جستجوی مقالات مرتبط با کلیدواژه "syenite" در نشریات گروه "زمین شناسی"

Intrusive masses are exposed in the Bostanabad-Mianeh axis with the northwest-southeast trend. The rocks are known as granite in general geological maps. Detailed studies in this study have also shown the presence of syenites which their petrology was considered in order to investigate the Zagros orogeny development in northwestern of Iran. The magmatic rocks of the region are the result of magmatism of the Uromieh-Dokhtar magmatic belt and include intrusive, volcanic and pyroclastic rocks with sedimentary units. Syenites of the Bostanabad-Mianeh axis are along with large volume of granites. Syenites provides important information about the interaction of the crust-lithosphere mantle, magma evolution processes, tectonics and crustal growth. In this study, syenites are divided from granitic rocks and their geochemical properties have been investigated to determine their tectono-magmatic and Petro-genetic conditions.

During field study, samples from the syenite and granite outcrops were collected for petrography, geochemistry and determining magmatic series and the magma origin. For geochemical studies, 13 samples of intrusive rocks with the lowest degree of alteration were chemically analyzed by ICP-MS and ICP-OES methods in the Act Lab Ontario Canada.

The Bostanabad-Mianeh axis in northwestern of Iran and in the East Azerbaijan province is part of the Cenozoic magmatism of the Lesser Caucasus towards southeastern Iran. Magmatism is related to the subduction of the northern ocean of Neotethys during the collision of the Arabian Plateau with Eurasia and its subsequent events. The presence of arc-type magmatism in the regions of Azerbaijan, the Alborz Mountains, Talesh and the Lesser Caucasus all indicate the subduction of the Neotethys branch with the Eurasian plate. Due to the LILE and LREE enrichment and the HREE depletion, the source of the magmas for the studied syenites are originated from an enriched mantle source in the continental lithosphere in the subduction zone belonging to post orogenic extension events. Consequently, the formation of the intrusions is related to mantle melting which is enriched and fed by fluids and melts and finally contaminated with crustal material during the ascent.

Ring-type Eocene-Miocene alkali syenite-syenite intrusions of the North and West Sardasht are part of north Sanandaj–Sirjan zone. The syenitic rocks are located in the central part of the complex near the appinite-gabbro outcrops. Field and microscopic evidences indicate that magma mingling between alkali syenite and appinite-gabbro magmas has occurred to form intermediate parts as syenite in some outcrops. Felsic outcrops are mainly composed of alkali feldspar in the form of perthite. Enclaves of olivine, clinopyroxene, plagioclase, and amphibole along with a few opaque minerals and apatite were formed in the syenites. The main textures of the rocks are granular and lamination. The high ratios of (La/Sm)n and (La/Yb)n, high levels of K, Rb, and less Ba, and low concentrations of Hf, Nb, Zr, and Ta indicate the interference of an arc-related setting for the formation of the rocks. Geochemical and tectonic setting evidences show that the intrusions wereresulted by partial melting of the continental crust base of submature-mature (evolved) island arc or active continental margin formed as a result of hydrous-mafic magma injection of the mantle wedge upper supra subduction zone to the base. Geothermal gradient was high in the base of the subduction. By injecting the hydrous-mafic magma, widespread melting occurred, and the alkali syenites were formed. These tectonomagmatic conditions are confirmed by large-scale ring-shaped outcrops of the intrusions and mafic micro-granular enclaves. Finally subduction of Neotethyan oceanic crust under the other part of the crust or active continental crust, caused to form the Sardasht crust and then evolve this area over time to Oligocene. As a result of the continuity of the subduction, different rock types were formed around Sardasht

The studied area is located at the 30 km northeast of the Bafq city and near the Esphordi phosphate mine. This area composed of Rizu Series rock sequence with Upper Precambrian- Lower Cambrian age. The mentioned sequence has been intruded by some seyenitic and gabbroic intrusions. Petrographical studies indicate that syenites contain hetero- granular, perthite and checkerboard textures and composed of alkali- feldspar (orthoclase), plagioclase, amphibole, pyroxene and biotite. Gabbros contain hetero- granular, and inter- granular textures, and composed of plagioclase, clinopyroxene, amphibole and biotite. Geochemical studies demonstrate that syenites and gabbros have high- K to shoshonitic alkaline nature. Based on the spider diagrams, the two mentioned intrusion have similar trend which can be indicative for their genetic relation. These diagrams indicate enriched LILEs along with negative anomalies of HFSEs. The chondrite normalized REE patterns demonstrate LREEs rich pattern with high ratio of LREE/HREE. The mentioned trends along with positive and negative anomalies of those elements probably are related to lower partial melting degrees of metasomatized mantle along with crustal contamination of this magma. Based on geochemical studies and using the discrimination tectonic setting diagrams, it seems that the studied intrusions were formed at the active continental margins toward post- collisional setting.

The Baba Ali deposit is located about 39 km to the north west of Hamadan city. The syenitic pluton intruded and metamorphosed the diorite host rock producing the skarn deposit. Geochemical considerations indicate that the concentration values of rare earth elements in the syenite and diorite range from 35.4 to 560 ppm. Rare earth elements variation in syenitic, skarn and diorite rock are similar indicating the similar source of the REE. Eu and Ce anomalies show varying values within the range 0.29 -1.24 and 0.8-1.09, respectively. Positive Ce anomalies occurred in the ores of low REE content and negative Ce anomalies occurred in the ores of high REE content. The concordance of the values of CaO with those of Eu revealed that the degree of plagioclase alteration. The Eu anomaly decreases with decreasing intensity of alteration. The La/Y values (suitable parameter for determination of pH in the environment of ore formation) range from 0.37 to 2.89. REE mobility depends on changes in pH. As a whole, epidote has been enriched in REE contents and actinolites, magnitite, are depleted in REE. These REE signatures indicate that hydrothermal fluids responsible for epidote were mostly magmatic origin and for actinolite and phlogopite were magmatic origin with low REE concentration or meteoric water involved in formation of these minerals.

The major syenitic bodies of Iran are spread on northwestern part, East Azerbaijan Province, which belong to late Eocene, early Oligocene magmatisem. Abbasabbad–Bashkand pluton is one of these intrusions, which is located as some minor and autonomous bodies in western side of the main Bozghush nepheline syenite pluton. Porphyritic, microgranular and porphyritic microgranular are common textures in the studied rocks. On the basis of modal classification, these rocks belong to pseudoleucite syenite, nepheline monzodiorite, analcime syenite and syenite types. The main mineral constituent of these rocks encompass K-feldspar, plagioclase, pseudoleucite, analcim and nepheline. Pyroxene, hornblende, biotite, olivine, apatite, and opaque exist as accessory minerals and seresite, chlorite, oralite, idengsite, iron oxides and clay minerals exist as secondary minerals. Results of X-ray analysis indicate the existence of analcime, natrolite, nepheline, barium-rich feldspar (Celsian) in these rocks. Based on clinopyroxenes mineral chemistry, the entire pyroxenes plotted in Ca-Mg and Fe pyroxenes region. The compound of pyroxene end members were changed between En40.75Fs9.40Wo43.98 and En43.23 Fs13.61Wo47.8, that indicate the existence of diopsidic augite clinopyroxenes in these rocks. Based on chemical classifications, the rocks are nepheline syenite, syenite and syenite-diorite. Agpaitic mineralogy index studies indicate studied rocks are classified as miascitic nepheline syenite. Magmatic series of the studied rocks are high potassium alkaline and shoshonitic. Al bearing, ferromagnesian and opaque minerals are the main controlling agent of CaO, MgO, K2O and Al2O3 amount. K2O amount increases as SiO2 increasing. Geochemical diagrams, spider diagrams and REE patterns of the studied rocks show that they are formed in an subduction-related tectonic setting. Distinct enrichment in Th, Ba, Rb, K and U probable depends on mantle metasomatism processes and/or continental crust mixing. Ta, Nb and Ti anomalies and metaluminous characteristics of investigated rocks in one hand, and Neotethys subduction occurrence in other hand, probably indicate subduction affects on enrichments of incompatible elements in mantle resources of the studied rocks.