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Geochemistry and fluid-inclusion microthermometry of the Farsesh barite deposit, Iran

Zarasvandi A., Zaheri N., Pourkaseb H., Chrachi A., Bagheri H.

Geologos

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2014

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Vol. 20, No. 3

201--214

EN

The Permian carbonate-hosted Farsesh barite deposit is located southeast of the City of Aligudarz in the prov-ince of Lorestan, Iran. Structurally, this deposit lies in the Zagros metallogenic belt and the Sanandaj-Sirjan Zone. Barite mineralisations occur as open-space filling veins, and as massive and replacement ores along fractures, faults and shear zones of the Permian carbonate host rocks. In order to determine the structure, in addition to pe-trographic and fluid-inclusions studies, an ICP-MS analysis was carried out in order to measure the major as well as the trace and rare earth elements. The Farsesh barite deposit has a simple mineralogy, of which barite is the main mineral, followed by calcite, dolomite, quartz, and opaque minerals such as Fe-oxides. Replacement of bar-ite by calcite is common and is more frequent than space-filling mineralisation. Sulphide minerals are minor and mainly consist of chalcopyrite and pyrite, which are altered by weathering to covellite, malachite and azurite. Petrographic analysis and micro-thermometry were carried out on the two-phase liquid/vapour inclu-sions in ellipsoidal or irregularly shaped minerals ranging in size from 5–10 μm. The measurements were conducted on fluid inclusions during the heating and subsequent homogenisation in the liquid phase. The low homogenisation temperatures (200–125°C) and low to moderate salinity (4.2–20 eq wt% NaCl) in-dicate that the barite had precipitated from hydrothermal basinal water with low to moderate salinity. It appears from the major and trace elements that geochemical features such as Ba and Sr enrichment in the barite samples was accompanied by depletion of Pb, Zn, Hg, Cu and Sb. The geochemistry of the rare earth elements, such as low ΣREE concentrations, LREE-enrichment chondrite-normalised REE patterns, the negative Ce and positive Eu anomalies, the low Ce/La ratio and the positive La and Gd anomalies, suggest that the Farsesh barite was deposited from hydrothermally influenced sea water. The Farsesh deposit contains low-temperature hydrothermal barite. The scatter plots of the barite (close to sea water) in different areas on the CeN/SmN versus CeN/YbN diagram support the possibility that the barite was formed from seawater-bearing hydrothermal fluids.

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Geochronology of plutonic rocks from the Sanandaj-Sirjan zone, Iran and new zircon and titanite U-Th-Pb ages for granitoids from the Marivan pluton

Sepahi A. A., Shahbazi H., Siebel W., Ranin A.

Geochronometria

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2014

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Vol. 41, no. 3

207--215

EN

The Sanandaj-Sirjan zone of Iran is a metamorphic belt consisting of rocks which were metamorphosed under different pressure and temperature conditions and intruded by various plutons ranging in composition from gabbro to granite. The majority of these granitoids formed along the an-cient active continental margin of the Neo-Tethyan ocean at the southeastern edge of the central Ira-nian microplate. Geochronological data published in recent years indicate periodic plutonism lasting from Carboniferous through Mesozoic to late-Paleogene times (from ca. 300 to ca. 35 Ma) with cli-max activity during the mid- and late-Jurassic. The age constraints for plutonic complexes, such as Siah-Kouh, Kolah-Ghazi, Golpayegan (Muteh), Azna, Aligoodarz, Astaneh, Borujerd, Malayer (Samen), Alvand, Almogholagh, Ghorveh, Saqqez, Marivan, Naqadeh and Urumieh, clearly indicate the periodic nature of magmatism. Therefore, the Sanandaj-Sirjan zone preserves the record of mag-matic activity of a complete orogenic cycle related to (1) Permocarboniferous(?) rifting of Gondwana and opening of the Neo-Tethyan ocean, (2) subduction of the oceanic crust, (3) continental collision and (4) post-collision/post-orogenic activities. The formation of the Marivan granitoids, northwestern Sanandaj-Sirjan zone, for which we present U-Pb zircon and titanite ages of ca. 38 Ma, can be related to the collisional and post-collisional stages of this orogenic cycle.

3

Mineral chemistry and thermobarometry of plutonic, metamorphic and anatectic rocks from the Tueyserkan area (Hamedan, Iran)

Sepahi A. A., Borzoei K., Salami S.

Geological Quarterly

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2013

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Vol. 57, No. 3

515–-526

EN

The study area is a part of the NW to SE striking Sanandaj–Sirjan metamorphic belt in western Iran. The Alvand Pluton, consisting of rocks that range in composition from gabbro to granite, is the major magmatic rock complex of this area. Gabbroic rocks include olivine gabbro, gabbro norite, norite and gabbro. Rocks around the Alvand Pluton were subjected to different P–T conditions due to polymetamorphism. Common metamorphic rocks are meta-pelites, but some meta-psammites, meta-basites and meta-carbonates also occur. Slates, phyllites, schists, migmatites and hornfelses are major rock units of meta-pelites in the metamorphic sequence. Based on mineral chemistry, the highest temperature of crystallisation (1300°C) was determined for the olivine gabbros, and the lowest temperature (950°C) was calculated for the hornblende-bearing gabbros. Clinopyroxene–plagioclase barometry suggests that pressures near 5 to 6 kbars prevailed during the crystallisation of the various mafic rocks. P–T estimates yield maximum temperatures of 700–750°C at 5–6 kbars for the high-grade metamorphic rocks from the metamorphic aureole around the pluton. These results indicate that the heat released from the Alvand Pluton (T = 950–1300°C), which intruded the metamorphic rocks at middle and upper crustal levels, was sufficient to cause partial melting leading to formation of the metatexites, diatexites and restite-rich S-type granites. During this process, part of the deep-seated gabbro-dioritic rocks were transported to higher crustal levels by viscous, enclave- and crystal-rich granitic magmas of the partial melting zone.