Sh. Shahabi; H. Shafaii Moghadam; Gh. Ghorbani
Abstract
The Ghoshchi granitic rocks are located in at north of Uromiyeh city and are mainly composed of alkali-feldspar granites, granites and aplitic dykes. These samples belong to calc-alkaline to shoshonitic series and show Fe enrichment and are classified as A-type granites. Ghoshchi granites have high K2O+Na2O, ...
Read More
The Ghoshchi granitic rocks are located in at north of Uromiyeh city and are mainly composed of alkali-feldspar granites, granites and aplitic dykes. These samples belong to calc-alkaline to shoshonitic series and show Fe enrichment and are classified as A-type granites. Ghoshchi granites have high K2O+Na2O, FeO/MgO, Gl/Al, Ce/Nb, Zr, Y/Nb, and low CaO, Ba, Sr and Eu and are A2-type granites. Geochemical and Sr-Nd isotopes evidences suggest that these rocks were generated by highly fractional crystallization of a parental magma (melts), was derived from an enriched mantle source, which have undergone contamination by crustal materials and formed in post-collisional extentional environments in a within-plate setting. The crystallization age of these rocks, according to biotite 40Ar-39Ar and Rb-Sr dating is 262±26 Ma and 256±20 Ma, as minimum age, respectively, and 320-330 Ma as crystallization age. Ghoshchi granites formed probably within extentional zones in at the late stages of Variscan tectonic events.
M Ebrahimi; H Kouhestani; M.A.A Mokhtari; M Feizi
Abstract
The Aqkand area is located at 48 km north of Zanjan and is a part of the Tarom subzone within the Western Alborz-Azerbaijan structural zone. Acidic rocks exposed in this area consist of Oligocene rhyolite-rhyodacite, perlite, pitchstone and ignimbrite. Rhyolites and rhyodacites are exposed as domes and ...
Read More
The Aqkand area is located at 48 km north of Zanjan and is a part of the Tarom subzone within the Western Alborz-Azerbaijan structural zone. Acidic rocks exposed in this area consist of Oligocene rhyolite-rhyodacite, perlite, pitchstone and ignimbrite. Rhyolites and rhyodacites are exposed as domes and lava flows. Perlites are located at the lower parts of the rhyolitic-rhyodacitic domes. Geochemical investigations indicate calc-alkaline nature along with magmatic arc affinity for the studied rocks. These rocks are characterized by LREE-rich patterns with high LREE/HREE ratio and distinctive negative Eu anomaly. Positive anomalies of Rb, Pb and Th on the spider diagrams suggest continental crust involvement in the genesis and evolution of the parental magma. Based on tectonic setting discrimination diagrams, Aqkand acidic rocks are plotted in the post-collision tectonic setting. In overall petrographic, petrologic and geochemical evidence demonstrate that during the final stages of the continental collision, the thickened sub-continental lithosphere in the Alborz was delaminated and replaced by hot asthenospheric mantle. Rapid upwelling of hot asthenosphere gave rise to the partial melting of sub-continental lithosphere which produced the Oligocene basaltic rocks of the study area. Emplacement of basaltic magma in the upper part of the continental crust led to the partial melting of the crust and generation of the acidic magmas. Rapid cooling of acidic lavas led to the generation of glassy rocks such as obsidian which are changed to perlite in contact with meteoric and warm waters.
A. Ansari; S. J. Sheikh Zakariaee; S. Dargahi; M. Arvin
Abstract
The Chargonbad batholith is located close to Sirjan and southeast of Urumieh-Dokhtar magmatic zone . This batholith is acidic to intermediate in composition and intruded into the Eocene volcanic rocks. The main volume of these rocks consisted of granodiorite and monzogranite, but it also consists of ...
Read More
The Chargonbad batholith is located close to Sirjan and southeast of Urumieh-Dokhtar magmatic zone . This batholith is acidic to intermediate in composition and intruded into the Eocene volcanic rocks. The main volume of these rocks consisted of granodiorite and monzogranite, but it also consists of quartzdiorite, tonalite and syenogranite. Their contacts are gradational. They have allotrimorphic granular texture with subordinate porphyritic texture. Their enclaves consist of xenoliths enclaves, microgranular mafic enclaves (diorite to quartzdiorite in composition) and autolith enclaves(tonalite, granodiorite and monzogranite in composition).The Chargonbad batholith rocks are also cut by different types of dykes which are mainly consisted of dykes and veins of pegmatitic stage, microgranular dykes (andesite and andesite basaltic in composition) and microgranular dykes that are similar to mafic enclaves. Evidenc show that the samples represent properties of I-type granitoids. Chargonbad granitoid has magnesium nature and shows cordellarian granites features. Based on the tectonomagmatic environment diagrams, all samples from the Chahargonbad plot in the island arc setting of a subduction zone and show active continental margin setting characteristics .
V Joudaki; R Ajalloeian
Abstract
In the present case study, a thick overburden above the Ghomroud tunnel locally reaching about 600 meters plus the existence of many fault/crushed zones along the tunnel led the full-face Tunnel Boring Machine (TBM) to encounter squeezing and collapsing of materials. In parts 3 and 4 of the tunnel, a ...
Read More
In the present case study, a thick overburden above the Ghomroud tunnel locally reaching about 600 meters plus the existence of many fault/crushed zones along the tunnel led the full-face Tunnel Boring Machine (TBM) to encounter squeezing and collapsing of materials. In parts 3 and 4 of the tunnel, a combination of these problems caused long-term and frequent pausing in digging processes (about 600 days). The plan is situated in the Sanandaj-Sirjan geological zone. Because of intense tectonic deformations through time, this zone consists of series of rock units, which have experienced moderate to high metamorphisms that caused schistosity and recrystallization of minerals. In the present paper, in addition to preparing thin sections of rocks for microscopic studies, the role of geological conditions with an emphasis on formation petrology is investigated to explore excavation hazards along the tunnel. Hence, by traversing along the axis of the tunnel, several samples were taken from the rocks exposed on surface and from those in the tunnel. Most problems occur in the foliated Jurassic rock units and in sections where faults and relatively thick tunnel overburden (high in-situ stress) have made the geological condition unfavorable. Results show that the petrological properties (texture, mineralogy, etc.) of the extensively foliated rock masses (schist, slate, graphite schist) and their interbedding with strong units (Quartz and quartzite veins) along with other geological factors have been effective on the occurrence of hazards and TBM pausing. Results of Cerchar abrasiveness index test also indicate high hardness and strength of quartzite veins, which played an important role in creating mixed face conditions and amplifying the hazards in easily squeezing and collapsing materials.
E Mohammadi; Gh Ghorbani; H Shafaii Moghadam
Abstract
The studied volcanic rocks are situated in NW of the Sabzevar, mainly at southern domains of the Northern Sabzevar ophiolitic belt. Abundant rhyolitic domes (e.g., Sarough, Zard-Kuhi, Kuh-e-Sefid Mehr and Nahr domes) in the southern margin of the Davarzan-Sabzevar ophiolitic belt crosscut the above-mentioned ...
Read More
The studied volcanic rocks are situated in NW of the Sabzevar, mainly at southern domains of the Northern Sabzevar ophiolitic belt. Abundant rhyolitic domes (e.g., Sarough, Zard-Kuhi, Kuh-e-Sefid Mehr and Nahr domes) in the southern margin of the Davarzan-Sabzevar ophiolitic belt crosscut the above-mentioned ophiolitic rocks. The Geochemical signatures of these volcanic rocks including enrichment in LREEs and LILEs relative to HREEs and HFSEs, depletion in TNT (Ta-Nb-Ti) elements, metaluminous to peraluminous and medium to high K-calc-alkaline characteristics, and their positions in discrimination tectonomagmatic diagrams, displayed that these rocks derived from a subduction-related environment. These adakitic domes are characterized by adakitic signatures (e.g., 69.2 wt.% < SiO2، 14.7 wt.% < Al2O3، MgO < 0.35 wt.% ، Sr > 273 ppm, enrichment in LREEs and LILEs, depletion in Y and HREE (Y < 9.7 and Yb < 0.86( and high ratio of Sr/Y > 58 and La/Yb > 12.1 and belong to high silica adakites (SiO2 ≥ 69.2 wt.%, MgO = 0.19-0.31 wt.% ، CaO+Na2O < 7.62 wt.% and Sr = 273-936). Nd-Sr-Pb isotopes characteristics of the adakitic rocks show similarities to a MORB-type and/or PREMA mantle source, highlighting that their magma (s) is originated from a depleted MORB-type mantle source associated with minor contamination with crustal materials. The geochemical and isotopes characteristics of the Sabzevar adakitic rocks display derivation from partial melting of subducted oceanic crust (garnet amphibolite) associated with subsequent fractional crystallization.
Gh Sohrabi; M.R Hosseinzadeh; A.A Calagari; B Hadjalilu
Abstract
The study area is located in north of East-Azarabaidjan (northwest of Iran). The most important intrusive bodies in the area include the Gharehdagh and Shivardagh batholiths and porphyry stocks of Sungun and Haftcheshmeh. The petrological and petrographical studies show that the composition of intrusives ...
Read More
The study area is located in north of East-Azarabaidjan (northwest of Iran). The most important intrusive bodies in the area include the Gharehdagh and Shivardagh batholiths and porphyry stocks of Sungun and Haftcheshmeh. The petrological and petrographical studies show that the composition of intrusives varies from gabbro through diorite, monzonite, and granodiorite to granite. All bodies are I-type and mostly metaluminous and calc-alkaline with medium to high potassium belonging to volcanic arcs. The most important alterations in ore-bearing areas include silicic, potassic, propylitic, phyllic, and argillic. Mo mineralization occurred mostly in quartz veins and veinlets within the potassic zone in porphyry systems and veins and also in endoskarn associated with garnet skarns. The amount of Mo increases in differentiated and biotite-bearing acidic bodies that have high values of Si, K, Rb, and REEs. The intrusive bodies enriched with K, Rb, and Ba and depleted in Zr, Ta, Y, Yb, and Nb elements indicate metasomatism of the upper mantle by subducting oceanic crust and subsequent generation of magma and its passes through relatively thick crust. The bodies bearing Mo mineralization are located mainly in the center of batholiths and have quartz monzonitic and granodioritic compositions.
M Derakhshi; H Ghasemi; T Sahami
Abstract
The Soltan Maydan Basaltic Complex indicates the most important, thickest, and most voluminous early Paleozoic magmatic activity in Iran outcropping in the eastern Alborz structural zone, in the north-northeast of Shahrud. This complex overlies the late Ordovician Ghelli Formation and is overlain by ...
Read More
The Soltan Maydan Basaltic Complex indicates the most important, thickest, and most voluminous early Paleozoic magmatic activity in Iran outcropping in the eastern Alborz structural zone, in the north-northeast of Shahrud. This complex overlies the late Ordovician Ghelli Formation and is overlain by the early Devonian Padeha Formation. The field evidences show more than 50 lava flows erupting frequently in the sub-aerial and submarine environments. This complex comprises of a continuous fractional spectrum including basalt, basaltic andesite, trachybasalt and basaltic trachyandesite that has undergone medium to high degrees of alteration. The geochemical data and diagrams signify transitional to alkaline nature of the primary magma, genetic relationship among all rocks of this complex due to fractional crystallization, none or weak role of magmatic contamination in magma evolution, and generation of primary magma by 15-17 percent partial melting of an enriched garnet peridotitic mantle source in an intra-continental extensional rift setting. This tectonic setting is concordant with the known extensional rift setting governed on the Alborz and Central Iran zones during the early Paleozoic, especially late Ordovician-Silurian, primary stages of generation and development of the Paleotethys.
M. A. A. Mokhtari; H. Moinvaziri; M. R. Ghorbani; M. Mehrpartou; G. Hosseinzadeh
Abstract
Kamtal skarn zone is located in the 20km north of Kharvana in the Eastern Azarbaijan. Skarn-type metasomatic alteration is the result of Kamtal monzonitic intrusion into the Upper Cretaceous impure carbonates. Kamtal skarn include exoskarn and endoskarn zones. Exoskarn is the major zone that its thickness ...
Read More
Kamtal skarn zone is located in the 20km north of Kharvana in the Eastern Azarbaijan. Skarn-type metasomatic alteration is the result of Kamtal monzonitic intrusion into the Upper Cretaceous impure carbonates. Kamtal skarn include exoskarn and endoskarn zones. Exoskarn is the major zone that its thickness varies between 100-600m. Field and mineralogical studies demonstrate that exoskarn zone composed of garnet rich sub-zone (garnet skarn), epidote rich sub-zone (epidote skarn) and marble sub-zone. Garnet is the most important calc- silicate mineral within the garnet skarn sub-zone. They are mainly grossularitic in composition (Ad33-35), but along the fractures, andraditic composition (Ad66-73) is predominant. Clinopyroxene is the other dominant mineral within garnet skarn sub-zone that has diopsidic composition (Di82.8-85.7). In the epidote skarn sub-zone, epidote is the predominant mineral while garnet and clinopyroxene present in some places and have low concentration. Petrographic studies indicate that marly limestone was the primary rocks of the garnet skarn sub-zone while clay-bearing marl was the primary rocks of the epidote skarn sub-zone. Skarnification process can be categorized into two discrete stages: 1) prograde and 2) retrograde stages. Prograde stage began immediately after the initial emplacement of the Kamtal monzonitic magma into the enclosing impure carbonate rocks. The effect of heat flow from the intrusion caused the enclosing rocks to become isochemically marmorized in almost homogeneous limestone layers and bimetasomatized (skarnoid–hornfels) in thin interlayers of clay-rich carbonates. Invasion of segregated fluid phase of Kamtal intrusion into the fractures and micro-fractures of the marmorized and skarnoid–hornfelsic rocks incorporate considerable amounts of Fe, Si and Mg into the metasomatic aureole. During retrograde stage, due to relatively low temperature hydrothermal fluids and processes such as hydrolysis, carbonation and sulfidation, considerable amounts of hydrous calc-silicates, sulfides, oxides and carbonates replaced the anhydrous calc-silicates. Garnet and clinopyroxene are the most abundant mineral assemblage in Kamtal skarn zone, which were formed in temperature lower than 550°C. Lack of wollastonite in this mineral assemblage, intergrowth of garnet and clinopyroxene crystals and lack of any reaction rim between these crystals, and lack of emplacement texture indicate that they formed contemporaneously within the temperature and ƒO2 ranges of 430–550ºC and 10-26–10-23, respectively.
M. Advay; A. Jahangiri; M. Mojtahedi; J. Ghalamghash
Abstract
The study area as a part of Maku-Tabriz zone is located in about 20 km NE of Khoy, NW Iran. Shah Ashan Dagh granite covers about 60 km2 of the area and emplaced into Permian host rocks and covered by Oligo-Miocene sedimentary rocks (Qom Formation). The Shah Ashan Dagh intrusive rocks composed of gabbro ...
Read More
The study area as a part of Maku-Tabriz zone is located in about 20 km NE of Khoy, NW Iran. Shah Ashan Dagh granite covers about 60 km2 of the area and emplaced into Permian host rocks and covered by Oligo-Miocene sedimentary rocks (Qom Formation). The Shah Ashan Dagh intrusive rocks composed of gabbro and alkali-feldspar granite. Porphyric and granophyric textures indicate shallow depth emplacement and perthitic texture shows hypersolvous nature of this body. The studied mafic rocks have high LREEs relative to HREEs and they indicate relatively enrichment of LILEs and depletion in HFSEs (exception Hf, Ta, Nb). The studied mafic rocks based on positive Nb and Ta anomalies show similarity to plum type MORB. These rocks are tholeiitic and they have mantle plum enriched source. Shah Ashan Dagh granite characterized with high-K, sub-alkaline, metaluminous to peraluminous and weakly peralkaline nature. They have high content of LILEs, especially Th and Rb, and low content of Eu, Sr, Ta, Nb, Ba, and Ti, implying the granites may have been derived from crustal melts.
M .A. Mokhtari; H. Moein Vaziri; M.R. Ghorbani; M. Mehr Parto
Abstract
Kamtal intrusion is located in East Azarbaijan province, NW of Iran, near the Armenia border. The Kamtal intrusion consist of an acidic part with monzogranitic composition and an intermediate- basic part which compositionally composed of monzonite, monzodiorite, quartz monzonite, quartz monzodiorite ...
Read More
Kamtal intrusion is located in East Azarbaijan province, NW of Iran, near the Armenia border. The Kamtal intrusion consist of an acidic part with monzogranitic composition and an intermediate- basic part which compositionally composed of monzonite, monzodiorite, quartz monzonite, quartz monzodiorite and gabbro. Gabbroic rocks exist in the form of small lenses in the southeast of Kamtal intrusion within the intermediate part. The intermediate- basic part has been intruded by the acidic part. Both acidic and intermediate parts are high-K calc-alkaline, metaluminous in character and classified as I-type granitoids; while, the gabbros have tholeiitic nature.
Both acidic and intermediate rocks show a LREE rich pattern and high LREE/HREE ratio. These two parts have differences in MREE enrichment. From similarity in REE patterns of acidic and intermediate rocks a genetic relation can be discerned. Negative anomalies of Nb and Ti can be seen in all rock phases of the Kamtal intrusion, representing the subduction zone setting. Comparison of trace element variations with those of granitoid rocks of different tectonic settings show similarities between Kamtal intrusion and Andean volcanic arc granitoids. Furthermore, Kamtal intrusion can be classified as VAG based upon tectonic setting discrimination diagrams. It is concluded that, Kamtal intrusion probably is the result of Neotethys oceanic crust subduction beneath the Caucasus continental plate.
H. Ghasemi; A. Ramazani; A. Khanalizadeh
Abstract
Silijerd intrusion with an age of Late Eocene – Oligocene (39.23.2 Ma) is located in Uromeyeh-Dokhtar magmatic arc, central Iran structural zone, northwest Saveh. This intrusion is composed of a continuous compositional range including: diorite/gabbro, ...
Read More
Silijerd intrusion with an age of Late Eocene – Oligocene (39.23.2 Ma) is located in Uromeyeh-Dokhtar magmatic arc, central Iran structural zone, northwest Saveh. This intrusion is composed of a continuous compositional range including: diorite/gabbro, granodiorite, syeno-monzogranite and alkali granite intruded into the Eocene volcanic and pyroclastic rocks.
Variation diagrams showing trends of major and trace elements indicate a continuous compositional range and a comagmatic origin for these rocks. Trends of compatible- incompatible elements indicate the important role of fractional crystallization in the genesis of these rocks. All samples are metaluminous with medium-high K with calc-alkaline nature. High values of Rb, Sr, K, U, Th, Zr and Ba and high ratios of K2O/Rb and FeO/MgO indicate the similarity of the rocks of this intrusion with the rocks of continental margin magmatic arc intrusions. Depletion in Nb,P,Ta and Ti and enrichment in K,Sr,Rb,Cs and Ba are obvious in the spider diagrams of these samples. The enrichment in LILE and depletion in HFSE reveal the I-type metaluminous magmatism of volcanic arcs (VGA). Whole rock 87Sr/86Sr ratios of this intrusion range from 0.704759 to 0.705166 and it can be correlated with the values of these ratios in the mantle and lower crust sources and low contamination of their magmas with upper crust.
Existence of K-feldspar megacrysts and mafic microgranitoid inclusions in this intrusion, high abundances of La and Ce , V enrichement in mafic terms and low whole rock 87Sr/86Sr ratios of this body, suggested a partial melting of mantle wedge, subducted oceanic crust (metabasaltic sources) or lower continental crust (metatonalitic sources) origins for it. The discrimination tectonic setting diagrams also indicate an I-type continental volcanic arc magmatism for this intrusion.
A. Kananian; M. Rezaei-Kahkhaei; D. Esmaeili
Abstract
The Lakhshak granitoid pluton which is located at 10 km northwest of Zahedan, has intruded into the Eocene flysch sediments with an elliptical shape and NW-SE direction. This pluton after emplacement has been cut by numerous dykes with NE-SW trend. These dykes comprised about ...
Read More
The Lakhshak granitoid pluton which is located at 10 km northwest of Zahedan, has intruded into the Eocene flysch sediments with an elliptical shape and NW-SE direction. This pluton after emplacement has been cut by numerous dykes with NE-SW trend. These dykes comprised about 20-30% of the Pluton with various compositions, ranging from granodiorite to monzodiorite in composition.
The Lakhshak plutonic rocks are mainly metaluminous, calc-alkaline and belong to I type granites based on the P2O5 and Th content versus SiO2. Regarding TiO2 content these rocks resemble the continental margin granites. The MgO, Na2O, Ni, Cr content as well as Mg# and depletion in Y, these plutonic rocks are similar to the adakite, a rock type produced by partial melting of young oceanic crust. The low Ba/La content of the studied samples may suggest that subducted slab suffered dehydration prior to partial melting.
These rocks are enriched in LIL, LREE, however, they are depleted in HREE and Y. In addition, they show negative anomalies of Nb, Ta, P and Ti, and positive anomaly of Pb. The negative anomalies of Nb and Ta may indicate the effect of mantle wedge metasomatism by oceanic crust. The positive anomaly of Pb may demonstrate continental crust assimilation by magma associated with mantle metasomatism.
It seems that Lakshak pluton has been formed by subduction of Sistan young oceanic crust under the Afghan Block. Moreover, the low content of HREE and Y besides a decreased ratio of Yb versus SiO2, Y<15.13, Yb<1.2 and existence of amphibolite enxenoliths in these rocks may suggest partial melting of amphibolites. The latter is formed during the oceanic crust subduction in depth more than 35 km.
