Volume 23, Issue 1 (4-2015)                   www.ijcm.ir 2015, 23(1): 15-30 | Back to browse issues page

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Mineralogical and petrological properties of feldspathoid rocks from SW Sarab, NW Iran . www.ijcm.ir. 2015; 23 (1) :15-30
URL: http://ijcm.ir/article-1-183-en.html
Abstract:   (3182 Views)

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.  

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