جستجوی مقالات مرتبط با کلیدواژه « شمال باختر ایران » در نشریات گروه « زمین شناسی »

There are discontinuous outcrops of volcanic rocks in the West Azarbaijan province and in the north of Maku city. These volcanic complex were bimodal and compose of acidic and basic lava and pyroclastic rocks. Mineral chemistry studies show that clinopyroxenes in the studied rocks are diopside. These pyroxenes have a high magnesium number (0.87 to 0.99). Magma series and tectonic determination diagrams show that the basaltic rocks that make up the studied clinopyroxenes have an alkaline nature and were formed in a whitin plate environment. According to geothermobarometry studies, clinopyroxenes were formed at temperature 1100 - 1250 ° C and pressure of 3 - 9 Kbar. The depth for generation of magma was at about 22 kilometers.

The Aghbolagh iron-copper skarn is located in ~21 km north of Oshnavieh, southwest of West-Azarbaidjan province. The intrusion of Cretaceous granitic body into the Cambrian Barut, Zagun, and Lalun Formations (carbonate, shale, and sandstone) was accompanied by development of calcic-type skarn, hornfels, and marble in the study area. The garnets of the Aghbolagh skarn belong to solid solution series of grossularite-andradite in which andradite is the dominant phase (>80%). These garnets are isotropic and lack zonation. The pattern of REE distribution in these garnets shows the enrichment of LREE relative to HREE and also the occurrence of negative anomalies of Eu/Eu* and Ce/Ce*. The comparison of the distribution pattern of REE in garnets with those in igneous (granite and monzonite) and sedimentary (carbonates and sandstones) rocks demonstrates that the REE in garnets were derived mainly from the igneous rocks rather than the sedimentary units. The increase in Pr/Yb ratios in parallel with increase in the ƩREE is indicative of the magmatic origin of the ore-forming fluids in the Aghbolagh skarn. However, the lack of sensible variations between Ce/CE* and ƩREE values indicate that the meteoric waters might have also played a part in skarn-forming fluids at Aghbolagh.

The Takht-e-Soleyman metamorphic complex is located at NE of Takab town, West Azerbaijan province. This complex having Precambrian-Cambrian age has been formed from low to high metamorphic rock types. The retrograde granulites are subject of this project. The retrograde metamorphic assemblages of the granulites are including of Amp᪻繊饾㪖ꪹ phases. Amphibole overprinted primary mafic phases of clinopyroxene and orthopyroxene highly. Spinel at the klyphitic texture around garnet porphyroblast forms the main feature for retrograde metamorphism of granulites. Rutile occur as inclusion within amphibole. The compositional profile of garnet indicates chemical variations from the core to the rim. Compositional variations from the core to the mid is characterized with a minor increase in XMg but decrease in XCa and XMn. This characteristic of garnet is indicative of pressure decompression with small increasing of temperature. Due to complete overprinting of high temperature phases by the retrograde phases as well as lack of preserved pick metamorphic minerals it is indeterminate pick metamorphic P-T estimations for M1 stage. On the basis of chemical compositions of porphyroblasts, retrograde evolutions of investigated granulites have been estimated at two stages: (1) pressure decompression (M2-a) and (2) cooling and exhumation (M2-b). The retrograde P-T conditions are obtained as T=810±10°C at P=10.5±0.7kbar for the first and second retrograde stages, respectively. Relatively coarse grained size of phases at the klyphitic margin are indicative of low cooling rate during uplifting of rocks from lower to upper levels. Highly overprinting of high temperature phases by amphiboles support this idea. Time of pick and retrograde metamorphism for the investigated granulites are not clear accurately. It seems reasonable to attribute pick metamorphic and granulite formation time to Oligocene-Miocene related to crustal thickening due to collision between the Central Iran microcontinent and the Arabia plate. The granulites have been metamorphosed under retrograde conditions in relation with thrusting and post collisional extensions which caused to uplifting, crustal thinning and exhumation of rocks. However more conclusions on tectonometomorphic evolutions need to precise studies.

Mahneshan­­–­­Mianeh Cenozoic basin, in southern part of SE­–­­termination of North Tabriz Fault, is located between two distinct NW and N Iran tectonic domains affected by different Quaternary tectonic and stress regimes, with a transitional boundary. Determining the Quaternary state of stress in the area of interest is a key to locate the locus of this transition between the two tectonic domains. In this study, Quaternary stress state of the area was studied using the inversion of fault kinematics data (with well-known sense and chronology) measured in 25 sites in the Mahneshan­­–­­Mianeh Cenozoic basin. Our results indicate a homogenous modern compressional stress field characterized by a NE-trending horizontal maximum stress axis (~N055) prevailing through Quaternary, and coherent with the direction of the Arabia­–­Eurasia convergence in Iran.

The study area (Siyah-Cheshmeh), is located to the south Maku in the Khoy-Maku ophiolite zone. The various outcropped metamorphic rocks include serpentinites, metabasites (green schist, amphibolite) and meta-pelitic rocks (slate, mica-schist) with interlayers of marble and quartzite. The amphibolites can be classified as actinolite-amphibolite, epidote-actinolite- amphibolite, biotite-amphibolite, amphibolite and garnet-amphibolite. They have fine- to coarse-grained granoblastic texture. On the basis of whole rock chemistry, the protolith composition of the amphibolites has been determined as basalts with tholeiitic and less commonly, calc-alkaline affinities, developed in an island arc setting. The negative anomaly of Nb as well as small enrichments in LILE and LREE support arc related and tholeiitic signatures for the protolith. Considering the unknown age of the studied amphibolites, it is difficult to propose an appropriate tectonic model for formation of the investigated rocks. If the amphibolites are related to the Khoy-Maku ophiolitic complex, then they would be the result of subduction of the northern branch of the Neotethys ocean basin, development of an island arc and eventually metamorphism of the rocks due to closure and collision. Since the age is not clear, it is not possible to conclude unequivocally if the rocks are results of the Neotethys subduction system or they are related to an older, possibly a Precambrian subduction system. Dating the rocks will help to propose a suitable model for their formation.

Determination of inter-seismic deformations such as fault slip-rate can usually be achieved by using geodetic observations, earthquake geology and paleo-seismology, as well as mechanical, empirical and numerical modeling. In these models, combination of the fault seismic parameters and the GPS data can help estimate the fault slip-rate, the elastic thickness of the lithosphere, the earthquakes recurrence time, the relaxation time of the asthenosphere, the elapsed time of earthquake and the locking depth of the fault. In this study, we utilize the geodetic data of the North Tabriz Fault (NTF) by using random Bootstrap sampling and conducting numerical modeling by code writing in the R and MATLAB softwares. In this concern, the fault slip-rate and elastic layer thickness are estimated to be ~4-6.5±1 mm/yr and ~5-25 km, respectively, for the NW segment of the NTF. Similarly, model results for the SE segment of the fault indicate a slip-rate of ~3.5-5.5±1 mm/yr and elastic layer thickness of ~8-16 km. For the NW segment of the NTF, the asthenosphere relaxation time, earthquake recurrence time and elapsed time are estimated to be ~160-185 years, ~650-950 years and ~200-1400 years, respectively. Model results for the SE segments of the NTF indicate an asthenosphere relaxation time of ~220-340 years, an earthquake recurrence time of ~750-1050 years and an elapsed time of ~200-1500 years, respectively. The results are well consistent with the other paleoseismological and geological results.

The North Tabriz Fault is one of the major strike-slip faults (trending NW-SE) in NW Iran، that trends from Sofian to Bostan Abad. Generally، the fault consists of two main fault segments. In present research، to study the last active tectonics at the North Tabriz Fault region، evaluated young morphotectonical features and paleoseismology of northwestern fault segment evaluated. On the basis of morphotectonic approaches on this region، horizontal slip last event (MW = 7. 4، 1780 AD) are found in the ranges 3. 5 ±0. 5 m and vertical slip between 0 and 0. 5 m. However، by attention to H/V ratio can propose that NW segment of North Tabriz Fault act as pure strike slip which confirm by new GPS data on this part of Iran. On the basis of paleoseismological researchs، by examining a wall perpendicular to the North Tabriz Fault in North Sahlan Village، four old paleoearthquakes with relative magnitude of MW = 6. 4 has been detected. A young magnitude of the event، recorded in deposits of the paleoseismologic trench of the study area، close to 7 have been estimated that according to geographic and stratigraphic location، this event can be associated with historical earthquakes since 1780 AD (MW = 7. 4).

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.

Tabriz city، the most highly population city of NW Iran، is located close to the North Tabriz Fault (NTF). This 150 km right-lateral strike-slip fault consists of two major fault segments arranged in right-stepping pattern. A pull-apart basin has been formed within the overlap zone of these fault segments due to the recent right-lateral motion. The basin margins mark by fault branches and fault splays، which connect these two major segments of NTF. High level historical earthquakes occurrence shows seismic activity of NTF. Among which، NTF is responsible of at least two destructive earthquakes occurred in 1721 A. D. (Ms 7. 3) and 1780 A. D. (Ms 7. 4). This fault has not experienced any strong seismic events since 1780 A. D. Within past decades، it has been tried to recognize large number of old earthquakes utilizing paleoseismological investigation. Previous paleoseismological studies have been focused on the NW and SE segments of the fault. In the present study، to complete the data sets necessary to assess the seismic hazard related to Tabriz city، we focus on overlap zone of the two main fault segments. Using aerial photos، satellite images and field investigations، a potential site has been recognized within the zone (6 km NW of Tabriz City) to perform paleoseismological studies. Trench opened perpendicular to fault scarp strike and focused paleoseismological investigations in that، show evidences of at least two macroseismic events.

Black shales of the abandoned antimony mine of Aq-Darreh Bala Village in northwest of Takab city, northwest Iran, contain high concentrations of toxic elements, especially As (4403–11883 ppm), Sb (405–1022 ppm) and Hg (30–58 ppm). Enrichment factor calculations revealed that some trace elements including As, Sb, Hg, Zn, U, Sr, Ni, V, Co, Cu, Mo, Ni, and Zr have been depleted, while, Pb, Th, Ga, Rb, and Ta are enriched during weathering. Mass balance calculation results show the highest release percents (% loss) belongs to Cd, Zn, U, Sr, Ni, V, Cu, As, Mo, Tl, Zr, Hg and Sb respectively. The highest weight amount of released elements belongs to As, Sb, Sr, Zn, Ni, V, Zr, Cu, U, and Hg respectively. As a result, it can be concluded that the black shale outcrops in the Aq-Darreh Bala abandoned antimony mine area have a main role as a geogenic source in environmental contamination of downstream environments.

Two distinct collision events have occurred between Arabia and Central Iran plates، during closing of the Neo-Tethys. Structural sections along the collision zone in northwest Iran show characteristics of collision structure. The first collision occurred during obduction of the oceanic components of the Neo-Tethys over the Arabian passive margin during the Late Cretaceous. Deformation along the Arabian passive margin in radiolarite and the high Zagros zones was the result of this event. The high Zagros frontal thrust fault is the maximum limit of this collision tectonic event. The obducted oceanic components، including the ophiolites in this region، unconformably are overlain by Oligocene-Miocene sediments. By the last continent-continent collision event during Late Miocene، the hinterland of the orogen was transported over the collided zone and deformation occurred by rejuvenation of the existing thrust faults in previously collided zone and the Zagros foreland basin was formed (Zagros fold-thrust belt).

Khankandi pluton is located in northwestren part of Iran, within Garadagh (Arasbaran) - south Armenia block. Main units of the pluton are monzonite and granodiorite associated with minor gabbro and lamprophyric and dacitic dykes. Granodioritic plutonism is followed by gabbro and monzonite. Lamprophyric and dacitic dykes are emplaced at the end of the granodioritic plutonism. Gabbro and monzonites are shoshonitic, and granodiorites and dacites have high K-calc alkaline nature and charactistics of C-type (potassic or continental) adakites and high Ba-Sr granitoides. Lamprophyres are alkaline and have camptonitic composition. The monzonites follow fractionation trend of gabbro with minor crustal assimilation and contamination. Melting of garnet bearing mafic lower crust, metasomatised lithospheric mantle and upwelling asthenosphere produced granodioritic and dacitic, shoshonitic gabbro and lamprophyric magma respectively. The production of various magma types in the Oligocene of the Arasbaran occurred in response to slab break off and/or delamination of lithospheric mantle and upwelling of asthenosphere. Plutonism occurred after collision between Iranian and Arabian plates and crustal thickening in the extensional post collisional tectonic setting.

In active tectonic regions, topographic features represent ways to quantitatively charactrize the interactions between tectonics and surface processes, providing a basis for modeling landscape evolution. This study examines the tectonic geomorphology of Northern Misho Fault (Northwest of Iran), focusing on the general topographic metrics (SL، Smf، Vf، Fmf، Fd and Eu), drainage patterns (AF and Bs), and river longitudinal profiles. The drainage pattern, topographic analysis and geomorphic properties express the tectonic influence on streams, competing to integrate the northern slope of Misho-Dagh drainage. As a result, oblique and right lateral movements of the northern Misho fault are more than uplift movements, at least in the Late Pleistocene and Holocene. This movement in the western Misho is more than that in eastern Misho. Longitudinal profiles of rivers indicate that present landscape of study area, in addition to the northern Misho fault effects, influenced by secondary faults especially in the eastern Misho, so that the morphometric indices such as Vf has been affected by this secondary faults, too. The northern slope of Misho-Dagh represents a landscape adjusting itself to the modern active tectonic setting.

Misho-Dagh Mountain range is part of Azerbaijan plateau in Northwest Iran. This E-W range is located between Marand and Shabestar plains. Northern Misho fault, the main fault in study area, and other parallel faults have separated the topographic units and geological structures. Rivers on the northern slope of Misho- Dagh, flowing from the south to the north, cut across geological structures and topographical units in their distal reaches, prior to joining in the Marand plain.The long-term drainage evolution and its creation, as transverse fluvial systems, have been examined by reconstruction of drainage network using a combination of geological and geomorphological records. This reconstruction is based on analysis of topographic and geologic maps and area photos and repeated field studies on fluvial remnants. Results show that drainage evolution in the study area has occurred in three stages: a) sedimentation of the Plio-Pleistocene non-compacted conglomerates (relict alluvial fans), b) uplift of the Plio- Pleistocene sediments in mid-? Late Pleistocene, separation of this sediments from main mountainous body of Misho-Dagh due to a E-W synclinal valley, formation of new block of mountains (anticline) in the north of the valley and eastward diversion of rivers in their distal reaches, and c) faulting of new relief block by S-N faults crossing the relief axis, verification of rivers to fault lines and formation of new alluvial fans.Neotectonic indices such as inclination of the Plio- Pleistocene sediments, separation of this sediments from main mountainous body of Misho-Dagh, verification and non-verification of rivers by tectonic and geologic structures, catchment morphometric properties, and situation and morphology of alluvial fans indicate that fluvial systems in the study area are influenced by the Pleistocene and Holocene tectonic activities, and tectonics is the main factor in the fluvial system replacement and their situation.