Showing 8 results for Alkaline
Zahra Goli, Dr Ghodrat Torabi, Hosna Maleki,
Volume 5, Issue 2 (12-2019)
Abstract
The Eocene volcanic rocks are exposed in Dastgerdo and Molla Ahmad areas (East of Isfahan province); the middle part of Urumieh - Dokhtar magmatic arc (UDMA). In this area, the UDMA width is about 13 kilometers which is one of its narrowest parts. These Eocene rocks consist of lava (trachyte, dacite, andesite, basaltic andesite and basalt) and pyroclastic rocks (littic tuff, tuff breccia and ignimbrite) which cross cut by Oligocene granodiorites. Andesites are the predominant rock unit with good outcrops. The main rock- forming minerals of andesites are clinopyroxene (augite), orthopyroxene (enstatite), plagioclase (andesine to bytonite), amphibole (magnesian hornblande), biotite, quartz, magnetite, ilmenite and sphene. Secondary minerals which are produced by alteration are chloritized olivine, malachite, chlorite, calcite, epidote, actinolite, albite and montmorillonite. The geochemistry of volcanic rocks show that the volcanic rocks of Dastgerdo to Molla Ahmad areas have a wide range of SiO2 (50.4 to 65.5 wt%) and belong to the calc-alkaline magmatic series. These rocks are more enriched in light rare earth elements (LREEs) than the heavy rare earth elements (HREEs) and represent evident negative anomaly of Eu. Whole rock chemistry and horizontal pattern of HREEs reveal that the spinel lherzolite is the source rock. Petrography and geochemistry of minerals and whole rock samples indicate that the studied andesites are formed by the same petrogenetic processes and are affected by magma mixing and contamination during crystallization. The field, petrography and geochemical data show that Dastgerdo to Molla Ahmad volcanic rocks belong to volcanic arc tectonic setting and are formed by subduction of Neothetys oceanic crust beneath the Central Iran.
Roya Aliakbari, Amir Ali Tabbakh Shabani , Shahryar Mahmoudi,
Volume 6, Issue 1 (8-2020)
Abstract
The study subvolcanic intrusion, comprising syenodiorite, monzonite and quartz-monzonite, is cropped out in Talkh-rud valley located in the northeast of Damavand volcano flank. This sub-volcanic intrusion possesses porphyritic texture and consists of plagioclase, alkali feldspar, phelogopite, amphibole, clinopyroxene, apatite and titanomagnetite. Evidences of disequilibrium such as zoning and sieve textures in plagioclase and opacity of phlogopite crystals could be due to variations in water vapor pressure during magma ascent. The intrusion is geochemically metaluminous, alkaline and shoshonitic and tectonically plots in the realm of within plate volcanics. Normalized to the chondrite and primary mantle multi elemental spider diagrams show enrichment of LREE and LILE and depletion of HREE and HFSE such as Ti, Nb. Comparison of these rocks with their extrusive counterparts, i.e., trachy-andesites and trachytes of Damavand shows no significant difference between the geochemistry and mineralogy.
Elaheh Miri, Dr Ali Kananian, Dr Alireza Badiei,
Volume 6, Issue 2 (12-2020)
Abstract
In this research, pyrophyllite phase transfer to tobermorite group and sodic to calcic zeolites was investigated in presence of NaOH and CaCl2 solutions. The experiments were carried out in three separate stages under constant hydrothermal conditions (temperature 150 °C, time 72 h) in the Teflon-lined autoclaves. The chemical composition of the initial sample was determined by XRF. Morphology and mineralogy of samples were characterized by SEM and XRD, respectively. The results showed that leucite and sodic zeolites (analcime, sodalite) were formed at variable concentration of NaOH (1–8 mol/l). The calcic zeolite was not synthesized in the presence of Na+ (1.5–2.5 mol/l) and Ca+2 (0.25-1 mol/l), but riversideite, hibschite, halite, hydroxycancrinite and trikalsilite were detected. Riversideite (a member of tobermorite group) and hibschite (a type of hydrogrossular) were formed at highest concentration of Ca+2 (1 mol/l), and halite was produced as a main product at lowest concentration of Ca+2 (0.25 mol/l). The concentration of Ca+2 and Na/Ca ratio are the main factors in the synthesis of these products.
Mis Asrin Shojaei, Dr Mohammad Rahgoshay, Mr Ayoub Veisinia, Dr Iman Monsef,
Volume 7, Issue 1 (8-2021)
Abstract
The Kamyaran ophiolites, with the age of Late Cretaceous, are a part of the Iranian Mesozoic ophiolites, which are exposed in the SW of Zagros Main Thrust. This massif is bordered at the NE by the Sanandaj-Sirjan metamorphic rocks and at the SW by the Bisotun limestones and Kermanshah radiolarites and then by the Zagros Fold-Thrust Belt. The Kamyaran ophiolite is made of the mantle and crustal sequences. The crustal sequence is distinguished by pillow lavas, sheeted dike complex, and lava flows. The positive LILE anomalies with the HFSE depleted confirm their arc-related affinity. The geochemistry signatures of sheeted dikes show that these rocks have two different patterns. The REE pattern in some of the sheeted dikes samples with the pillow and flow lavas sample is similar to E-MORB; their element ratios support this likeness too. The positive LREE and LILE anomalies with the depletions of the HFSE suggest the calc-alkalic tendency and subduction-related affinity for these rocks; however, dacitic dikes with the flat REE pattern, LILE enrichment, and HFSE depletions have the Island-arc tholeiites affinity. The similarity of element ratios in all the samples may suggest that these rocks have the same magma source, and the tectonic environment of the ophiolitic rocks can be correlated with the oceanic subduction environment.
Dr Morteza Khalatbari Jafari, Mr Amir Shariari, Dr Mohamad Faridi,
Volume 9, Issue 1 (9-2023)
Abstract
The study area is located in the north of the Yusef -Kandi village, north of Lahrud, Ardabil Province (northwestern Iran). This area comprises portions of the Alborz-Azarbaijan structural zone, which together with the Little Caucasus and the highlands of southeastern Turkey have evolved due to the convergence of the Arabian and Eurasian plates during the Alpine-Himalayan orogeny. The study area includes outcrops of Eocene volcanic and volcano-sedimentary sequences which were deposited in marine to continental environments. The volcanic portion of these sequences consists of volcanoclastic rocks as well as lava flows. A few acidic volcanic rocks and ignimbrite are locally exposed in this area. The petrographic studies show that the Yusef-Khan-Kandi volcanic rocks include picrobasalt, basalt, tephrite, basanite, trachybasalt, basaltic trachyandesite, phenotephrite, tephrophenolite, trachyandesite and trachyte compositions. Phyric texture is common within the volcanic lavas. The majority of the samples show transitional to potassic trends, with only a few samples exhibiting sodic trends. The transitional trend observed in a significant number of the studied samples probably has resulted from the mingling of the sodic and potassic magmas. The Harker binary variation diagrams indicate trends that are consistent with fractional crystallization. The chondrite-normalized REE patterns and primitive mantle-normalized spider diagrams show high LREE/HREE ratios which could be explained by partial melting of an enriched mantle (including asthenospheric) or a metasomatized mantle in collisional to continental arc environments. Most of the studied volcanic rocks plot in the active continental arc or within plate domains. It seems that following the convergence between the Arabian and Eurasian plates in the Late Cretaceous, the northward subducting Neotethyan slab in the Eocene, triggered partial melting of the metasomatized subcontinental lithospheric mantle. Therefore, we suggest that the Yusef-Khan-Kandi Eocene volcanic rocks were erupted in a post-collision extensional environment.
Pouya Besharati, Ali Kananian, Fatemeh Sepidbar,
Volume 9, Issue 2 (12-2023)
Abstract
The high K-volcanic rocks of the Eslamieh Peninsula (Saray) are exposed in the northwestern Urumieh-Dokhtar magmatic belt. They mainly include phonolitic lavas and related xenoliths. The xenoliths can be subdivided into two types with basaltic and trachyandesitic compositions. The phonolites and related xenoliths are characterized by enrichment in large ion lithophile elements (LILEs: Th, Ba, Rb and K) and light rare earth elements (LREE), depletion in high field strength elements (HFSE: Eu, Ta, Nb and Ti) and flat patterns in heavy rare earth elements (HREE). They have typical high–K and shoshonitic signatures formed in post-collisional arc setting. The studied pyroxenes from phonolitic hosts were crystallized at moderate to high pressures (6-15 kbar) and temperatures of 1200-1300 ̊C, whereas those from trachyandesite and basaltic xenoliths were formed at lower pressures (6-10 kbar and 2-5 kbar) and temperatures (1150-1200 ̊C and 1100-1150 ̊C), respectively. Due to the lack of evidence for melting, dissolution and the presence of accumulated microcrystals at the mineral boundary, it seems that the xenoliths were detached from the walls and been transported to the surface during magma ascent
Ashraf Torkian, , Mohsen Mohammadi,
Volume 10, Issue 1 (4-2024)
Abstract
The study area is located in the SaSZ, NE of Songhor city, Kermanshah Province. Based on field observations and mineralogical data, the Azizabad-Hazarkhani I-type calc-alkaline granitoid consists of granites, monzonites and diorites with small volumes of gabbroic rocks. Co-variations in major and trace elemental abundances do not indicate a continuous compositional suite and therefore do not suggest a co-magmatic origin. According to geochemical evidence, the samples are enriched in incompatible elements such as Th, Rb, La, Ce and Nd and depleted in Nb, Ti and Eu, with metaluminous affinity. These characteristics reflect the role of continental crust and crust-derived melts. Tectonic setting discrimination diagrams suggest that this complex belongs to the volcanic arc and is related to an active continental margin setting. According to the geological history of this area, it can be attributed to the subduction of Neo-Tethyan oceanic crust below the Central Iran microplate. We suggest that the Parishan and Darvazeh mantle-derived basaltic magmas may have provided the heat required for the partial melting of various source rocks, including amphibolites, meta-basites, and meta-andesites, through diffusive heating.
Mohammad Najari, Ahmad Jahangiri, Ryo Anma,
Volume 10, Issue 1 (4-2024)
Abstract
In the northwestern part of the Sanandaj-Sirjan zone, mafic intrusive bodies are aligned with the trend of the Zagros orogenic belt. In this part of the Iranian lithosphere, magmatic activity occurred during three main periods: Cretaceous, Eocene, and Miocene-Quaternary. In the first of two stages, the magmatic activity was associated with subduction-related magmatism at the active continental margin, whereas the last phase was characterized by calc-alkaline magmatism related to post-collision regime. The intrusive mafic bodies of Qobadlo, Chupankareh, and Qaraqoshun at the southern margin of Lake Urmia in the northern part of the Sanandaj-Sirjan zone intruded within the complex of Cretaceous shale, shale-sandstone, and siltstone. U-Pb dating on zircon performed on these bodies indicates an age of 99 Ma. The SiO2 content of these bodies ranges from 46.17 to 53.35%, Al2O3 13.1 to 18.49 % Fe2O3 3.11 to 5.8%, and their TiO2 content ranges from 1.9 to 4.0%. Positive anomalies of large ion lithophile elements and LREE compared with negative anomalies of elements such as Nb, P, Zr, and Ta (HFSE), the La/Nb, Ba/Nb ratios, and the REE pattern show a good correlation with the magmatic rocks of subduction zones.
