Urumieh-Dokhtar Magmatic Belt Research Articles

Petrogenesis of the late Miocene Chenar volcanism in the southeast Urumieh-Dokhtar magmatic belt, Kerman, Iran: evidence from geochemical, U-Pb geochronologic, and Hf isotopic constraints

The Chenar volcanic cone intruded the southeastern part of the Dehaj-Sarduiyeh volcano-sedimentary belt, in the southeast Urumieh-Dokhtar magmatic arc in Iran. The adakitic rocks, with porphyritic texture, mainly consist of rhyodacites and dacites,commonly comprised of phenocrysts of plagioclase, hornblende and biotite, with rare K-feldspar in a groundmass composed of plagioclase, K-feldspar and quartz. They yielded U-Pb zircon ages of 5.52±0.099Ma, 5.46±0.12Ma, and 6.44±0.12Ma, and radiogenic ɛHf(t) values ranging from +3.1 to +12.7. The whole-rock geochemical analysis of these rocks reveals transitional calc-alkaline to shoshonitic characteristics. The geochemical characteristics of the study rocks, particularly their high Sr/Y (⁓51.6-136.8) at low Y (⁓4.43–16.2ppm) and high La/Yb (⁓28.4–118.4ppm) at low Yb (⁓0.2–1.3ppm), are coherent with a high silica adakitic signature. The whole-rock positive Eu/Eu* anomaly and zircon Ce/Ce* anomaly reflect the effects of an oxidized magmatic signature where the rocks of the study area originated from a mantle source. The high silica adakite geochemical characteristics of the Chenar volcanic cone support formation by partial melting of the modified mantle under the influence of metasomatized subducted oceanic slab in a post-collisional environment.

A comparative assessment of the effects of sodium and magnesium sulfates on the physico-mechanical characteristics of Abasabad Travertine, Mahallat, Urumieh-Dokhtar Magmatic Belt, Iran

A comparative assessment of the effects of sodium and magnesium sulfates on the physico-mechanical characteristics of Abasabad Travertine, Mahallat, Urumieh-Dokhtar Magmatic Belt, Iran

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.

A comparative analysis of multi-index overlay and fuzzy ordered weighted averaging methods for porphyry Cu prospectivity mapping using remote sensing data: the case study of Chahargonbad area, SE of Iran

One of the specific features of porphyry copper (Cu) mineralization is the distinct occurrence of hydrothermal alteration zones, which can be mapped by processing various satellite images. Among free multispectral images, Landsat 8 OLI and ASTER data are known to be efficient in mapping different geological features, such as alteration zones and tectonic lineaments. This study aims to show the potential of these data types in mapping porphyry Cu mineralization by proposing a framework for employing and integrating different image processing methods. These methods include principal component analysis (PCA), spectral angle mapper (SAM), and matched filtering (MF) employed on these satellite images to map target al.teration zones. Moreover, PCA and directional filtering are applied to the ASTER dataset to enhance and map structural features. The results are evaluated and then combined to provide a potential map of Cu mineralization in the Chahargonbad area, located within the Urumieh-Dokhtar magmatic belt (UDMB) in Kerman province, Iran. The prediction-area plot and normalized density, which are data-driven methods, are used to assign the relative weight of each layer and evaluate them. Finally, using the calculated weights, data-driven multi-index overlay (DMIO) and fuzzy ordered weighted averaging (FOWA) methods are applied to combine the evidential layers. The potential mineralization maps created by the DMIO and FOWA provide a prediction rate of 80% and 82%, respectively. Furthermore, the accuracy of the integrated maps is investigated using the area under the curve (AUC) of the receiver operating characteristic (ROC) curves. The AUC scores obtained from the ROC curves of DMIO and FOWA methods are 0.85 and 0.88, respectively, representing powerful positive spatial relationships with mineralization areas. Based on the results, the proposed framework can be applied to provide a potential map of porphyry Cu mineralization, particularly in arid regions, with reasonable accuracy.

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

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.

Geochronology, geochemistry and petrology of the oligocene magmatism in SE segment of the UDMB, Iran

Despite diverse geochronological-geochemical studies on Cenozoic igneous rocks from the SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran, the nature of the Oligocene magmatic rocks from the farthermost end of the SE segment- where it is linked to the Makran magmatic belt- has been ignored due to the difficulty of access. In this study, we focus on syn-collisional mafic to felsic igneous rocks of calc-alkaline and high-K calc-alkaline affinities from the SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB) near Nagisun, south of Bam. The Nagisun rocks have low Sr/Y and La(n)/Yb(n), similar to igneous rocks from typical arcs. Zircon UPb ages show comparable ages for plutonic (~ 34–25 Ma) and volcanic (~34–27 Ma) rocks. The εHf(t) values for zircons from plutonic rocks range from −0.3 to +12.8, whereas the εHf(t) values for the volcanic rocks vary from −2.6 to +13. Modelling of trace elements compositions using Nagisan basaltic samples indicate that an 87:2:11 mixture of the depleted MORB mantle, subducting (trench)-sediments and altered oceanic crust with 5% aggregated fractional melting closely matches the trace-element abundances of the Nagisun basaltic rocks. Indeed, the modelling of Sr and Nd isotopic data emphasizes that the Nagisun magmatic rocks could be products of bulk mixing between a depleted MORB mantle and/or a mixed, fertilized mantle with the Cadomian lower and upper continental crust. Furthermore, our compiled data display that the magmatism in the SE segment of the UDMB changed through time from normal calc-alkaline magmatism to adakitic magmatism at ~20 Ma, after the collision with Arabia began ca 27 Ma.

The Chah-Mesi epithermal Cu-Pb-Zn-(Ag-Au) deposit and its link to the Meiduk porphyry copper deposit, SE Iran: Evidence from sulfosalt chemistry and fluid inclusions

The polymetallic Chah-Mesi epithermal vein deposit is located about 2.5 km south of the Meiduk porphyry Cu-(Mo-Au) deposit in the Kerman Cenozoic Magmatic Arc (Kerman Belt), representing the southeastern sector of the Urumieh-Dokhtar Magmatic Belt in Iran. The veins are N-S to NNE-SSW oriented and hosted in volcanic rocks of basaltic, andesitic to dacitic composition and pyroclastics, which were affected by intense local silicification and sericitization in proximity to mineralized veins. Propylitic, argillic, as well as potassic alteration show a more regional distribution; the latter only observed closer to the Meiduk deposit. Mineralization occurs in various types of veins (massive, banded, crustiform) and to minor extent in replacement and breccia bodies. It encompasses several stages: An early higher-sulfidation stage, characterized by pyrite, chalcopyrite, enargite/luzonite and bornite, is followed by the main intermediate-sulfidation state assemblage with pyrite, chalcopyrite, tetrahedrite group minerals and sphalerite. The late Pb-Zn rich stage with sphalerite, galena, chalcopyrite and pyrite overprints the earlier associations. Gold and silver of up to 7 g/t and 150 g/t, respectively, are associated with the main and late stages of mineralization. The main carriers of these precious metals are Ag-rich gold (electrum) and tetrahedrite; other Ag-bearing sulfosalts like pearceite are rare. The chemical composition of tetrahedrite group minerals ranges from tennantite-(Fe) to tetrahedrite-(Fe) and tetrahedrite-(Zn) exhibiting a positive correlation between Sb and Ag contents. The tetrahedrite group minerals show complex zoning and display an increase of Sb away from the Meiduk deposit. Primary fluid inclusions in sphalerite and quartz from the banded and crustiform veins are low saline aqueous H2O-salt inclusions with only traces of CO2. Homogenization temperatures of two-phase LV inclusions (Th LV→L) have an average of 210 °C in sphalerite and 260 °C in quartz. Salinity values range from 1.2 to 9.9 and 2.1 to 9.2 mass% NaCl equivalent in sphalerite and quartz, respectively with an average of c. 6 mass% NaCl equiv. Low CO2 concentrations in the vapor phase detected by Raman spectroscopy together with previously published stable isotope data indicate fluids of magmatic origin as the main fluid source that were mixed with meteoric water. Mineralization is linked to ascending hydrothermal fluids which evolved from high- to intermediate-sulfidation state due to cooling, dilution with meteoric water and progressing fluid-wallrock interaction. Similar low salinity, but higher CO2-bearing fluids were previously reported from the nearby Meiduk porphyry deposit. Conclusively, Chah-Mesi is classified as an intermediate-sulfidation epithermal deposit that developed in the peripheral parts of the Meiduk porphyry system.

Temporal changes in subduction- to collision-related magmatism in the Neotethyan orogen: The Southeast Iran example

Continental-arc igneous rock compositions change in response to the transition from subduction to collision and these changes can reveal how the crust, lithosphere and magma sources evolved. Neotethys-related Late Cretaceous to Pleistocene subduction- and collision-related magmatic rocks from the ~350 km long southeast Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran provide an excellent natural laboratory to better understand these changes. These igneous rocks are well-exposed and moderately eroded to reveal a nearly complete record since subduction initiation at ~95 Ma. We analyzed new samples for major and trace elements (83 samples), SrNd isotopic compositions (47 samples), and UPb zircon ages (26 samples) and compiled geochemical and geochronological data on the southeast segment of the UDMB. The geochronological data reveal two magmatic pulses at ~80–70 Ma and ~50–0 Ma. Important changes in magmatic compositions reflect initial collision with Arabia at ~32 Ma, changing from normal calc-alkaline to increasingly adakitic immediately after collision began. Five stages can be identified: 1) normal continental-arc magmatism during the Late Cretaceous; 2) arc quiescence in Paleocene and Early Eocene time; 3) Middle-Late Eocene extensional arc magmatism related to slab rollback; 4) early collision and crustal thickening during the Early Oligocene; and 5) slab breakoff, asthenospheric upwelling, and associated adakitic magmatism from Middle Miocene onward. Temporal changes in UDMB magmas reflect the response of the overriding plate to changes in the geometry of the subducting Neotethyan lithosphere and to collision between Arabia and Iran. Crustal thickening and arc narrowing during Miocene to Pleistocene post-collisional magmatism caused adakitic magmatism and associated Cu mineralization. Zircon OHf and apatite O isotopes as well as bulk-rock Nd isotopes of Cu-bearing adakitic rocks are similar to other barren rocks, but nearly all fertile rocks have higher Hf/Y, Eu/Eu⁎(n) in zircon and higher Sr/Y, V/Y, Eu/Eu⁎(n) in apatite than barren rocks.

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.

Geochemistry and petrogenesis of alkaline rear-arc magmatism in NW Iran

High Na- to K- alkaline magmatism is common in the rear-arc region of the Cenozoic Urumieh-Dokhtar Magmatic Belt of Iran, but their geochemical signatures, as well as their formation mechanisms, have been poorly studied thus far. In the Kleybar area of NW Iran, Middle Eocene magmatic activity comprises silica-undersaturated to -saturated gabbros, monzogabbros, monzosyenites to nepheline-monzosyenites, and nepheline syenite as well as tephritic to trachy-basaltic and trachy-andesitic dikes. New 40Ar39Ar results show a restricted age range (39.2–43.6 Ma) for the intrusive rocks (43.16 ± 0.43 and 43.34 ± 0.43 Ma for gabbros, 43.56 ± 0.44 for monzogabbros, 39.22 ± 0.48 and 42.09 ± 0.42 Ma for nepheline syenites, 42.17 ± 0.42 Ma for nepheline-monzosyenites), whereas a cross-cutting trachy-andesitic dike yielded an 40Ar39Ar age of 41.78 ± 0.42 Ma. The Kleybar rocks are enriched in alkalis (K2O and Na2O) with variable K2O/Na2O ratios (0.14 to 2.93), light rare earth elements and large ion lithophile elements such as Th, Rb, K, U and Pb. High field strength elements such as NbTa are depleted in these rocks.The isotopic compositions of the different rock types are quite variable: gabbros and monzogabbros have 87Sr/86Sr(t) = 0.70419–0.70436, εNd(t) = +3.1 to +3.8 and εHf(t) = + 7.8 to +10.1; nepheline monzosyenites and nepheline syenites have 87Sr/86Sr(t) = 0.70359–0.70566 (except a nepheline syenite with a ratio of 0.74833 and very high Rb/Sr), εNd(t) = +1.5 to +4.2 and εHf(t) = +4.6 to +8.8; and trachy-basaltic to trachy-andesitic to tephritic dikes have 87Sr/86Sr(t) = 0.70437–0.70469, εNd(t) = +2.8 to +4.2 and εHf(t) = +8.3 to +10. In the thorogenic-Pb isotope diagram, the Kleyber igneous rocks define an array above the Northern Hemisphere Reference Line (NHRL), with ∆8/4 (deviation from the NHRL) of ~40–60. These samples also plot above the NHRL in uranogenic Pb space (∆7/4–5-10). The positive ∆8/4 Pb and ∆7/4 Pb may reflect the involvement of subducted terrigenous sediments in their mantle source during the subduction of the Neotethyan oceanic lithosphere. Two nepheline syenite samples have significantly higher thorogenic and uranogenic Pb isotopic compositions, that may reflect assimilation of surrounding clay-rich sedimentary rocks.Modelling of trace elements compositions using less fractionated Kleybar trachybasalt and fine-grained monzogabbro samples indicate that a 96:4 mixture of the depleted mantle and subducting (trench)-sediment melts with 6% aggregated fractional melting closely matches the trace-element abundances of the Kleybar trachybasalt and monzogabbro. Together with previous studies on high-K volcanic rocks from NW Iran, our results indicate that Neotethyan slab retreat and related extension of the Iranian continental lithosphere in the rear-arc region of the Urumieh-Dokhtar Magmatic Belt generated alkali-rich magmatic rocks throughout the NW Iran rear-arc during Middle-Late Eocene.

Geology and petrography of the volcanic rocks in the Yakhab area, central Iran

Eocene to Quaternary volcanic and plutonic rocks are exposed in eastern of Kashan in the Urumieh-Dokhtar magmatic belt that located in the Central Iran structural zone. These volcanic rocks have compositions ranging from basaltic andesites, andesites, rhyolite, dacite, tuff to granidiorites. A total of 100 rock samples were taken and based on petrographic and geochemical studies with field observations volcanic rocks in the Yakhab area were evaluated. Geochemical studies show these rocks are a slightly meta-aluminous to per-aluminous. The rocks have SiO 2 contents ranging between 42% and 75%. The geochemical characteristics of the volcanic rocks show that magma was derived from an enriched lithospheric source and indicated magma derived from lower crust or upper mantle lithosphere.

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.

Saveh-Nain-Jiroft Magmatic Belt replaces Urumieh-Dokhtar Magmatic Belt: Investigation of genetic relationship between porphyry copper deposits and adakitic and non-adakitic granitoids

بر اساس شواهد نبود ماگماتیسم بین ساوه تا حدود تکاب و نبود آنومالی مغناطیس هوایی، در این پژوهش نام کمربند ماگمایی ارومیه- دختر به کمربند ماگمایی ساوه- نایین- جیرفت تغییر‌یافت. ماگماتیسم ارومیه تا تکاب، ادامه کمربند ماگمایی البرز غربی است. بر اساس ویژگی­های ماگماتیسم و کانی­سازی، SNJMB را می­ توان به دو کمربند مجزا تقسیم کرد: 1) کمربند ماگمایی ساوه- نایین که اغلب شامل گرانیتوئیدهای میوسن سری مگنتیت نوع I عقیم غیرآداکیتی است. بر اساس نسبت (La/Yb)n (اغلب زیر 10)، این گرانیتوئیدها از عمق 60 تا 80 کیلومتری و گوه گوشته ­ای منشأ گرفته و بر اساس مقدار Eu/Eu* (بین 43/0 تا 1 با میانگین 65/0) شرایط اکسایش در محل ذوب‌بخشی کم بوده است. نسبت 87Sr/86Sr اولیه نشان می ­دهد آلودگی زیادی با پوسته قاره­ای داشته ­اند. ضخامت پوسته در SNMB کمتر از 48 کیلومتر است، 2) کمربند ماگمایی نایین- جیرفت که میزبان کانسارهای مس پورفیری است. گرانیتوئیدهای میوسن این کمربند سری مگنتیت و نوع I بارور آداکیتی هستند. بر اساس نسبت (La/Yb)n (بین 15 تا 38)، این گرانیتوئیدها از عمق پایداری گارنت (بیش از 90 کیلومتری) و ذوب‌بخشی اسلب منشأ گرفته و بر اساس Eu/Eu* (بین 82/0 تا 3/1 با میانگین 2/1) شرایط اکسیدان در محل منشأ برقرار بوده است. نسبت 87Sr/86Sr اولیه نشان می­ دهد آلودگی کمی با پوسته قاره­ ای داشته ­اند. ضخامت پوسته در NJMB بین 48 تا بیش از 52 کیلومتر است. سنگ­ های آتشفشانی آداکیتی ایران اغلب سن میوسن-پلیوسن دارند و در شمال‌غربی ایران، SNJMB و کمربند ماگمایی قوچان- سبزوار رخنمون دارند. ویژگی ژئوشیمیایی‌– ایزوتوپی آنها شبیه گرانیتوئیدهای بارور آداکیتی NJMB است؛ اما این واحدها هیچ‌گونه کانی ­سازی ندارند. ویژگی ­های اسلب اقیانوسی نئوتتیس در طول SNJMB کاملا متفاوت بوده که به ماگماتیسم و کانی ­سازی مختلف منجر‌شده است. گرادیان حرارتی، عمق دهیدراسیون، مقدار آب، سنگ منشأ و درصد ذوب‌بخشی در طول کمربند، نوع ماگماتیسم و تشکیل کانی ­سازی را کنترل‌کرده است.

Petrography, mineralogy, litho-geochemistry and fluid inclusion gold-copper deposit Gheshlaghe Mil, northwest of Saveh

The Gheshlaghe mil deposit is located in the Urumieh-Dokhtar magmatic belt. Vein- type mineralization is concordance within the rhyodacitic and rhyolite meta-tuff with Eocene age. Alteration zones of sericite, silica, argillic and iron oxides are observed in the investigated area. Primary sulfide minerals of pyrite, fine-grained chalcopyrite and Oxidized specularite and Secondary minerals goethite, limonite, malachite and quartz in Microscopic and field studies have been identified. Based on X-ray diffraction analysis studies minerals such as chlorite, illite, kaolinite, hematite, quartz, mica group and calcite have been observed in the bearing gold veins. According litho-geochemical studies, the gold element has a positive correlation with iron, molybdenum, nickel and lead. A number of 157 fluid inclusion studies in the Gheshlaghe Mil ore mineralizaion area has been showed mineralization temperature of 99 to 299 ° C, rate of salinity ore deposit 1.81 and 12.30 equivalent to the Nacl weight percent. Using Raman laser studies (13 points), the presence of gaseous phases (CO2, N2, H2O) in the fluid inclusions have been demonstrated. Regarding to studies have been done in this area, the Gheshlaghe Mil ore mineralization can to know to a vein type- hydrothermal bearing gold-copper ore deposit.

Cenozoic temporal variation of crustal thickness in the Urumieh-Dokhtar and Alborz magmatic belts, Iran

We present regional variations of whole-rock Sr/Y and (La/Yb)N ratios of magmatic rocks along the Cenozoic Urumieh-Dokhtar and Alborz magmatic belts, Iran. Both the magmatic belts are located at the north of the main Zagros Neo-Tethyan suture. The Urumieh-Dokhtar magmatic belt (UDMB), which trends NW-SE for 1000 km across Iran, was characterized by the intensive volcanism and plutonism, and defined the magmatic front (MF) of the Zagros orogenic belt. The Alborz magmatic belt (AMB) is situated to the north, and characterized by less intense magmatic activity. The Alborz magmatic belt was formed behind it in the rear-arc (RA) domain. A striking feature of the both magmatic belts is the transition from normal calc-alkaline arc magmatism during the Eocene–Oligocene to adakite-like calc-alkaline magmatism during the Middle to Late Miocene–Pliocene. The late-Cenozoic magmatism of the UDMB and AMB shows higher Sr/Y and (La/Yb)N. However, it should be noted that crustal thickening event is intensive in the UDMB than AMB during Late Cenozoic. Using the composition of the Lale-Zar zircons from the SE UDMB we determined the oxygen fugacity (fO2) during zircon crystallization to be between FMQ (fayalite–magnetite–quartz buffer) -0.69 to +2.41, whereas those of the Hashroud-Teckmdash-Gormolla zircons from NW AMB range from −1.22 to +5.99. The fO2 estimates suggest relatively more oxidized conditions for the Late Cenozoic igneous rocks of the AMB. Compiled data from the UDMB and AMB intrusions show an increase in average zircon crystallization temperatures with decreasing age. These outcomes have been interpreted in terms of variation of the crustal thickness, from 30 to 35 km during Eocene-Oligocene to 40–55 km during the middle-late Miocene. We propose the increase in crustal thickness is associated with the collision between the Arabian plate and Iran and subsequent convergence during the middle-late Miocene.

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.

Evaluation of crystallization conditions and porphyry Cu Mineralization potential of the Gheshlagh-Aftabrow pluton, central part of the Urumieh-Dokhtar magmatic belt, Iran

Gheshlagh-Aftabrow granodiorite (GAG) is emplaced within Eocene volcanic rocks in the central part of the Urumieh-Dokhtar magmatic belt (UDMB) of Iran and comprises of host granodiorites and associated mafic microgranular enclaves (MMEs). The Al-in-hornblende barometry and the amphibole–plagioclase thermometer are applied to calculate pressure and temperature. The host granodiorite yields crystallization temperatures and pressures varying from 635 to 715 °C (with an average of 670 °C) and from 0.5 to 1.8 kbar (with an average of 1.3 kbar, equivalent to a depth of 4.5 km), respectively. The mafic enclave shows a slightly higher crystallization temperature (690–720 °C, with an average of 705 °C) and pressure (1.1–1.8 kbar, with an average of 1.4 kbar), equivalent to a depth of 5 km. The estimated ƒO2 contents by amphibole chemistry in the host rocks and their mafic enclaves range − 11.2 to − 13.3 and − 11.5 to − 12.8, respectively, indicating that these rocks probably crystallized at relatively oxidizing conditions above the nickel–nickel oxide (NNO) buffer, yielding an overall range between NNO + 1.1 and NNO + 2.6, that is consistent with the general presence of magnetite and corresponds to their calc-alkaline affinity and the formation of the rocks in the subduction environment. The granodiorites and associated MMEs yield broadly similar water contents of 2.5–3.7 wt% and 2.6–3.7 wt%, respectively. The calculated densities of the host granitic magmas vary from 2319 to 2353 kg/m3, which are different from the determined densities of the mafic magma from which the enclaves are derived (2500–2626 kg/m3). The minimum calculated solidification time for the Gheshlagh-Aftabrow intrusion is about 20 × 104 years, and for the enclaves, it is less than 0.2 to 14 h that could not be enough time for pervasive mixing. Most of the amphiboles have Mg# value between 0.5 and 0.7, that together with low difference in densities of the magmas forming host rocks and enclaves may indicate that mantle–crust mixing was significant in the GAG generation. However, some geochemical signatures together with high ƒO2 content in the GAG samples indicate that these rocks are essentially comparable to granitoids associated with porphyry copper deposits, but according to the field evidences, the lack of extensive alteration, whole-rock chemistry (e.g., low Sr/Y and high Zr/Hf), plagioclase geochemistry, low water contents, and mineralogical evidences (e.g., lack of the common alteration phases in porphyry systems), it can be concluded that the studied pluton is barren regarding porphyry Cu mineralization.

The Paleogene ophiolite conundrum of the Iran–Iraq border region

New and compiled geochemical, isotopic and geochronological data allow us to propose a new explanation for Paleogene oceanic magmatic rocks along the Iran–Iraq border. These rocks are represented by a thick pile (>1000 m) of pillow lavas and pelagic sediments and underlying plutonic rocks. These are sometimes argued to represent a Paleogene ophiolite but there are no associated mantle rocks. Integrated zircon U–Pb ages, bulk rock major and trace element and radiogenic isotope data indicate that these rocks are more likely related to forearc rifting due to extreme extension during Late Paleogene time which also triggered high-flux magmatism in the Urumieh–Dokhtar Magmatic Belt and exhumation of core complexes in Iran. These observations are most consistent with formation of the Paleogene oceanic igneous rocks in a >220 km long forearc rift zone. Supplementary material: Detailed analytical procedure and tables S1 to S6 are available at: https://doi.org/10.6084/m9.figshare.c.4972994

Geology, mineralization, fluid inclusion, and stable isotope characteristics of the Zaghar and Sarabadan Cu-(Au) skarn deposits, Tafresh, Central Iran

The Zaghar and Sarabadan copper-(gold) deposits are located in the northern part of the Urumieh-Dokhtar magmatic belt. Mineralization occurred in contact of the post-Eocene diorite-tonalite stocks with the upper Triassic-Jurassic shale and sandstone series in the Zaghar, and lower Eocene volcanic and pyroclastic rocks in the Sarabadan. Based on field observation and mineralogical studies, three stages of mineralization can be distinguished: (1) prograde skarn; (2) retrograde skarn; and (3) supergene stages. The prograde skarn is characterized by association of andradite, diopside, cordierite, and minor actinolite. The retrograde skarn stage is divided into two sub-stages: (1) retrograde skarn I; and retrograde skarn II. The retrograde skarn I, is marked by deposition of the main alteration minerals (e.g., tremolite, actinolite, chlorite, epidote), magnetite, ilmenite, pyrrhotite, pyrite, barite, and small amount of other sulfide minerals. The retrograde skarn II or quartz-sulfide-carbonate stage, is characterized by quartz and calcite vein-veinlets associated with Cu-Au mineralization. The supergene stage is marked by Fe oxy-hydroxides, covellite, malachite, azurite, and minor clay minerals and calcite. Ore-forming fluids associated with the quartz, calcite, and sphalerite from the retrograde II stage of mineralization is represented by LVS fluid inclusions with the temperature of 218–512 °C and salinity of 6.73–59.09 wt% NaCl, and LV type fluids with the temperature of 130–215 °C and salinity of 1.70–30.00 wt% NaCl equivalent. Stable isotope analysis of quartz yielded values of −85.30 to −60.70 δD‰, and +7.82–9.60‰ δ18Ofluid, indicating that the ore-forming fluids were mainly magmatic fluids with some contributions from meteoric waters. The δ34S values of pyrite vary from +4.90–8.10‰, demonstrate that the sulfur in deposit was probably originated from the magma. The geological and geochemical features introduce the Zaghar and Sarabadan as Cu-(Au) skarn deposits are related to the magmatic-hydrothermal activity of diorite stocks within continental magmatic arc.