Tectonics
Mohammad Reza Sheikholeslami
Abstract
Bajgan metamorphic complex is located at the southeastern termination of the Sanandaj-Sirjan zone in north of Makran. The metamorphic rocks, having igneous and sedimentary origins, are in tectonic contact with ophiolite assemblages and colored mélange. The rocks can be divided in four units based ...
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Bajgan metamorphic complex is located at the southeastern termination of the Sanandaj-Sirjan zone in north of Makran. The metamorphic rocks, having igneous and sedimentary origins, are in tectonic contact with ophiolite assemblages and colored mélange. The rocks can be divided in four units based on lithological characteristics. These units are covered by Pliocene and Quaternary sediments. Structural study indicates the presence of three syn-metamorphic stages of deformation in ductile condition. The main structures elements are different generation of folds, foliation and lineation, each of them has been generated during a specific stage and superimposed on each other. The structural elements in this complex have emerged during subduction, ophiolite obduction and exhumation, respectively.
Petrology
Leila Maleki; Nematollah Rashidnejad Omran; Abdolrahim Houshmandzadeh
Abstract
Boneh shurow metamorphic complex is located in the east of Saghand area, Central Iran. This complex consists of quartz-feldspatic gneiss (mafic minerals < 5%), biotite-amphibole gneisses, metabasics rocks, schists, subordinate dolomitic marble and quartzite interlayers and mafic and felsic magmatic ...
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Boneh shurow metamorphic complex is located in the east of Saghand area, Central Iran. This complex consists of quartz-feldspatic gneiss (mafic minerals < 5%), biotite-amphibole gneisses, metabasics rocks, schists, subordinate dolomitic marble and quartzite interlayers and mafic and felsic magmatic intrusions that they have been retrogressed to lower amphibolite facies. In MORB-normalized plots, the metabasic samples can be classified into two groups: first group does not display Nb-Ta anomaly and second group displays negative Nb-Ta anomaly. Whole rock geochemistry and Sr– Nd isotopic composition of metabasic unites suggest derivation from two different mantlic sources in the back arc setting. A source enriched in Ti, such as plume tail, and an old enriched mantle that has been affected by subduction, can be involved in generation of the first and second group, respectively
M.R Sheikholeslami
Abstract
Different characteristics of the rock units and their stratigraphic relationships, as well as magmatic and metamorphic activities in the southern part of the Sanandaj-Sirjan Zone resulted in identification of different tectono-stratigraphic units based on their tectonic environments reflecting the opening ...
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Different characteristics of the rock units and their stratigraphic relationships, as well as magmatic and metamorphic activities in the southern part of the Sanandaj-Sirjan Zone resulted in identification of different tectono-stratigraphic units based on their tectonic environments reflecting the opening and closure of the Neotethys Ocean in southern Iran. The major tectono-stratigraphic units identified in this study are as follows: sediments deposited in the aulacogen setting in southern part of the Central Iranian platform of Paleozoic to Middle Triassic age; Triassic volcanic rocks and turbiditic sediments; low-grade flysch-type sediments of Jurassic-Early Cretaceous age deposited in a forearc basin; Lower Cretaceous carbonate platform sediments; suture zone-related rocks containing ophiolite, radilolarite and glaucophane schists; Tertiary flysch-type sediments containing exotic blocks of Lower Cretaceous carbonate, ophiolite and of the Zagros Formations formed over the edge of High Zagros zone; retro-arc foreland sediments of Central Iran which unconformably overlie the deformed rocks of northeastern part of the area; and finally post-orogenic molasse-type sediments resulted from post uplift erosion of the Zagros orogeny, deposited in the internal and marginal parts of the southern Sanandaj-Sirjan zone.
M.R Sheikholeslami
Abstract
The effects of the Mid-Cimmerian event in the BinaludMountains can be investigated in the Mashhad Phyllite around Mashhad and in the Aghdarband Group in the Aghdarband area. In the Eastern Binalud, this event acted in prehnite-pumpellyite to lower greenschist facies and influenced the Shemshak group, ...
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The effects of the Mid-Cimmerian event in the BinaludMountains can be investigated in the Mashhad Phyllite around Mashhad and in the Aghdarband Group in the Aghdarband area. In the Eastern Binalud, this event acted in prehnite-pumpellyite to lower greenschist facies and influenced the Shemshak group, which deposited as a post Early Cimmerian molasse blanket in a Rhaetian–Lias back-arc basin. The result is transformation of these sediments into the slate, phyllite and metasandstone. Tight to open folds, axial plane foliations and crenulation folds with NW-SE trending are the Mid-Cimmerian deformational structures. Due to the lower grade of metamorphism and deformation, there isn’t any important effect of this event on the rocks, which were previously deformed and metamorphosed by the Early Cimmerian event. The exhumation and erosion of deformed rocks by the Early and Mid-Cimmerian events generated the intramontane basins in the internal part of the eastern BinaludMountains. In the Aghdarband area, this event is characterized by folding of the Sina Formation from the Aghdarband Group, which is unconformably overlain by the Kashafroud Formation.
L Izadi kian; M Mohajjel; S.A Alavi
Abstract
Hamedan area is in the NW of the Sanandaj-Sirjan Zone. Different types of plutonic rocks are outcropped in this area which in turn, surrounded by the various metamorphic rocks (regional and contact metamorphism). Four ductile deformation stages were recognized. Each of them is accompanied with formation ...
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Hamedan area is in the NW of the Sanandaj-Sirjan Zone. Different types of plutonic rocks are outcropped in this area which in turn, surrounded by the various metamorphic rocks (regional and contact metamorphism). Four ductile deformation stages were recognized. Each of them is accompanied with formation of fold, foliation and lineation. The first generation foliation (S1) and folds (F1) formed at the first stage of deformation (D1). The second deformation defined by refolding of the first axial surface and forming of the second foliation (S2) and folds (F2). This stage is the strongest deformation and formed main foliation in this area. Axis of these folds changes from horizontal to vertical. The direction of this fold axis follows the Alvand pluton form. The second foliation shows wide dispersal in orientation and their trends follows the Alvand pluton form. The third deformation (D3) defined by close to open, mostly upright with curved hinges folds (F3) and the axial-plane foliation (S3). This foliation (S3) is predominant in areas east of the Alvand pluton and is crenulation cleavage to fracture foliation. The most axis of F3 show N165 plunging. Because of the interference pattern between the first, second and third folding at the regional and contact metamorphic rocks, these stages of deformation are coaxial deformation. D4 is characterized by a crenulation cleavage (S4) and a mineral lineation (L4(. L4 have a NE-SW plunging. This lineation does not exist at the contact metamorphic rocks. The rotation of axis of F2 and the second foliation is obvious around the Alvand pluton. This rotation shows that the final strain field is followed the pluton forms and probably the main granitic Alvand pluton intruded during the second deformation in this area.
K. Mohammadiha; M. Sabzehie; M. Ghahraie pour; J. Radfar
Abstract
A large widespread outcrop of granitoid - mylonitic gabbros complexes is observed in northeastern part of Serow, NW Iran. Those rocks were considered as Precambrian gneiss and metamorphic rocks (Haghipour and Aghanabati, 1977), or alternatively, a complex of acidic to basic igneous rocks which have undergone ...
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A large widespread outcrop of granitoid - mylonitic gabbros complexes is observed in northeastern part of Serow, NW Iran. Those rocks were considered as Precambrian gneiss and metamorphic rocks (Haghipour and Aghanabati, 1977), or alternatively, a complex of acidic to basic igneous rocks which have undergone intense deformation and dynamic metamorphism by shearing (Mohammadiha, 2000; Mohammadi Torkabad, 2001). The basic mylonitic rocks in the studied area are simply composed of plagioclase, hornblende, actinolite, chlorite, and epidote. They display minor remains of primary pyroxenes which are largely replaced by amphibole. Feldspars have been altered to epidote, and secondary plagioclase (more sodic) and roughly sericite. There are some gabbros with clastic and lentiform fabric which were not affected by dynamic deformation in the shear zone. Cataclastic flow, micro fracturing, dislocation creep, recovery, diffusion creep, grain boundary sliding and pressure dissolution are the dominant deformation mechanisms influenced the complexes. The consequent structures are foliation, lineation, undoluse extinction, porphyroclasts with core-mantle structure, micro fractures parallel and unparallel with brecciation, mechanical twining, mica fish structure, banded differentiated structure and kinked foliation. We conclude that the whole observed evidences demonstrate a major dynamic deformation in a brecciated zone in the studied 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.
