جستجوی مقالات مرتبط با کلیدواژه « granitoid » در نشریات گروه « علوم پایه »

The granitoides of west Ardakan are outcropped in the middle part of the Central Iran zone. Quartz, orthoclase and plagioclase are the main minerals and amphibole, biotite, sphene, zircon and apatite are secondary minerals. The dominant textures are medium to fine grain granular, granophyry and myrmikite[r1] . According to mineral chemistry data, calcic amphiboles of magnesiohornblende to actinolite nature have crystallized at temperatures of 530-890 ºC. Oligoclase to andesine plagioclased crystallized at 700-800 ºC. Magnesium biotites was crystallized at 650-730 ºC. On the basis of the oxidant conditions, magnetite are formed as opaque. The chemical analysis of all these minerals show the mantle nature of the magma. Magma seems to suffer produced these minerals, moderate to severe crustal contamination during its ascent. These granitoides are I type and calc-alkaline and were formed in the subduction setting related to the active continental margin.

The Early Jurassic (≈180 Ma) Gowd-e-Howz (Siah-Kuh) granitoid stock is located in the southern part of the Sanandaj-Sirjan metamorphic belt, southeast of Iran in Kerman Province. This granitoid stock is intruded into the Upper Paleozoic metamorphic and Triassic igneous-sedimentary rocks and covered by Jurassic rock units and Lower Cretaceous limestones. The main part of the stock is granodiorite with medium- to coarse-grained anhedral granular texture and mineral assemblage of amphibole, biotite, plagioclase, alkali feldspar, and quartz. Biotite, as one of the main ferromagnesian minerals of this body, has a primary igneous origin and iron rich composition. The different magmatic series and tectonic discrimination diagrams indicate that the magma was of subduction zone-related I-type calc-alkaline series, crystallized under medium to high oxygen fugacity, and equilibrated at temperatures and pressures of 589 to 875 °C and 0.45 to 2.27 kbar, respectively, during magma emplacement in the crust.

The study area is located about 30 km south of Ramsar, in the central Alborz zone. In addition to the Nusha granitoids (with an age of about 56 million years), the outcrops in this area, mainly include Paleozoic and Mesozoic rock units. Petrographically, the Nusha granitoids have diorite, syenite, monzonite, monzodiorite, granodiorite and quartz monzonite compositions. Moreover, mineralogically, feldspar is the principal mineral, and the texture superiority in them belongs to the granular type. In terms of magmatic series these rocks are metaluminous and range from high K calcalkaline to shoshonitic. The geochemical characteristics of the major and rare elements, as well as the petrographic ones indicate that these granitoids are I type granites, and at the same time they belong to high temperature ones based on the behavior of Ba, Ce and Y elements. Enrichment in LILE and LREE and low concentrations of heavy rare earth elements HREE and high field strength elements HFSE, together with Nb and Ti negative anomaly in the spider diagrams are signs of magmas related to the subduction zone. The high temperature nature and characteristics such as Y/Nb, Rb/Sr and Rb/Ba ratios show that the Nusha granitoids have the geochemical properties of both crustal and mantle origin materials with different ratios. Based on tectonomagmatic discrimination diagrams and trace element compositions, these granitoids belong to an active continental margin environment. The parental magma has originated from melting of an enriched mantle source and contaminated with continental crust during ascent.

Tourmaline is an indicator mineral of pegmatite, granites and pneumatolytic veins. In metamorphic rocks, it is formed by the process of boron metasomatism and in sediments by the recrystallization of destructive particles. This mineral crystallizes in various temperatures, pressures and geological environments so can be widely used in lithological studies.The study areas are part of the geological map of Kashan located in the west of the volcanic belt of Central Iran (Urmia-Dokhtar belt). A number of studies have been carried out regarding the geological and petrological of the areas of study: Among those, petrology and geological studies of metamorphic aureole in Qohroud granitoid (Ahankoub, 2003), petrography and petrology of Qohroud plutonic rocks (Jafari, 2001), the type of garnet zoning in skarns of Qohroud Intrusion (Farazdel et al., 2005) and geochemistry and petrology of mafic-intermediate intrusions in mineralized region of Qamsar, Kashan Yar-Ali (2016) are more notable. The purposes of the present study are to determine the origin of tourmalines from the study areas on the base of their petrographic and geochemical characteristics as well as their structural formula and to compare these minerals as well.

Following field observations, 25 thin sections were prepared for mineralogical and textural studies using Olympus polarizing microscope (BH2). 10 samples of tourmalines were analzyed by XPM analysis at Binalood Company. The results of microprobe analyses of tourmalines from hornfelses (Ahankoub, 2003) carried out at the Oklahoma University (USA) were also used for the present study. All these data are given in Tables 1 and 2.

The areas under investigation are predominantly compose of sedimentary, metamorphic (hornfels, marble, skarn) and intrusive (granodiorite, monzogranite, tonalite) rocks. Plagioclase, orthoclase, quartz, hornblende, and biotite as major with sphene, zircon, tourmaline and opaque as minor minerals are dominant. Tourmalines in these areas are metasomatism in nature and as needles and small crystals. are mainly found in fractures. Tourmaline crystals with zoning, formed in post-crystallization and hydrothermal stages, were subjected to influence of boron-rich solutions presumably point to mixing of fluids in open systems. Green tourmalines replaced feldspars possibly caused by tourmalinization in the pneumatolitic stage by reactions of boron with wall rocks.Based on X position and Ca, Na, K contents, most of tourmalines are alkaline. The chemical composition of tourmaline in hornfels is mainly dravite and in granitoids is dravite with a tendency towards schorlite. The formation of tourmaline instead of biotite and chlorite in metamorphic rocks shows the its formation as a result of reactions of boron fluids with aluminosilicates. The studied tourmalines lie below the line  and therefore, have Al substitution in the Y position. As the Fe-Mg-Ca and Al-Mg-Fe diagrams display these tourmalines are mainly plotted within the metapelites and metapesamites in calcium poor quartz- tourmaline rocks. The ratio of FeO / FeO + MgO tourmalines from the hornfels is between 0.58 to 0.6 (ave. 0.59), which confirms they have crystallized in an open magmatic system with the presence of boron with an external origin and indicates the involvement of atmospheric water during their formation in the hydrothermal system. This ratio in tourmalines from the granitoids are between 0.56 to 0.69 (ave. 0.63), which can indicate the formation of these tourmalines during the mixing of magmatic and hydrothermal fluids.

The chemical composition of the studied tourmalines based on cationic substitutions is in the range of alkaline tourmalines, which indicates a higher amount of K and Na at position X compared to Ca and confirm their formation in acidic and low temperature conditions. The chemical composition of tourmalines from granitoids is in the range of dravite and schorlite and the chemical composition of tourmalines from hornfels are mainly dravite, which represents the cation exchanges of Fe, Mg in constant values of Ca and Al. The studied tourmalines are located in the range of calcium-poor metapelites and metapsamites and calcium-poor quartz-tourmaline rocks and coexist with the aluminum-saturated phase. Based on the amount of FeO / FeO + MgO in tourmalines, the openness of the system and the presence of boron from an external source is confirmed.

Fe skarn deposits are the largest skarn deposits which are exploited for Fe as well as by-products of Cu, Co, Ni and Au (Meinert et al., 2005). They are one of the most important Fe deposits in the Zanjan province which have been exploited in recent years. The Alamkandi Fe deposit is one of these Fe skarn deposits which is located at 35 km west of the Mahneshan within the Takab-Takht-e-Soleyman subzone, northern Sanandaj- Sirjan zone. In this area, alternation of amphibolite, amphibole schist and biotite schist with intercalations of marble belonging to Paleozoic and intruded by late Oligocene alamkandi granitoid exist. This intrusion has caused contact metamorphism and formation of Fe mineralization. Some of the Fe skarn deposits in the Zanjan province were studied during the past years (i.e., Nabatian et al., 2017; Mokhtari et al., 2019) and valuable information is present about their geological and mineralization characteristics. However, the Alamkandi granitoid and Fe deposit have not been studied until the present. In this research study, geochemistry and petrogenesis of the Alamhandi granitoid along with mineralogy, textures and geochemistry of Fe deposit and thermodynamic conditions for formation of contact metamorphic rocks have been studied.

This research can be divided into two parts including field and laboratory studies. Field studies include recognition of different parts of granitoid intrusion and skarn aureole along with sampling for laboratory studies. During field work, 65 samples were selected for petrographic and analytical studies. 19 thin sections and 13 polished thin sections were used for petrographical and mineralogical studies. For geochemical studies, 15 samples from granitoid and ore skarn sub-zone were analyzed by XRF and ICP-MS methods at the Zarazma laboratory, Tehran, Iran. 
  

Based on petrographic studies, the Alamkandi granitoid is composed of granodiorite, quartz diorite and porphyritic diorite. Granodiorites with hetrogranular texture are composed of plagioclase, quartz, K-feldspar, hornblende and biotite. Quartz diorites indicate porphyroid to seriate and hetrogranular textures and are composed of plagioclase, clinopyroxene, hornblende and quartz. Porphyritic diorites have porphyritic texture with plagioclase and amphiboles phenocrysts. The Alamkandi granitoids demonstrate calc-alkaline to high-K calc-alkaline affinity and can be classified as metaluminous I-type granitoids. Primitive mantle-normalized (McDonough and Sun, 1995) trace elements patterns for the Alamkandi granitoids indicate LILE and LREE enrichment along with negative HFSE anomalies and positive Pb anomaly. Chondrite-normalized (McDonough and Sun, 1995) REE patterns for these rocks demonstrate LREE enrichment (high LREE/HREE ratio). Based on tectonic setting discrimination diagrams, the Alamkandi granitoids were formed in the active continental margin.Fe mineralization in the Alamkandi area crops out in discrete places as massive and lens-shaped bodies. The Northern outcrop body has 150m length and up to 50m width, while the southern outcrop body has 100m length and up to 20m width.  Microscopic studies reveal that the skarn zone at the Alamkandi granitoid is composed of garnet skarn, pyroxene skarn, epidote pyroxene skarn, serpentine skarn, and ore skarn sub-zones. Magnetite is the main ore mineral along with some pyrite and chalcopyrite. Garnet, clinopyroxene, olivine, serpentine, epidote, actinolite, calcite and quartz are present as gangue minerals. Based on the field and microscopic studies, the Alamkandi Fe deposit has massive, banded, disseminated, brecciated, vein-veinlets, replacement and relict textures. Based on mineralogical and textural studies, the skarnization processes in the Alamkandi deposit can be divided into 3 stages including: (1) isochemical metamorphic stage, (2) prograde metasomatic stage and (3) retrograde metasomatic stage.

Based on skarn mineralogy, the XCO2 vs. T and T vs. logƒO2 diagrams were used to determine the possible physio-chemical conditions. According to these diagrams and considering mineralogical and textural evidence, maximum temperature for formation of olivine in XCO2≈0.1 and P=1kb was about 450-600°C. Furthermore, garnet and clinopyroxene were formed simultaneously at 430-550°C and ƒO2 equal 10-18 to 10-22. In temperatures less than 450°C, olivine was replaced by serpentine while in temperatures less than 430°C and increasing ƒO2, garnet and clinopyroxene were replaced by epidote + quartz + calcite and actinolite + quartz + calcite, respectively. In temperatures less than 430°C, fluids in equilibrium with granitic intrusion and with relatively high sulfidation (ƒS2>10-6), were not in equilibrium with andradite. Therefore, andradite was replaced with quartz + calcite + pyrite. With reducing ƒS2 (<10-6), andradite was replaced by quartz + calcite + magnetite. During the early retrograde stage, magnetite and pyrite were formed along with quartz and calcite. Mineralogical studies indicate that pyrite was formed after magnetite. In this regard, it seems that metasomatic fluids probably had ƒS2≈10-6.5 and less than 430°C temperature in the beginning of the retrograde stage. Presence of hematite lamella within the magnetite demonstrates that ƒO2 was probably about 10-22 in the beginning of retrograde stage.

Baghche-Maryam granitoid (in south of Ghorveh Area) is a part of the intrusive bodies of the Sanandaj-Sirjan zone with NW-SE trending. Based on field observations and mineralogical studies, the intrusion complex of Baghche-Maryam including of two acidic and intermediate units: diorite, monzodiorite, granite, syenite, and aplite. Geochemical studies show the rocks of this complex are metaalumine type (A/CNK= 0.81-0.46) and calc-alkaline. Petrological, mineralogical, and geochemical studies together with field observations indicate that these rocks are generated by various magmatic processes and are related to the active continental margin geodynamic environment (e.g. LREE enrichments and HREE depletions) and have I-type magmatic characteristics. According to thermobarometery studies, the average temperature in the studied samples is about 700 oC and the average depth is about 7-10 kilometers.

The chemical composition of biotite in mineralization associated with granitoids and copper porphyry deposits is sensitive to several chemical and physical factors. It is also related tomagmatic and hydrothermal activities including water concentration, halogen and metal deposits, oxidation-sulfidation equilibrium, volatility (in melt-fluid-vapor equilibrium), elemental distribution relationships, and temperature and pressure of economic deposits (Webster, 1997, 2004).

Detailed field studies have been done, and several thin sections and polished thin sections were studied by conventional petrographic methods. Thirty points of biotite grains were selected and analyzed by a CAMECA SX Five electron probe micro-analyzer with 15 kV accelerator voltage and 20 nA beam current (5 μm beam size) at the Institute of Geology and Geophysics in the Chinese Academy of Sciences (IGG-CAS). The results were processed using MICA + software (Yavuz, 2003a, 2003b).

The Geysour granitoid pluton (Lower Cretaceous) consists of granodiorite, mafic microgranular enclaves, and micro-granite sill. The granodioriticrocks are mainly composed of plagioclase, quartz, K-feldspar and biotite along with accessory minerals of zircon, apatite and magnetite. Mafic microgranular enclaves are composed of quartz diorite, granodiorite and biotite granite, with fine-grained to porphyry texture and large eyes of quartz and plagioclase assemblages. The microgranite has porphyry texture with a fine-grained groundmass. Its phenocrysts are plagioclase, quartz and biotite along with accessory minerals of allanite, needle like apatite, epidote and calcite.Biotite is the only ferromagnesian mineral in theGeysour granitoid which falls into the category of real trioctahedral mica. The biotites of granodiorite and enclave samples are in group I and group of ferrous biotites. The biotitesof microgranite samples are in group I and group of magnesium biotites (Tischendorf et al., 1997). In the 10*TiO2-(FeOtot+MnO)-MgO ternary diagram (Nachit et al., 2005) all the analyzed biotites fall into the field of reequilibrated primary biotite. The formation temperatures of biotites in granodiorite, enclave and microgranite are 653-732 oC, 631-724 oC and 689-732 oC, respectively (Luhar et al., 1984; Henry et al., 2005). The mean pressure values are about 4 Kbar ​​for granodiorite and enclave and 2 Kbar for microgranite (Uchida et al., 2007). Biotites of granodioriteand enclave biotites are located on top of the NNO buffer, which correspond to biotite compositions of magnetite series magmas, and biotites ofmicrogranite lie below the NNO buffer line and within the QFM buffer range. Biotite composition based discriminant diagrams cannot be used to determine the tectonic setting of the Geysour granitoids because they are low temperature I-type granites. The mean logarithmic ratios of fH2O to fHF and fHCl, and fHF to fHCl for the rocks studied are as follows: log(fH2O/fHF)fluid=4.56, log(fH2O/fHCl)fluid=4.47 and log(fHF/fHCl)fluid=-0.53. The first two values ​​are much larger than 1 indicating that the fluids are rich in water. Also, all biotites have high angles with linear trends of log(fHF/fHCl), log(fH2O/fHCl) and log(fH2O/fHF) indicating changes in fugacity conditions and halogen content of the fluid due to wall-rock reaction (Boomeri et al., 2009). Hydrothermal fluid fugacity ratio has been calculated for biotites of granodiorite, enclaves and microgranite samples at mean temperature of 661 oC, 654 oC and 703 o C, respectively, which indicate that hydrothermal fluids are of potassic type, because the log(fH2O/fHCl) is high, the log(fHF/fHCl) is slightly negative and the log(fH2O/fHF) is lower than that of phyllic alteration (Selby and Nesbitt, 2000). Meanwhile the magmatic fluid is significantly different from porphyry-type fluids (Baldwin and Pearce, 1982; Mason and Feiss, 1979; Selby and Nesbitt, 2000).

The Iranian plateau is part of the Alpine-Himalayan orogenic belt, which consists of several continental fragments separated from each other by major boundary faults and/or ophiolitic suture zones (Gansser, 1981). Generally, the tectonic evolution of Iran has been controlled by the opening and closure of the Proto-Tethys, Paleo-Tethys and the Neo-Tethys during the Precambrian-Cambrian, Paleozoic and Cenozoic, respectively.The study area is located in the northwest of Iran (the Kurdistan province) and 20 km northeast of the city of Saqez. This area is a part of the northern Sanandaj-Sirjan Zone (Aghanabati, 2005). This belt is response to opening and subduction of Neo-Tethyan oceanic crust beneath the Central Iran (Alavi, 1994). During Cretaceous-Tertiary eras, numerous granitoid bodies were formed in this belt. The Saheb granitoid is one of these granitoid bodies which mainly consists of monzogranite, quartz monzonite and quartz monzodiorite. The aim of this research study is to discuss the evolution of the Late Cretaceous-Early Paleocene Saheb granitoids in the Sanandaj-Sirjan zone based on geology, petrography and geochronology results.

In this study, 70 rock samples were collected from different types of intrusive rocks from which 30 thin sections were prepared for petrographic studies. Furthermore, four samples from the granitoid bodies (quartz monzonite, quartz monzodiorite and monzogranite) were selected for U-Pb dating. Approximately 100 to 150 zircon grains were hand-picked by a binocular microscope from each sample. Cathodo-luminescence imaging and dating of zircon grains were examined at the China University Geosciences (Wuhan branch). Geochronological analysis were performed by using the (LA)-ICP-MS method at the China University Geosciences (Wuhan branch). The detailed analytical method is presented in Liu et al. (2010a, 2010b).

Geology of the study area:

The Saheb granitoid body is located in the Sanandaj-Sirjan zone. According to the geological map of Chapan (scale: 1/100000, Kholghi khosraghi, 1999), the Precambrian to Quaternary units are exposed in the study area. The oldest units are the Kahar, Bayandor and Soltanieh Formations with Precambrian to Cambrian age. The Permian sediments, the Ruteh and Doroud Formations, include sandstone, shale and carbonate. The Jurassic units are found in the northwest of the region, and include sandstones and shale. The Cretaceous sedimentary units are located in the south of the study area. These sediments contain sandstone, limestone, silty-limestone, shale and dolomitic limestone. During Late Cretaceous-Early Paleocene era the Saheb granitoid intruded within the oldest units and caused Fe skarn type deposits in the Saheb area. The Saheb granitoid have been cut by a series of diabasic dikes.

The Saheb granitoid consists of several intrusive bodies containing quartz monzonite, quartz monzodiorite and monzogranite. The major minerals in the quartz monzodiorite consist of plagioclase (35- 40%), quartz (15- 20%), orthoclase (20- 25%), and mafic minerals such as biotite and amphibole (10-15%) with granular texture. The quartz monzonitic rocks show granular and poikilitic textures. Plagioclase (25- 35%), quartz, orthoclase (30- 40%), biotite and amphibole (10-15%) are the main important minerals in the quartz monzonite. Plagioclase (20-25%), quartz (20-30%), orthoclase (30-40%), biotite and amphibole (15%) are the major minerals in the monzogranite.Zoning in zircon crystals from all four samples is well developed representing their magmatic origin (Hancar and Miller, 1993). Measurements of U-Pb in the Saheb granitoid zircon grains of quartz monzonite samples show their ages to be 62.03±0.56 Ma and 58.9±0.9 Ma. The age of monzogranite is 67.9±1.3 Ma and the age of quartz monzodiorite is 61.1±0.56 Ma. Generally, the age of this granitoid body indicates that the Saheb granitoid has occurred during the Cretaceous- Paleocene time.

Based on field and microscopic studies, the Saheb granitoid bodies have been divided into three types of quartz-monzonite, quartz-monzodiorite and monzogranite. The field and mineralogical studies suggest that the Saheb granitoid is an I-type granitoid. The mineralogical variations in this granitoid suggest that the fractional crystallization has played an important role in differentiation of different compositional phases in the Saheb granitoid.According to the geochronological results, during Late Cretaceous to Early Paleocene, the Saheb granitoid intruded within the Permian and Cretaceous units in the magmatic-metamorphic Sanandaj-Sirjan zone. These granitoids were formed by subduction of Neo-Tethys Ocean beneath the Iranian plateau. It should be mentioned that the intrusion of these granitoids into the Permian carbonates and Cretaceous carbonate and shale caused formation of skarn type iron oxide mineralization.

The Saheb Fe-Cu skarn deposit is located in the Sanandaj-Sirjan metamorphic belt, SE Saqqez, western Iran and has been formed along the contact between the Oligo-Miocene aged Saheb granitoid and the Permian aged impure calcareous rocks and includes endoskarn and exoskarn. Exoskarn is widely developed and include garnet and epidote skarn zones. The majority of mineralized zones are concentrated in garnet skarn. The relatively oxidizing mineralogical assemblage of the Saheb skarn includes garnet (andradite-grossular), pyroxene (diopside-hedenbergite), magnetite and hematite. Magnetite is the main and abundant ore mineral throughout the ore deposit. Based on field evidences and microscopic studies of skarn zone samples, two stages of prograde and retrograde alteration are distinguishable. According to the results of sample analysis of Saheb skarn productive intrusive body by XRF and ICP-MS techniques, the combination of this body is chiefly granite to granodiorite-diorite and belong to the I-type granitoids, metaluminous and K-rich calc-alkaline series. The Saheb granitoid is related to the VAG (Volcanic Arc Granite) tectonic setting.

Fe skarn deposits are one of the important Fe deposits in the Zanjan province which have been exploited in recent years. The Qozlou Fe deposit is one of these Fe skarn deposits which is located at 65 km west of Zanjan. In this area, alternation of micro-sparitic limestone, marly limestone, shale and sandstones of Upper Cretaceous were intruded by Late Eocene granitoids. This event caused to metamorphism contact and it caused the formation of Fe mineralization. Some of the Fe skarn deposits in the Zanjan province were studied during the past few years (e.g. Nabatian et al., 2017) and valuable information is present about their geological and mineralization characteristics. However, Qozlou granitoid and Fe deposit have not been studied yet. In this research, petrology and geochemistry of the Qozlou granitoid along with petrographic characteristics, mineralogy, structure and texture of Fe deposit and thermodynamic conditions for formation of contact metamorphic rocks have been studied.

This research study can be divided into two parts including field and laboratory studies. Field studies include The recognition of different parts of granitoid intrusion and skarn aureole along with sampling for laboratory studies. Thus, 50 samples were selected for petrographic and analytical studies. 16 thin sections and 16 thin-polish sections were used for petrographical and mineralogical studies. 13 samples from granitoid and ore skarn sub-zone were analyzed by XRF and ICP-MS methods at the Zarazma laboratory, Tehran for geochemical studies.

Based on petrographic studies, the Qozlou granitoid is composed of porphyritic granite-granodiorite and quartz monzodiorite. Porphyritic granite-granodiorite have porphyritic to porphyroidic, micro-graphic and felsophyric textures and are composed of plagioclase, quartz, K-feldspar, hornblende and biotite phenocrysts within quartz-feldspatic groundmass. Quartz monzodiorites indicate porphyroidic texture and they are composed of plagioclase, hornblende, quartz and K-feldspar. The Qozlou granitoid demonstartes high-K calc-alkaline affinity and it is classified as metaluminous I-type granitoids. Trace elements normalized by primitive mantle (Sun and McDonough, 1989) for Qozlou granitoid indicate LILE and LREE enrichment along with negative HFSE anomalies and distinctive positive Pb anomaly. Chondrite-normalized (Nakamura, 1974) REE patterns for the Qozlou granitoid demonstrate LREE enrichment (high LREE/HREE ratio). Based on tectonic setting discrimination diagrams, the Qozlou granitoid were formed in active continental margin. Microscopic studies reveal that the skarn zone in Qozlou is composed of garnet skarn, garnet-pyroxene skarn, pyroxene skarn, epidote skarn, and pyroxene-bearing marble sub-zones. The Ore zone is present as massive and lens-shaped with 300m length and up to 30m width. Magnetite is the main ore mineral along with some pyrite, chalcopyrite and pyrrhotite. Garnet, clinopyroxene, epidote, actinolite, calcite and quartz present in skarn zone. Based on field and microscopic studies, the Qozlou Fe deposit indicates massive, banded, disseminated, brecciated, vein-veinlets, replacement and relict textures. Based on mineralogical and textural studies, skarnization processes in the Qozlou deposit can be divided into 3 stages including: (1) isocheimal metamorphic stage, (2) prograde metasomatic stage and (3) retrograde metasomatic stage. Chondrite-normalized (Sun and McDonough, 1989) REE and trace element patterns for different skarn samples and porphyritic granite demonstrate similar patterns.

Since all of minerals present in the Qozlou skarn aureole are located in Ca-Fe-Si-C-O-H system, we used the temperature vs. logƒO2 diagram (Einaudi, 1982) to determine possible physico-chemical conditions for skarn formation in the Qozlou. Based on this diagram and considering mineralogical and textural evidence, garnet and clinopyroxene were formed simultaneously in 430-550°C and ƒO2 equal 10-23 to 10-26. In the temperature less than 430°C and increasing ƒO2, garnet and clinopyroxene replaced by epidote, actinolite, quartz and calcite, respectively. Furthermore, in temperature of less than 430°C, fluids in equilibrium with granitic intrusion and with relatively high sulfidation (ƒS2>10-6), were not in equilibrium with andradite. Therefore, andradite was replaced by quartz, calcite and pyrite. With reducing ƒS2 (<10-6), andradite was replaced by quartz, calcite and magnetite. During the early retrograde stage, magnetite and pyrite were formed along with quartz and calcite. Mineralogical studies indicate that pyrite was formed after magnetite. Based on this, it seems that metasomatic fluids probably had ƒS2≈10-6.5 and had less than 430°C temperature in the beginning of the retrograde stage. Presence of hematite lamellae within the magnetite demonstrates that ƒO2 probably was 10-22 in the beginning of retrograde stage.

The late Paleocene – early Eocene granitoid intrusions in the northern Sistan suture zone are regarded as potential tools to record tectonic events. A structural study of the Zahri granitoid body, based on the anisotropy of magnetic susceptibility (AMS) technique provides new data to characterize the internal structure and the kinematic reconstruction. The NW–SE trending body consists basically granite to leucogranite. Based on the results of the analysis of over 360 samples collected from 36 sites, the granitoid body is characterized by a low susceptibility and petrographic observations indicate that paramagnetic minerals such as biotite and amphibole are the most important iron-bearing mineral and can be considered as the main carrier of magnetic susceptibility. Magnetic foliations dominated by moderate dip and foliation strike mostly parallel to the elongated shape of the body, the magnetic lineation mainly trends NE-SW to N-S with plunges to the SW (mean orientation N 197°/32°) and formed during the emplacement and crystallisation of the magma. The Zahri body emplaced in an extensional setting controlled by a NNE-SSW opening direction associated with spaces of the sinistral shear zone in the terminations of Nehbandan fault system during the early Eocene.

The Nokeh intrusion exposed in the northern Semnan area. The intrusion is composed of monzonite-quartz monzonite and granite-granodiorite and was intruded in the Eocene carbonaceous tuffs, where the country rocks converted to magnetite-skarn. Plagioclase, orthoclase, quartz, biotite, amphibole and clinopyroxene are the constituent minerals of Nokeh intrusion. The study rocks represent granular, granophiric and mirmekitic textures. The Nokeh intrusion is metaluminous to peraluminous, calc-alkaline, I-type and belongs to subalkaline magmatic series. Based on EMPA data, clinopyroxenes, amphiboles, biotites and plagioclases are diopside, edenite, Mg-biotite and oligoclase to labradorite in compositions and formed in temperatures ranged from 1110 to 1160, 700, more than 800 and less than 700 °C respectively. Clinopyroxene, amphibole and biotite calc-alkaline affinity, low Ti and Ca-Si enrichment in the clinopyroxene composition and amphibole formation in a high-fugacity environment, confirm that Nokeh intrusion formed in a magmatic arc of active continental margin. On the basis of tectonic discrimination diagrams, the investigated samples fall into volcanic arc domain resulted in subduction of Neothetian oceanic lithosphere beneath Central Iran block.