Ghasem Ghorbani

Igneous activity in the rear-arc of the Paleogene Urumieh-Dokhtar Magmatic Belt of Iran has to date been poorly studied. An example of such activity, Late Eocene potassic mafic to intermediate magmatic rocks in the Lahrud area of NW Iran, is the focus of this work. These lavas include olivine-bearing clinopyroxene-phyric basalts, analcime-bearing leucite-clinopyroxene-phyric basalts, andesites, and trachytes, and Paleocene-Early Eocene pyroclastic rocks. Monzo-syenite plugs (dated here at ~37 Ma), clinopyroxene-phyric basaltic dikes, and leucite-bearing clinopyroxene- phyric basaltic dikes intrude older lavas and pyroclastic rocks. Olivine-bearing clinopyroxenephyric basalts and analcime-bearing leucite-clinopyroxene-phyric basalts are characterized by large phenocrysts of olivine, clinopyroxene, leucite, and analcime. Clinopyroxene-rich enclaves and partially resorbed mantle xenoliths also occur. Olivine phenocrysts are zoned from high-Mg# cores (Mg# = 90) to Fe-rich rims (Mg# = 66). Clinopyroxene phenocrysts from the olivine-bearing clinopyroxene-phyric basalts, analcime-bearing leucite-clinopyroxene-phyric basalts and clinopyroxene crystals in the enclaves show complex oscillatory zoning, sieve textures, and resorption textures, but with systematic core-rim compositional trends. Their 87Sr/86SrSr isotopic compositions measured in situ range from 0.7037 to 0.7068 (mean = 0.705260±0004), suggesting negligible crustal assimilation during fractional crystallization. The Lahrud lavas are potassic and are enriched in light rare earth elements and large ion lithophile elements such as Th, Rb, K and U. High field strength elements (HFSE), such as Nb, are depleted in the olivine-bearing clinopyroxene-phyric basalts and analcime-bearing leucite-clinopyroxene-phyric basalts, but enriched in the trachytes and trachytic ignimbrites. The isotopic compositions vary: 87Sr/86Srt from 0.7045 to 0.7052, eNd(t) from +2.8 to +3.3, and eHf(t) from +7.2 to +7.7. The rocks have radiogenic lead 206Pb/204Pb from 18.66 to 18.76, 207Pb/204Pb from 15.58 to 15.62, and 208Pb/204Pb from 38.73 to 38.81. Modeling of major and trace elements using the MELTS algorithm indicates that the geochemical variations in the basaltic to andesitic rocks are reasonably explained by shallow fractional crystallization with some complications owing to source heterogeneity, crustal assimilation, and magma mixing. The isotopic data imply that partial melting of old sub-continental lithospheric mantle was not responsible for the Lahrud potassic magmas; Hf isotopes and Zr/Nb ratios suggest derivation from an enriched mantle wedge, whereas ratios of incompatible trace elements (e.g. La/Yb, Ba/La, Ce/Pb, Th/Yb) and high 87Sr/86Sr suggest mantle metasomatized by slab-derived fluids or melts dominated by a sediment component. Geochemical modeling using the Arc Basalt Simulator version 5 reveals that the HFSE-depleted, olivine-bearing, clinopyroxene-phyric basalts originated from a high-temperature mantle wedge (2.2 GPa, 1310°C) fluxed intensively (5%) by melts from a deep hot slab (6 GPa, 1000°C). The moderately HFSE-depleted, olivine-bearing, clinopyroxene-phyric basalts reflect melting of a lower-temperature mantle wedge (2.2 GPa, 1300°C) with a lesser amount of slab melt flux (4%) from a lower temperature and shallower slab (3 GPa, 866°C). In contrast, the leucite- clinopyroxene-phyric basalts and andesites are from a similar source to the moderately HFSEdepleted, olivine-bearing, clinopyroxene-phyric basalts (3 GPa, 866°C) but with a contribution from a lower temperature mantle wedge (2.2 GPa, 1270°C). During Late Eocene times, slab retreat and upper-plate extension occurred in the rear-arc region of the Urumieh-Dokhtar Magmatic Belt. The Lahrud potassic magmas were generated from a high-temperature mantle wedge, which resulted in melting of the slab; this slab melt flux further promoted melting of the mtle wedge. © The Author(s) 2018. Published by Oxford University Press. All rights reserved.

The authors regret to have inadvertently an incorrect affiliation for one of the co-authors. The following affiliation should be replaced in the authors and affiliation lists for Dr. Ghasem Ghorbani. aGhasem Ghorbani aSchool of Earth Sciences, Damghan University, Damghan 36716-41167, Iran The authors would like to apologise for any inconvenience caused. © 2017

The Cadomian orogen of NW Iran includes a series of metamorphic rocks with zircon U-Pb ages between ca 562 and 505 Ma (Ediacaran to middle Cambrian). The Ediacaran-Cambrian basement is intruded by a series of Late Eocene-Late Oligocene I-type granitic rocks. U-Pb geochronology, integrated with geochemical and isotopic data for the basement rocks in NW Iran, provides further evidence of a Cadomian (562-505 Ma) arc-related magmatic event lasting~60 Myr. Cadomian magmatism in Iran was a part of ã100 Myr long episode of subduction-related arc magmatism at the northern margin of Gondwana. Zircon Hf-isotope compositions show that during Cadomian magmatic arc activity, juvenile arc magmas interacted with reworked Archean crust to generate the Ediacaran-Cambrian igneous rocks. Our results document both inheritance of old zircons and the presence of zircons with juvenile signatures in NW Iran, suggesting that the geotectonic setting for the Cadomian rocks was an Ediacaran continental magmatic arc and probably a neighboring back-arc basin. The occurrence of Ediacaran ophiolitic slices in NW Iran may provide evidence of back-arc basin opening at that time. Cenozoic plutonism in NW Iran is part of an Eocene-Oligocene magmatic 'flare-up' along the Urumieh-Dokhtar Magmatic Belt in central Iran, which lasted for ca 30 Myr. The melts responsible for the formation of these rocks had an essentially juvenile signature with minor contamination by Archean to Cadomian middle-lower continental crust. Continuous convergence between Arabia and Iran was accompanied by the transition of SW Eurasia from a compressional to an extensional convergent plate margin in Eocene-Oligocene times, leading to orogenic collapse, core-complex formation, exhumation of Cadomian crust and a major increase in arc magmatism. © The Author(s) 2018. Published by Oxford University Press. All rights reserved.

Magmatic “flare-ups” are common in continental arcs. The best-studied examples of such flare-ups are from Cretaceous and younger continental arcs, but a more ancient example is preserved in Late Ediacaran–Cambrian or Cadomian arcs that formed along the northern margin of Gondwana. In this paper, we report new trace-element, isotopic and geochronological data on ∼550 Ma magmatic rocks from the Taknar complex, NE Iran, and use this information to better understand episodes of flare-up, crustal thickening and magmatic periodicity in the Cadomian arcs of Iran and Anatolia. Igneous rocks in the Taknar complex include gabbros, diorites, and granitoids, which grade upward into a sequence of metamorphosed volcano-sedimentary rocks with interlayered rhyolites. Granodioritic dikes crosscut the Taknar gabbros and diorites. Gabbros are the oldest units and have zircon U–Pb ages of ca 556 Ma. Granites are younger and have U–Pb zircon ages of ca 552–547 Ma. Rhyolites are coeval with the granites, with U–Pb zircon ages of ∼551 Ma. Granodioritic dikes show two U–Pb zircon ages; ca 531 and 548 Ma. Geochemically, the Taknar igneous rocks have calc-alkaline signatures typical of continental arcs. Whole-rock Nd and zircon O–Hf isotopic data show that from Taknar igneous rocks were generated via mixing of juvenile magmas with older continental crust components at an active continental margin. Compiled geochronological and geochemical data from Iran and Anatolia allow identification of a Cadomian flare-up along northern Gondwana. The compiled U–Pb results from both magmatic and detrital zircons indicate the flare-up started ∼572 Ma and ended ∼528 Ma. The Cadomian flare-up was linked to strong crustal extension above a S-dipping subduction zone beneath northern Gondwana. The Iran–Anatolian Cadomian arc represents a site of crustal differentiation and stratification and involved older (Archean?) continental lower–middle crust, which has yet to be identified in situ, to form the continental nuclei of Anatolia and Iran. The Cadomian crust of Anatolia and Iran formed a single block “Cimmeria” that rifted away from northern Gondwana and was accreted to southern Eurasia in late Paleozoic time. © 2017 Elsevier B.V.

The Biarjmand granitoids and granitic gneisses in northeast Iran are part of the Torud-Biarjmand metamorphic complex, where previous zircon U-Pb geochronology show ages of ca. 554-530 Ma for orthogneissic rocks. Our new U-Pb zircon ages confirm a Cadomian age and show that the granitic gneiss is ~30 million years older (561.3 ± 4.7 Ma) than intruding granitoids (522.3 ± 4.2 Ma; 53707 ± 4.7 Ma). Cadomian magmatism in Iran was part of an approximately 100-million-year-long episode of subduction-related arc and back-arc magmatism, which dominated the whole northern Gondwana margin, from Iberia to Turkey and Iran. Major REE and trace element data show that these granitoids have calc-alkaline signatures. Their zircon O (δ18O = 6.2-8.9‰) and Hf (-7.9 to +5.5; one point with εHf ~ -17.4) as well as bulk rock Nd isotopes (εNd(t) = -3 to -6.2) show that these magmas were generated via mixing of juvenile magmas with an older crust and/or melting of middle continental crust. Whole-rock Nd and zircon Hf model ages (1.3-1.6 Ga) suggest that this older continental crust was likely to have been Mesoproterozoic or even older. Our results, including variable zircon εHf(t) values, inheritance of old zircons and lack of evidence for juvenile Cadomian igneous rocks anywhere in Iran, suggest that the geotectonic setting during late Ediacaran and early Cambrian time was a continental magmatic arc rather than back-arc for the evolution of northeast Iran Cadomian igneous rocks. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

A major magmatic flare-up is documented along the Bitlis-Zagros suture zone in Eocene-Oligocene times. The Cenozoic magmatism of intraplate Central Iran is an integrant part of this tectono-magmatic scenario. The Cenozoic magmatism of the Sabzevar structural zone consists of mostly intermediate to felsic intrusions and volcanic products. These igneous rocks have calc-alkaline and adakitic geochemical signatures, with nearly coincident zircon U-Pb and mica Ar-Ar ages of ca. 45 Ma. Adakitic rocks have quite low HREE and high Sr/Y ratio, but share most of their geochemical features with the calc-alkaline rocks. The Sabzevar volcanic rocks have similar initial Sr, Nd and Pb isotope ratios, showing their cogenetic nature. Nd model ages cluster tightly around ~. 0.2-0.3 Ga. The geochemistry of the Sabzevar volcanic rocks, along with their isotopic signatures, might strangle that an upper mantle source, metasomatized by slab-derived melts was involved in generating the Sabzevar calc-alkaline rocks. A bulk rock trace element modeling suggests that amphibole-plagioclase-titanite-dominated replenishment-fractional crystallization (RFC) is further responsible for the formation of the middle Eocene Sabzevar adakitic rocks. Extensional tectonics accompanied by lithospheric delamination, possibly assisted by slab break-off and melting at depth was responsible for the Eocene formation of the Sabzevar magmatic rocks and, more in general, for the magmatic "flare-up" in Iran. © 2016.

We study migmatites and other metamorphic rocks in the Zanjan-Takab region of NW Iran and use these results to report the first evidence of Oligocene core complex formation in Iran. Four samples of migmatites associated with paragneisses, including leucosomes and associated para-amphibolite melanosomes were selected for U-Pb dating and Hf-O isotopic analysis. Zircon cores - interpreted as originally detrital zircons - have variable ages that peak at ca. 100-110 Ma, but their sedimentation age - indicated by the youngest 206Pb/238U ages - is ca. 35-40 Ma. New zircons associated with incipient melting occur as overgrowths around zircon cores and/or as newly grown grains. Morphologies and internal structures suggest that rim growth and formation of new zircons were associated with partial melting. All four samples contain zircons with rims that yield 206Pb/238U ages of 28-25 Ma, indicating that partial melting occurred in Late Oligocene time. δ18O values for zircon rims vary between 8.2 and 12.3‰, significantly higher than expected for mantle inputs (δ18O ~6‰) and consistent with equilibrium with surface materials. Zircon rims yield εHf(t) between 2.2 and 12.4 and two-stage Hf model ages of ~448-562 Ma, indicating that the region is underlain by Cadomian-Caledonian crust. According to the Hf-O isotopic values, the main mechanism forming zircon rims was dissolution of pre-existing detrital zircons with reprecipitation of new zircon shortly thereafter. Oligocene ages indicate that partial melting accompanied core complex formation in the Zanjan-Takab region. Extension, melting, and core complex formation in south-central Iran are Eocene in age, but younger ages of Oligocene-Miocene in NW Iran and Turkey indicate that extension was distributed throughout the region during Cenozoic time. © 2015 Elsevier B.V..

Podiform chromitites are common within the mantle section of the Late Cretaceous Sabzevar ophiolite in NE Iran. We studied chromitite pods and related ultramafic rocks from three Sabzevar massifs: Baghjar-Kuh Siah, Gaft Chromitite Mine and Forumad peridotite-chromitite. These represent an upper mantle sequence just below the Sabzevar Moho. The Baghjar-Kuh Siah mantle sequence contains plagioclase lherzolites, enriched in bulk REEs, with low Cr# spinels and MORB-like clinopyroxenes. These lherzolites formed due to the impregnation of MORB-like melts. The Gaft and Forumad harzburgites are depleted in trace and rare earth elements and thus are residues after high degree of partial melting (more than exhaustion of Cpx). The Gaft Chromitite Mine includes two types of podiform chromitites, high Cr# and low Cr#. The melt precipitating high Cr# spinel was boninitic whereas the melt forming the low Cr# chromitites was tholeiitic. Most Forumad massif chromitites have high Cr# spinels, although those rich in silicate inclusions are aluminous. Trace and REE element patterns of Forumad harzburgite clinopyroxene are similar to those in supra-subduction zone (SSZ) peridotites while those of Baghjar-Kuh Siah lherzolites are similar to MOR peridotite clinopyroxenes. These mineral data are also consistent with bulk rock trace and rare earth elements composition of their host peridotites. Field observations indicate that early tholeiitic magmas were followed by late boninites, as revealed in chromitite compositions as well as mantle rocks and dikes. We suggest a time-integrated model for the evolution of the Sabzevar mantle sequence during an early stage of subduction initiation associated with formation of an incipient arc. In this scenario, MORB-like melts (forearc basalts) formed first, causing low Cr# chromitites and plagioclase-clinopyroxene impregnations. Subsequent arc-like or boninitic melts with increasing contribution of slab-derived fluids were responsible for the formation of replacive dunites and high Cr# chromitites. © 2013 International Association for Gondwana Research.

Carboniferous igneous rocks constitute volumetrically minor components of Iranian crust but preserve important information about the magmatic and tectonic history of SW Asia. Ghushchi granites and gabbronorites in NW Iran comprise a bimodal magmatic suite that intruded Ediacaran-Cambrian gneiss and are good representatives of carboniferous igneous activity. Precise SIMS U-Pb zircon ages indicate that the gabbronorites and granites were emplaced synchronously at ~320Ma. Ghushchi granites show A-type magmatic affinities, with typical enrichments in alkalis, Ga, Zr, Nb and Y, depletion in Sr and P and fractionated REE patterns showing strong negative Eu anomalies. The gabbronorites are enriched in LREEs, Nb, Ta and other incompatible trace elements, and are similar in geochemistry to OIB-type rocks. Granites and gabbronorites have similar εNd(t) (+1.3 to +3.4 and -0.1 to +4.4, respectively) and zircon εHf(t) (+1.7 to +6.2 and +0.94 to +6.5, respectively). The similar variation in bulk rock εNd(t) and zircon εHf(t) values and radiometric ages for the granites and gabbronorites indicate a genetic relationship between mafic and felsic magmas, either a crystal fractionation or silicate liquid immiscibility process; further work is needed to resolve petrogenetic details. The compositional characteristics of the bimodal Ghushchi complex are most consistent with magmatic activity in an extensional tectonic environment. This extension may have occurred during rifting of Cadomian fragments away from northern Gondwana during early phases of Neotethys opening. © 2014 Elsevier B.V..

Kashmar granitoids outcrop for ~100km along the south flank of the Sabzevar ophiolite (NE Iran) and consist of granodiorite and monzogranite along with subordinate quartz monzonite, syenogranite and aplitic dikes. These granitoids intruded Early to Middle Eocene high-K volcanic rocks and can spatially be grouped into eastern and western granitoids. Five samples of granite have identical zircon U-Pb ages of ca. 40-41Ma. The granitoids have quite high K2O (~1.3-5.3wt.%) and Na2O (~1.1-4.6wt.%) with SiO2 ranging between ~62 and 77wt.%. They are metaluminous to peraluminous, calc-alkaline and I-type in composition. Their chondrite-normalized REE patterns are characterized by LREE enrichment and show slight negative Eu anomalies. Kashmar granitoids have low whole rock εNd (-0.43 to -2.3), zircon εHf values (-1.9 to +7.2), and somewhat elevated δ18O (+6.1 to +8.7‰) in the range of I-type granites. The Kashmar granitoids show Early Neoproterozoic zircon second-stage Hf and bulk rock Nd model ages at ca. 500-1000Ma (associated with ca. 640Ma old inherited zircons). Bulk rock Nd-Sr isotopic modeling suggests that 10-20% assimilation of Cadomian lower crust by juvenile mantle melts and then fractional crystallization (AFC process) can explain the Sr-Nd isotopic compositions of Kashmar granitoids. Kashmar granitoids are products of crustal assimilation by mantle melts associated with extension above the subducting Neotethyan Ocean slab beneath SW Eurasia. Similar subduction-related extension was responsible for the flare-up of Eocene-Oligocene magmatism across Iran, associated with core complex formation in central Iran. © 2014 Elsevier B.V..

Middle to Late Paleozoic ophiolites, which are remnants of the Paleo-Tethys Ocean, are aligned in two main zones in northern Iran: Darrehanjir-Fariman-Mashhad, and Rasht in the north and Jandagh-Anarak ophiolites to the south. Our new U-Pb zircon dating results show that the ~200km long Darrehanjir-Mashhad mafic-ultramafic body is not a single ophiolite but a composite igneous complex composed of Permian pillow lavas and pelagic sediments in fault contact with a small outcrop of Devonian intrusive and ultramafic rocks. Darrehanjir intrusive rocks have U-Pb zircon ages of 380.6±3.7Ma and 382.9±3.7Ma respectively, ~100Ma older than published ages for gabbros and radiolarites intercalated with lavas near Mashhad and Fariman. Mantle peridotites from the Devonian complex contain low Cr# spinel, similar to that in MORB-type peridotites. Devonian Darrehanjir gabbros and Permian Mashhad sequences both have boninitic and calc-alkaline signatures, respectively. The δ18Ozircon values from the Devonian ferrodiorite (δ18Ozircon~4.6±0.3‰) are slightly lower than the 5.2 to 5.4‰ expected for MORB-type zircons whereas Devonian plagiogranitic zircons mostly have δ18Ozircon <5‰, perhaps reflecting involvement of hydrothermally altered crust. Similar, strongly positive values of zircon εHf(t) for plagiogranite (av. +14.9) and ferrodiorite (av. +13.8) indicate melt derivation from depleted asthenosphere. Darrehanjir-Mashhad ophiolitic rocks can be divided into groups with high εNd (>10.3) and low εNd (<5.4) for both Permian and Devonian suites. Most Darrehanjir-Mashhad rocks are characterized by radiogenic 207Pb/204Pb and 208Pb/204Pb, indicating the involvement of subducted terrigenous sediments in the source. The Mashhad-Darrehanjir mafic-ultramafic complex demonstrates that this part of Paleo-Tethys evolved from oceanic crust formation above a subduction zone in Devonian time to accretionary convergence in Permian time. Iranian Paleozoic ophiolites and oceanic igneous complexes along with those of the Caucasus and Turkey in the west and Afghanistan, Turkmenistan and Tibet to the east, define a series of diachronous subduction-related marginal basins that were active from at least Early Devonian to Late Permian time. © 2014 International Association for Gondwana Research. [/accordion]
AUTHOR KEYWORDS: Komatiite; Paleozoic ophiolites; Supra-subduction zone-type magmatism; U-Pb zircon dating; Zircon εHf(t)
PUBLISHER: Elsevier Inc.

Moghadam, H.S., Corfu, F., Chiaradia, M., Stern, R.J., Ghorbani, G. Sabzevar Ophiolite, NE Iran: Progress from embryonic oceanic lithosphere into magmatic arc constrained by new isotopic and geochemical data (2014) Lithos, 210-211, pp. 224-241.

DOI: 10.1016/j.lithos.2014.10.004

The poorly known Sabzevar-Torbat-e-Heydarieh ophiolite belt (STOB) covers a large region in NE Iran, over 400km E-W and almost 200km N-S. The Sabzevar mantle sequence includes harzburgite, lherzolite, dunite and chromitite. Spinel Cr# (100Cr/(Cr+Al)) in harzburgites and lherzolites ranges from 44 to 47 and 24 to 26 respectively. The crustal sequence of the Sabzevar ophiolite is dominated by supra-subduction zone (SSZ)-type volcanic as well as plutonic rocks with minor Oceanic Island Basalt (OIB)-like pillowed and massive lavas. The ophiolite is covered by Late Campanian to Early Maastrichtian (~75-68Ma) pelagic sediments and four plagiogranites yield zircon U-Pb ages of 99.9, 98.4, 90.2 and 77.8 Ma, indicating that the sequence evolved over a considerable period of time. Most Sabzevar ophiolitic magmatic rocks are enriched in Large Ion Lithophile Elements (LILEs) and depleted in High Field Strength Elements (HFSEs), similar to SSZ-type magmatic rocks. They (except OIB-type lavas) have higher Th/Yb and plot far away from mantle array and are similar to arc-related rocks. Subordinate OIB-type lavas show Nb-Ta enrichment with high Light Rare Earth Elements (LREE)/Heavy Rare Earth Elements (HREE) ratio, suggesting a plume or subcontinental lithosphere signature in their source. The ophiolitic rocks have positive εNd (t) values (+5.4 to +8.3) and most have high 207Pb/204Pb, indicating a significant contribution of subducted sediments to their mantle source. The geochemical and Sr-Nd-Pb isotope characteristics suggest that the Sabzevar magmatic rocks originated from a Mid-Ocean Ridge Basalt (MORB)-type mantle source metasomatized by fluids or melts from subducted sediments, implying an SSZ environment. We suggest that the Sabzevar ophiolites formed in an embryonic oceanic arc basin between the Lut Block to the south and east and the Binalud mountains (Turan block) to the north, and that this small oceanic arc basin existed from at least mid-Cretaceous times. Intraoceanic subduction began before the Albian (100-113 Ma) and was responsible for generating Sabzevar SSZ-related magmas, ultimately forming a magmatic arc between the Sabzevar ophiolites to the north and the Cheshmeshir and Torbat-e-Heydarieh ophiolites to the south-southeast. © 2014 Elsevier B.V.

Post-collisional volcanism in northwestern Iran is represented by the Saray high-K rocks including leucite-bearing under-saturated and leucite-free silica saturated rocks. We report Ar-Ar age data which constrain the age as ca. 11Ma (late Miocene). Most of clinopyroxene phenocrysts from the volcanic rocks have complex oscillatory zoning, with high Ti and Al cores, low Ti and high Al mantled clinopyroxenes, grading into low Ti and Al outer rims. All the rocks are highly enriched in incompatible trace elements and have identical Sr-Nd-Pb isotopes. Enrichment in incompatible elements and other geochemical features for the Saray lavas suggest a metasomatized sub-continental lithospheric mantle (SCLM) as the magma source. The negative Nb-Ta-Ti anomalies for the Saray lavas compare with the features of subduction-related magmatism with negligible contamination with ancient crustal components. The highly radiogenic 87Sr/86Sr and 207Pb/204Pb isotopic values of the Saray lavas imply the involvement of slab terrigenous sediments and/or a continental lithosphere. Isotopically, the volcanic rocks define a binary trend, representing 5-8% mixing between the primary mantle and sediment melts. Our melting models suggest residual garnet in the source and are incompatible with partial melting of amphibole and/or phlogopite bearing lherzolites, although the complex geochemical features might indicate the result of mixing between melts produced by different sources or a homogenous melt passing through a compositionally-zoned mantle during multiple stages of partial melting and melt migration. The geochronological, geochemical and isotopic data for the Saray rocks suggest that these Late Miocene magmas were derived from a small degree of partial melting of subduction-metasomatized (subcontinental) lithospheric mantle source in a post-collisional setting. 11Ma. © 2013 International Association for Gondwana Research.

The studied area is situated about 70 Km in west of Damghan, and from the structural point of view, the area is part of south of central Alborz zone. Granitoid bodies intruded into late Eocene volcanic and volcanoclastic, mainly composed of monzonite and granite composition. Mineralogically, these rocks contain quartz, plagioclase, alkalifeldspare, amphibole, clinopyroxene, biotite, zircon, apatite, and opaque minerals. Textures of rocks are microgranular and field and textural evidences show that the plutones are hypabyssal. In variation geochemical diagrams show two distinct fields and is categorized as monzonite (metalminous) and granite (peraluminous). Geochemical studies indicate that the nature of magma from these rocks located in calc-alkaline field and belongs to I-type granitoids of continental volcanic arcs. Iron mineralization with mainly composition of hematite occurred at the contact of masses and host pyroclastic and limestones rocks, along faults and fractures zones. © SGEM2011 All Rights Reserved by the International Multidisciplinary Scientific GeoConference SGEM.

Lajaneh Fe skarn deposit is located in south of Shahrood City, North East of Iran. Mineralization is occurred as massive, veins and breccias in the contact of the dioritic intrusion with limestone. The dioritic intrusions in Lajaneh Fe skarn deposit display calc alkaline and metaluninous nature with I type characteristic. Tectonic setting discrimination diagrams show that dioritic intrusions in Lajaneh deposit belongs to volcanic arc granitoids (VAG). Negative anomalies of HFS elements like Nb, Ti, Ta and P and positive anomalies of K and Pb show a volcanic continent arc related to subduction. SiO2 content of intrusive rocks in Lajaneh deposit coincide with pluton rocks related to worldwide Fe skarn mineralization. But major oxide content of Al2O3, TiO2, MgO, P2O5 of dioritic intrusions of Lajaneh deposit coincide with pluton composition related to Cu and Fe skarns mineralization. The content of trace elements like V, Cr and Ni in Lajaneh deposit is similar to pluton composition of worldwide Fe skarn deposits. © SGEM2011 All Rights Reserved by the International Multidisciplinary Scientific GeoConference SGEM.