Petrology
Zohreh Salimi; mohsen moazzen; Robab hajialioghli
Abstract
The ophiolitic-metamorphic complex of Allahyarlu, attributed to pre-Cretaceous, is exposed at the core of Allahyarlu anticline in NW Iran and NE of Meshginshahr. The metamorphic rocks are important constituents of this complex. These rocks include garnet schist, garnet gneiss, amphibolite, marble, associated ...
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The ophiolitic-metamorphic complex of Allahyarlu, attributed to pre-Cretaceous, is exposed at the core of Allahyarlu anticline in NW Iran and NE of Meshginshahr. The metamorphic rocks are important constituents of this complex. These rocks include garnet schist, garnet gneiss, amphibolite, marble, associated with blocks of serpentinite and tectonic slices of gabbro, dunite and diabase. Quartz, garnet, biotite, muscovite and chlorite are the primary minerals in the garnet schists, while zircon, secondary chlorite, opaque minerals and plagioclase make the minor phases. The main minerals in the garnet gneiss samples are K-feldspar, quartz, plagioclase, muscovite, biotite and garnet and tourmaline, zircon and secondary chlorite are the minor phases. Garnet in garnet schists and garnet gneisses is almandine-rich and white mica is muscovite –rich. According to microprobe analyses, brunvigite is the main constituent in chlorite solid-solution. Te average temperature estimated for metamorphism of garnet schists and garnet gneisses, using different methods is 530 to 570 C. Using apetrogenetic grid indicates pressure of ca. 4.5 kbar for the paek of metamorphism. The estimated pressure and temperature are in accordance of Barrovian metamorphic gradient for these rocks, which occurs in crustal thickenning zones such as island arcs, volcanic arcs and collision zones.
R. Hajialioghli; M. Moazzen
Abstract
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 ...
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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 Amp+Grt+Spl+Opaque 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.
M Aflaki; E Shabanian; Z Davoodi
Abstract
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 ...
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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.
R Hajialioghli; H Fakharinezhad; M Moazzen
Abstract
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 ...
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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.
M Talebian; M Shahpasand-Zadeh; Y jamour; M.R Sepahvand; A Arabpour
Abstract
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 ...
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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.
M Roustaee; B Zamani; P Navabpour; M Moayyed
Abstract
Siah Cheshmeh- Khoy fault system is one of the principal faults in NW of Iran and that its right- lateral strike- slip activity has reported for different segments of this fault zone. Landsat 7 satellite images of the area, confirm the right- lateral strike- slip motion of this fault system by deflected ...
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Siah Cheshmeh- Khoy fault system is one of the principal faults in NW of Iran and that its right- lateral strike- slip activity has reported for different segments of this fault zone. Landsat 7 satellite images of the area, confirm the right- lateral strike- slip motion of this fault system by deflected drainage of large rivers, cutting and displacement of alluvial fans across the segments of the fault zone. The amount of alluvial fans displacement in -Dasht e zurabad- (along the segment of the Kamarkassan fault) was estimated nearly 1.8 km. In this research, the neotectonics and mechanism of the Siah Cheshmeh- Khoy fault zone has been studied by Inversion method, based on the combination of focal mechanisms of earthquakes and different shear- fault planes. In this paper, we utilized all of the focal mechanism solutions of earthquakes existent in this area. Besides, the data measured conclude shear planes whit slickenside and the measured fault planes across the Siah Cheshmeh- Khoy fault zone. These data were gaged in 7 sites and 45 shear planes with slickenside. Initially the main axis were obtained in all sites by Inversion method; then by combination of focal mechanisms of earthquakes and the measured data, the stress state of this region was evaluated. The results obtained of this analysis indicate strike- slip stress with NNW-SSE (N162°) direction of compression component and ESE-WNW (N255°)direction of extension component in this area. It can be stated that the mentioned stress regime was the main factors controlling the recent kinematic movements of faults and strong earthquakes in the region. Also the right- lateral strike- slip motion of the Siah Cheshmeh- Khoy fault segments are affected by this stress (under the influence of this stress). The results of this research are compatible with the results of the geodetic studies and the GPS measurements in the region that were done by other researches.
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.
A. Fathian Baneh; S. Solaymani Azad; H. Nazari; M. Ghorashi; M. Talebian
Abstract
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 ...
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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.
Soroush Modabberi; Y. Rahimsouri; A. Yaghubpur; S. Alipour
Abstract
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 ...
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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.
M. Aghazadeh; M. H. Emami; H. Moin Vaziri; N. Rashidnezhad Omran; A. Castro
Abstract
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 ...
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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.
Nasrollah Abbassi
Abstract
Cretaceous flysch deposits of the Abshar-e Asyab Kharabeh (30 meters) in west of Siah-rud village in the Jolfa area, NW Iran, consist of conglomerate, sandstone, siltstone and mud- or marlstone layers, which mainly belong to A, B, D and E divisions of Bouma sequence. A divers trace fossils preserved ...
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Cretaceous flysch deposits of the Abshar-e Asyab Kharabeh (30 meters) in west of Siah-rud village in the Jolfa area, NW Iran, consist of conglomerate, sandstone, siltstone and mud- or marlstone layers, which mainly belong to A, B, D and E divisions of Bouma sequence. A divers trace fossils preserved on the lower bedding planes of sandstones and siltstones as positive hyporelief, includes: Bergaueria hemispherica, Bergaueria isp., Cochlichnus isp., Granularia isp., Halopoa imbricate, Helminthoida crassa, Helminthopsis abeli, Imponoglyphus torquendus, Neonereites multiserialis, Paleodictyon latum, Paleodictyon cf. majus, Paleodictyon nodosum, Palaeophycus alternatus, Palaeophycus sulcatus, Phycodes templus, Phycodes isp., Planolites annularis, Planolites beverleyensis, Protovirgularia longespicata, Squamodictyon isp., Strobilorhaphe isp., Thalassinoides isp., Taphrhelminthopsis recta, Taphrhelminthopsis convolute, Treptichnus pollardi. These trace fossils are mainly grazing-feeding or feeding traces of Nereites Ichnofacies and classifiable in six rang/frequency, based ichno-assemblages. Obtained trace fossils were produced during post-event calm periods. So, muddy sediments deposited after turbulence currents and traces have been made on these layers, activates of trace makers were developing when accessible feeding materials or dissolved oxygen increased in environment. Base on founded Nereites trace fossils, these sediments deposited in the deep marine abyssal zone environment.
M. Advay; A. Jahangiri; M. Mojtahedi; J. Ghalamghash
Abstract
The study area as a part of Maku-Tabriz zone is located in about 20 km NE of Khoy, NW Iran. Shah Ashan Dagh granite covers about 60 km2 of the area and emplaced into Permian host rocks and covered by Oligo-Miocene sedimentary rocks (Qom Formation). The Shah Ashan Dagh intrusive rocks composed of gabbro ...
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The study area as a part of Maku-Tabriz zone is located in about 20 km NE of Khoy, NW Iran. Shah Ashan Dagh granite covers about 60 km2 of the area and emplaced into Permian host rocks and covered by Oligo-Miocene sedimentary rocks (Qom Formation). The Shah Ashan Dagh intrusive rocks composed of gabbro and alkali-feldspar granite. Porphyric and granophyric textures indicate shallow depth emplacement and perthitic texture shows hypersolvous nature of this body. The studied mafic rocks have high LREEs relative to HREEs and they indicate relatively enrichment of LILEs and depletion in HFSEs (exception Hf, Ta, Nb). The studied mafic rocks based on positive Nb and Ta anomalies show similarity to plum type MORB. These rocks are tholeiitic and they have mantle plum enriched source. Shah Ashan Dagh granite characterized with high-K, sub-alkaline, metaluminous to peraluminous and weakly peralkaline nature. They have high content of LILEs, especially Th and Rb, and low content of Eu, Sr, Ta, Nb, Ba, and Ti, implying the granites may have been derived from crustal melts.
