نشریه پترولوژی
پیاپی 23 (پاییز 1394)

The studied area is located in east of Nahavand which is a part of Sanandaj-Sirjan zone. The petrographic and geochemical investigations show that, these rocks consist of basalt, andesite-basalt, andesite, trachy-andesite and dacite. Porphyritic, glomeroporphyritic, microlitic, hyalomicrolitic and comb textures are the common textures in the studied volcanic rocks. Two alteration zones including: argillitic and sericitic zones developed in this region. Alteration products are sericite, kaolinite, chlorite, hematite and calcite. Copper mineralization has occurred primarily in these rocks as filling voids and fractures. Malachite, covellite, magnetite, hematite and bornite are found within the veins. The geochemical data show that these rocks are related to calc-alkaline and shoshonitic magma series. Enrichment in LILE and LREE and depletion in HREE and HFSE with negative anomalies of Ti, Nb along with other evidences, such as high Th/Yb and their position on the tectonic discrimination diagrams indicate that the volcanic rocks in discussion were emplaced into the subduction zone related to an active continental margin setting. The Nahavand volcanic rocks lie in young and immature volcanic arcs or in the initial stages of volcanic arc formation. This situation is consistent with geological history of Sanandaj-Sirjan zone during the Jurassic to the Cretaceous ages.

The gabbroic intrusion of the Parishan Mountain in the south of Qorveh (Kurdistan province) is located between the villages of Zarrineh to Tekyeh-bala and based on structural divisions, it is a part of the Sanandaj-Sirjan zone. Based on petrographic features it consists of hornblende-pyroxene gabbro, gabbro, quartz-gabbro, dioritic gabbro, diorite and quartz-diorite rocks. Geochemical studies indicate that magma has metaluminous and calc-alkaline nature with medium potassium. Variation diagrams trends don’t confirm the continuous chemical between the samples. The negative correlation between the variations of SiO2 against oxides of Mg, Fe and Ca suggest fractional crystallization process for both of magmas. Tectonic setting discrimination diagrams indicate that magma depends to volcanic arc in active continental margin of related subduction zones. LREE enrichment in comparison to HREE and LILE enrichment and depletion of elements (i.e. Ti, Zr, Nb and Ta) can be due to crustal contamination and dependence of the body to subduction zones. The low Mg# value, high SiO2 contents, positive Yb and negative Ho anomalies suggest that mafic magma was originated from a metasomatized mantle, which it has melted lower crust. The linear and positive trends of incompatible elements against each other, suggests the role of fractionation crystallization in the mafic-intermediate magmas. Furthermore, field relationship and petrographic evidences show that mingling process of two magmas, including mafic and felsic magmas (intermediate), which are consistent with the tectonic setting of the studied area.

The Quaternary volcanism from north of Sanandaj-Sirjan zone, in the west of Iran is a part of widespread series of the Quaternary syn-collisional magmatism in the Turkish- Iranian high plateau. This plateau is a part of the active Arabian-Eurasian collision zone. The basic lavas (basanites, hawaiites and alkali basalts) were erupted with main trend (NW-SE) of the Bitlis-Zagros Suture. Most of the basic lavas from the study area (Qorveh-Bijar region) show enrichment in the large ion lithophile elements (LILE, e.g., Rb, Ba, Sr) and light rare earth elements (LREE), the Takab basaltic rocks have lower LREE. The La/Nb ranging for all of the lavas is >1. Sr- Nd isotope ratios of these basalts reflect mantle source characteristics. The negative Nb anomaly and fractionation of LILE in these rocks may be depending on fractionation of minerals (Amphibole, Rutile) in the source. The geochemical characteristics suggest that, these rocks could be developed from small melting of thick Eurasia lithospheric mantle underneath the Turkish-Iranian plateau. The lithosphere delamination or slab break-off mechanisms in the study area with this thickness (~150-200 km) from metasomatised lithospheric mantle could not be the causes for partial melting of this mantle and finally ascent the magma in the study area. The generation of the Kurdistan lava is related to the melting of metasomatized mantle beneath this area which is an indication of subduction of Tethys underneath Eurasia prior to collision.

The outcrop of mylonitic granite-gneiss in the northwest of Azna city and the northeast of the Jan building stone mine is a part of Sanandaj-Sirjan zone. The tourmalines from these rocks are black and patchy or fine association. Based on EPMA data the tourmalines studied are shorl-dravite in composition with more tendency towards shorl. They belong to granitic environment and precipitated during hydrothermal condition. The chemical composition of the host granite is a major factor in distribution of elements in the studied tourmaline structural framework during the process of differentiation, as well as, faulting and uplifting of granitoid body. Some of the dominant substitution mechanisms in the structure of the investigated tourmalines are as follow: □X Al (Na R2+)-1, 21 xNa-1 zAl-1+xCa1 YR (OH)-1, Fe2+ Fe3+) (Mg Al)-1.

The Baba-Nazar garnet deposit mineralized in hornfelsic body is located 80 km of NE of Takab town, Western- Azarbayedjan province. Ten samples from coarse-grained garnets of various colors were selected for major elements analysis by XRF and nine of these samples were analyzed for trace elements by ICP-OES. The presence of hornfels and carbonates in the contact with Doran granite intrusion indicates a skarn contact metamorphism garnet deposit in the area. Garnet crystals of 1-2 cm size are observed in anhedral to subhedral form of mainly deep green color. They show isotropic and high relief features in polarized light associated with abundant fractures. Major element analysis indicates that the Baba-Nazar Garnet consists of andradite-grossularite groups but in three samples the pyrope content is exceptionally higher than that of the grossular. The presence of grossular and andradite is revealed by XRD analysis. All the garnet minerals with different colors indicate enrichment of Zr, U, Y, Ti and V and depletion of Ba, Hf, Nb, Ta, Sc, Co and Th. REE's elements normalized to chondrites, in garnet with various colors garnet indicate enrichment of LREE's compared to HREE's and weak positive europium and positive cerium anomaly.

The study area is located in NW of Varzeghan in the Eastern Azarbaijan province. Based on tectonic units, this area is situated in the Alborz-Azarbaijan subzone of the Central Iran zone. According to field studies the studied volcanic rocks are composed of andesitic cones and lava flows with porphyritic texture. Petrographic studies indicate that they have porphyritic texture with fine-grained to glassy matrix. Glomeroporphyritic, vesicular and poikilitic textures are also present. The main phenocrysts minerals are: plagioclase, hornblende, clinopyroxene and opaque minerals. Apatite, quartz, biotite are the accessories and the secondary minerals are: sericite, iddingsite, epidote, clays minerals, chlorite and opaques. According to geochemical classification, the studied rocks are intermediate and are plotted on the field of andesite. These rocks are plotted on the fields of calc-alkaline to high-K calc-alkaline series. On the REE diagrams the studied rocks display enrichment of LREE's respect to HREEs, which is a feature of calc-alkaline rocks of active continental margin volcanoes. Based on various geochemical diagrams, tectonic setting of the studied rocks is analogous with tectonic features of active continental margin arc settings. Investigation on the source nature of the studied rocks by using various geochemical diagrams and petrological modeling indicate that they have been generated by 1-5% partial melting of garnet lherzilitic source which enriched by addition of releasing fluids from subducting slab in the subduction environment and this magma has been subjected to upper crust contamination through ascending to above levels.

The post-ophiolite igneous rocks with dacite/rhyolite composition outcropped in the ophiolitic complex of Sabzevar zone. The calc-alkaline and high silica adakitic nature of these rocks has been proved previously. The rocks display initial 87Sr/86Sr ratios and εNd(t) values of 0.70444 to 0.70382 and +5.30 to +6.18 respectively, as same as these values in MORB compositions. These isotopic signatures are corresponding to adakitic compositions derived from melting of the Cenozoic oceanic subducted slabs. The emplacement age of these rocks into the Sabzevar ophiolitic zone obtained about 48 Ma by SHRIMP II U–Pb method on separated zircons. The results show that parental magma of the Sabzevar adakitic rocks generated by partial melting of a garnet-amphibolite or eclogite source derived from metamorphism of Sabzevar subducted oceanic lithosphere in early Eocene time. Magma differentiation via amphibole fractionation was the main factor in the manifestation of more adakitic signatures in more-evolved rocks (rhyolites).

The Keybarkuh area is situated in the northeast of the Lut block. The rock units of the area are the Paleozoic metamorphic rocks and the Cretaceous to Tertiary intrusions with granite to diorite composition. The intrusive rocks are divided into oxidant and reduced series. The reduced intrusive rocks are granite and granodiorite with hypidiomorphic granular texture. The main minerals consist of feldspars, quartz, muscovite and less biotite. The reduced intrusions are mostly moderate to high-K and mostly metaluminous. Their tectonic setting mostly plot in the boundary between subduction and continental collision. LREE enrichment relative to HREE is observed. The Eu negative anomalies and depletion of Sr and Ba can be attributed to the presence of residual plagioclase in a source and redox conditions. Depletion of Sr, Zr, Hf and Ti relative to Rb, K, La, Ce, Nd and Tb indicate the involvement of continental crust in generation of magma. The initial 87Sr/86Sr isotope ratio, initial 143Nd/144Nd isotope ratio and εNd values could be considered as representative of reduced continental crust derived magmas. The age of muscovite granite unit was determined 137 Ma, belong to the early Cretaceous (Valanginian), using zircon U-Pb method. Field observation (lack of exnolith), petrography (the presence of amphibole and lack of restite minerals), geochemical data (high-K calc-alkaline, metaluminous and radiogenic isotopes) and magnetic susceptibility (reduced type) indicate these intrusions are reduced I-type intrusive rocks resulting by partial melting of continental crust, which mostly show metagreywackes to amphibolite source.

The study area is located in the north of Eastern Azarbaidjan (NW Iran). In this area, mineralization of molybdenum-copper is associated with intrusive bodies and developed in the center of Gharehdagh (Gharehchilar-Gharehdarreh) batholith. Petrological and petrographic investigations show that the intrusive bodies have compositions from diorite,through monzonite and granodiorite to granite. These bodies are I-type and mainly metaluminous and calc-alkaline with medium to high potassium belonging to volcanic arcs (VAG) tectonic setting. The principal alterations zones in the mineralized areas include silicic, potassic, phyllic and propylitic. Potassic and potassic-phyllic alterations are frequently seen around the molybdenum-bearing veins and veinlets. The proportions of Mo, Si, K, Rb, Ba and REE's are increased in differentiated biotite-bearing acidic intrusive bodies. Enrichment of K, Rb and Ba and depletion of Zr, Ta, Y, Yb and Nb in intrusive bodies indicate metasomatism of upper mantle materials with subducting oceanic crust and subsequent generation of magma and its passage through relatively thick crustal rocks.The intrusive bodies associated with Mo-mineralization have often quartz-monzonitic to granodioritic composition.

The metabasites of the Nain ophiolites consisting of amphibole + plagioclase ± garnet ± clinopyroxene ± epidote rock forming minerals. On the basis of mineralogical paragenesis, thermobarometry calculations, textural and mineral relations as well as the stability field of different mineralogical assemblages, the metamorphic evolution of the area contain three metamorphic stages as prograde, peak and retrograde indicating clockwise metamorphic trajectory. According to the mineralogical evidences and thermobarometry data, the temperature and the pressure conditions of metamorphic climax stage of garnet-clinopyroxene amphibolite samples is equivalent to high pressure granulite subfacies and transition zone between amphibolite and high pressure granulite. The genesis setting of such high grade metamorphic rocks in the ophiolitic regions are the root of mature islands arc and hot subduction zones. The consensus about the existence of narrow and young oceanic basins (back arc) derived from Neo-Tethys subduction beneath Central Iran micro-continent indicating subduction of young oceanic slab in a hot subduction zone and the generation of high grade metabasites in the Nain ophiolitic complex.