نشریه پترولوژی
پیاپی 22 (تابستان 1394)

The Sungun porphyry copper deposit is located in the NW of Iran. Most rock outcrops in the region and the surrounding area comprise the Cretaceous metamorphosed and skarnish carbonates and the Eocene volcanic rocks that intruded by the Sungun monzonitic to quartz monzonitic stock. The Sungun stock crosscut by late-and post mineralization dykes. The Sungun porphyry stock was emplaced in 21 Ma ago and then late-and post mineralization dykes intruded at the 19.78 and 19.51 Ma ago, respectively. Zircon trace element data indicates that all the studied zircons are magmatic in origin and the source of the Sungun porphyry monzonite is different from late-and post mineralization dykes. According to Ti-in- zircon thermometry, the porphyry Sungun stock and the late dykes were crystalized at about 650 and 700 °C, respectively. Rare earth element abundances in the zircon crystals show that the Sungun porphyry has crystallized from productive and high ƒO2 melt. Our dating results indicate that porphyry mineralization in the Arasbaran belt occurred in the early Miocene time and about 10 m.y. earlier than the Kerman belt and in a post-collisional tectonic setting.

The Tutak metamorphic complex located in the southern part of the Sanandaj-Sirjan zone, is among the areas where the Paleozoic rocks are well exposed. This metamorphic complex mainly comprise of the Cambrian to the early Carboniferous marble, schist, amphibolite and genesis units. Garnet-biotite thermometric method and Garnet-biotite-muscovite barometric method carried out on dark schist from the Tutak metamorphic complex repersent 423 °C and 1.6 kb in the early stage of metamorphism to 708 °C and 5.9 kb during peak of metamorphism. These temperatures and pressures point to amphibolite facies conditions. The thermal cessation and also the marked difference in the degree of metamorphism between the Tutak complex and the late Carboniferous- early Permian succession in Surian, indicate that this phase of metamorphism probably occurred prior to the Late Carboniferous period.

The Chah Nali Au-Ag silicic veins are located 160 km northwest of Iranshahr and 70 km north of Bazman town in Lut block. The veins are mainly hosted by basaltic and andesitic rocks that were altered to silicic, phyllic, argillic and propylitic alterations around the veins. Symmetrical crustified structures and colloform, cockade and breccia textures are the common features of the veins. The gold grade is high in the veins (up to 16 ppm Au). The sulfides mainly occur in silicic zone and can be divided into primary and secondary sulfides. The chemistry of sulfides and elemental maps of As, Au and Ag were determined and provided by an electron probe micro analysis (EPMA). The elements that were quantitatively measured are Sb, Zn, Pb, Hg, Cd, Bi, Au, Se, Te, Cu, Fe, Mn, As, Ag and S. Pyrite, chalcopyrite, galena, sphalerite and tetrahedrite occur as primary sulfides and covellite, Ag-rich covellite and an Ag-rich new mineral occur as secondary sulfides. In general, Au concentration is low in the studied sulfides but Ag concentration is relatively high in the sulfide-bearing ores. The investigated Au-Ag mineralization is an Ag-rich low sulphidation epithermal system that was probably formed by hydrothermal solutions that are related to the young volcanic activities.

In the south of Tabriz northern part of Uromieh-Dokhtar magmatic zone a set of volcanic rocks crop out with composition of andesite, dacite, rhyodacite and rhyolite with Upper Miocene to Plio-Quaternary in age. This paper reports the dacitic, rhyodacitic and rhyolitic lavas erupted within the pyroclastic rocks. The most abundant minerals in these rocks are plagioclase and amphibole with various textures such as felsitic porphyric, microlitic porphyric, sieve, flow and glomeroporphyric. Based on geochemical study, these rocks are characterized by SiO2 ranging from 58.2 to 69.7 wt%, high Al2O3 (15.1-17.5 wt%) and Sr (391-804 ppm), high Sr/Y (30.7-84.46), La/Yb (13.27-67.36) ratios, and low Y (3.6-20.8ppmindicating the adakitic characteristic of the parent magmas. The parent magma of these rocks has calc-alkaline and per-aluminous nature which is characteristics of the arc volcanics. These rocks fall into the field of high-silica adakites (HAS) in classification diagrams. Enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in heavy rare earth elements (HREEs) are observed in their MORB, primitive mantle and chondrite normalized spider diagrams. Strong depletion in HFSEs including Nb, Ti and P which is signature of arc volcanic, can be observed in these rocks. Intensive fractionated pattern of REEs and low quantities of HREEs and Y may prove existence of garnet or amphibole in the residua of melt. High Sr and negative anomalies of Ta, Nb, and Ti may be resulted from lack of plagioclase and having iron and titanium oxides in the residua phase. According to the petrogenetic diagrams, the parental magma of the rocks studied generated by partial melting of an eclogitic-garnet amphibolitic source derived from metamorphism of the Neotethyan subducted oceanic slab underneath the Cetral Iranian zone. Also, the magma has been subjected to assimilation, fractional crystallization (AFC) and crustal contamination during ascend to higher levels and emplacement. The presence of the corrosion and chemical disequilibrium of the phenocrysts and their sieve textures in these rocks support the occurrence of these processes.

The Alborz-Azerbaijan magmatic plateau (AAMP), in the northwestern part of Iran, is one of the main exposes of magmatic activities in the Cenozoic. The Salavat range is located in the eastern part of AAMP, and widely occur in alkaline lavas and dykes Based on field studies, mineral chemistry, and whole-rock geochemistry, alkaline rocks in the Salavat range are classified into two groupsthat are composed of analcimite, analcime bearing breccias and analcime bearing tephrite pillow lavas (group I), tephrite-phonotephrite and lamprophyre dykes (group II). These rocks cover a broad compositional range from sodic to transitional sodic-potassic and potassic series, all of which are high-K in character. On the basis of whole-rock chemistry, alkaline rocks in the Salavat range resulted from a phologopite/amphibole-bearing peridotite source in garnet-spinel lherzolite transitional zone that underwent metasomatism processes. Geochemical data indicated partial melting of subcontinental lithospheric mantle source, played major roles in the formation and evolution of the Salavat range rocks, whereas crustal contamination seems to be restricted to minor effect. The Salavat range magma was generated in a collision-related extensional setting, following the closure of the Neotethys Ocean in the Cenozoic.

The Bultaq shear zone is located 185 km north-west of Isfahan. The study area is a part of the Sanandaj–Sirjan zone, which is affected by ductile and brittle–ductile deformation and consists of slate, schist(garnet-muscovite schist, enriched quartz-muscovite schist and biotite-muscovite schist), amphibolite marble, metavolcanic, andesite and tuff. There are several duplex structures and thrusts with NW-SE-trend and NE dip in the Bultaq shear zone. This shear zone is parallel to the Zagros Organic thrust. Also, boudinage structures geometric analysis, mesoscopic scale asymmetric folds, microscopic studies of S-C, S-Ć cleavages and σ- type porphyroclast confirmed right-lateral strike-slip movement. These fabrics show right rounded cuts in region in some parts. Mylonitic foliations were used to calculate elongation (e) and stretch (s) in this area. The microstructures were formed under green schist to amphibolite facies conditions. The metamorphic rocks have been formed in a Barrovian metamorphism type (medium temperature - pressure) and affected by three metamorphic and deformation phases. The metamorphic phases include dynamothermal, dynamic and retrograde and the deformation phases are D1, D2 and D3.

The sub volcanic rocks in Shazand area (the Markazi province) which formed a part of the Sanandaj-Sirjan zone are composed of dacitic rocks with major minerals such as plagioclase, quartz, alkali feldspar and minor minerals such as biotite, zircon and apatite. One of the characteristic features of these rocks is the existence of two types of enclaves with dacitic and andesitic compositions. The former, share similar mineralogical composition with the host dacitic rocks and the latter is characterized by the presence of amphibole phenocryst (pargasite), orthopyroxene (enstatite) and plagioclases (labrador-bytownite). Thermometry on biotite and feldspar from the host dacite rocks showed temperature range of 675 and 600 ºC, respectively. The calculated temperature formation for biotite, feldspar and pargasite from the andesitic enclaves are 620, 650 and 810 ºC, respectively. LREE enrichment in comparison with HREE, high LILE relative to HFSE, negative anomalies of Nb, Ti, P, and positive anomalies of Pb, K indicate that these rocks formed in subduction zones. Also, the geochemical characteristics of these rocks reveal that the nature of magma is calc-alkaline enriched in potassium derived from partial melting of continental crust units related to normal active continental margin volcanic arc.

The study area is situated in the south of Sahand volcano in the northwest of Iran. The volcanic rocks in this area are part of young activity of Sahand volcano, erupted as flow lavas and tuff or tephra units consisting of ash, punce, lapilli, agglomerate and volcanic breccia which overlay the Pliocene sedimentary units. The r composition of rocks is predominantly dacite with porphyry texture with fine grain matrix and glassy and trachyte textures. Geochemical data show that the subalkaline dacite rocks is adakitic composition and are characterized by high amount of Sr, LREE, LILE and high ratios of Na2O/K2O with differentiated pattern of REE, low ratios of HREE and Y. Depletion in Nb, Ti and HREE and enrichment in LILE and LREE are all evidences of subduction adakitic magmatism. The adakitic rocks in the study area were probably formed by slab break off and melting of oceanic isolated crust. Post collisional magmatism related to the Neotethyan subduction caused the formation of adakitic magmatic rocks in the south of Sahand and the northernmost of the Uromieh-Dokhtar magmatic zone.

The Jebale-Barez plutonic complex is composed of granitoid intrusive bodies and is located in the east and northeast of Jiroft and south of the Kerman province. The plutonic complex is composed of granodiorite, quartz diorite, syenogranite and mostly granite. This plutonic complex includes abundant rounded and ellipsoid magmatic enclaves ranging in size from a few millimeters to 30 centimeters and varying in composition from quartz diorite, monzodiorite to quartz monzodiorite. These enclaves are very fine-grained and show chilled margin and their crystal size gradually decreases from center to the margin. The chilled margin is an evidence of rapid magma cooling once the enclaves were surrounded by host felsic magma. The mingling of two magmas is testified by presence of the disequilibrium textures such as: poikilitic and antipertite textures in the K-feldspar megacrysts, rounded, corroded and altered plagioclases, mafic clots, acicular apatites, small lath-shaped plagioclases in the large plagioclases as well as the occurrence of mafic microgranular enclaves with crenated and cuspate contact with the felsic -host rocks. Also, the plagioclase crystals display essentially normal and occasionally oscillatory zoning. The enclaves and their host rocks, geochemically is different. The former is Na-enriched whilst the latter is enriched in K. Furthermore, the enclaves are depleted in LREE and LILE while are enriched in HREE and Ti in analogy to their host granodiorites. Therefore, it seems that the enclaves and granodiorites have been originated from two different magmas which were placed adjacent to each other by magma mingling and mixing process.

The Robat ophiolite complex is located along the Nain- Baft fault and at the western margin of the Lut block. The volcanic rocks in the Robat ophiolites consisting of pillow lavas, lava flows and massive units that are classified as andesi-basalts, andesites, trachy-andesites, dacites and rhyolites. Geochemical results show that these rocks have tholeitic and calc -alkaline affinities and reside in supra-subduction related arc settings in tectonic discrimination diagrams. Studying the geochemical behavior of elements by using various petrogenetic diagrams suggest the occurrence of two different mantle sources for Robat volcanic rocks: 1) a mantle source which was affected slightly to moderately by slab fluids and/or melts and is responsible for arc island tholeitic series, 2) a mantle source which is highly effected by melts derived from melting of sediments associated with subducting slab, and is responsible for calc -alkaline series. It seems that the emplacement of the volcanic rocks in the Robat ophiolitic sequence was probably the result of processes related to the initial subduction process, upwelling and partial melting of subducted sediment and asthenospheric fluids in the source, along with differentiation and melting of portions of the oceanic crust.