Petrology
Hamid Karimzadeh; Mohammad Rahgoshay; Iman Monsef
Abstract
The petrographical examination of peridotites of the Nehbandan ophiolitic complex revealed that the peridotites of Kalateh Shahpouri, Qadamgah, Lah-Kouh, Cheshmeh anjir, Bandan, and Zolfaghari were of harzburgite type and Sefid-Kouh and Nasfandeh-Kouh were of lherzolite type. Generally, the types of ...
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The petrographical examination of peridotites of the Nehbandan ophiolitic complex revealed that the peridotites of Kalateh Shahpouri, Qadamgah, Lah-Kouh, Cheshmeh anjir, Bandan, and Zolfaghari were of harzburgite type and Sefid-Kouh and Nasfandeh-Kouh were of lherzolite type. Generally, the types of clinopyroxenes in the peridotites of this complex were diopside. The geochemical investigation of clinopyroxenes in Mg# vs. Al2O3, Cr2O3, and TiO2 graphs and Ti vs. Nd, Zr, and Sr graphs shows that the peridotites of Nasfandeh-Kouh, Bandan, Zolfaghari, and Sefid-Kouh with a low degree of partial melting belong to the Abyssal tectonic setting and back-arc basin.on the other side, the harzburgites of Kalateh Shahpouri and Cheshmeh anjir were formed in the Supra-subduction zone tectonic setting and fore-arc basin and have a high degree of partial melting. The study of incompatible elements, LILE and HFSE in spider diagrams normalized to the primary mantle and as well as the study of REEs in spider diagrams normalized to the chondrite for clinopyroxenes confirm this issue. Therefore, Nasfandeh-Kouh and Sefid-Kouh lherzolites as well as Qadamgah, Lah-Kouh, Bandan, and Zolfaghari harzburgites with a low degree of depletion were more consistent with the Mid-oceanic ridgestectonic setting, and the harzburgites of Kalateh Shahpouri and Cheshmeh anjir were close to the Supra-subduction zone tectonic setting with a high degree of depletion.
Petrology
Farzaneh Valinasab Zarnagh; Mohsen Moayyed; Ahmad Jahangiri; Hossein Azizi
Abstract
There are discontinuous outcrops of volcanic rocks in the West Azarbaijan province and in the north of Maku city. These volcanic complex were bimodal and compose of acidic and basic lava and pyroclastic rocks. Mineral chemistry studies show that clinopyroxenes in the studied rocks are diopside. These ...
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There are discontinuous outcrops of volcanic rocks in the West Azarbaijan province and in the north of Maku city. These volcanic complex were bimodal and compose of acidic and basic lava and pyroclastic rocks. Mineral chemistry studies show that clinopyroxenes in the studied rocks are diopside. These pyroxenes have a high magnesium number (0.87 to 0.99). Magma series and tectonic determination diagrams show that the basaltic rocks that make up the studied clinopyroxenes have an alkaline nature and were formed in a whitin plate environment. According to geothermobarometry studies, clinopyroxenes were formed at temperature 1100 - 1250 ° C and pressure of 3 - 9 Kbar. The depth for generation of magma was at about 22 kilometers.
Petrology
Ashraf Torkian; nafiseh salehi
Abstract
The Ahmadabad, Tahmoures and Ghareh-toreh volcanoes are part of the volcanic centers located on the Qorveh-Bijar axis and constitute a part of the magmatic outcrops of the northern arm of the Sanandaj Sirjan Zone, Hamadan-Tabriz. Volcanic rocks have basaltic composition and show porphyritic, microlithic ...
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The Ahmadabad, Tahmoures and Ghareh-toreh volcanoes are part of the volcanic centers located on the Qorveh-Bijar axis and constitute a part of the magmatic outcrops of the northern arm of the Sanandaj Sirjan Zone, Hamadan-Tabriz. Volcanic rocks have basaltic composition and show porphyritic, microlithic porphyry and glomeroporphyritic textures. Major phenocrysts include clinopyroxene and olivine. The abundance of clinopyroxene is found to be lower in Ghareh-toreh basalts, olivine is major phenocryst in this center. Clinopyroxene phenocrysts show normal, in some cases, reverse zoning and gulf corrosion indicating disequilibrium with the host's melt. The results of thermobarometric calculation (temperature and pressure) using clinopyroxene mineral indicate the temperatures of 1100-11300 °C and pressures of 3 to 11 kbar for Ahmadabad and Tahmoures volcanoes, and volcanic basalts at Ghareh-toreh reveal the temperature of 800 Up to 1100 °C and pressure of 0 to 3 kbar. The high oxygen fugacity in these rocks and the coherence of the temperature and pressure of the olivine phenocryst in this region with the temperature and pressure of the clinopyroxene in Ahmedabad and Tahmoures, all show that clinopyroxene crystals of Ghareh-toreh volcano formed at a lower depth and possibly in a shallow reservoir
Z. Nasr Esfahani; M. H. Emami; S. J. Sheikhzakariaee; S. H. Tabatabaei
Abstract
The study area is located in the Isfahan province and at the north of East Alloun Abad village. This area is a part of Urmia - Dokhtar belt in Central Iran. A large part of the area is formed from Eocene igneous rocks. These rocks include basaltic andesite and pyroclastic rocks of ignimbrite and ...
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The study area is located in the Isfahan province and at the north of East Alloun Abad village. This area is a part of Urmia - Dokhtar belt in Central Iran. A large part of the area is formed from Eocene igneous rocks. These rocks include basaltic andesite and pyroclastic rocks of ignimbrite and tuff. These rocks show porphyritic and microlithic texture with plagioclase, amphibole and clinopyroxene as the main mineral constituents. The secondary minerals such as chlorite, calcite, epidote and iron oxide are formed due to alterations. Electron microprobe analyses reveals that clinopyroxenes are diopside - augite. The study of clinopyroxene chemistry showed that the water was between 2 to 10% during clinopyroxene crystallization. The parental magma was calc-alkaline and tectonic setting is a subduction-related environment, based on clinopyroxene composition. Geothermobarometry of clinopyroxene gives temperature range of 925-1091°C and pressures range of 2-10 kbars for the formation of clinopyroxene in these rocks.
M Fadaeian; A Jahangiri; M Moayyed
Abstract
The study area is located in the Ardabil province and in the north east of Meshkinshahr city.More than 200 small and large Eocene age dykes have outcrops in this area with basaltic, tephritic, andesitic and trachy andesit composition. Clinopyroxene, plagioclase, analcime and sometimes coarse olivine ...
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The study area is located in the Ardabil province and in the north east of Meshkinshahr city.More than 200 small and large Eocene age dykes have outcrops in this area with basaltic, tephritic, andesitic and trachy andesit composition. Clinopyroxene, plagioclase, analcime and sometimes coarse olivine crystals are present in these rocks. Mineral chemistry studies suggested that clinopyroxene type in rocks is Diopside type. Existence of normal and reverse zoning in clinopyroxens deduces differentiation were effective factors on evolution of the rocks. Enriched elements Ti, Al, Na, and K of pyroxene core to the rim of the effect of metasomatism to in these rocks. Tectonomagmatic diagrams and compare the chemical composition of study area clinopyroxenes with other tectonic environment suggested that characteristics of alkaline rocks related to volcanic arc. According to geotermobarometric studies clinopyroxenes in study rocks formed at temperature 1150-1200ºC and pressure of 7-14 Kbars. The depth for generation of magma between 55-65 Km and average 60 Km estimated for these rocks.
Z Azimzadeh; A Jahangiri; E Saccani; Y Dilek
Abstract
The Misho gabbroic massif with an east- west trend, 30 Km length and 7 Km wıdth is penetrated in the Infra-Cambrian Kahar formation. The micro-gabbroic dykes have cut this intrusive massif. Gabbros have homogenous compositions and major phases are plagioclase and pyroxene and minor minerals are ...
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The Misho gabbroic massif with an east- west trend, 30 Km length and 7 Km wıdth is penetrated in the Infra-Cambrian Kahar formation. The micro-gabbroic dykes have cut this intrusive massif. Gabbros have homogenous compositions and major phases are plagioclase and pyroxene and minor minerals are olivine, amphibole, biotite, K-feldespar and opaque minerals. Their texture is granular. The results of EMP analysis of clinopyroxenes show that they have diopside to augite compositions. In different diagrams, gabbros mostly show tholiitic composition with MORB affinities in tectonic setting. Pyroxenes generally have high SiO2 (50.02-52.69 wt %), high Mg number [Mg/ (Mg+Fe2+)] (78.59-82.42wt %), variable Al2O3 (1.8–5.09 wt %), low TiO2 (0.53-1.33 wt %), low Na2O (0.21-0.47 wt %) contents and low Al [6]/Al [4] ratios (0-0.39), suggesting relatively low pressure crystallization conditions of the magma. The temperature calculated for the clinopyroxenes in gabbros is 1027-1306oC and pressure is less than 8 Kbars. The investigations of variation trends of clinopyroxene compositions don’t show any zoning in clinopyroxenes and clinopyroxenes are in chemical equilibrium with other minerals in the rocks. The obtained textural and mineral chemical data, suggest that the clinopyroxenes may have crystallized from a tholiitic magma derived from a depleted lithospheric mantle. This is confirmed by the whole-rock chemistry. The gabbroic massif intrusion in a tectonic setting of extensional rifting followed by the opening of Paleotethyan oceanic crust in early Carboniferous in NW Iran.
