Petrology
Abdolhamid Ansari
Abstract
The Chahargonbad batholite is located close to Sirjan and southeast of Urumieh-Dokhtar magmatic zone. The batholite's composition is acidic to intermediate that is intruded into the Eocene volcanic rocks. Although the main volume of these rocks consisted of granodiorite and monzogranite, this mass ...
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The Chahargonbad batholite is located close to Sirjan and southeast of Urumieh-Dokhtar magmatic zone. The batholite's composition is acidic to intermediate that is intruded into the Eocene volcanic rocks. Although the main volume of these rocks consisted of granodiorite and monzogranite, this mass contains numerous mafic microgranular enclaves with a combination of diorite and monzodiorite. Also, microgranular dykes have cut the mafic mass. Existence of field evidence such as mafic microgranular enclaves with spherical to oval shapes, bell and rod shaped mafic microgranular enclaves, the presence of synplutonic mafic dykes, as well as textural disequilibrium evidences indicate the absence of plagioclase with oscillatory zoning and repeated analytical levels, and Osley quartz in the presence of enclaves. As they grow, they are minerals and evidence for magmatic mixing. Enclaves show higher values than the host rock in most of the basic elements, such as Al2O3, CaO, MgO, Fe2O3, TiO2, P2O5. The elements (REE), host granite rocks and associated enclaves show relatively differentiated REE patterns with sloping LREE patterns and flat MREE and HREE patterns. Based on the tectonomagmatic environment determination diagrams, all samples from the Chahargonbad (studied area) are located in the arc island setting due to subduction and show the characteristic of active continental margin setting.
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
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.
M Refoseh; A Shaker Ardakani; H Ranjbar
Abstract
Volcanic, sub-volcanic (dyke) and pyroclastic (agglomerate and tuff) rocks of Eocene age are located in the Kalmard block in the north and northeast of Kerman City. Petrographically, the lavas are basalt, andesite, rhyodacite and rhyolite, whereas the dykes and pyroclastic rocks are andesite and crystal ...
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Volcanic, sub-volcanic (dyke) and pyroclastic (agglomerate and tuff) rocks of Eocene age are located in the Kalmard block in the north and northeast of Kerman City. Petrographically, the lavas are basalt, andesite, rhyodacite and rhyolite, whereas the dykes and pyroclastic rocks are andesite and crystal tuff in composition respectively. The porphyritic, microlitic-porphyritic and trachytic are the main textures and mineralogically consist of plagioclase± quartz± K-feldspar ± biotite± amphibole± clinopyroxene± olivine+ opaque minerals. Plagioclases show evidences of disequilibrium textures such as sieve texture, resorption and zoning; whereas quartzes have resorbed margins, and amphiboles and biotites are only slightly opacitized. These textures can be resulted from magma mingling, PH2O variations, and decompression with minor loss of temperature during magmatic ascent. Geochemical studies revealed that the volcanic rocks belong to a sub-alkaline magmatic series with calc-alkaline nature. Furthermore, acidic volcanic rocks are metaluminous to peraluminous and show characteristics of I-type granitoids. The trace element discrimination diagrams along with chondrite-normalized rare earth element patterns show that the igneous rocks formed in an active continental arc environment.
M Poosti; M Fadaeian
Abstract
The study area is located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais formed of Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and occasionally analcimite. They are silica saturated or relatively saturated. ...
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The study area is located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais formed of Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and occasionally analcimite. They are silica saturated or relatively saturated. According to tectonomagmatic diagrams, the original setting of the parental magma was a volcanic arc and subduction zone. The negative anomalies of Nb, the high ratio of LILE/HFSE, the high mounts of Al2O3& P2O5, the low titanium contents, and the degree of partial melting of the metasomatized upper mantle, strengthens the subduction related processes for the formation of the primary magma (alkali olivine basalt). Petrographic evidences suggest that the primary magma is mixed with crustal materials. The chemical composition of rocks, according to geochemical diagrams, is shoshonitic. These rocks may have been formed by the subduction of the oceanic crust of Neoteties during the Mesozoic and early Cenozoic periods. Releasing fluids exerted from the subducting slab, metasomatism of the lithospheric mantle and subsequently the appropriate conditions for melting of the metasomatized mantle, all led to the formation of potassic magmatism and finally, generation of magma with a shoshonitic nature found its way to the surface under the influence of an extension phase and complex fault systems.
F Sarjoughian; A Kananian; J Ahmadian
Abstract
The alkali feldspars and plagioclases in the Kuh-e Dom intrusive rocks show compositionally and microtexturally zoning structure. The feldspar crystals in the various lithologies such as granite- granodiorite samples, diorite- gabbro samples and relatively high frequency microgranular mafic enclaves ...
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The alkali feldspars and plagioclases in the Kuh-e Dom intrusive rocks show compositionally and microtexturally zoning structure. The feldspar crystals in the various lithologies such as granite- granodiorite samples, diorite- gabbro samples and relatively high frequency microgranular mafic enclaves existing in the acidic intrusion were analyzed using electron microprobe. The results of the microprobe analysis in the acidic, basic- intermediate rocks and enclaves indicated the normal and reverse zoning in the samples. The chemical compositions of plagioclases ranges from albite (An 9.4) in the rim to labradorite (An: 50.6) in the core for acidic rocks, and from andesine (An: 30.5) in the rim to labradorite (An: 56.4) in the core for the basic- intermediate rocks, and from oligoclase (An: 19.8) to labradorite (An: 66.5) in the enclaves. The frequently of rare elements such as Ba, Sr, Fe and Mg in the feldspars show various and oscillatory patterns. The oscillatory pattern of the major and minor elements from core to rim in the feldspar crystals suggests an effective role of magma mixing phenomena in forming of the Kuh-e Dom intrusion.
M Farmahini Farahani; A Khakzad; H Asadi Harooni; M.H Emami
Abstract
Kahang copper and molybdenum mine is located in Esfahan province and 10 Km far from the east of Zefreh town that is on Urumieh-Dokhtar volcanoplutonic belt. The Kahang region is an alteration and breccia zone. Generally, hydrothermal fluids have affected more than % 90 of rocks of this region. These ...
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Kahang copper and molybdenum mine is located in Esfahan province and 10 Km far from the east of Zefreh town that is on Urumieh-Dokhtar volcanoplutonic belt. The Kahang region is an alteration and breccia zone. Generally, hydrothermal fluids have affected more than % 90 of rocks of this region. These alteration are related to Copper (Cu) and Molybdenum (Mo) porphyry deposits. Most of the rocks are acidic, semi acidic and sub volcanic. Several kinds of alteration are observable in kahang as propylitic, argilic, silisification and phyllic. The basic oxides were highly decreased in dacite and rhyodacites of exploration area. This is an evidence of argilic alteration effect on the rock units considering that main deposit is not affected by erosion, placed in depth and potassic alteration is not exposed at surface. In study of existing alteration several methods such as remote sensing, studying of thin section and the chemical analysis of samples were used. Another issue that has taken into consideration in this paper is the magma mixing. This subject is confirmed by petrographic evidence such as sieve texture, corroded rims in primary phenocryst quartz, and hydrothermal effects on plagioclases especially in porphyritic andesites. Moreover, the extensive acidic rocks, notable alteration expanse, and also two generations of mineralization reveal assimilation in the studied area. This text has examined the similarities between Kahang and other porphyries in the Urumieh-Dokhtar zone.
M.A Sajadi Nasab; M Vosoughi Abedini; M.H Emami; M Ghorbani
Abstract
The studied granitoidic intrusion with about 50 km2 area is located in the SW of Kelardasht, one of the regions in MazandaranProvince. It is one of the pluton masses of the Central Alborz structural zone. The mass has an age between 54±4 and 56±3 million years (late Paleocene to early Eocene) ...
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The studied granitoidic intrusion with about 50 km2 area is located in the SW of Kelardasht, one of the regions in MazandaranProvince. It is one of the pluton masses of the Central Alborz structural zone. The mass has an age between 54±4 and 56±3 million years (late Paleocene to early Eocene) and has intruded in the Mobarak and Shemshak formations. Petrologically it contains of two units of felsic (granite, qz-syenite, and qz-monzonite) and intermediate to mafic (monzonite to monzodiorite, diorite, and gabbro). The rocks of the first group especially granites and q-monzonites show many mineralogical and textural similarities and in which the evidences of magma mixing like rapakivi texture, poikilitic texture, acicular apatite, calcic plagioclase "spikes" in plagioclase, and micro granular mafic enclaves can be seen. These rocks have weak metaaluminous to peralumine nature (granite samples) and are richer in K2O+Na2O, K2O and the elements of Rb, Th, Hf than the second group. Due to the diagram related to REE, the rocks of this group have remarkable enrichment of LREE and related to the behavior of Y, Ba, Ce, and Zr in segregation process, they show the properties of low temperature I-type granites. In the second group, monzonite and monzodiorite rocks also show the evidences of alkaline metasomatism, associated with magma mixing textures including acicular apatite, septum biotites and anortite spikes in plagioclases. These rocks have meta alumine nature and show more richness in FeOT, MgO, CaO, bP2O5, TiO2, and the elements such as Sr, Ba, V, and Y than the first group; and also they show the properties of the high temperature I-type granites. Due to the geochemical evidences and the age of the mass, it can be categorized as post orogenic granite types, which have the properties between VAG and WPG. The isotopic investigation of 143Nd/144Nd revealed that only the granites of the region have can have enriched lithospheric source (negative εNd) and the other rocks have a depleted mantle source (positive). According to the petrographical and geochemical evidences, magma mixing has played an important role in magma evolution, and therefore, the crust melting model by mantle-derived magma is suggested for the magma generation of the area.
D. Raeisi; S. Dargahi; H. Moeinzadeh; M. Arvin
Abstract
Gandom Beriyan, as a part of Quaternary volcanism of Iran, is a kind of messa which is covered by very dark lava flows. The flows are generally fresh to rarely altered alkali olivine basalts and cover an area around 480 km2 in southern part of the Lut desert in northeast of Kerman. The common textures ...
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Gandom Beriyan, as a part of Quaternary volcanism of Iran, is a kind of messa which is covered by very dark lava flows. The flows are generally fresh to rarely altered alkali olivine basalts and cover an area around 480 km2 in southern part of the Lut desert in northeast of Kerman. The common textures of basaltic lava flows are porphyry to glomeroporphyry with an intersertal to intergranular groundmass. Their major minerals are olivine and clinopyroxene phenocrysts along with plagioclase microlites. Plagioclase microlites are recognized as the major silicate phase in these rocks. Three-dimensional shape of plagioclase crystals and also rate of nucleation and growth time was estimated by thin section image processing and using crystal size distribution (CSD) method. Based on this, it is revealed that the shape of plagioclase microlites is tablet with aspect ratio of 1:10:10 for short: intermediate: long axes, respectively. The uniformity of CSD graph and its constant slope show that the effect of physical processes such as magma mixing was limited during ascent of basaltic magma toward the surface. Based on these calculations, growth time (t) and rate of nucleation (J) were estimated 2.53 to 3.21 years and 10.17×10-9 to 9.53×10-9 mm-3/s-1, respectively. The results are completely matched with nature of alkali basalt magmas.
Z. Azimzadeh; M. H. Emami; R. Hajialioghli
Abstract
The Zand-Abad area is located in NW Ahar of north Azerbaijan. Magmatic rocks in this area consists of granitoids including monzogranite, granodiorite, monzonite and syenogranite as well as mafic rocks mainly diorite and associated extrusive rocks as andesite, trachyandesite, dacite, trachydacite, rhyolite. ...
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The Zand-Abad area is located in NW Ahar of north Azerbaijan. Magmatic rocks in this area consists of granitoids including monzogranite, granodiorite, monzonite and syenogranite as well as mafic rocks mainly diorite and associated extrusive rocks as andesite, trachyandesite, dacite, trachydacite, rhyolite. Subvolcanic rocks are porphyritic diorite and porphyritic monzodiorite. According to the different geochemical studies, the tectonic environment of Zand-Abad volcanic and plutonic rocks is determined as continental arc setting related to dilatory creep down subduction. This will be interpreted in relation with the Neotethyse post-collision activities. Considering the mineralogy and chemical evidence, we suggest that the Zand-Abad magmatic rock types (i.e. volcanic, sub-volcanic and plutonic rocks) have been derived from single magmatic source and undergone fractional crystallization, magma mixing and crustal contamination, resulting from hybrid granitoids. Magmatic series of the different types of magmatic rocks is alkaline. Calc-alkaline and shoshonite property of some samples is interpreted related to magma mixing and crustal contamination processes.
R. Deevsalar; M.V. Valizadeh
Abstract
The results of field studies (i.e. shape, dimensions, spatial distribution, condition of enclaves and xenoliths in the host rocks at available outcrops) experimental observations (i.e. petrographical and microstructural study of enclaves and xenoliths and whole rock geochemistry of magmatic encalves) ...
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The results of field studies (i.e. shape, dimensions, spatial distribution, condition of enclaves and xenoliths in the host rocks at available outcrops) experimental observations (i.e. petrographical and microstructural study of enclaves and xenoliths and whole rock geochemistry of magmatic encalves) show that magmatic enclaves are mafic and felsic types, while xenoliths are hornfelsic. Elongation of magmatic enclaves and hornfelsic xenoliths along their apparent longitude axis in the margin of intrusive body are attributed to influence of stress on enclaves in melt or semi-solid phases and xenoliths in plastic form. In addition, this is related to impact of high force of magmatic flow in contact with metamorphic wall rocks. This indicates that the origin of xenoliths is the metamorphic rocks which lie at the periphery of the intrusive body. Existing of aligned mafic enclaves in the host, in addition to, presence of signs of plastic deformations (in microscopic scale) in micro-scale fluid features can be attributed to superimposition of solid-state deformation on magmatic flow. Due to lack of solid-state plastic deformation evidences, applicability of magmatic flow criteria and distinguishable interface of magmatic enclaves with host rocks in microscopic and macroscopic scales, spherical, globular, ellipsoidal and spindle shapes of mafic magmatic enclaves attributed to presence of theirs as mafic globule and packets in the host felsic magma, and also their similarity in superficial appearance, textural, mineralogy and geochemistry with the host rock, attributed to their different origin and magma mixing event. The formation of irregular shaped magmatic felsic enclaves with recognizable mineralogical and geochemical similarity to the host rocks, which are observed at the periphery or ceiling of the plutons, related to peripheral interruption in the primary phase of magmatic injection caused by the high pressure of consecutive injection pulse and replacement of new magmatic charge.
M. H. Kholghi; M. Vossoughi Abedini
Abstract
Safakhaneh batholith, situated at 47 km southwest of Shahin Dezh, northwest of Iran, is located in the central Iran structural zone intersecting the Cretaceous rocks. The absolute age of the batholith, determined for the first time by K – Ar method, has been calculated ...
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Safakhaneh batholith, situated at 47 km southwest of Shahin Dezh, northwest of Iran, is located in the central Iran structural zone intersecting the Cretaceous rocks. The absolute age of the batholith, determined for the first time by K – Ar method, has been calculated 69.535 Ma. showing upper Cretaceous – Paleocene epoch and Laramide tectonic orogeny. Geochemical investigations of the batholith show that the major part of the batholith is of mantle magma, in which magmatic changes of the crystalline differentiation and contaminations have occurred. The crystalline differentiation has caused the formation of different rock types of quartz monzonite, quartz monzodiorite, tonalite, granodiorite and monzogranite respectively. Primary magma of the rocks is of calc - alkaline and generally metaluminous. The specifications of batholith rocks can be compared with the I – Type Caledonian granites. From the tectonic point of view, the specifications of the batholith can be comparable with the volcanic arc granitoids (VAG).
A. Zahedi; H. Ahmadipour
Abstract
The Abaregh area is located in 40 km northwest of Bam city in Kerman province. Rock units of the region consist of lava flows and dikes that crop out along a fault system trending NS. Mineralogically, the rocks contain plagioclase, augite, hypresthen, and minor olivine. Heterogenous ...
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The Abaregh area is located in 40 km northwest of Bam city in Kerman province. Rock units of the region consist of lava flows and dikes that crop out along a fault system trending NS. Mineralogically, the rocks contain plagioclase, augite, hypresthen, and minor olivine. Heterogenous mineralogy, field and textural evidences such as sieve texture in plagioclase, resorption rims in crystals, oscillatory zoning in plagioclase, high normative quartz and rounded enclaves suggest that the primary magma undergone magmatic evolution including fractionation, contamination, and magma mixing during ascending. The Y/Rb ratio and AFC (assimilation and fractionational crystalization) petrogenetic models confirm the occurrence of evolution in primary magma. Concentration of elements such as K, Pb, P, Zr, Sr, Ba, Rb shows that these rocks belong to the calcalkaline series. Similarity between the andesitic lava and dykes shows a considerable similarity with the calcakaline andesite from Turkey and from this point of view; these rocks belong to the post - collisional arcs. In this tectonic setting, magma ascent is controlled by strike - slip faulting and associated pull- apart extensional tectonics. This post - collisional magmatism may have been occurred due to the Arabian- Iranian collision events.