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Volume 16, Issue 1 (4-2008)
Abstract
Eocene volcanic rocks of north Anarak area are as scattered as masses. These rocks cross the Anarak schists and Ashin-Zavar ophiolites but had not metamorphosed them. Their outcrops follow the direction of within the area faults. Mineralogicaly, these rocks are limited in composition from Andesi-Basalt and Andesite to Dacite. These rocks have phenocrysts of amphibole and plagioclase in microcrystalline and microlitic matrix. The andesitic and andesibasaltic rocks in the study area have a lot of enclaves that contain many amphiboles. Type of the amphiboles is Magnesiohastingsite. Similarity of composition of amphiboles and biotites in the volcanic rocks and their enclaves indicate that these volcanic rocks and their enclaves are possibly cogenesis. There are three types of feldspar in these rocks that are andesine-oligoclase, alkali feldspar and bytownite. Bytownite is found only in certain enclaves. Geothermometry studies on phenocrysts of plagioclase and amphibole, that are in equilibrium, indicate that crystallization temperature of these phenocrysts is 835°c to 925°c.
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Volume 17, Issue 4 (1-2010)
Abstract
Eocene volcanic rocks in NE of Ordib, have a very good exposures near and along the Turkmeni-Ordib fault. These rocks, that are situated in the inner part of the Central Iran and margin of the Yazd block, comprise trachyte, trachy-andesite and basaltic trachy-andesite. Trachy-andesite is the pervasive rock unit. Rock forming minerals of these rocks are chloritized olivine, plagioclase, pyroxene, mica, amphibole, K-feldspar, quartz, ilmenite, magnetite and calcite. The most important mineralogical characteristics of the studied trachy-andesites are wide range of minerals in one rock sample, including two types of clinopyroxene, mica, plagioclase, sanidine, formation of reactionic clinopyroxene and calcite around the quartz, and oscillatory zoning of feldspars and amphiboles. Chemistry of clinopyroxenes and biotites with whole rock geochemical analyses, reveal that these rocks are similar to the continental volcanic arc rocks. Petrography and mineral chemistry demonstrate the magma mixing occurrence in formation of these rocks.
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Volume 22, Issue 3 (10-2014)
Abstract
Eocene volcanic rocks in SW of Choupanan are exposed along the Choupanan fault as lava with andesite, trachyandesite to dacite composition and pyroclastic rocks. This area is a part of Central Iran (Yazd block). Andesite is the most predominant rock unit of the area and is composed of feldspars (andesine, oligoclase, and sanidine), amphibole (magnesio hastingsite, magnesian hastingsite, magnesio hornblende, and ferropargasite), mica (biotite and phlogopite), quartz, clinopyroxene (diopside, augite), garnet, opaque minerals (ilmenite, magnetite, titanomagnetite, and hematite), zircon, sphene and apatite. Minerals which are produced by alteration are calcite, chlorite (diabantite), and prehnite. SiO2 content of these rocks ranges 55.1 to 61.1 wt% and LREEs exhibit an evident enrichment. These volcanic rocks present a transitional affinity (between calc-alkaline and shoshonitic) and geochemically are similar to the volcanic arc rocks. The field, petrography and geochemical studies reveal that the studied andesites are formed by same petrogenetic processes and affected by magma mixing and contamination during crystallization.
Miss Marzieh Ghadirpour, Mr Ghodrat Torabi, Mrs Marjan Ghaderi, Mrs Fereshteh Bayat, Mrs Nargess Shirdashtzadeh,
Volume 31, Issue 3 (10-2023)
Abstract
The Kuh-e-Kalut-e-Ghandehari is located about 40 Km northwest of the Anarak (northeast of Isfahan). This area is a part of the Central Iran that is situated in west of the Yazd block; near to the Ashin ophiolite and drastic directional changes of the Great Kavir Fault. In the northwest of Anarak, the Ashin ophiolite is covered by the Cretaceous limestones, and crossed by the Eocene volcanic rocks. The Upper Eocene gabbro-diorite stock cross cuts the Eocene volcanic rocks. Andesites are the predominant unit of the Eocene volcanic rocks. They are grey to dark- grey in colour and have amphibolite xenolith. The main textures of these volcanic rocks are porphyritic, poikilitic, trachytic, sieved texture and glomeroporphyritic. The main phenocrystic minerals of andesites are plagioclase, amphibole and clinopyroxene situated in a matrix of the same minerals and sanidine, magnetite and apatite. Secondary minerals are formed as a result of the hydrothermal alteration and comprise zeolite, chlorite, epidot, sericite, kaolinite and calcite. Mineral chemistry indicates that plagioclases are andesine to labradorite (An= 30-52%), K-feldspars are sanidine (Or= 68-71%), amphiboles are calcic with pargasite composition (Mg#= 0.58-0.71), and clinopyroxenes are diopside (Mg#= 0.91-0.93) in composition. Whole rocks chemical analyses indicate that these andesite and trachy-andesite rocks have calc-alkaline property. The chondrite and primitive mantle-normalized REE and multi-element patterns show LREE and LILE enrichment and HFSE (Ti, Ta, Nb) depletion, which are characteristics of the subduction-related magmas. These data indicate that the primary magmas were genarated by medium degrees of partial melting of the lithospheric mantle spinel lherzolite. Subduction of the Central-East-Iranian Microcontinent (CEIM)-confining oceanic crusts (Naein and Ashin oceanic crusts) are possibly the reason of this volcanism. Geochemistry of these volcanic rocks are similar to the arc-related ones.
