates. Despite numerous recent studies examining the deformation and related exhumation history of the Arabia–Eurasia collision zone, the exhumation history of the Urumieh–Dokhtar Magmatic Belt (making up the majority of the Iranian Plateau) is largely unknown. In this work, apatite and zircon (U-Th)/He thermochronometry and thermal modelling analysis are applied to the (mainly) granitoid intrusive bodies in the Nodushan Plutonic complex in order to unravel the exhumation history of this region in the context of collisional tectonics. The results document two main phases of exhumation in the early Miocene (~ 22–20 Ma) and middle Miocene (~ 11 Ma). The distribution of (U-Th)/He ages suggests that these deformation episodes are related to the collision between the Arabian and Eurasian Plates. The ‘soft’ initial stages of Arabia–Eurasia collision in the Nodoushan plutonic complex occurred when the stretched Arabian passive margin reached the subduction zone in the early Miocene. Subsequently, the final ‘hard’ collision with the harder continental margin occurred in the middle Miocene. The results of this work mark the first thermochronometric data related to SE Iranian Plateau evolution and identify exhumation that initiated in the early Miocene and developed regionally during middle Miocene times.

Origin and Development of Skarn-Forming Fluids from the Band-e-Narges Skarn Iron Ore- Central Iran

The Band-e-Narges magnetite deposit is located in the central part of Urumieh–Dokhtar Magmatic Arc. Wide I-type calk-alkaline and alkalin magmatic activity in the Koh-e Latif region has been reported due to Eocene intrusive processes in UDMA. Five stages of paragenesis have been observed in the mineralization in this area: prograde stage, retrograde stage, sulfide- quartz stage, carbonate stage and Oxidation stage.The result of all δ34S values of pyrite and anhydrite + pyrite shows values are positive with a magmatic sulfur origin in these deposits. fluid inclusions have been observed according to the petrographic and microtermometric inclusions within garnet, quartz, and calcite minerals at various stages. According to high temperature and middle salinity of fluid inclusions in prograde skarn-stage, the fluid inclusions shows reaction with the calcareous wall rock and fluid inclusions were trapped at pressures of 400 to 500 bars, corresponding to depths of 1.5 to 2 km .Fluid inclusions in quartz have moderate temperatures and low salinity indicating quartz-sulfide stage and late retrograde stage. fluid inclusions with moderate homogenization temperature (300 to 350 oC ) suggest that reboiling coccurred under hydrostatic pressure of 150 to 250 bars, equivalent to a depth of 1 to 1.5 km in the late retrograde skarn and quartz-sulfide stages. Fluid inclusions in calcite have moderate temperatures and low to high salinities . The geology, mineralogy, geochemistry, salinities and homogenization-temperatures from the fluid inclusions populations at the Band-e-Narges iron deposit are follows a model of boiling as a result of decrease pressure, mixing and cooling.

Chemistry of rock-forming silicate and sulfide minerals in the granitoids and volcanic rocks of the Zefreh porphyry Cu–Mo deposit, central Iran: Implications for crystallization, alteration, and mineralization potential

Abstract Cu–Mo mineralization and associated hydrothermal alteration zones in the Zefreh porphyry Cu–Mo deposit are a result of the emplacement of the early Miocene granodioritic-to-granitic porphyritic intrusions into the Eocene volcanic rocks (dacites, pyroclastic rocks, and andesitic lavas) during active subduction along the Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran. The compositions of rock-forming minerals, such as plagioclase, amphibole, and biotite, in the granitoids of the Zefreh magmatic suite are used to determine temperature and oxygen fugacity in the magma during crystallization and emplacement. Plagioclase is locally unaltered and ranges widely in composition with reverse, normal, and oscillatory zoning, but there is no evidence of excess aluminum. Primary calcic amphiboles in the granodiorite porphyry are mainly magnesio-hornblende with high Mg#’s. The crystallization temperature of the granodiorite is in the range of 765–867 °C (average 821 ± 28 °C for amphibole–plagioclase geothermometer) and 706–861 °C (average 808 ± 35 °C for amphibole alone). Whereas, the zircon saturation temperature for the Zefreh granodiorite is lower and ranges from 724° to 733 °C (average 729 ± 4 °C). Biotites in the least-altered granodiorite and in the potassic alteration are Mg-rich and Ti-poor, and mainly fall within the fields of phlogopite and re-equilibrated primary biotite, because of their low TiO2 contents (2.7–4.5 wt%, average 3.5 wt%). Copper and molybdenum in the Zefreh porphyry deposit appear to have been transported by Cl-rich hydrothermal fluids as chloride complexes, based on the calculated halogen fugacity ratios of the fluid in equilibrium with hydrothermal biotite that range from 5.0 to 5.4 for log (ƒH2O)/(ƒHF), 4.3 to 4.8 for log (ƒH2O)/(ƒHCl), and –2.0 to –1.4 for log (ƒHF)/(ƒHCl). The calculated fugacity ratios indicate that the biotites equilibrated with hydrothermal fluids that varied in composition, including oxygen, sulfur, and halogen fugacities. The intercept values for biotites from the Zefreh porphyry Cu–Mo deposit [IV(F) = 1.9 to 2.2 and IV(Cl) = –4.8 to –4.3] correspond to those from other well-known porphyry Cu–(Mo–Au) deposits worldwide [IV(F) = 1.5 to 2.8 and IV(Cl) = –5.0 to –3.5]. On the other hand, hydrothermal chlorite and epidote in the propylitically altered granodiorite of the Zefreh deposit are more Fe-rich and Mn-poor than those in some mineralized porphyry systems. The calculated temperatures of chlorite formation by the geothermometer of Cathelineau (1988) are all similar (300–330 °C), suggesting the potassically altered granodiorite was also affected by later, cooler hydrothermal fluids associated with the distal propylitic alteration zone. Disseminated chalcopyrite in the matrix of the potassically and propylitically altered granodiorite hosts as much as 1.3 wt% Zn and 0.1 wt% As. Based on whole-rock and mineral compositions, we conclude that the Zefreh magmatic system is similar in many regards to subduction-related ore systems, but it is unlikely to host a major porphyry Cu–Mo deposit.