Petrology
Saeid Samarbakhsh; Mohammad Hashem Emami; Seyed Mojtaba Mortazavi; Mansour Vosoughi-Abedini
Abstract
The study area, situated 50 km north of Ghaemshahr, structurally belongs to the Central Alborz tectonic zone. The volcanic rocks of the area, including basalt, andesite, trachyandesite, and dolerite are the products of fractional crystallization and some contamination processes. Clinopyroxene, olivine, ...
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The study area, situated 50 km north of Ghaemshahr, structurally belongs to the Central Alborz tectonic zone. The volcanic rocks of the area, including basalt, andesite, trachyandesite, and dolerite are the products of fractional crystallization and some contamination processes. Clinopyroxene, olivine, and plagioclase are the main minerals of these rocks. Porphyritic to mega-porphyritic texture with microlithic, glomeroporphyritic, and amygdaloidal matrix are observed in these rocks. Plagioclase, hornblende, and pyroxene can be considered the main mineral phases of these rocks. The rocks are enriched in LIL and LREE elements and depleted in HFS elements. The ratios of trace elements and rare earth elements in the studied region indicate that the basalts were formed by melting a garnet bearing peridotite at great depths and pressures. Negative Ce anomaly, Nb negative anomaly, Pb positive anomaly the role of continental lithosphere in contaminating the magmatic sources of volcanic rock in the study area. The Pb/Ce ratio similar to ocean island basalt (OIB) sources, induces OIB sources, the asthenospheric mantle, in the initial formation of basaltic magma. it can be concluded that the volcanic rocks of the area have formed in an intra-plate environment in an extensional regime.
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.
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.
GH Abbasi; M Ebrahimi; M Sharifi; N Shirdashtzadeh; J Ahmadian
Abstract
The studied volcanic rocks to the northeast of the Gavkhuni playa lake are composed of rhyolite, trachydacite, trachyandesite and pyroclastic rocks including lithic tuff and volcanic breccia. Rhyolitic rocks have flow structure and hyalophyric texture with glassy to cryptocrystalline ...
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The studied volcanic rocks to the northeast of the Gavkhuni playa lake are composed of rhyolite, trachydacite, trachyandesite and pyroclastic rocks including lithic tuff and volcanic breccia. Rhyolitic rocks have flow structure and hyalophyric texture with glassy to cryptocrystalline matrix in which quartz and feldspar crystal are present. The dominant texture in trachydacitic and trachyandesitic rocks in porphyritic texture in which plagioclase and rarely sanidine phynocrysts are set in a glassy to microcrystalline groundmass containing feldspar microlites. In trachydacites, quartz is present as small crystals and rarely as microphynocrysts. Plagioclase phynocrysts in trachydacitic and trachyandesitic rocks display sieve-texture. Amphibole and biotite are the mafic minerals of the volcanic rocks and they are partialy, at rims, or completely altered to Fe-Ti oxides. All of the studied rocks are high- K calc-alkaline in nature. According to the geochemical data, the volcanic rocks are depleted in high field strength elements such as Nb, Ti and Ta and enriched in large ion lithophile elements like Cs, K, Ba, Rb and Th which are characteristics of subduction related volcanic rocks. Nb negative anomaly is characteristic of continental rocks and indicates the continental crust involvement in the magmatic processes. The rocks are enriched in Cs, Rb, Ba and Pb indicating mantle metasomatism by fluids released from subducting oceanic lithosphere. Therefore, magma contamination and mantle metasomatism have affected the magma from which the volcanic rocks of the Gavkhuni playa lake have were generated. The calc-alkaline magmatism in the study area was associated with the closure of the Neotethyan Ocean.
M. H. Emami; R. Monsef; N. Rashid Nejad Omran
Abstract
Miocene to Pliocene volcanic rocks in the Raveh region have exposed northern part of the Urumieh - Dokhtar Magmatic Belt. Neogene volcanic rocks are situated on Upper Red Formation. Magmatic activity separated in two phase. The first phase is composed of basic to intermediate volcanic rocks such as basaltic-andesite ...
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Miocene to Pliocene volcanic rocks in the Raveh region have exposed northern part of the Urumieh - Dokhtar Magmatic Belt. Neogene volcanic rocks are situated on Upper Red Formation. Magmatic activity separated in two phase. The first phase is composed of basic to intermediate volcanic rocks such as basaltic-andesite to andesitic lavas and pyroclastics (Ngv1).The second phase has intermediate to acidic rocks as well as andesite, quartz andesite and dacite (Ngv2).According to geochemical data, these samples show magmatic affinities to the calc-alkaline series. REE and trace element patterns show LREE enrichment relative to HREE, depletion in Nb, Ta and Ti, and also high Th/Yb and Th/Nb ratios relative to MORB and OIB. The parent magma of the Raveh volcanic rocks, with calc-alkaline compositions, has been originated probably from the metasomatized mantle with effective of fluids and sediment resulted from the Neothytian subducting slab. After collision between Arabian plate and Central Iran Block in Early Cenozoic, region experienced of crustal thickening and volcanism activity formed in relation to localized extensional basin in Early Miocene to Early Pliocene. The volcanism postdates continental collision, occurring in transtentional tectonic setting.
I. Monsef; M. Rahgoshay; M. H. Emami
Abstract
The Late Jurassic to Early Cretaceous Orzuieh volcanic sequence is exposed in the southern part of the Sanandaj – Sirjan Zone. Major and trace element geochemistry shows magma evolution from the transitional to the calc-alkaline series. Clinopyroxene compositions are similar to their composition ...
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The Late Jurassic to Early Cretaceous Orzuieh volcanic sequence is exposed in the southern part of the Sanandaj – Sirjan Zone. Major and trace element geochemistry shows magma evolution from the transitional to the calc-alkaline series. Clinopyroxene compositions are similar to their composition in subduction setting and support a volcanic arc related environment. REE and trace element diagrams show enrichment patterns in LREE relative to HREE and depletion in Nb and Ta elements. This magmatic sequence has been originated from the mantle source with effect of liquids and sediment resulted from the subducting slab. The Orzuieh volcanic sequence is probably originated during the subduction of the Neo-Tethyan Oceanic lithosphere under the Sanandaj – Sirjan Zone, during the Late Jurassic to Early Cretaceous time, in the volcanic arc tectonic environment.
R. Mohamadi; M.H., Emami; M. Vosoghiabedi
Abstract
The area is located about 230 km of southwest of Tehran. Based of geological observations, the plutonic rocks in the area consist of Neogene (Miocene) alkaline gabbro , gabbrodiorite, locogabbro and diabase . The Oligo - Miocene calc-alkaline extrusive rocks are dacite - ryodacite , andesite trachyandesite ...
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The area is located about 230 km of southwest of Tehran. Based of geological observations, the plutonic rocks in the area consist of Neogene (Miocene) alkaline gabbro , gabbrodiorite, locogabbro and diabase . The Oligo - Miocene calc-alkaline extrusive rocks are dacite - ryodacite , andesite trachyandesite , hornblendandesite , basaltic andesite and trachybasalt .Studing on isotopic analyses of Nd and Sr indicate that surveyed area were contaminated with crustal rocks of Sialic composition . In isotopy geochemical studies, The Andesite samples are plotted in the limit of BSE; however, it seems that mantling rocks besides being settled in crust (esp. the upper continental crust) have been contaminated with in. The combination of BSE towards enrichment, from the proportion of 87Sr/86Sr has shifted; a sample of rocks shows this position. Spider diagrams related to trace elements of plutonic samples which are used for identifying the tectonic setting show intrusives are in the extensive regime; while the lavas don’t have a steady trend and are similar to subduction zones. This shows that the intrusives of the the investigated area are different genesis from the southern volcanic rocks.
