Petrology
Jalil Ghalamghash; Meysam Akbari; Reza Jamal
Abstract
The Taftan volcano hosts an extensive volcanic activity during Late Miocene to Quaternary where took place over Makran-Chagai subduction zone. Taftan rocks are mainly basaltic andesite, andesite, trachyandesite, and dacite that occur as lavas and pyroclastic rocks. They are characterized by basic-intermediate ...
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The Taftan volcano hosts an extensive volcanic activity during Late Miocene to Quaternary where took place over Makran-Chagai subduction zone. Taftan rocks are mainly basaltic andesite, andesite, trachyandesite, and dacite that occur as lavas and pyroclastic rocks. They are characterized by basic-intermediate inclusions enclosed by acidic groundmass, and disequilibrium textures in plagioclase phenocrysts including sieve texture, zoning, and dissolution margin, which may reflect magma mixing. These rocks record high-K calc-alkaline to calc-alkaline affinity with enrichment in LREE and LILE relative to HREE and HFSE, respectively. These features, coupled with the clear depletion in HFSE (such as Nb, Ta, and Ti) are consistent with typical subduction-related volcanic arcs. Taftan primary melts might have been produced by ~15% partial melting of spinel lherzolite mantle. The normalized multi-element patterns which mimic the upper continental crust values, and enrichment in Pb, Th, U, and Rb agree well with magma evolution by assimilation and fractional crystallization (AFC). The available isotopic geochronology dataset reveal that the youngest volcanoes of the Makran-Chagai magmatic arc are Bazman and Kuh-e-Sultan volcanoes. A geochemical comparison of these volcanoes highlights that magmatism in the Taftan where the crust is thick, underwent a higher degree of crustal assimilation en route to the surface.
Petrology
Ashraf Torkian; Jamal Abdolahpour; Nafiseh Salehi
Abstract
Pyroclastic rocks in the Badam area (E-Mahabad, west Azarbaijan Province), are located at the most extreme northern part of the Sanandaj-Sirjan zone. Petrographic studies revealed that they are basanitic in composition and have porphyric and microlithic porphyric textures. Olivine and clinopyroxne occur ...
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Pyroclastic rocks in the Badam area (E-Mahabad, west Azarbaijan Province), are located at the most extreme northern part of the Sanandaj-Sirjan zone. Petrographic studies revealed that they are basanitic in composition and have porphyric and microlithic porphyric textures. Olivine and clinopyroxne occur as phenocrysts and clinopyroxene and nepheline as microliths. Opaque minerals and glass have occupied the space between different minerals. In classification diagram, they have basanitic composition. Geochemical features such as enrichment in LILE, high LREE concentrations and negative anomalies in Nb, Ta and Y, with positives anomalies in Ba, Pb and Th and enrichment in Th/Yb, all suggest that these rocks have mantle source that are enriched by melt/fluids from the metasomatized subducted oceanic slab. These features are inherited from mantle source and they are not caused by crustal contamination. Regarding MREE and HREE ratios, these basanites originated from 1 % partial melting of a garnet lherzolite source in the garnet stability field (85 Km). Melting trigger in this area is not clear, but old theories such as lithosphere delamination or slab break up are not applicable any more. There is three suggestions about melting in these are: 1) break up of hydrated phases by depth increase, 2) changing and turbulence in convection follows, 3) subduction and dehydration of Arabic passive margin.
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.
Monireh Kheirkhah; M. H. Emami
Abstract
At the farthest end of NW Iran, the Quaternary basalts crop out in Azerbaijan province, located in Alpine – Himalaya belt and highly pleatue of Iran-Turkish, eastern Anatolian. The Quaternary volcanic units of NW Azerbaijan cover a broad compositional range from basalts, basaltic andesite, trachy ...
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At the farthest end of NW Iran, the Quaternary basalts crop out in Azerbaijan province, located in Alpine – Himalaya belt and highly pleatue of Iran-Turkish, eastern Anatolian. The Quaternary volcanic units of NW Azerbaijan cover a broad compositional range from basalts, basaltic andesite, trachy andesite to trachyte. These rocks are erupted from deep tension, strike-slip faults in a pull a part basin and volcanic centers. Source of primary magmas and crustal contamination processes have certainly contributed to the understanding of the origin of basaltic rocks. Based on field area, petrography and petrology studies, 10 samples were selected for 143Nd/144Nd and 87Sr/86Sr measurements. The obtained results were correlated with other isotopic data of similar Quaternary basaltic rocks from Turkey. Isotopic study indicates that all of these rocks are derived from mantle and plot in Bulk Earth field and mantle array. The basaltic rocks in the northern area are derived from a depleted mantle and those from the southern area shows contamination by crust.
S. Malecootyan; Sh. Hagh-Nazar; M. Ghorbani; M. H Emami
Abstract
Petrological,geochemical and isotropic evidence of crustal contamination of the Quaternary basic rocks of Ghorveh-Takab axis is presented in this paper. These rocks are olivine basalt and basalt and they are plotted in the field of alkaline suites in geochemical diagrams.
Some ...
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Petrological,geochemical and isotropic evidence of crustal contamination of the Quaternary basic rocks of Ghorveh-Takab axis is presented in this paper. These rocks are olivine basalt and basalt and they are plotted in the field of alkaline suites in geochemical diagrams.
Some evidence, such as the presence of gneissic xenoliths, quartz xenocrysts with reaction rims and biotite phenoblasts in the basic rocks of the study area and high amount of potassium and high values of ratios, high concentration of LREE in comparison with HREE, high values of ratios and low values of ratios all indicate the crustal contamination of basic magma during its ascent.
