Petrology
Ashraf Torkian; Sara Damchin-Mashak; Zohreh Yarali; Maryam Souri
Abstract
The studied area is located in N-Sonqor and in the Sanandaj-Sirjan zone. Field relationships and petrographic evidence show that volcanic rocks of the north of Bashirabad comprise of trachydacite to trachyandesite (and altered basaltic trachyandesite) and in the south of this area, it consists of andesite ...
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The studied area is located in N-Sonqor and in the Sanandaj-Sirjan zone. Field relationships and petrographic evidence show that volcanic rocks of the north of Bashirabad comprise of trachydacite to trachyandesite (and altered basaltic trachyandesite) and in the south of this area, it consists of andesite to trachyte. Their texture is mainly porphyry. Geochemical data {total abundance of (Na2O+K2O), enrichment of large lithophile ion elements and rare light earth elements) indicate that these rocks belong to the alkaline series. Spider diagrams show enrichment in LREE and depletion HREE, and parallel patterns in all volcanic samples confirm their common origin. According to modeling magmatic processes, fractional crystallization, assimilation and crustal contamination have played an important role in the magma forming the studied rocks. The discriminating diagrams the tectonic setting the Bashirabad volcanic rocks indicate their subduction-related volcanic arc that was formed in an active continental margin environment with local tensions.
R Dabiri; M.H Emami; H Mollaei; M Ghaffari; M Vosougi Abedini; N Rashidnejad Omran
Abstract
Quaternary volcanic rocks are widely developed in NW of Ahar, NW Iran. Based on geochemical data, these rocks mainly consist of alkali basalts, trachybasalts, basaltic trachyandesites and trachyandesites. The major- and trace-element chemistry indicates that the lavas are dominantly alkaline in character. ...
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Quaternary volcanic rocks are widely developed in NW of Ahar, NW Iran. Based on geochemical data, these rocks mainly consist of alkali basalts, trachybasalts, basaltic trachyandesites and trachyandesites. The major- and trace-element chemistry indicates that the lavas are dominantly alkaline in character. The studied rocks display microlithic porphyritic texture with phenocrysts of olivine, clinopyroxene, and plagioclase ± amphibole ± biotite. Major and trace element abundances vary along continuous trends of increasing SiO2, Al2O3, K2O, Na2O, Ba and Rb decreasing CaO, Fe2O3* and Cr with decreasing MgO.The volcanic rocks in this area are characterized by the LILE and LREE enrichments and negative HFSE anomalies. The Sr and Nd isotopic ratios vary from 0.704463 to 0.704921and from 0.512649 to 0.512774, respectively.CaO/Al2O3 ratios versus MgO, La/Sm ratios versus Rb and Ba and Zr versus Th suggest that that fractional crystallization was a major process during the evolution of magmas. AFC modeling and isotopic data as well as microscopic evidence, clearly indicate that crustal contamination accompanied by the fractional crystallization played an important role in petrogenesis of the trachyandesites. Also, geochemical and isotopic compositions indicate that magma mixing was not essential process in the evolution of Ahar magmas. Alkali basaltswith high 143Nd/144Nd ratio, low 87Sr/86Sr ratio and high MgO, Ni and Cr contents indicate that they crystallized from relatively primitive magmas. REE modelling and Trace element ratios indicate that the alkali baslats were derived by small degrees (~1-3%) of partial melting from the spinel lherzolite.
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.
M. Sadeghian; H. Ghasemi; Z. Farsi
Abstract
Chah Salar granitoidic pluton is located in the N of Chah-Salar village, SW of Neishabour, in the northern margin of structural Central Iran zone. This pluton intruded in Sabzevar ophiolitic Zone and based on the field observations, petrographical and geochemical classification diagrams, its lithological ...
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Chah Salar granitoidic pluton is located in the N of Chah-Salar village, SW of Neishabour, in the northern margin of structural Central Iran zone. This pluton intruded in Sabzevar ophiolitic Zone and based on the field observations, petrographical and geochemical classification diagrams, its lithological composition composed of diorite, quartzdiorite, granodiorite and alkali feldspar granite. Alkali feldspar granites as a much fractionated end-members of this rock association are intruded in this pluton in the form of dikes or apophyse shapes. Granitic pegmatites and their associated quartzolites are the most differentiated end-member of this rock association. Their subvolcanic equivalents such as pyroxene-bearing andesite, andesite, trachyandesite and dacite cut this pluton in the forms of dikes or domes. The studied rocks show variety of textures including granular, myrmekitic, graphic, porphyritic, microlitic porphyry and pilotaxitic. Except alkali feldspar granites which are highly fractionated, the other lithological compositions, on the variations diagrams of major, trace and rare earth elements versus SiO2 or differentiation index show continuous compositional variations. This pluton has calc-alkaline and metaluminous nature and belongs to I-type granitoids. Also tectonic setting discrimination diagrams indicate that the Chah Salar granitoidic pluton belongs to volcanic arc granitoids (VAG) and continental arc granitoids (CAG). Detailed investigations of field geology, petrography and geochemical characteristics indicate that magma-forming of this pluton is resulted from partial melting of subducted oceanic slab (metabasite) or metasomatized mantle wedge and then evolved by fractional crystallization, magma contamination or magma mixing.
