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Mineral chemistry and petrogenesis of chromitites from the Khoy ophiolite complex,Northwestern Iran: Implications for aggregation of two ophiolites 下载免费PDF全文
Fatemeh Zaeimnia Ali Kananian Shoji Arai Mirsaleh Mirmohammadi Ali Imamalipour Mohamed Zaki Khedr Makoto Miura Khadidja Abbou‐Kebir 《Island Arc》2017,26(6)
The Khoy ophiolitic complex in Northwestern Iran is a part of the Tethyan ophiolite belt, and is divided into two sections: the Eastern ophiolite in Qeshlaq and Kalavanes (Jurassic–Cretaceous) and the Western ophiolite in Barajouk, Chuchak and Hessar (Late Cretaceous). Our chromitites can be clearly classified into two groups: high‐Al chromitites (Cr# = 0.38–0.44) from the Eastern ophiolite, and high‐Cr chromitites (Cr# = 0.54–0.72) from the Western ophiolite. The chromian spinels in high‐Al chromitite include primary mineral inclusions mainly as Na‐bearing diopside and pargasite with subordinate rutile and their formation was probably related to reaction between a MORB (mid‐ocean‐ridge basalt)‐like melt with depleted harzburgite, possibly in a back‐arc setting. Their host harzburgites contain clinopyroxene with higher contents of Al2O3, Na2O, Cr2O3, and TiO2 relative to Western harzburgites and are possibly residue after moderate partial melting (~15 %) whereas the Western harzburgite is residue after high partial melting (~25 %). The chromian spinel in the Western Khoy chromitites contains inclusions such as clinopyroxene, olivine and platinum group mineral‐bearing sulfides. These Western chromitites were possibly formed at two stages during arc growth and are divided into the moderately high‐Cr# chromitites (Barajouk and Hessar) and the high‐Cr# chromitites (Chuchak A and C). The former crystallized from island‐arc‐tholeiite (IAT) melts during reaction with the host depleted harzburgites, whereas the latter crystallized from boninitic melts (second stage melt) during reaction with highly depleted harzburgite in a supra‐subduction‐zone environment. Based on the mineral chemistry of chromian spinels, pyroxenes, and mineral inclusions, the chromitites and the host peridotites from the Eastern and Western Khoy ophiolites were formed in a back‐arc basin and arc‐related setting, respectively. The Khoy ophiolitic complex is a tectonic aggregate of the two different ophiolites formed in two different tectonic settings at different ages. 相似文献
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Najmeh?Khalili Saeed?Reza?KhodashenasEmail author Kamran?Davary Mohammad?Mousavi?Baygi Fatemeh?Karimaldini 《Arabian Journal of Geosciences》2016,9(13):624
In this paper, we have utilized ANN (artificial neural network) modeling for the prediction of monthly rainfall in Mashhad synoptic station which is located in Iran. To achieve this black-box model, we have used monthly rainfall data from 1953 to 2003 for this synoptic station. First, the Hurst rescaled range statistical (R/S) analysis is used to evaluate the predictability of the collected data. Then, to extract the rainfall dynamic of this station using ANN modeling, a three-layer feed-forward perceptron network with back propagation algorithm is utilized. Using this ANN structure as a black-box model, we have realized the complex dynamics of rainfall through the past information of the system. The approach employs the gradient decent algorithm to train the network. Trying different parameters, two structures, M531 and M741, have been selected which give the best estimation performance. The performance statistical analysis of the obtained models shows with the best tuning of the developed monthly prediction model the correlation coefficient (R), root mean square error (RMSE), and mean absolute error (MAE) are 0.93, 0.99, and 6.02 mm, respectively, which confirms the effectiveness of the developed models. 相似文献
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Mananeh Akbarimehr Seyed Ataollah Hosseini Fatemeh Shariati Seyed Mohammad Hodjati 《Water Resources》2016,43(2):369-376
Nutrients are important building blocks for healthy aquatic ecosystems and are generally nontoxic; but they can change with alteration in environmental parameters. The main objective of this study was to consider the seasonal variability of NO 3 – , PO 4 3– and total suspended solids (TSS) concentrations in water. The study sites, stream crossings (L30, L15) and river (R), are located in the hyrcanian forests, district 1 of Darabkola forest. The sampling was conducted in winter and spring. Water samples were taken into plastic bottles, labeled, and carried out to the laboratory for NO 3 – , PO 4 3– and TSS analysis. T-test results showed that there was a seasonal change in nutrient concentrations (p < 0.05) except for NO 3 – concentration at L30. Also, there was no significant seasonal change in TSS concentrations at all stations. Pearson correlation analysis did not reveal the same trend. Further analysis showed that the effect of road age on water quality parameters was statistically significant for PO 4 3– in spring and winter. Atmospheric precipitation plays vital role in nutrient loss and increasing concentration of suspended sediment. To prevent soil erosion from activities and discharge of wastes in the vicinity of river and stream an effective management should be planned and enforced. 相似文献
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Investigation on the Distribution of Gold Across the Ahar Area (NW Iran) Using Stream‐Sediment and BLEG Methods 下载免费PDF全文
Vartan Simmonds Fatemeh Jahangiryar Mohssen Moazzen Ahmad Ravaghi 《Resource Geology》2016,66(2):213-225
The Ahar area is located in NW Iran. The main part of the area is covered by Eocene andesitic and andesi‐basaltic rocks within which several granitoid intrusives of Oligocene age are emplaced. This caused vast hydrothermal alterations and Cu and Au mineralization. In this regard, this contribution aims to explore the distribution of gold across the region based on systematic sampling of stream sediments and using the secondary geochemical halos, as well as the bulk leach extractable gold (BLEG) method. Meanwhile, the results obtained from these two methods will be compared in order to find out if the anomalous zones match with each other. For this, 620 stream sediment samples of ?80 mesh grain size and 422 BLEG samples were collected and analyzed by Fire Assay and atomic absorption spectroscopy (AAS) methods, respectively. For BLEG samples, gold was first dissolved using KCN before being analyzed by the AAS method. Furthermore, 84 rock samples were also collected during the field control surveys and were analyzed by Fire Assay and ICP‐OES methods for gold and other elements, respectively. After determining the distribution characteristics and statistical parameters of gold in each group of samples, anomaly maps of gold for each method were prepared, revealing almost similar anomalous zones across the region. Based on these maps, most of the discovered anomalies correlate well with granitoid intrusives of Oligocene age and the related hydrothermal alterations, which have occurred within the intrusives and the host andesitic‐basaltic rocks of Eocene age, especially at the NE and central parts of the area and east of Ahar. Some silicic veins and veinlets have been observed during field surveys in these parts, within which high concentrations of Au and sometimes Cu are determined. Another anomalous zone is located over the hydrothermal alterations within trachy‐andesitic and andesitic volcanics of Pliocene age at the SE part of the quadrangle, where vast alterations caused by volcanic fumaroles and epithermal mineralization of gold and Pb–Zn is discovered. In this regard, the SE and NE parts of the area and the east Ahar area are proposed, in order of importance, for further detailed investigations. 相似文献
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The source of fluoride toxicity in Muteh area,Isfahan, Iran 总被引:1,自引:0,他引:1
Behnam Keshavarzi Farid Moore Ali Esmaeili Fatemeh Rastmanesh 《Environmental Earth Sciences》2010,61(4):777-786
Endemic dental fluorosis has been observed in most inhabitants of three villages of Muteh area, located in northwest of Isfahan
province, with mottled enamel related to high levels of fluoride in drinking water (1.8–2.2 ppm). Forty-seven groundwater
samples from six villages were collected and fluoride concentrations along with physico-chemical parameters were analyzed.
Fluoride concentration in this area varies from 0.2 to 9.2 mg/l with highest fluoride level at Muteh gold mine (Chahkhatun
mine). Fluoride concentration positively correlates with pH and HCO3
− indicating that alkaline pH provides a suitable condition for leaching of fluoride from surrounding rocks. The district is
mainly covered by three lithological units, namely, metamorphic and granite rocks, alluvial sediments, and carbonate rocks.
Factor analysis shows that parameters can be classified into four components: electrical conductivity (EC), total dissolved
solids (TDS), Cl−, Na+ and K+, pH and F−, SO4
2−and Mg2+, HCO3
− and Ca2
+. The groundwaters from the three geological units were compared using Mann–Whitney U test. The order of median fluoride concentration is: metamorphic and granite rocks > alluvial sediments > carbonate rocks.
Hence, the fluoride content is most probably related to fluoride-bearing minerals such as amphibole and mica group minerals
in metamorphic and granitic rocks. The concentration of fluoride in drinking water wells located near the metamorphic complex
in Muteh area is above 2 ppm. 相似文献
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Theoretical and Applied Climatology - High spatiotemporal climate variability in the northeast Iran has led to increased production risk for rainfed crops. Hence, to explore potential opportunities... 相似文献
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The Sangan Magmatic complex (SMC) is, a large I-type magmatic complex, located in the northeastern Iran. Zircons extracted from the intrusive and volcanic rocks within the SMC record a similar Hf compositions and REE patterns, indicating that these chemical signatures have likely been inherited from the same source and simple history of magmatic crystallization during the evolution of the orogeny. The zircon from volcanic rocks yield Ti-in-zircon crystallization temperatures of 667–1145?°C with average temperatures of 934?°C while those from granitoids indicate crystallization temperatures of 614–898?°C with an average of 812?°C. Ti-in-zircon, Ti in biotite thermometries also indicates that the crystallization temperatures of volcanic rocks are relatively higher than those of granitoids. The biotite chemistry studies reveal that this mineral crystallized at approximately 725°–800?°C and 758° to 816?°C for granitoid and volcanic rocks, respectively, which is similar to obtained temperatures by Zir-saturation of Eq. (1). Tzicsat and Tmagma trend lines on the T-SiO2 diagram cross at high silica contents of ~68?wt.%, at which temperature the magma becomes zircon-saturated and new zircons are crystallized. The zircon REE data including Ce/Ce*, Eu/Eu*, and Th/U ratios suggest that SMC igneous rocks are formed from oxidized magma. However, the zircon Th/U and Hf data suggest that the SMC became progressively more oxidized and also indicate lower temperatures from volcanic and plutonic rock with decreasing time. 相似文献
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Fatemeh Sarjoughian Somayeh Javadi Hossein Azizi Wenli Ling Yoshihiro Asahara David Lentz 《International Geology Review》2020,62(13-14):1769-1795
ABSTRACT Soheyle-Pakuh granitoid rocks, with a variety of quartz diorite, quartz monzodiorite, granodiorite, tonalite, and granite, have been emplaced into the Tertiary volcanic rocks in the Urumieh-Dokhtar magmatic arc in central Iran. Zircon U–Pb dating yields an age of 39.63 ± 0.93 Ma for the crystallization of this body. Whole-rock compositions show that SiO2 changes from 52.31 to 65.78 wt.% and Al2O3 varies from 15.54 to 18.24 wt.%, as well as high concentrations of large-ion lithophile elements (LILE, e.g. Cs, Rb, Ba, and K) and quite low contents of high field strength elements (HFSE, e.g. Nb, Ti, P), as expected in I-type arc granitoids formed in an active continental margin setting. Initial ratios of 87Sr/86Sr and 143Nd/144Nd exhibit ranges 0.7043–0.7047 and 0.51284 to 0.51287, respectively, with positive εNd(t) from +4.9 to +5.5 with a young TDM1 age (483–674 Ma); this tracer isotopic data suggesting that the SPG originated from juvenile basaltic crust derived from depleted mantle (~90%) with variable contributions from undepleted mantle and approximately 10% old lower crust, despite diverse processes (e.g. magma mixing and fractional crystallization) during their evolution and emplacement into a local extensional setting within the continental margin arc. The isotopic data are similar to those of other Phanerozoic granitoids of the Central Asian Orogenic Belt and corroborate melting of predominantly mantle-derived juvenile crustal protoliths and indicating extensive addition of new continental crust, during Cambrian-Neoproterozoic time, in the suprasubduction zone beneath the central Urumieh-Dokhtar magmatic arc. Generation of these types of granitoids favours a model whereby rollback and (or) break-off of a subducted slab with subsequent lithospheric extension triggered by mantle upwelling, heat advection, and underplating resulting in melting of the central UDMA mantle-derived juvenile lower continental crust in the Late Eocene. 相似文献