Urumieh-Dokhtar Magmatic Arc Research Articles

Geological, geochemical and fluid inclusion studies on the evolution of barite mineralization in the Badroud area of Iran

A sequence of andesitic to dacitic volcanic and volcano-sedimentary rocks from the Late Eocene in the central part of the Urumieh–Dokhtar Magmatic Arc (UDMA) hosts a number of barite occurrences. The Badroud barite deposit is economically important deposit in the study area. The petro-geochemical characteristics of the deposit indicate that the least-altered volcanic host rock was produced as orogenic volcanic rock in the continental margin arc setting. It displays characteristics of a high-K and calc-alkaline series. Mineralized host rock mostly consists of barite crystals, and subordinate quartz, calcite, gypsum, fluorite and rare pyrite, chalcopyrite, galena, stibnite and cinnabar minerals. Petrographic studies revealed three types of barite. The early stage barite occurs as stockworks of large tabular and bladed crystals trending NW-SE in dextral strike-slip faults. The second stage barite precipitated as thick lensoid veins (50 × 3 m) of medium tabular crystals extending in a N-S direction. The third stage of barite mineralization occurs as thin acicular veins trending in a NW-SE direction. Chemically, the barite deposit is characterized by the low amounts of Sr, K, Ca and low Sr/Ba ratio. Fluid inclusion studies, applied to the first stage of bladed crystals of barite veinlets, show a high homogenization temperature of 256–338 °C and 8–13% (wt.) NaCl eq. salinity. Fluid inclusions in the second stage of barite mineralization are characterized by low salinity of 1–9% (wt.) NaCl eq. at a 160–214 °C homogenization temperature. The fluid inclusions occurring in the third stage of thin barite veins revealed high salinity of 19% (wt.) NaCl eq. with a 166–212 °C homogenization temperature. The fluid inclusion characteristics of the first stage barite show a hydrothermal origin with a deeper-seated source on the seafloor associated with a lower sequence of the Late Eocene felsic rock. The second stage barite, exposed beneath the upper sequence of Late Eocene andesite, was formed due to increased dilution, possibly with seawater. The third stage barite mineralization is associated with saline water and the interaction of fluid with volcanic and conglomerate host rocks. The obtained data show that the mineralization at Badroud barite deposit is similar to the Kuroko-type massive sulfide deposits in an arc setting.

Petrogenesis of Rabor-Lalehzar magmatic rocks (SE Iran): Constraints from whole rock chemistry and Sr-Nd isotopes

The Urumieh-Dokhtar magmatic arc (UDMA) of Central Iran has been formed during Neotethyan Ocean subduction underneath Eurasia. The Rabor-Lalehzar magmatic complex (RLMC), covers an area ∼1000 km2 in the Kerman magmatic belt (KMB), SE of UDMA. RLMC magmatic rocks include both granitoids and volcanic rocks with calc-alkaline and adakitic signatures but with different ages.Miocene adakitic rocks are characterd by relatively enrichmented in incompatible elements, high (Sr/Y)(N) (>40), and (La/Yb)(N) (>10) ratios with slightly negative Eu anomalies (EuN/Eu*≈ 0.9), depletion in HFSEs, and relatively non-radiogenic Sr isotope signatures (87Sr/86Sr = 0.7048–0.7049). In contrast, the Oligocene granitoids exhibit low Sr/Y (<20) and La/Yb (<9) ratios, negative Eu anomalies (EuN/Eu* ≈ 0.5), and enrichment in HFSEs and radiogenic Sr isotope signatures (87Sr/86Sr = 0.7050–0.7052), showing affinity to the island arc rocks. Eocene volcanic rocks which crusscut the younger granitoid rocks comprise andesites and dacites. Geochemically, lavas show calc-alkaline character without any Eu anomaly (EuN/Eu* ≈ 1.0). Based on the geochemical and isotopic data we propose that melt source for both calc-alkaline and adakitic rocks from the RLMC can be related to the melting of a sub-continental lithospheric mantle (SCLM). Basaltic melts derived from a metasomatized mantle wedge might be emplaced at the mantle-crust boundary and formed the juvenile mafic lower crust. However, some melts fractionated in the shallow magma chambers and continued to rise forming the volcanic intermediate-mafic rocks at the surface. On the other hand, the assimilation and fractional crystallization in the shallow magma chambers of may have been responsible for the development of Oligocene granitoids with calc-alkaline affinity. In the mid-Late Miocene, following the collision between Afro-Arabia and Iranian block the juvenile mafic crust of UDMA underwent thickening and metamorphosed into garnet-amphibolites. Subsequent upwelling of a hot asthenosphere during Miocene was responsible for partial melting of thickened juvenile crust of the SE UDMA (RLM complex). The adakitic melts ascended to the shallow crust to form the adakitic rocks in the KMB.

Metal endowment reflected in chemical composition of silicates and sulfides of mineralized porphyry copper systems, Urumieh-Dokhtar magmatic arc, Iran

The present work attempts to discriminate between the geochemical features of magmatic-hydrothermal systems involved in the early stages of mineralization in high grade versus low grade porphyry copper systems, using chemical compositions of silicate and sulfide minerals (i.e., plagioclase, biotite, pyrite and chalcopyrite). The data indicate that magmatic plagioclase in all of the porphyry copper systems studied here has high An% and Al content with a significant trend of evolution toward AlAl3SiO8 and □Si4O8 endmembers, providing insight into the high melt water contents of the parental magmas. Comparably, excess Al and An% in the high grade deposits appears to be higher than that of selected low grade deposits, representing a direct link between the amounts of exsolving hydrothermal fluids and the potential of metal endowment in porphyry copper deposits (PCDs). Also, higher Al contents accompanied by elevated An% are linked to the increasing intensity of disruptive alteration (phyllic) in feldspars from the high grade deposits. As calculated from biotite compositions, chloride contents are higher in the exsolving hydrothermal fluids that contributed to the early mineralization stages of highly mineralized porphyry systems. However, as evidenced by scattered and elevated log (fH2O)/(fHF) and log (fH2O)/(fHCl) values, chloride contents recorded in biotite could be influenced by post potassic fluids. Geothermometry of biotite associated with the onset of sulfide mineralization indicates that there is a trend of increasing temperature from high grade to low grade porphyry systems. Significantly, this is coupled with a sharp change in copper content of pyrite assemblages precipitated at the early stages of mineralization such that Cu decreased with increasing temperature. Based on EMPA and detailed WDS elemental mapping, trace elements do not exhibit complex compositional zoning or solid solution in the sulfide structure. Nevertheless, significant amounts of Cu and Au are contained in pyrite assemblages as micro- to nano-sized inclusions, especially in the high grade fertile porphyry deposits. However, unexpectedly high concentrations of Te, Se, and Re may be associated with early stage of sulfide mineralization, especially when there is no epithermal lithocap. This may highlight the significance of trace metals partitioning in the sulfides formed at the early stages of mineralization in PCDs.

Geochemical and isotopic constraints on the role of juvenile crust and magma mixing in the UDMA magmatism, Iran: evidence from mafic microgranular enclaves and cogenetic granitoids in the Zafarghand igneous complex

The Zafarghand Igneous Complex is composed of granite, granodiorite, diorite, and gabbro that contain many mafic microgranular enclaves. This complex was emplaced during the late Oligocene (24.6 Ma) to form part of the Urumieh–Dokhtar magmatic arc of Central Iran. The enclaves have spheroidal to elongated/lenticular shapes and are quenched mafic melts in felsic host magma as evidenced by fine-grained sinuous margins and (or) locally transitional and diffuse contacts with the host rocks, as well as having disequilibrium textures. These textures including oscillatory zoning with resorption surfaces on plagioclase, feldspar megacrysts with poikilitic and anti-rapakivi textures, mafic clots, acicular apatites, and small lath-shaped plagioclase in larger plagioclase crystals all indicate that the enclaves crystallized from mafic magma that was injected into and mixing/mingling with the host felsic magma. The studied rocks have calc-alkaline, metaluminous compositions, with an arc affinity. They are enriched in large ion lithophile elements, light rare-earth elements, and depleted in high field strength elements with significant negative Eu anomalies. The Sr–Nd isotopic data for all of the samples are similar and display ISr = 0.705123–0.705950 and eNd (24.6 Ma) = − 1.04–1.03 with TDM ~ 0.9–1.1 Ga. The host granites and enclaves are of mixed/mingled origin and most probably formed by the interaction between the juvenile lower crust with a basaltic composition and old lower or middle continental crust as a major component and lithospheric mantle as a minor component; this was followed by fractional crystallization and possibly minor crustal assimilation. The source seems to be comprised of about 90–80% of the basaltic magma and about 10–20% of lower/middle-crust-derived magma. Geochemical characteristics indicate that the intrusion of these rocks from a subduction zone setting below the Central Iran micro-continent was related to an active continental margin, although was transitional to a transtensional setting possibly due oblique convergence to slab rollback or break-off.

Compositional characteristics and geodynamic significance of late Miocene volcanic rocks associated with the Chah Zard epithermal gold–silver deposit, southwest Yazd, Iran

AbstractWhole‐rock geochemical and Sr–Nd isotopic data are presented for late Miocene volcanic rocks associated with the Chah Zard epithermal Au–Ag deposit in the Urumieh‐Dokhtar Magmatic Arc (UDMA), Iran, to investigate the magma source, petrogenesis and the geodynamic evolution of the study area. The Chah Zard andesitic to rhyolitic volcanic rocks are characterized by significant Large Ion Lithophile Element (LILE) and Light Rare Earth Element (LREE) enrichment coupled with High Field Strength Element (HFSE) depletion. Our geochemical data indicate an adakitic‐like signature for the volcanic rocks (e.g. SiO2 &gt; 62 wt%, Al2O3 &gt; 15 wt%, MgO &lt; 1.5 wt%, Sr/Y &gt; 70, La/Yb &gt; 35, Yb &lt; 1 ppm, and Y &lt; 18 ppm, and no significant Eu anomalies), distinguishing them from the other volcanic rocks of the UDMA. The Chah Zard volcanic rocks have similar Sr and Nd isotopic compositions; the 87Sr/86Sr(i) ratios range from 0.704 902 to 0.705 093 and the εNd(i) values are from +2.33 to +2.70. However, the rhyolite porphyry represents the final stage of magmatism in the area and has a relatively high 87Sr/86Sr ratio (0.705 811). Our data suggest that the andesitic magmas are from a heterogeneous source and likely to result from partial melting of a metasomatized mantle wedge associated with a mixture of subducted oceanic crust and sediment. These melts subsequently underwent fractional crystallization along with minor amounts of crustal assimilation. Our study is consistent with the model that the volcanic host rocks to epithermal gold mineralization in the UDMA are genetically related to late Miocene Neo‐Tethyan slab break‐off beneath Central Iran.

Discovery of the Hendou-abad copper mineral district and its association to dikes: A reconstruction scenario for exploration of Cu-porphyry, northeast Isfahan, Iran

The Hendou-abad copper mineral district is located along the eastern margin of the central part of Urumieh–Dokhtar Magmatic Arc (UDMA). The mineralization is hosted in the Late Eocene basaltic andesite and trachybasalt, where it is associated with epidote, calcite, and quartz as alteration minerals, and red, white, and green breccias. Two main events of mineralization with alteration have been distinguished: hypogene and supergene. Abundant parallel dike swarms intrude Late Eocene volcanic rocks of the Henduo-abad. The Hendou-abad dikes are seen as a few cm to 4m wide and <1200m long. The purpose of this work was to survey their petrogenesis and the tectonic implication of the dikes. Further, to investigate the relationship between dikes and known copper mineralization in Hendou-abad, and then examine exploration potential in adjacent areas. The Hendou-abad dikes, based on trend, relative age, and geochemical composition, are divided into two groups: early and late dikes. The geochemical character of these dikes displays an arc setting and the late dikes show higher contents of Nb, Zr, P, K, Rb, Ba, and slightly elevated Ti. The geochemical composition of the dikes suggests two magmatic stages over time: a subduction-modified mantle source is thought of for the host basaltic andesites and the early dikes in a primitive arc stage, while an enriched asthenospheric mantle source is pictured for the late dikes in a later, more mature arc stage. Structural evidences from field-work of dikes, strike-slip and thrust faults, and microscopic studies of the associated hypogene mineralization imply that they may have formed through north-south directed extension during an uplift event. The pattern of dike orientations, their intense propylitic alteration, and the spatially association with mineralized breccias, sheeted calcite, and mineralized quartz veins, could suggest emplacement of a porphyry stock at depth. Our data show that the east-trending green dikes are associated with red and green breccias in southern Ardestan and that they could be used as an exploration target for copper mineralization.

Zircon Hf isotopic constraints on magmatic and tectonic evolution in Iran: Implications for crustal growth in the Tethyan orogenic belt

This study presents coupled zircon U-Pb and Hf isotopic analyses of 82 igneous rocks that are mainly from the Urumieh-Dokhtar magmatic arc (UDMA) and Sanandaj-Sirjan zone (SSZ), Iran, together with additional 11 samples from Armenia, along the central part of the Neotethyan orogenic belt. The results provide an overview of the isotopic variations for several important magmatic stages, which can improve our understanding of magmatic and crustal evolution regarding the life cycles of Tethys oceans during the past ∼600Myr in Iran and adjacent regions. Late Neoproterozoic-Cambrian (595–511Ma) basement rocks in the SSZ and Central Iran, which were part of the Cadomian magmatic arc, yield zircon εHf(T) values from +11 to −3 and are attributed to have partially evolved with juvenile magmas in the Arabian-Nubian Shield along the northern margin of Gondwana. Carboniferous (349–311Ma) A-type granitoids in the northwestern SSZ show mostly positive zircon εHf(T) values from +5 to −1, and they are interpreted as the product involving a moderate mantle contribution in an extensional environment affiliated with the initial rifting of the Neotethys. Late Triassic (219–203Ma) granitoids in the eastern Alborz give slightly lower zircon εHf(T) values between +3 and −3 as a result of the progress of closing the Paleotethys. Middle Jurassic (∼165Ma) granitoids in the SSZ and Central UDMA, representing an early phase of Neotethyan subduction-related magmatism, exhibit similar zircon εHf(T) values from +5 to −3, implying an origin of mixed juvenile and reworked sources to form the magmas. Late Cretaceous (81–72Ma) intrusive rocks in the Southeast UDMA yield bimodal zircon εHf(T) values from +15 to +11 in the Jiroft and from +5 to −9 in the Bazman areas, suggesting that the latter involves a reworked crustal component. At the latest Cenozoic, magmatic rocks with ages <55Ma that occurred widely across Iran and Armenia before and after the Arabia-Eurasia collision give dominantly positive zircon εHf(T) values ranging between +15 and −1, except for the Eocene granitoids in Central Iran, which have remarkably lower zircon εHf(T) values down to −7. Therefore, these Cenozoic rocks yield younger zircon Hf crustal model ages (TDMC), mainly from ca. 1.2 to 0.2Ga, than the Late Neoproterozoic-Mesozoic rocks. As the whole, the highly radiogenic Hf isotopes with positive εHf(T) values recorded by most (∼90%) of the measured magmatic zircons from Iran suggest that the mantle input has played a significant and long-standing role in the magmatic genesis and crustal growth throughout the Mesozoic and Cenozoic evolution in this particular part of the Tethyan orogenic belt.

Application of Landsat-8 and ASTER satellite remote sensing data for porphyry copper exploration: a case study from Shahr-e-Babak, Kerman, south of Iran

The Shahr-e-Babak region located in the Kerman metallogenic belt is one of the high potential segments of Urumieh–Dokhtar magmatic arc for porphyry copper and epithermal gold mineralization in the south of Iran. This high potential zone encompasses several porphyry copper deposits under exploitation, development and exploration stages. The aim of this study is to evaluate Landsat-8 data and comparison with the Advanced Spaceborne Thermal Emission and Reflection Radiometer data-sets for mapping hydrothermal alteration zones related to Cenozoic magmatic intrusions in Shahr-e-Babak region. Previous studies have proven the robust application of ASTER in lithological mapping and mineral exploration; nonetheless, the Landsat-8 data have high capability to map and detect hydrothermal alteration zones associated with porphyry copper and epithermal gold mineralization. In this investigation, several band combinations and multiplications, developed selective principal component analysis and image transformations were developed for discriminating hydrothermal alteration zones associated with porphyry copper mineralization using Landsat-8 data.

Geological characteristics and geochronology of the Takht-e-Gonbad copper deposit, SE Iran: A variant of porphyry type deposits

The Takht-e-Gonbad, or simply Takht, copper deposit in the Kerman belt in southern section of the Cenozoic Urumieh-Dokhtar magmatic arc (UDMA) of Iran is spatially associated with late Oligocene shallow granodiorite porphyries intruded into pyroclastic rocks. Hypogene ore minerals include pyrite, chalcopyrite, magnetite and rare molybdenite and bornite, occurring as veinlets and disseminations mostly in the pyroclastic rocks. Hydrothermal alteration is marked by an extensive phyllic assemblage and irregular zones of propylitic and calc-silicate assemblages with no consistent zoning patterns. The various igneous rocks at Takht area are calc-alkaline to shoshonitic, and are distinguished by enrichments in LILEs relative to HFSEs, and LREEs relative to HREEs (14.41≥LaN/YbN≥2.85). These features suggest a subduction-related setting for the rocks and the associated copper deposit in the area. A late Oligocene age is obtained for the main Takht granodiorite porphyry and the granodiorite batholith (24.2Ma and 25.0Ma, respectively, zircon U-Pb). The age of the main Takht porphyry is distinctly older than the middle-late Miocene ages reported for most porphyry Cu deposits occurring to the north of the Takht deposit, including the world-class Sarcheshmeh and Meiduk.Three distinct types of fluid inclusions are identified: F1: L+V, V<50%; F2: L+V+S; and F3: V+L, L<10%. The F2 type inclusions with Th values ranging between 340°C and >600°C and salinities from 55 to 68wt% NaCl eq best represent characteristics of the mineralizing hydrothermal fluids. The δ34S values are measured for pyrite and chalcopyrite; the calculated δ34S values for ore fluids fall in the range +4.4 to +7.4‰, slightly heavier than those reported from most other porphyry copper deposits (PCDs) elsewhere. The shift towards more positive values could be attributed to contribution of isotopically heavy sulfur from crustal sources or involvement of marine sulfate in the magma source. The δ18OSMOW values for quartz veins in the phyllic assemblage define a narrow range, between +7.6 and +8.1‰. The calculated δ18O values for ore fluids range between +6.0 and +6.6‰ suggesting a magmatic source for the hydrothermal fluids.In spite of clear similarities with classic PCDs, in terms of ore mineralogy, ore texture/structure, and ore fluid characteristics, the Takht deposit stands distinct from most known PCDs in the Kerman belt in that most mineralization occurs in the pyroclastic host rocks and in close association with phyllic alteration.

Zircon U-Pb geochronology and emplacement history of intrusive rocks in the Ardestan section, central Iran

The Urumieh-Dokhtar Magmatic Arc (UDMA) is part of the Alpine–Himalayan orogenic belt and interpreted to be a subduction-related Andean-type magmatic arc. Along this belt, Eocene volcanics and some gabbroic to granitic bodies crop out. The main rock types of the studied intrusion are granite, granodiorite, and diorite. They have geochemical features typical of magnesian, calc-alkaline, metaluminous to slightly peraluminous granites and I-type intrusive rock that have a strong enrichment in Large-Ion Lithophile (LIL) elements (e.g. Rb, Ba, Sr), and a depletion in High Field Strength (HFS) elements (e.g. Nb, Ti, P), typical of subduction-related magmas. Zircon U-Pb dating was applied to determine the emplacement ages of the different intrusions in the Ardestan area. Among them the Kuh-e Dom diorite is 53.9±0.4Ma old; the Kuh-e Dom granodiorite is 51.10±0.4Ma old; the Mehrabad granodiorite is 36.8±0.5Ma old, the Nasrand granodiorite is 36.5±0.5Ma old, the Zafarghand granodiorite is 24.6±1.0Ma old, and the Feshark granodiorite is 20.5±0.8Ma old. These results delineate more accurately the magmatic evolution related to the Neotethyan subduction from the Lower Eocene to Lower Miocene, and the subsequent Zagros orogeny that resulted from the Arabia-Eurasia collision. The emplacement of these intrusive rocks inside the UDMA, which has a close relationship with the collisional orogeny, is transitional from a subduction-related setting to post-collisional setting in the Ardestan area.

Constraining the timing of porphyry mineralization in northwest Iran in relation to Lesser Caucasus and Central Iran; Re–Os age data for Sungun porphyry Cu–Mo deposit

ABSTRACTThe Neo-Tethyan subduction in Iran is characterized by the Urumieh–Dokhtar magmatic arc (UDMA), formed by northeast-ward subduction of the oceanic crust beneath the central Iran. This belt coincides with the porphyry copper metallogenic belt that comprises several metallogenic zones, including Ahar–Jolfa in northwest Iran. The Ahar–Jolfa metallogenic zone encompasses two main batholiths of Qaradagh and Sheyvardagh and numerous intrusive bodies of Cenozoic, which have produced many base and precious metal deposits and prospects. The former is considered as continuation of the Meghri–Ordubad pluton in South Armenian Block (SAB), which also hosts porphyry copper deposits (PCDs). The Sungun PCD is the largest occurrence in northwest Iran. Rhenium-Osmium ages of Sungun molybdenites are early Miocene and range between 22.9 ± 0.2 and 21.7 ± 0.2 Ma. Comparison of the ages obtained here with published ages for mineralization across the region suggests the following sequence. The earliest porphyry Cu–Mo mineralization event in northwest Iran is represented by Saheb Divan PCD of late Eocene age, which is followed by the second epoch of middle Oligocene, including the Cu–Mo–Au mineralization at Qarachilar and the Haftcheshmeh PCD. Mineralization in Sungun, Masjed Daghi, Kighal and Niaz deposits corresponds to the third mineralization event in northwest Iran. The first epoch in northwest Iran postdates all Eocene mineralizations in SAB, while the second epoch is coeval with Paragachay and the first-stage of Kadjaran PCDs. Its third epoch is younger than all mineralizations in SAB, except the second stage in Kadjaran PCD. Finally, the Cu mineralization epochs in northwest Iran are older than nearly all PCDs and prospects in Central Iran (except the Bondar Hanza PCD), altogether revealing an old to young trend along the UDMA and the porphyry Cu belt towards southeast, resulted from diachronous, later closure of the Neo-Tethyan oceanic basin in central and SE Iran.

Thermobarometry in the Sarvian Fe-skarn deposit (Central Iran) based on garnet–pyroxene chemistry and fluid inclusion studies

The Sarvian Fe skarn deposit is located in the Urumieh–Dokhtar magmatic arc, western Iran. The Sarvian quartz diorite intruded the surrounding Permian to Tertiary limy formation, culminated in thermal metamorphism as well as skarnification in which the Sarvian deposit formed. Microthermometry studies in the Sarvian skarn deposit reveal two distinct inclusion groups; group A with medium–high temperature and hypersaline and group B with low–medium temperature and low salinity. Group A inclusions which are entrapped during formation of prograde are thought to be derived from the magmatic source. Fluid boiling and subsequent developing of hydraulic fracturing led to inflow and/or mixing of early magmatic fluids (group A) with circulating groundwater culminated in formation of low salinity and low temperature fluid inclusions (group B) during the formation of retrograde assemblage. Fluid inclusion thermometry reveals the formation temperature and the salinity of 300–370 °C and 31–33 wt% NaCl for the prograde stage and 180–230 °C and 1–15 wt% NaCl for the retrograde stage of skarnification at Sarvian skarn rocks. Fe-mineralization as well as hydrothermal minerals occurred during retrograde metasomatism. The estimated depth and pressure of occurrence for prograde stage are 1000–1200 m and 100–150 bars, and for retrograde stage, these are about 200 m and 50 bars, respectively. Garnet and pyroxene, as the main constituent minerals of prograde stage, are the most informative minerals offering a suitable tool to constrain the skarnification conditions. Garnets in the Sarvian deposit are mainly grossular and andradite, showing both normal and inverse zoning as the result of variation in their chemical composition. Such types of zoning represent alternation of high acidity oxidation and low acidity oxidation conditions that were prevailed on skarnification in the Sarvian prograde assemblage. Also, chemical composition of the Sarvian pyroxenes shows an alternation of high oxygen fugacity and low oxygen fugacity conditions for their formation. This is also supported by fluctuation of the ratios of andradite to grossular and diopside to hedenbergite, denoting to an obvious shifting that was prevailed between oxidizing and redox conditions during formation of prograde assemblage in the Sarvian. Garnet–pyroxene thermometry determines the formation temperature of prograde assemblage between 370 and 550 °C at Sarvian skarn rocks which is verified also by fluid inclusion thermometry. Decomposition of limestone by reaction of high-temperature hydrothermal fluids with carbonate host rock resulted in injection of CO2 into the Sarvian system that caused oxidation, changing Fe+2 to Fe+3 culminated in the magnetite deposition.

Petrological constraints on the origin of the plutonic massif of the Ghaleh Yaghmesh area, Urumieh–Dokhtar magmatic arc, Iran

The Oligocene Ghaleh Yaghmesh plutonic massif (GYPM) consists of diorite, quartz-diorite, tonalite and granodiorite and evolving from metaluminous nature. All the samples are predominantly medium-K calc-alkaline series, having typical characteristics of I-type granitoids. A significant geochemical criteria of the GYPM is the impoverishment of high-field-strength elements (HFSE) (e.i. Zr, Nb, Ti and Hf) and the overabundance of large-ion-lithophile elements (LILE) (e.i. K, Sr, U, Ba and Cs), with respect to the light rare elements (LREE) as compared to chondritic concentration. These geochemical criteria suggest the involvement of sedimentary components in the generation of rocks studied. Furthermore, variable Pb/Ce amounts, linear trend of all rocks studied on Ti/Zr vs. Yb/Hf diagram, as well as some characteristics petrographic features (e.i. acicular apatite, corroded margin of the plagioclases, the amphiboles and some of the pyroxenes, oscillatory zoning of plagioclases) and the presence of mafic microgranular enclave (MME) indicate that the Ghaleh Yaghmesh parental magma was likely generated by the partial melting of a mixed source dominantly composed of amphibolite and possibly meta-sedimentary source. The overall geochemical and petrographic features are consistent with the interpretation of the Urumieh–Dokhtar Magmatic Arc as an active continental margin during subduction of the Neo-Tethyan oceanic crust underneath the Central Iranian microcontinent.

The south Zagros suture zone in teleseismic images

The geometry of intra-continental lithosphere boundaries along the Zagros orogenic belt in the Arabia-Eurasia collision is investigated by means of teleseismic data. The data are gathered over a seismic linear profile extending across south Zagros, the Sanandaj–Sirjan metamorphic zone, the Urumieh–Dokhtar magmatic arc, Central Iran, and the Kopeh Dagh - Binalud mountains. We exploit the P and S receiver functions leading to map the geometry of the crustal and subcrustal interfaces. The migrated depth sections reveal an abrupt crustal thickening and a gentle crustal thinning ~60km north and ~30km south of the Zagros suture, respectively. Associated to the buckled antiformal Moho south of the suture, a deeper synform in the lithospheric lid of the lower Arabia plate is shown by migrated depth sections affecting the lithospheric mantle of the Arabia plate beneath the suture zone. This geometry implies an unexpected intra-lid decoupling. These features imply that the Central Iran lithosphere acts as a relatively strong backstop producing significant internal deformation expressed by shortening and thickening at the edge of the Arabian lithosphere. The 410km and 660km transition zones are imaged by P to S converted phases and showed lateral continuity implying an originally low dip angle subduction of the oceanic Arabian plate beneath Central Iran.

New age and geochemical constraints on the origin of Quaternary adakite-like lavas in the Arabia–Eurasia collision zone

Adakite-like lavas from the Iranian segment of the Arabia–Eurasia collision zone have been considered as partial melts derived from a subducted Neotethyan slab, a hypothesis that cannot be further evaluated due to the lack of systematic age and radiogenic isotopic data. Here, we revisit the Anar region, Iran where such lavas were reported by providing these data to examine their probable origin as slab melts. New SIMS zircon U–Pb ages attest to eruption at ca. 1 to 2Ma, postdating the Arabia–Eurasia collision. The lavas are characterized by dacitic to rhyolitic, metaluminous to slightly peraluminous and trondhjemitic compositions, and incompatible element patterns similar to continental crustal rocks. Extreme depletion in Nb, Ta, Y and the heavy REE relative to the light and middle REEs reflects control by garnet and rutile. Except one sample presumably affected by secondary gain of radiogenic Sr, the depleted Sr–Nd–Hf isotopic compositions relative to the Bulk Silicate Earth [(87Sr/86Sr)i=0.7040 to 0.7043; εNd(t)=+3.2 to +5.3; εHf(t)=+10.5 to +11.3] indicate magma genesis from juvenile source rocks. A slab melt origin for the Anar lavas is very unlikely and the reason is twofold. First, the Y and HREE of the source rocks estimated by inversed batch melting models assuming garnet pyroxenite residue are far too low compared with MORB-like lithologies and subducted sediments. Second, the low MgO, Ni and Cr of the lavas point to limited interaction with peridotites in a mantle wedge. Fractionation-related models are also unlikely due to the apparent lack of broadly coeval, mafic precursor magmas without adakitic signature. The low-Y and low-HREE source rocks revealed by the melting models, together with the low MgO, Ni and Cr of the Anar lavas, can be explained by lower crustal melting under eclogite-facies conditions. These source rocks were most likely high-pressure cumulates in the root of the Urumieh–Dokhtar magmatic arc, a Neotethyan arc that was active in the Paleogene. Lower crustal melting might be related to localized destruction of the continental mantle, giving rise to the temporally and spatially associated ultrapotassic magmas. The hypothesis of an ‘adakitic province’ near Anar where slab detachment and melting occurred does not hold in light of available data and observations.

Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks, Nain, Central Iran

Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO2 (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO2, P2O5, MnO, Al2O3 and Fe2O3 define linear trends with negative slopes against SiO2, whilst Na2O and K2O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO2, whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (LaN/YbN=4.5–6.4) with moderate HREE fractionation (SmN/YbN=1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (<400ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the 87Sr/86Sr initial ratios vary from 0.704432 to 0.705989, and the 143Nd/144Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks.

A comprehensive VIKOR method for integration of various exploratory data in mineral potential mapping

The central Iranian volcanic-sedimentary belt in Kerman province of Iran that is located within the Urumieh-Dokhtar magmatic arc zone is chosen to integrate diverse evidential layers for mineral potential mapping. The studied area has high potential of mineral occurrences especially porphyry copper, and the prepared potential maps aim to outline new prospect zones for further investigation. Two evidential layers including the downward continued map and the analytic signal of filtered magnetic data are generated to be used as geophysical plausible traces of porphyry copper occurrences. The low values of the resistivity layer acquired from airborne frequency domain electromagnetic data are also used as an electrical criterion in this study. Four remote sensing evidential layers including argillic, phyllic, propylitic, and hydroxyl alterations are extracted from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images in order to map the altered areas associated with porphyry copper deposits. The Enhanced Thematic Mapper Plus (ETM+) images are used as well to prepare iron oxide layer. Since potassic alteration is generally the mainstay of copper ore mineralization, the airborne potassium radiometry data is used to explore both phyllic and potassic alteration. Finally, the geochemical layers of Cu/B/Pb/Zn elements and the main geochemical component responsible for ore mineralization extracted from principal component analysis are included in the integration process to prepare final potential maps. The conventional and the extended version of VIKOR method (as a well-known algorithm in multi-criteria decision making problems) produced two mineral potential maps, and the results were compared with the ones acquired from prevalent methods of the index overlay and fuzzy logic operators of sum and gamma. The final mineral potential maps based upon desired geo-data set indicate adequately matching of high potential zones with previous working and active mines of copper deposits.

Geochemistry and fluid characteristics of the Dalli porphyry Cu–Au deposit, Central Iran

The Miocene Dalli porphyry Cu–Au deposit in the central part of Urumieh–Dokhtar magmatic arc is the first reported Au-rich porphyry Cu deposit in the Zagros orogenic belt. The Cu–Au mineralization is mainly hosted in diorite and quartz diorite intrusions, presenting as numerous veinlets in the altered wall rocks, with potassic, phyllic, and propylitic alteration developed. Based on the mineral assemblages and crosscutting relations of veinlets, hydrothermal mineralization–alteration occurred in at least three stages, characterized by veinlets of (1) Qtz+Kfs+Mag±Ccp, (2) Qtz+Py+Ccp±Bn±Cv±Cc and, (3) Qtz+Chl+Bt. The ore-bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas, including LREE fractionated pattern, strong enrichment in LILE (Cs, Rb, Ba, Pb, and U), and depletion of HFSE, with marked negative Ti and Nb anomalies. The adakite-like ore-hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of Y and Eu/Eu∗ with increasing SiO2 content, respectively. Moreover, they exhibit a significant increasing trend of Sr/Y with decreasing of Y, which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma. A relatively flat HREE pattern with low Dyn/Ybn and Nb/Ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust. Based on the phase assemblages confirmed by detailed laser Raman spectroscopy analyses and proportion of solid, liquid, and gaseous components, five types of fluid inclusions were recognized, which are categorized as; (1) liquid-rich two phase (liquidH2O+vaporH2O) (IIA), (2) vapor-rich two phase (vaporH2O/CO2+liquidH2O) (IIB), (3) high saline simple fluids (IIIA; liquidH2O+vaporH2O+Hl), (4) high saline opaque mineral-bearing fluids (IIIB; liquidH2O+vaporH2O+Hl+Hem+Ccp+Py) and (5) multi-phase type (IIIAB; liquidH2O+vaporH2O+Hl+Anh+Hem+Mag+Ccp). In early stage veins, the homogenization temperature of multiphase inclusions as high as 620°C, with corresponding salinities of up to 75wt.% NaCl equivalent represent the initial ore-forming fluids. From early to late stage veins, the gradual decrease of homogenization temperature of saline inclusions (IIIAB, IIIA, and IIIB) from 620 to 340°C (corresponding salinities of 75–35wt.% NaCl equivalent) may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater. The common association of hematite and anhydrite daughter phases with the most primitive inclusions (IIIAB) in early-stage veins and the lack of CO2-bearing inclusions in the middle to late stage veins reveal CO2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization (second generation of veins). It seems that magnetite crystallization and CO2-escape have a decisive role in oversaturation of S2− and subsequent rapid and large-scale precipitation of sulfides in second generation of veins at the Dalli deposit.

Geochemistry and petrogenesis of Ghohroud Igneous Complex (Urumieh–Dokhtar zone): evidence for Neotethyan subduction during the Neogene

The Oligo–Miocene Ghohroud granitoid is located in the north of Isfahan, in the Urumieh–Dokhtar magmatic arc (UDMA). The rock composition ranges from granodiorite to tonalite. Rocks mainly include quartz, plagioclase, and alkali feldspar with minor biotite and amphibole. Dacitic and basaltic rocks outcrop as dykes. Geochemical data show that these rocks are subalkaline, calc-alkaline, and metaluminous. Microgranular enclaves, sieve texture, oscillatory zoning in plagioclase, and clear roundness of quartz pieces demonstrated magma mixing. The magma has experienced fractional crystallization that has led to the presence of different petrological units. Large-ion lithophile element (LILE) and Pb enrichment is evidence of crustal contamination. Considering the clear negative anomaly of Nb and Ti, the magma has been formed in a volcanic arc environment. The geochemistry of major and rare earth elements reveals that initial magma has been formed by partial melting of lower crustal protoliths. An underplating magma can supply heat source for the dehydration melting of lower crust and generation of Ghohroud granitic melt by melting of a mafic source during the subduction of the Neotethyan oceanic plate and the Central Iran continental crust.

Evaluating physicochemical conditions of Miocene–Pliocene volcanic rocks in the middle part of the Urumieh-Dokhtar Magmatic Arc

Urumieh-Dokhtar Magmatic Arc (UDMA) resulted from subduction of the Arabian plate beneath the Eurasian plate. Miocene–Pliocene volcanic rocks in the middle part of UDMA located in the north of Isfahan (Central Iran) are mainly dacite. They are chiefly composed of phenocrysts of plagioclase, amphibole, and biotite lying in a matrix made of feldspar, quartz, opaque, glass, and microlite. Having a relatively invariable composition, plagioclases are all andesine. Amphiboles are calcic and tschermakite type. The chemical composition of biotites hardly varies. All of them are Mg-biotite. On average, they are composed of 55.3 % phlogopite, 15.7 % talc, 12.8 % Ti-phlogopite, 11.6 % eastonite, 3.7 % Ferri-eastonite, and 0.9 % muscovite. The chemical composition of biotite indicates the nature of calcalkaline for magmatic series of magma generating biotites. An estimation of the temperature and pressure of crystallization resulted from integrating amphibole and amphibole-plagioclase thermobarometry equations indicates that amphibole-plagioclase phenocrysts were crystalised in the temperature range of 763–823 °C with average of 797 °C and in the pressure range of 2.2–4.5 kbar with the average of 3.4 kbar. An estimation of the oxygen fugacity of the magma, based on chemical composition and Fe3+ content of biotite, shows the oxygen fugacity was equal to that of the FMQ buffer. Quantifying oxygen fugacity shows that logfO2 was about −15.