جستجوی مقالات مرتبط با کلیدواژه « ahar » در نشریات گروه « زمین شناسی »

Azerbaijan Plateau is a part of the Alpine-Himalayan fold and orogeny belt, which is located in a compressional regime and between Talesh Mountains, south of Lesser Caucasus Mountain, east of Anatolia, north of Zagros Mountain. The studied area has located in the geographical longitudes of 47° to 48° and latitudes of 38° to 39° in East Azerbaijan province. There are wide ranges of Plio-Quaternary basalts and andesite basaltic in the sheet of 1.250000 Ahar. These rocks are gray to black in color. They also are formed of lava flows with scattered sometimes prismatic structures on the Paleocene andesitic lavas or conglomerate, siltstone and red marl Pliocene.

After the field investigations, we were taken 30 fresh and unaltered samples. Then, they were prepared as a thin section, then go undrer petrographic studies with a microscope in the laboratory.  Finally, we selected 10 samples were sent to the Amdel laboratory in the Australia for chemical analyses by ICP-MS, and OES.  Consequently, the results of whole rock chemical analysis data, were processed by GCD-KIT software. Then, all data were interpreted by geochemical conditions of all analyzed samples and also with their tectonic environment in the area.

The studied area is a part of the lesser Caucasus mountain range with high deformation and seismicity, which has located in a crustal convergence in the northwest of Iran. This area has a faulted system and with active strike-slip faults (Kocyigit et al., 2001). These systems often coincided with previous crustal discontinuities and have been widely effective in generating Quaternary magmatic activities locally through pull-part zones (Shabanian et al., 2012; Avagayan et al., 2010). Almost all the Quaternary magmatism in the region has occurred due to the operation of these fault systems and in the tensile position of the continental crust. Therefore, active fracture and fault systems and even old hidden faults have played a major role in the occurrence of the Quaternary magmatism.Volcanic rocks of the studied area are hyalo-aphanitic to hyalo-microlithic porphyry texture with large crystals of olivine, plagioclase and pyroxene. Also, porphyry, trachyte, intersertal and intergranular texture canbe seen in these samples. These samples have the nature of basaltic, thrachy andesite, mojearite and dacite, which are located in a calc-alkaline range. These rocks are rich in LREE and depleted in HREE.They also have enriched of Cs, Th, Pb and depletion of Ba, Nb, Eu, La. The presence of garnet in the source of magma can indicated the involvement of processes and crystallization of olivine, pyroxene, and plagioclase. In addition, metasomatism or contamination with enriched crustal materials (Menzies & Wass, 1983) leads to the abundance of LREE elements. Therefore, the metasomatized mantle can be a suitable origin for the magma of the studied volcanic rocks. Enrichment of elements Cs, Rb, Pb, Ba, LILE and depletion of elements HFSE (Nb, Zr) indicated the magma of subduction arc zones (Wilson, 1989). The negative anomaly of Nb, P, Ti, Zr and the positive anomaly of Pb are the characteristics of crust contamination of quaternary basalts (Wilson, 1989; Hofman, 1997). Negative Nb anomaly is characteristic of continental rocks and crustal involvement in magmatic processes (Hofman, 1997). Also, the negative anomaly of Ti and Nb in the normalized pattern with primary mantle composition can indicate magmas related to subduction (Pearce, 1983; Wilson, 1989). All the samples are in the range of intraplate basalts (Figure a10) (Mesched, 1986), and show the orogenic situation (Pearce et al., 1977). The studied volcanic samples are volcanic arc (Muller et al., 1992) belong to the continental arc after the collision (Groves, 1997).  Also, the studied samples show the origin of lherzolite garnet mantle and lherzolite spinel with a rate of 2 to 5% of partial melting.The tensile positions of the continental margins are active, where partial melting has occurred due to pressure reduction and rupture of the subcontinental lithosphere. Its compressive force resulting from crustal collision and crustal shortening, thickening and uplift leads to disturbance of subcontinental lithosphere thermal levels in these regions. Therefore, it seems that since the Eocene, the post-collision regime (Omrani et al., 2008) and since the Miocene (Hasanpour, 2008) has been ruling in the Arsbaran.

The Quaternary volcanic rocks in the eastern part of Ahar area, include a set of basaltic, andesite basaltic and andesite with calc-alkaline nature. The special depletion and enrichment of rare earth elements, these rocks are very similar to enriched mantle magmas and OIB, which were formed in the volcanic arc environment after impact on the active continental margin. For these samples, the mantle origin is lherzolite garnet to lherzolite spinel with 1 to 10% partial melting. Also there were happened metasomatisms of subducting oceanic lithosphere fluids. The geochemical evidences show some degrees of crustal contaminations during magma ascent. This magmatism has occured due to the subduction and the system of faults and fractures of the region and the tension tectonic situation. This tension system in the active continental margin after the collision has led to a decrease in pressure and finally the pouring out of basaltic magma.

The mineralization index of Yeylaghe Gharachi, as part of Arasbaran metallogenic belt, is located about 25 km northwest of Ahar, East-Azarbaidjan Province, NW Iran. The host rocks of this index consist of composite intrusive rocks with lithologic compositions of granite, quartz monzonite, granodiorite and diorite of Oligocene and Oligo-Miocene age. The alteration zones in this area are mainly potassic, phyllic, argillic, propylitic, silicic and carbonate. Mineralization occurred principally as disseminations, cross-cutting veins-veinlets and replacement in two separate stages of hypogene and supergene. Pyrite is the major hypogene sulfide mineral accompanied by magnetite, chalcopyrite, molybdenite, sphalerite and galena. The main supergene minerals in this area include hematite, goethite, limonite, bornite, chalcocite, covellite and malachite that accompany the hypogene mineral assemblage. In investigation of the phase contents of fluid inclusions in the quartz- sulfide veins-veinlets along with the potassic, phyllic and argillic alterations, five types of fluid inclusions have been recognized: mono-phase liquid (L), mono-phase vapor (V), liquid-rich two-phase (L+V), vapor-rich two-phase (V+L), and multiphase (L+V+S). Homogenization temperatures of the studied fluid inclusions vary from 190 to 530 °C. Considering the last ice-melting temperature of aqueous two-phase inclusions and halite melting temperature in the aqueous multiphase inclusions, the salinity ranges between 0.4 to 59 wt.% NaCl equivalent. Based on the microthermometric results of fluid inclusions, it can be conceived that episodic boiling and dilution by underground water of meteoric origin were the main mechanisms in development and evolution of this index. The zonation pattern of the alteration, mineralization and fluid inclusion data indicate that the Yeylaghe Gharachi mineral index is the most similar to porphyry copper deposits and the associated metallic veins.

The Noghduz  prospecting area, as a part of the Arasbaran metallogenic zone is located about 20 km east of Ahar, East-Azarbaijan Province. The mineralization host rocks are andesite-trachy andesite with the age of  Late  Eocene. The hydrothermal alterations exposed in this area are silicic, argillic, and propylitic. Pyrite is the main hypogene sulfide mineral which is accompanied by lesser amounts of chalcopyrite and bornite. The most important supergene minerals in this area are iron oxyhydroxides (hematite, limonite and goethite) and malachite that accompany the hypogene mineral assemblage. Gold mineralization occurred within quartz-sulfide veins/veinlets in this area. The microthermometric measurements in the primary 2-phase (L+V) fluid inclusions in quartz crystals associated with  mineralization  indicate that  the mineralizing fluids had temperatures and salinities within the range of 160-334°C and 0.53-3.39 wt% NaCl equivalent. respectively. The presence of hydrothermal breccias, pseudomorph of quartz after bladed calcite, and mono-phase gas inclusions are indicative of boiling of the hydrothermal fluids responsible for mineralization. The sulfur isotopic analysis of pyrite shows  that  the values of isotopic composition of this element  is  close to the range of magmatic source. Also, the oxygen and hydrogen isotopic data demonstrated that  the meteoric waters constituted a great portion of the ore-bearing fluids at Noghduz area. The presence of structural and textural evidence along with fluid inclusion studies (salinity and homogenization temperature) indicate that the gold mineralization at Noghduz area is of epithermal type.

The Zailic gold-bearing veins are located in the Arasbaran metallogenic zone, east of Ahar, East-Azarbaidjan Province. The most important lithologic units in this area are andesitic and trachy-andesitic tuffs and lavas of Upper Eocene age hosting vein-type gold mineralization. Theses rocks have suffered silicic, argillic, phyllic, and propylitic alterations brought about by hydrothermal fluids. The geochemical study of alteration zones in this area showed that in the silicic zone, due to the acidic nature of altering fluids and hence intense leaching, depletion of most major and trace elements took place. The degree of leaching towards the propylitic zone, owing to the pH increase of the hydrothermal fluids, gradually decreases. The presence of minerals with high adsorption capacity, such as clay minerals, resulted in concentration and fixation of many elements in the argillic, phyllic, and propylitic zones. Consideration of the behavior of rare earth elements (REE) in silicic zone relative to almost fresh volcanic rocks showed that most of REE suffered depletion. Geochemical indices such as TiO2 and (Ce + Y + La)-(Ba + S), showed that the hypogene hydrothermal fluids played an important role in the development of alteration zones at Zailic

The Shirbit polymetal prospect area is located in 30 km north-east of Ahar city within the Ahar- ore filed in around of Shivardagh batholith. Intrusion of granodiorite igneous bodies into the Eocene trachyte to andesite associated with pyroclastic interlayers caused widespread silicic, argillic and propylitic hydrothermal alteration associated with the Cu, Mo, Pb mineralization as quartz-sulfide (±oxide, carbonate, sulphate) vein and veinlets. Most of chalcopyrite, pyrite and molybdenite veins together with malachite, azurite and iron hydroxides were concentrated in the trachytic-andesitic units with silicic-argillic alteration. The turning point of this study includes investigating the possibility of log-log C-P method for separating geochemical anomalies of ore forming elements from the background, accurately determining the cut-off grade, decreasing the area of anomalies, and determining the number of stages of enrichment of elements in the study area compared to the multivariate statistical methods. For this purpose, 85 stream sediment samples taken from a systematic geochemical network were analyzed using ICP-MS method. In order to identify the susceptible mineralization areas by using of concentration-perimeter double logarithmic method, thee background values and anomalies were separated for each element in the region. Then, elemental anomaly maps were prepared and finally the distribution maps of the ore-forming elements were mapped and the relevant anomalies were distinguished. The results of using C-P fractal method indicates the presence of possible anomalies of Cu, Mo and Ti elements in the eastern, northeastern, and southwest parts of Shirbit area.

The Studied area is located in vicinity of the Sherbit village, about 28 km to the northwest of Ahar (in Eastern Azerbaijan province. Quartz monzonite intrusion is the host rock of hydrothermal tourmaline in this area. On the basis of their textural features, the tourmalines can be divided into four groups: 1) tourmaline veins, 2) tourmaline-breccias, 3) massive tourmaline and 4) pore space filling tourmaline. Based on the petrography and electron microprobe analysis studies, tourmalines of Sherbit area are correspond to intermediate schorl-dravite with more tendencies toward dravite composition and have been formed in hydrothermal conditions. According to reasons such as more Mg values compared to Fe, low Al amounts, fine scale zoning, content of fluorine, tendency toward outer side of alkali- and proton-deficient vectors and lack of negative correlation between Fe and Mg. Separated tourmaline from the quartz– tourmaline vein shows a very similar pattern to the quartz monzonite samples, which are characterised by a pattern with depletion in HREEs relative to LREEs. It can be concluded that REE concentrations and patterns of tourmaline from the different studied tourmaline rocks are controlled by the host rock and not by the hydrothermal fluid causing boron metasomatism.

The properties and situation of copper mineralization in the Haj Alibay Kandi area determined by quartz vein fluid inclusion and geophysical explorations in this study. The most important rock units include Oligocene intrusive rocks with monzonite and quartzmonzonite compositions. These rocks belong to calc-alkaline series and post orogenic and post collision regimes. The mineralization in this area was controlled by faults with NE-SW direction. These mineralizations are related to the Sheivar-Dagh and younger intrusives. Chalcopyrite, pyrite, chalcocite, digenite, covelite, malachite, bornite and iron oxides were determined by mineralographical studies. On the basis of geophysical explorations, the chargebility anomaly at the depth of 40 to 50 meters is related to the concentration of sulphide minerals. This anomaly is conforms with faulting system in the area. The salinity of ore bearing fluid is 5 to 50 wt% of NaCl and the homogenization temperature is 200 to 2400c and higher, on the basis of fluid inclusions studies. Fluid inclusions data are conformable with porphyry and epithermal copper deposits. This study shows that the boiling of ore fluids occurred at the mineralization stage. The shape of copper mineralization is vein and veinlets in this area and similar to cordilleran vein type deposit which can be observed at the top of porphyry copper deposits. Therefore, the formation of porphyry copper deposit at the deep levels of this area is expected.

The region of northwestern Iran is exceptional within the Arabian-Eurasian continental collision zone. The tectonics is dominated by the NW-SE striking right-lateral North Tabriz Fault (NTF) and regional seismicity (historical and modern one) concentrates. The NTF is a major seismogenic fault in NW Iran. The last damaging earthquakes on this fault occurred in 1721، rupturing the southeastern fault segment، and in 1780، rupturing the northwestern one. The understanding of the seismic behavior of this fault is critical for assessing the hazard in Tabriz، one of the major cities of Iran; the city suffered major damage in both the 1721 and 1780 events. The north of the NTF seismicity is rare، and almost nothing has been revealed about activity of the structures until now. On 11th of August 2012، the region was surprisingly struck by a shallow Mw 6. 5 earthquake with a pure right-lateral strike-slip character only about 50 km to the north of the NTF. An east-west striking surface rupture of about 20 km length was observed in the field by Geological Survey of Iran. Only 11 minutes later and about 6 km further to NW، a second shallow event with Mw 6. 2 occurred. It showed an NE-SW oriented oblique thrust mechanism. This earthquake sequence provided an opportunity to understand better the processes of active deformations and their causes in NW Iran. Ground-motion relations describing the expected amplitudes of this motion as functions of the magnitude and distance are key components of seismic hazard analyses. Ground-motion (attenuation) relations are used to estimate strong ground motion for many engineering and seismological applications. Where strong motion recordings are abundant، these relations are developed empirically from strong-motion recordings. Where recordings are limited، they are often developed from seismological models using stochastic and theoretical methods. The stochastic model is a widely-used tool to simulate acceleration time series and develop ground motion relations (Hanks and McGuire، 1981; Boore، 1983; Boore and Atkinson، 1987; Atkinson and Boore، 1995 and 1997; Atkinson and Silva، 1997 and 2000). The stochastic method begins with the specification of the Fourier spectrum of the ground motion as a function of magnitude and distance. The acceleration spectrum is modeled by a spectrum with ω2 shape، where ω is the angular frequency (Aki، 1967; Brune، 1970; Boore 1983). Finite fault modeling has been an important tool for the prediction of ground motion near the epicenters of large earthquakes (Hartzel، 1978; Irikura، 1983; Joyner and Boore، 1986; Heaton and Hartzel، 1986; Somerville et al.، 1991; Tumarkin and Archuleta، 1994; Zeng et al.، 1994; Beresnev and Atkinson، 1998a). One of the most useful methods to simulate ground motion for a large earthquake is based on the simulation of some small earthquakes as subfaults that comprise a big fault. A large fault is divided into N subfaults، and each subfault is considered as a small point source (introduced by Hartzel، 1978). In this study، the first region-specific ground motion relations were developed for seismic hazard analysis of NW Iran. The attenuation relation for the horizontal acceleration response spectrum in a period of 0-4 s، with a magnitude range of Mw=5 to 7. 7 and distances up to 150 km were established. We used 51 waveforms recorded on a rock site in the NW Iran. Due to the paucity of the data at small distances and large magnitudes، we applied the stochastic method to simulate waveforms for different magnitudes and distances. To overcome the incompleteness of the data set، we simulated 1240 acceleration time series for magnitudes from M5. 0 to M7. 7 and magnitude steps of 0. 2 units for the North Tabriz fault and M5. 0 to 6. 7 and magnitude steps of 0. 5 units for the Ahar fault. The relations were derived by a maximum likelihood regression algorithm from Joyner and Boore (1993) on a set of 1240 simulated strong-motion records and 51 observed ground motions recorded on the rock site in this region. The theoretical-empirical ground motion relation for NW Iran was compared to the ground motion relations for the other regions and had a good agreement with them especially with Akkar and Bommer relations for Europe، the Mediterranean Region and the Middle East. The present results will be useful in estimating strong ground motion parameters and in the earthquake resistant designs in this region.

Seismic values are the main parameters in evaluating the neotectonic activity of a region. In August 11, 2011, two Mb=6.4 and Mb=6.3 earthquakes occurred in Ahar-Varzaghan region within 11 minutes. Seismotectonic investigations imply that the faults generating the events are the young faults of the regions. Also, distribution of the epicenters represent a pattern consistent with the fault trends in the area. Temporal and spatial distribution of the earthquakes (fractal analysis) as earthquake pre-indicators together with a-b values were used toassessthe neotectonic activity and explore the seismic model of the Ahar area. Results showa sharp decrease in b-value,indicating that the main shock was associated with a zone of high strain rate. The seismic model presented for the Ahar area illustrates three periods after the main shock including: 1) an early quiescence Q1, 2) an aftershock period B, and 3) a late quiescence Q2. The rather increase in b-value during the Q2period is interpreted to indicate stress decrease in the region.

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 0.704921 and 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.

During the past decade, studies related to earthquake forecasting and assessment of seismic hazard have been focused on stress transfer and fault interactions. According to the earthquake interaction phenomenon, occurrence of any earthquake alters the stress state (the shear and normal stress) on its neighboring faults which can delay (decrease), or trigger (increase) subsequent events (Stein, 1999). In recent years, one of the models which have been widely used to estimate coseismic stress perturbations has been the static Coulomb stress changes. These calculations are done based on Okada’s code with assumption of a shear modulus of 3.2 × 105 bars and Poisson’s ratio of 0.25 using the program Coulomb 3.3 (Toda et al. 2005, Lin and Stein, 2004). The aim of this research is to explore the fault interaction through static stress transfer between Ahar-Varzaghan double earthquakes and the possible stress triggering relationships between these main shocks and their aftershocks. These double earthquakes occurred on August 11, 2012, near the cities of Ahar and Varzaghan in the East- Azerbaijan Province in the northwest of Iran. The first event with a magnitude of Mw 6.5 occurred at 16:53 local time, and the second one with Mw 6.3 took place about 10 minutes later. These earthquakes killed more than 306 people and a large number of people were injured. Ahar-Varzaghan double earthquakes followed by many aftershocks the largest of which occurred with a magnitude of MN 5.4. These double earthquakes occurred in places where no active faults have been identified, but there are numerous active faults in their surrounding area such as the North Tabriz Fault, Bozquosh Fault, and Ahar Fault. In order to investigate the fault interactions between Ahar-Varzaghan double earthquakes, Coulomb stress perturbations due to slip on the first source fault were calculated on a specified oriented receiver fault parallel to the second main shock. Receiver faults were planes with a specified strike, dip and rake, upon which the stress changes caused by source faults were resolved (Toda et al. 2005, Lin and Stein, 2004). Calculations of Coulomb stress changes indicated that the second earthquake occurred when the Coulomb stress was increased by the first event. Hence, the second event of Ahar-Varzaghan double earthquakes appears to have been triggered by an increase in the static Coulomb stress transferred by the first event. This means that the positive stress changes caused by the first source fault have promoted the failure on the second fault. In order to examine the triggering relationship between the aftershocks and the main shocks, the stress field due to Ahar-Varzaghan double earthquakes were calculated along two kinds of receiver faults including a specified oriented receiver fault and an optimally oriented strike - slip receiver faults (OOPs). The optimal receiver fault orientation is defined by the orientation of the principal axes of the regional stress field. The analysis shows that there is a good correlation between the spatial distribution of the aftershocks and the stress increased in the regions along the specified orientation receiver fault. Therefore, the aftershocks took place in response to the coseismic stress caused by the occurrence of Ahar-Varzaghan double main shocks. Hence, the stress-enhanced regions on this type of receiver fault can be introduced as the most likely site of the next earthquakes.

The study area is located in the east of Ahar town in Eastern Azerbaijan Province and is part of the Ahar-Arasbaran Cenozoic magmatic belt of NW Iran. The geological units of the Eocene age are volcanic rocks with andesite, latite - andesite and basaltic andesite composition.Khankandi and Useflu Oligocene intrusive bodies intruded in the volcanic rocks and caused widespread alteration and copper and gold mineralization. The intrusive bodies include I type granite, grano-diorite, quartz monzonite, monzonite-monzodiorite and gabbro. Granite, granodiorite and quartz monzonite belong to calk-alkaline series, while monzonite- monzodiorite and gabbro belong to alkaline series. They are related to continental margin tectonic regime and generated at post collisional tectonic settings. Alkaline basic rocks postdate calk-alkaline acidic rocks and are barren. The low sulfidation epithermal Au veins occurred in the Eocene volcanic rocks and Useflu quartz monzonitic body. Also Au-bearing quartz veinlets with relatively widespread alteration zone occurred at the eastern side of the Useflu intrusive body. Argillic and sericitic alteration accompanied the Au mineralizations. Pyrite, sphalerite, galena, chalcopyrite and bornite are the common ore minerals and occurred as disseminated and open space fillings. Stockwork and disseminated Cu mineralization occurred in the quartz monzonitic rocks at the SW side of Khankandi intrusive body. Pyrite, chalcopyrite, bornite with minor amounts of magnetite are the common ore minerals. Phyllic - pottasic alterations accompanied the Cu mineralization. Similar mineralizations of Cu occurred in other parts of the area (for example around the Useflu) in quartz monzonitic rocks which are accompanied by magnetite- mafic (amphibole and biotite) mineral veinlets.