Petrology
Leili Bastami; Reza Moussavi; Mahboobeh Hosseini-Barzi; Bahaedin Hamdi Hamdi
Abstract
The sandstones of the Dorud Formation (Early Permian) have been subjected to petrographic and geochemical studies in order to investigate provenance, tectonic setting, source rock and paleoclimate conditions in Khur section, Central Alborz. The Dorud Formation with a thickness of 360 m is mainly composed ...
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The sandstones of the Dorud Formation (Early Permian) have been subjected to petrographic and geochemical studies in order to investigate provenance, tectonic setting, source rock and paleoclimate conditions in Khur section, Central Alborz. The Dorud Formation with a thickness of 360 m is mainly composed of fine to medium grained sandstones with lesser amounts of carbonate and mudstone. In order to achieve the above-mentioned goals, 125 thin sections were subjected to petrographic studies. Modal analysis was performed on 20 thin sections and 13 samples of sandstones were analysed for major and trace elements. Based on petrographic studies the sandstones of the Dorud Formation are classified as quartzarenite with high textural and mineralogical maturity. Plotting point counting data on (Qt99.6, F0.2, L0.2( and (Qm95.9, F0.2, Lt3.9) triangles implies craton interior provenance. Also, major and trace elements based geochemical diagrams indicate that these sandstones deposited in a passive continental margin tectonic setting. According to petrographic and geochemical evidence the sandstones of the Dorud Formation derived from erosion of middle- to high-grade metamorphic, felsic igneous and quartoze sedimentary rocks. High mineralogical maturity, high values of chemical index of weathering (CIW) and chemical index of alteration (CIA) as well as SiO2 (%) versus Al2O3 + K2O + Na2O (%) diagram imply moderate to intense weathering under warm and humid climatic conditions. Passive continental margin tectonic setting and warm and humid paleoclimatic conditions is consistent with paleogeographic position of Iran during the Early Permian.
Petrology
mozhgan Taheri; afshin ashjaardalan; Mohammad hashem Emami; Seyed Jamal Shaikh Zakariay
Abstract
Abstract In the west and south-west part of Salafchegan near Zavarian village in Iran (In central Iranian volcano plotonic belt) there are some Plutonic rocks. Based on petrography and geochemistry findings these Plutonic rocks are Diorite, Monzonite and less Quartz monzonite. The main texture in Dioritic ...
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Abstract In the west and south-west part of Salafchegan near Zavarian village in Iran (In central Iranian volcano plotonic belt) there are some Plutonic rocks. Based on petrography and geochemistry findings these Plutonic rocks are Diorite, Monzonite and less Quartz monzonite. The main texture in Dioritic rocks is intergranular and in Monzonite is Porphyritic. Based on TAS diagram Samples located in Diorite, granodiorite and gabbrodiorite. Tectono-magmatic diagram Y Versus Zr shows the magmatic arc setting and Zr/TiO2 Versus Ce/P2O5 diagram contrasts postcolligenal magmatic arcs. Based on Chondrite and primitive mantle Spider diagrams, LREE have enriched to HREE in this area that makes the overal slope of these diagrams declined from left to right and this consident with the overal pattern of subduction zone. The results of petrography, geochemistry and tectonic setting studies in this area, indicate that neogene magmatism occurred in post colligenal tectonic setting - subduction of Neo-thetise ocean under central Iranian plate in neogen era.
Petrology
Maryam Kouchi; Malihe Nakhaei
Abstract
In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The ...
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In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The main texture of these rocks are porphyry with microlitic-glass groundmass, glomeroporphyritic, poikilitic and vesicular. The mineral constituents of andesitic rocks are plagioclase, pyroxene and amphibole with small quantities of biotite and sanidine and in rhyolite and dacite include of quartz, sanidine, plagioclase, amphibole and biotite. Disequilibrium textures such as chemical zoning, sieve texture, rounded and gulf shape margins in phenocrysts of these rocks are observed. Geochemical study results show that these lavas belong to high to medium-K calc alkaline series. Enrichment in LREE and LILE, depletion in HREE and HFSE with negative anomaly of Ti, Nb and P in these rocks indicated active continental margin volcanic arc magmatism. Based on tectonic discrimination diagrams, also support the relation of Zoolesk area lavas with subduction zone and active continental margin. Low ratio of Dy/Yb(<2) in studied lavas, indicated spinel lherzolite mantle source for magma.
Petrology
Habib Biabangard; Farzad Molazadebravate
Abstract
Kuh-Som, KuhzaBozorg and KuhzaKochak volcanic cones are located in the southeastern of Bam and northwest of Bazman cites. From the perspective geology these cones are belong to the Iranian central zone and south-eastern edge of Lut block. These cones are composed of extrusive igneous rocks such as basalt, ...
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Kuh-Som, KuhzaBozorg and KuhzaKochak volcanic cones are located in the southeastern of Bam and northwest of Bazman cites. From the perspective geology these cones are belong to the Iranian central zone and south-eastern edge of Lut block. These cones are composed of extrusive igneous rocks such as basalt, olivine basalt, andesite and basaltic andesite, and are predominant trachytic texture. Plagioclase, pyroxene and olivine are main minerals. Pyroclastic deposits, lapilli, tuff, ash and volcanic bombs, along with lava flows are main construction volcanic cones. These volcanoes are monogenitic and limited eruption. Based on type material that construction cone of the volcanoes, it seems they are among between Hawaii to Strambolian volcanoes. These rocks shows enrichment to LILE relative to HREE (Ce / Yb= 33-45) , high ratio Zr / Y (33.4), enrichment to LILE and negative anomaly from Ni, Cr and nearly Eu that reveals these rocks related to Calc-alkaline magmatism. In spider diagrams of trace elements and rare earth elements that normalized to Chondrites and primitive mantle show light rare earth elements enriched more than high rare earth elements and show pattern similar to affiliate subduction zones. Geochemical characteristics such as ratio of La / Yb 8/6 to 7/13, low Rb content with the tectonic setting discrimination diagrams indicate that they are related to subduction environments and low tendency to intapalate zone. Source of magma that formed these volcanoes resulted from melting of a garnet Lherzolite at depth of 100 to 110 Km. Tectonomagmatic diagrams shows these rocks dependence on of continental subduction environments to show slightly into the intraplate zone, so that it seems the volcanic cones of them related to the Makran and Oman subduction and related to Makran- Chaghy magmatic arc.
Petrology
Ashraf Torkian; Jamal Abdolahpour; Nafiseh Salehi
Abstract
Pyroclastic rocks in the Badam area (E-Mahabad, west Azarbaijan Province), are located at the most extreme northern part of the Sanandaj-Sirjan zone. Petrographic studies revealed that they are basanitic in composition and have porphyric and microlithic porphyric textures. Olivine and clinopyroxne occur ...
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Pyroclastic rocks in the Badam area (E-Mahabad, west Azarbaijan Province), are located at the most extreme northern part of the Sanandaj-Sirjan zone. Petrographic studies revealed that they are basanitic in composition and have porphyric and microlithic porphyric textures. Olivine and clinopyroxne occur as phenocrysts and clinopyroxene and nepheline as microliths. Opaque minerals and glass have occupied the space between different minerals. In classification diagram, they have basanitic composition. Geochemical features such as enrichment in LILE, high LREE concentrations and negative anomalies in Nb, Ta and Y, with positives anomalies in Ba, Pb and Th and enrichment in Th/Yb, all suggest that these rocks have mantle source that are enriched by melt/fluids from the metasomatized subducted oceanic slab. These features are inherited from mantle source and they are not caused by crustal contamination. Regarding MREE and HREE ratios, these basanites originated from 1 % partial melting of a garnet lherzolite source in the garnet stability field (85 Km). Melting trigger in this area is not clear, but old theories such as lithosphere delamination or slab break up are not applicable any more. There is three suggestions about melting in these are: 1) break up of hydrated phases by depth increase, 2) changing and turbulence in convection follows, 3) subduction and dehydration of Arabic passive margin.
Petrology
Masoumeh Ahangari; Mohssen Moazzen
Abstract
Amphiboles in olivine-bearing hornblende- gabbros from NW of Salmas were crystallized in various textures including oikocryst and interstitial textures in the matrix, outer part of reaction rims around olivine, and at the rim and cleavages of clinopyroxene. On the basis of petrographical and textural ...
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Amphiboles in olivine-bearing hornblende- gabbros from NW of Salmas were crystallized in various textures including oikocryst and interstitial textures in the matrix, outer part of reaction rims around olivine, and at the rim and cleavages of clinopyroxene. On the basis of petrographical and textural studies, amphiboles were formed later than the other minerals in the olivine-bearing hornblende- gabbros. The REE and trace element composition of amphiboles from two different textures including interstitial and matrix amphiboles (group one) and amphiboles after clinopyroxenes (group two), indicate that the studied amphiboles were formed by either crystallization of interstitial melt/fluid or interaction of interstitial melt/fluid with early crystalized minerals such as clinopyroxene and plagioclase. Hence, according to the textural and mineralogical data and trace element composition of amphiboles, olivine-bearing hornblende- gabbros were crystallized at least at two stages. The first stage include fractional crystallization and formation of olivine, clinopyroxene and plagioclase and the second stage was interaction of the relict melt/fluid with early crystalized minerals, specially clinopyroxene and plagioclase and formation of amphibole.
Petrology
Rahimzadeh Bahman
Abstract
Scoria cones are one of the main parts of East of Kurdistan volcanoes. Olivine, Pyroxene, Plagioclase and Biotite are main phonocrystals with Amygdaloidal-glassy matrix. This paper was studied processes of bubbles nucleation and grow during the eruption of scoria's unite using the Bubble Size Distribution ...
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Scoria cones are one of the main parts of East of Kurdistan volcanoes. Olivine, Pyroxene, Plagioclase and Biotite are main phonocrystals with Amygdaloidal-glassy matrix. This paper was studied processes of bubbles nucleation and grow during the eruption of scoria's unite using the Bubble Size Distribution (BSD) method including study of population density, bubbles volume, 3D modeling, nucleation and bubble growth. For selected sample from different cone, in total was measured 3623 bubbles and drawn that bubbles volumes calculated from 40 to 85 percent. Using the 2D bubbles shape renovated 3D bubbles schematic shape and compared together. Most population for four samples bubbles shapes are near to sphere and for other four samples are ellipsoid. Longest ellipsoid bubbles shape has 1:3.2:8 diagonals ratio that it’s flat ellipsoid. The longest diameter (L) is perpendicular to the surface and parallel to lower pressure dictated on magma and bubbles could be growth more than other sides. Presence of 2-5 peaks in frequency distribution versus bubble size diagram, suggesting unimodal, polymodal, exponential and power low events for bubbles generation in the east of Kurdistan Scoria's. Nucleation density increased from first to lasts generation but bubbles growth reduced. Recur of bubble forming in macroscopic samples, microscopy, SEM and nucleation and grow model suggested fractal model.
Petrology
Soghra Razaghi; mohsen nasrabady; Kazem Gholizadeh; Zeinab Davoodi
Abstract
The Gash metamorphic complex is situated at the west of Rasht city. Gasht-e-Rodkhan metamorphic rocks are considered as a part of this metamorphic complex. Metapelites (schist, gneiss and migmatite) are the most important lithological unit of the Gasht-e-Rodkhan area. Index minerals consist of staurolite, ...
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The Gash metamorphic complex is situated at the west of Rasht city. Gasht-e-Rodkhan metamorphic rocks are considered as a part of this metamorphic complex. Metapelites (schist, gneiss and migmatite) are the most important lithological unit of the Gasht-e-Rodkhan area. Index minerals consist of staurolite, garnet, sillimanite and kyanite. The main rock forming minerals of muscovite-free melanosome of migmatites are sillimanite and biotite. There is garnet in some melanosome as well. Quartz, K-feldspar and plagioclase are the rock forming minerals of leucosome. Tourmaline, garnet, muscovite and sillimanite are accessory minerals. Average pressure and temperature calculated by Thermocalc software and conventional thermobarometers for schist, gneiss and migmatite samples are 8.6 Kb, 630°C; 6.7 Kb, 650°C and 6.3 Kb, 720°C respectively. Mineralogical parageneses and geothermal gradient resulted from thermobarometry calculations of the Gasht-e-Rodkhan metapelites are compatible with metamorphic Barrovian gradient or orogenic type. Gash complex probably represents metamorphic rocks of medium crustal depth of a collisional tectonic setting between Alborz block and Turan plate. Partial melting of metapelites and generation of associated leucogranites have taken place as a consequence of muscovite dehydration melting.
Petrology
Mehdi Rezaei-Kahkhaei; Dariush Esmaeily; Hanieh Sahraei
Abstract
Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve ...
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Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve texture, two generation of fresh and altered plagioclase, reaction rim, corrosion and rounding of phenocrysts. Major and trace element diagrams show, although crystal differentiation was effective in the evolution of the study rocks, the scatter and unusual trends, which are observed in some diagrams in comparing with fractionation trend, reflect magma mixing and contamination were also important during magma generation. Inconsonance and high variations in Sr concentrations together with binary diagrams of Nb/Y-Nb and Rb-Zr/Rb reveal magma mixing role in the evolution of Neshveh volcanic rocks. Considering the above facts, we can conclude that magma mixing and magmatic differentiation were the important processes in formation of the Neshveh volcanic rocks. As well as, the incorporation of new magmatic pulse(s) with differentiation magma is the most effective mechanism for the evolution of volcanic rocks from the study area.
Petrology
S. M. Tabatabaei Manesh; M. A. Mackizadeh; saeideh ranjbar; R. Gholinezhad
Abstract
Javinan skarn is located at 115 km north west of Isfahan (40 km south of Kashan and east of Ghohrud), is included in Central Iran structural zone and spread in contact with Ghohrud granitoid (Middle Miocene age) with shale, sandstone and limestone succession of the Jurassic age known ...
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Javinan skarn is located at 115 km north west of Isfahan (40 km south of Kashan and east of Ghohrud), is included in Central Iran structural zone and spread in contact with Ghohrud granitoid (Middle Miocene age) with shale, sandstone and limestone succession of the Jurassic age known as Shemshak Formation. Skarnification is made up of endo- and exoskarn subzones. Wide mineralization in these skarns hasn’t observed. Endoskarn subzone has limited occurence (from a few millimeters to a few centimeters) and exoskarn has the greatest development (from 1 meter to more than 10 meters). Endoskarn with the formation of the skarn minerals garnet, pyroxene, plagioclase, epidote and sphene, is formed in the intrusive host rock and is in the vicinity of the carbonate part. In its immediate neighborhood, exoskarn subzone starts with the formation of minerals garnet, pyroxene, idocrase, epidote, phlogopite, chlorite, quartz and calcite in the carbonate section. Mineralogical studies and textural relationship of minerals have shown that the metamorphic facies اhas reached to pyroxene hornfels in skarn rocks of this area.
Petrology
M. Sadeghian; S. H. Hosseini; A. Hemmati; S. Shekari
Abstract
Granitoid plutons of SW Mayamey (60 Km east of Shahrood), located at the most northern margin of the central Iran structural zone, have granite composition (in general) and calk alkaline and peralouminous nature. In spite of coverage of these granitoids by Late Triassic – Early Jurassic sedimentary ...
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Granitoid plutons of SW Mayamey (60 Km east of Shahrood), located at the most northern margin of the central Iran structural zone, have granite composition (in general) and calk alkaline and peralouminous nature. In spite of coverage of these granitoids by Late Triassic – Early Jurassic sedimentary rocks, Late Neoproterozoic host gneiss are exposed in limited areas. These granitoids invaded by two series of the Late Neoproterozoic and middle Jurassic diabasic dikes. Although post – Liass, Pre- Dogger, younger than Jurassic and older than Cretaceous ages are considered for these granitoids, but for the first time U–Pb age dating on separated zircons indicates Late Neoproterozoic age (Late Ediacaran) (545±10 Ma) for them and they are a part of very ancient basement rocks of Iran. The studied rocks are similar Band -e-Hezar Chah, Sefid Sang, Delbar, Shotor Kuh, Reza Abad and Do Chah granitoids in age. Mayamey granitoids are resulted from partial melting of metapelites and metagraywackes, and they belong to S-type granioids. SW Mayamey granitoids were generated in a collisional tectonic setting in the Late Neoproterozoic, in relation to closing of intracontinental back arc basin and then metamorphism of the associated rocks from greenschist facies to amphibolite and rarely granulite facies, which finally companied with s-type granitization
Petrology
Z. Gharamohammadi; A. Kananian; M. Eliassi
Abstract
The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite ...
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The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite and diorite-gabbro while the host rocks comprise mainly granodiorite. The presence of disequilibrium textures in enclaves, such as plagioclase phenocrysts with repeated resorption surfaces and sieve texture, quartz ocelli and acicular apatite, suggest a varity of magma mixing processes affecting the Dehe Bala pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMEs and the felsic host rocks. Unusual REE enrichment of the enclaves compared to the country rocks can be attributed to significant differences in their parent magma compositions. The complexity of the morphology of the enclaves (fractal dimension) caused by magma mixing processes. Fractal dimensions of the enclaves vary between 1.14 to 1.29. The frequencies of Dbox = 1.29 is the highest frequency in histogram. According to the fractal dimensions of enclaves, the logarithm of the viscosity ratio between the host granodiorite and the enclave ranges between 0.56 to0.96 with most values clustering around 0.96. The most of enclaves in the Dehe Bala pluton characterized by silica content around 56 w% and a high fractal dimension. These evidence confirmed the occurrence of slight hybridization between the mafic enclave magma and surrounding felsic magma, causing increasing of viscosity difference between the host granodiorite and the enclave magmas.