R. Elyaszadeh; M. Mohajjel; B. Farahani; S. R. Jafari
Abstract
Structural analysis of the NW-SE oriented Alborz fault in north Qom, demonstrates young left-lateral reverse displacement evidence, based on the rake of the striations on young fault planes (45-53). Strong structural evidence exists for its previous right-lateral reverse displacement. Young left-lateral ...
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Structural analysis of the NW-SE oriented Alborz fault in north Qom, demonstrates young left-lateral reverse displacement evidence, based on the rake of the striations on young fault planes (45-53). Strong structural evidence exists for its previous right-lateral reverse displacement. Young left-lateral displacement evidence in NW-SE oriented oblique and strike-slip faults recently was documented in central-west (eg. Mosha and Talegan faults) and south Alborz mountains (eg. Ipak and Kusk-e-Nosrat faults) due to the compression direction of the south Caspian oceanic crust with Alborz mountains. Replacement of right-lateral reverse mechanism by young left-lateral reverse mechanism in the Alborz fault in north Qom implies that the inversion of the central-west Alborz faults is being transferred through to the same oriented faults in south Alborz mountain up to the Qom area.
H. A. Tajeddin; E. Rastad; A. Yagoubpour; M. Mohajjel
Abstract
Barika deposit is the first and only recognized gold (and silver) rich – massive sulfide deposit in Iran which is located at 18 km east of Sardasht city, north western part of Sanandaj-Sirjan metamorphic zone. Rock units outcropped in this area are volcano sedimentary metamorphosed rocks in green ...
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Barika deposit is the first and only recognized gold (and silver) rich – massive sulfide deposit in Iran which is located at 18 km east of Sardasht city, north western part of Sanandaj-Sirjan metamorphic zone. Rock units outcropped in this area are volcano sedimentary metamorphosed rocks in green schist facies, and include association of metaandesite, metatuffite, phyllite and slate rocks, among which the metaandesitic unit (KMv1) is host rock of the deposit. Ore mineral assemblages in stratiform part of the deposit, which contain massive and banded pyrite and barite associated with subordinary silica bands, are very variable in composition and consist of pyrite, sphalerite, galena, stibnite and a variety of sulfosalt minerals and electrum. Ore mineral assemblage in silicic veins in stringer zone, are simpler and consist of pyrite, galena, sphalerite, tetrahedrite and rare chalcopyrite. Average gold and silver grades in stratiform ore are 4.2 and 260 g/t respectively and in silica stringer veins are 0.7 and 30 g/t. Base metal content in both part of the deposit is less than 1%. Lithotectonic study and trace and rare earth elements diagrams associated with Ce/Pb and Nb/U ratios of the metavolcanic rocks in the deposit area indicate that the rocks were generated from a lithospheric mantle source in the active continental margin of the SSZ. A geochemical study of Barika deposit reveals that distribution patterns and correlation coefficient of ore elements in parts of the Barika stratiform ore and stringer zone are completely in correlation with an undeformed massive sulfide deposit. The geochemical documents indicate that despite the metamorphism and highly deformation on the deposit, the primary distribution patterns and proportion of the ore elements are well conserved, as geochemical characteristics of the Barika deformed deposit is as well as correlated with an undeformed gold- rich volcanogenic massive sulfide deposit. However there is clear textural evidence for remobilization of As, Sb, Ag and Pb minerals together with Au in Barika deposit, but, remobilized constituents of the ores do not appear to have moved beyond the margins of the ore bodies and primary metal zonation.
M. Aflaki1; M. Mohajjel
Abstract
Laibid (northwest Esfahan) metamorphic rocks are situated in complexly deformed sub zone of the Sanandaj-sirjan zone, in which bounding faults emplaced Permian metamorphosed, beside the younger Triassic-Jurassic metamorphic rocks. Structural study of these units reveals three deformation stages of a ...
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Laibid (northwest Esfahan) metamorphic rocks are situated in complexly deformed sub zone of the Sanandaj-sirjan zone, in which bounding faults emplaced Permian metamorphosed, beside the younger Triassic-Jurassic metamorphic rocks. Structural study of these units reveals three deformation stages of a progressive deformation in this area. The first stage includes tight to isoclinal folds, the second stage includes open to close folds and the third one includes gentle to open folds. From the first to the third stage, fold's wavelength gradually become longer, so that their aspect ratio change respectively from tall and short, for the first stage, to broad, for the second stage, and to wide, for the third one. Superposition of these fold generations caused in coaxial interference patterns. It seems that during Late Jurassic, these three folding stages consequently formed and passively rotated in a continuous deformation condition, by gradually decreasing deformation depth. Dikes alternatively injected into the extensional fractures and through the axial plane foliation and gradually deformed in to the fold, boudin, folded boudin, and boudined fold.
R. Elyaszadeh; M. Mohajjel
Abstract
High Zagros zone in southeast Kermanshah is bordered between two Radiolarite and Zagros Fold Belt and consist of abundant NW-SE trending thrust faults and folds sub-parallel to Zagros fold belt. Several structural cross-sections were prepared in NE-SW direction perpendicular to the trend of the structures. ...
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High Zagros zone in southeast Kermanshah is bordered between two Radiolarite and Zagros Fold Belt and consist of abundant NW-SE trending thrust faults and folds sub-parallel to Zagros fold belt. Several structural cross-sections were prepared in NE-SW direction perpendicular to the trend of the structures. Main thrusts were cut by some local strike-slip faults due to difference in their displacement. The Kohsefid thrust fault (FA) is one of the main thrusts that divide the northern Radiolarite zone from the High Zagros Zone. This fault is limiting the southern boundary of the Radiolarite zone. It displaced as a reverse fault during contraction tectonic in Late Cretaceous. The flysh facies of Amiran formation in Zagros Fold Belt with Paleocene age contain radiolarite fragments and confirms this event. It seems that the Garo Formation plays a detachment surface role for these thrusts in the High Zagros zone. The foreland in Zagros, commenced to deform by thrusting and folding in Late Cretaceous in the High Zagros zone and by later collision of the Arabian plate with the Iranian plate, rock units in the Zagros Fold Belt were deformed.
R. Samanizadegan; M. Mohajjel
Abstract
The Ali Abad Damag granitoid is intruded in Triassic-Jurassic schists located 35km south of Hamadan, southeast of the Alvand batholith. Northeast-southwest oriented mylonitised Ali Abad Damag granitoid has been intruded into a strike-slip dextral ductile shear zone. Abundant deformed enclaves exist in ...
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The Ali Abad Damag granitoid is intruded in Triassic-Jurassic schists located 35km south of Hamadan, southeast of the Alvand batholith. Northeast-southwest oriented mylonitised Ali Abad Damag granitoid has been intruded into a strike-slip dextral ductile shear zone. Abundant deformed enclaves exist in this granitoid that all were strongly elongated along the main extension direction (X axis). The elongation of the enclaves is concordant with the strain rate and development of the mylonitic foliation and stretching lineation. Structural analysis of exposed rocks in this shear zone indicates that the mylonitic foliation is sub-vertical or steeply dipping to NW in the western half and shallowly to moderately dipping to the same direction in the eastern half, but the stretching lineation is sub-horizontal sub-parallel to the strike of the mylonitic foliation throughout the shear zone. Dextral strike-slip displacement is identified by the shear sense indicators. The change of foliation dip of the eastern half against the western part is interpreted by rotation along the NW-SE trending Darreh-Gar strike-slip fault.
L. Izadi kian; A. Alavi; M. Mohajjel
Abstract
The Simin- Darreh Moradbeik shear zone is located in the south of Hamedan city with 5 km width and at least 10 km length. The portion of contact metamorphic rocks, plutonic rocks and migmatits are affected by this shear zone. At least three ductile deformation stages are recognized by folding and foliation ...
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The Simin- Darreh Moradbeik shear zone is located in the south of Hamedan city with 5 km width and at least 10 km length. The portion of contact metamorphic rocks, plutonic rocks and migmatits are affected by this shear zone. At least three ductile deformation stages are recognized by folding and foliation of each stages of deformation. All of deformation stages are coaxial and created interference pattern of folding. Field evidence shows tension and shear stress in this area. The shear zone dips to northeast and northwest with normal sense of shear movement. This shear zone deformed locusom of migmatite, boudinage of andalusite porphyroblast and formed granitic mylonite from Khako granite. Distribution of mylonitic foliation poles show refolding of this shear zone at the next deformation stages. According to deformation stages in Hamadan tectonites, possibly this shear zone formed syn to post second deformation (D2)
M. Mohajjel; M. Biralvand
Abstract
Abundant chevron folds were produced in well-bedded red thin layers radiolarites in Kermanshah area. Various fold hinge area structures were produced due to competency contrast and change of thickness in radiolarian shale and thick-bedded limestone intercalation in radiolarite sequence. Different styles ...
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Abundant chevron folds were produced in well-bedded red thin layers radiolarites in Kermanshah area. Various fold hinge area structures were produced due to competency contrast and change of thickness in radiolarian shale and thick-bedded limestone intercalation in radiolarite sequence. Different styles of folding exist in massive to thick-bedded limestone and shale where they are inter-bedded with radilarites. Unique thin layers of the radolarite layers were folded in parallel shape but change of folds shape and mechanism were produced where thick bedded limestone or thin layers of radiolarian shale intercalations exist. Fold accommodation faults were generated in cases during folding. Geometry and style of folding indicate that deformation in radiolarites was produced by parallel folding due to buckling mechanism with southwest vergence. Thrust faults were generated during later stages, displacing some parts of the folded radiolarites.
F. Masoudi; M. Mohajjel; F. Shaker Ardekani
Abstract
The Zarrin area in the north of Ardekan is the part of Central Iran Zone. Some homogenous parts of Zarrin granite located in the shear zone changed to mylonites and ultramylonites. Microstructural evidence and deformation investigation show that chemical and structural changes occurred during the progressive ...
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The Zarrin area in the north of Ardekan is the part of Central Iran Zone. Some homogenous parts of Zarrin granite located in the shear zone changed to mylonites and ultramylonites. Microstructural evidence and deformation investigation show that chemical and structural changes occurred during the progressive deformation in mylonites. The most obvious chemical change is the noticeable decrease on Ti, Mg, Fe and P from mylonites to ultramylonites. Silica shows a slight increase in the mylonitic zone with progressive increase in modal quartz, but Al2O3 is nearly constant during the mylonitization. Because of decrease on feldspar porphyroclasts and feldspar grains in the matrix, compare to protomylonites, K2O decreases in mylonites. However, with relative increase on plagioclase, K-feldspar and epidote in the matrix, Ca, Na and K increase in ultramylonites. As a result of structural changes, quartz grains in weakly deformed protolith and protomylonite show recrystallization and sub grain. In a progressive deformation process, quartz in mylonites and ultramylonites reveals grain boundary migration in recrystallization. During the progressive deformation, K-feldspars become perthitic with fractures and plagioclases show kinking in their twins. With progress in deformation, recrystallization on K-felspar's margins and twins in plagioclase grains are formed. Based on structural evidence, temperature of 400ºC has been estimated for deformation in Zarrin area in protogranites and protomylonites. The temperature continuously increases up to 500ºC or more in green schist facies in the mylonites and ultramylonites.
M.A. Ghorbani; M. Mohajel; M. Pourkermani; M. Alimohammadi; H. Kheyrollahi
Abstract
Hired area is located in the northeastern border of Lut zone and western vicinity of Sistan suture zone. Northern part of Sistan suture zone trending NW-SE with complicated structure is the locality of several considerable ore deposits. We have employed aeromagnetic data, satellite images and field observations ...
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Hired area is located in the northeastern border of Lut zone and western vicinity of Sistan suture zone. Northern part of Sistan suture zone trending NW-SE with complicated structure is the locality of several considerable ore deposits. We have employed aeromagnetic data, satellite images and field observations to consider the relation of surface and subsurface structures to the significant superficial structural features of Hired mining area. Aeromagnetic data were processed by applying appropriate filters including Reduction to pole and First vertical derivative for proper distinguishing the magnetic features. In addition, highpass filters were used for edge sharpening of the ASTER images.
Aeromagnetic data have shown two main N-S and NW-SE structural directions which follow the northern Sistan suture zone. Presence of mineralized and altered veins and brittle shear zones with the same trend around the fractures is noticeable. Moreover, fractures intersections and conjuncture places are dramatically compatible with mineralization areas. Another result from aeromagnetic data is identification of a circular structure in the east of study area. The gold mineralization has occurred in the west part of mentioned structure which is strongly affected by NNW striking features. Satellite images in addition to confirmation of aforesaid structural trends imply a third structural NE-SW strike. This structure is not vivid on the aeromagnetic map and has only an ambiguous trace on it. Our field measurements verify this new structural trend as well.
