Petrology
Shima Shomali; Mansour Ghorbani; Mohamad Reza Ghasemi
Abstract
The Marphioon pluton in the central part of Urmia-Dokhtar magmatic arc is among the Neotethyan oceanic lithosphere subduction-related intrusions. The composition of this pluton changes from granodiorite to tonalite. Marphioon granitoid gives rise to contact aureole zone with different peripheral thicknesses. ...
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The Marphioon pluton in the central part of Urmia-Dokhtar magmatic arc is among the Neotethyan oceanic lithosphere subduction-related intrusions. The composition of this pluton changes from granodiorite to tonalite. Marphioon granitoid gives rise to contact aureole zone with different peripheral thicknesses. U-Pb geochronology of a sample from southern outcrop suggests that these rocks have crystallized at 18.89±0.20 Ma in Early Miocene.These rocks belong to medium-K calc-alkaline series with I-type affinities. In terms of geodynamic setting, this intrusion is classified as volcanic arc granites and active continental margin granites. Qualitative interpretation of aeromagnetic data suggested a diorite to gabbroic composition due to high magnetic susceptibility.The Marphioon intrusion is strongly tectonized due to faulting. Basement dextral strike-slip faults and their sinistral conjugates are potential mechanisms for its exposure. It seems that the Marphioon magma in an active continental margin, originated from the partial melting of the lower continental crust with the involvement of mantle-derived melts, where mafic magma in mantle wedge has provided optimal temperature and fluids for this melting in the lower crust. Collectively, Marphioon intrusion seems to be emplaced during the transition time from subduction to collision in the Urmia-Dokhtar magmatic arc contemporaneous with the closure of the Neotethyan ocean.
Petrology
Mohammad Saadat; Robab Hajialioghli; Mohssen Moazzen
Abstract
The Qotur metamorphic complex in west of Khoy is consist of various metamorphic rocks including of metabasites, metapelitic and meta-calcareous rocks and serpentinites. The metagabbros form main outcropping rocks in the area. Plagioclase and pyroxene are the main porphyroclasts of metagabbros. Epidote, ...
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The Qotur metamorphic complex in west of Khoy is consist of various metamorphic rocks including of metabasites, metapelitic and meta-calcareous rocks and serpentinites. The metagabbros form main outcropping rocks in the area. Plagioclase and pyroxene are the main porphyroclasts of metagabbros. Epidote, tremolite/actinolite, calcite and chlorite are formed during low grade metamorphism of these rocks. Based on geochemistry results, protolite compositions of the investigated rocks are plotted on the gabbroic field of the classification diagram. They have calc-alkaline magmatic series. Considering the discrimination tectonic diagrams the Qotur metagabbroic rocks have been formed at the island arc tectonic setting. On the basis of U-Pb zircon geochronological data, the rocks are formed at 162.6±7.6 Ma corresponds to the late Jurassic (Oxfordian). On the basis of results obtained from isotopic dating and geochemical data of the Qotur metagabbros, we suppose that they formed related to the sialic back arc basin of Neotethys, Jurrasic Island arc rocks of Sevan-Akera zone corresponds to the North branch of Neotethys oceanic suture and/or in continuation of the Piranshahr and Serow ophiolites as a Zagros-Bitlis Zone. However perecise results will be need to tectonic works and more geochemical and isotopic data from variety of metamorphic and igneous rocks.
Petrology
Atefeh Nimroozi; gholamreza ghadami; Jamshid Hassanzadeh; Mohammad posti
Abstract
The study area is located near Abarkoh city and in Sanandaj –Sirjan zone. The volcanic activity of this region is in the form of dacite and rhyolite domes and lava flow and in the petrographic studies includes coarse plagioclase, quartz and hornblende. The volcanic rocks are considered as the separate ...
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The study area is located near Abarkoh city and in Sanandaj –Sirjan zone. The volcanic activity of this region is in the form of dacite and rhyolite domes and lava flow and in the petrographic studies includes coarse plagioclase, quartz and hornblende. The volcanic rocks are considered as the separate units interlayered with calcareous sedimentary units. Geochemical classification confirms the rhyolitic and dacitic composition of the volcanic unites and show their belonging to the calc-alkaline magmatic series, which is the characteristic of the subduction tectonic setting. Significant characteristics observed in spider and multi-element diagrams, such as their enrichment in LREE, high LREE / HREE ratio, Nb and Ti trough, and enrichment of Pb, Rb and Th elements demonstrate the continental crustal contribution to the development of the volcanics and their formation in the subduction environment in the active continental margin setting. Tectonic setting diagrams confirm this idea and determined a continental arc setting for the volcanic rocks of the area. The dating studies on zircon minerals yield the age of about 17.7.2 ± 7.6 ma equivalent to Jurassic for this part of the Sanandaj-Sirjan zone, which matches with the subduction stage of the Neotethyan Ocean below the central Iran zone.
S Sedighian; S Dargahi; M Arvin
Abstract
Khunrang intrusive complex, as a one of the largest complexes in the southern part of the Sanandaj-Sirjan zone, is located at northwest of Jiroft, in Kerman province. The complex mainly consists of acidic-intermediate rocks such as diorite, quartzdiorite, tonalite, granodiorite, and granite with subordinate ...
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Khunrang intrusive complex, as a one of the largest complexes in the southern part of the Sanandaj-Sirjan zone, is located at northwest of Jiroft, in Kerman province. The complex mainly consists of acidic-intermediate rocks such as diorite, quartzdiorite, tonalite, granodiorite, and granite with subordinate amounts of mafic members such as hornblende gabbro and microgabbro. Field studies together with mineralogical and geochemical evidence show that the Khunrang intrusive complex belongs to calc-alkaline series and its felsic members are metaluminous to weakly peraluminous which display features typical of I-type granites. On the primitive mantle-normalized spider diagrams, all mafic and felsic samples are enriched in LILE (such as Rb, Cs and K) and depleted in Ti, Ta and Nb which is a main characteristic of subduction-related magmas. Based on geochemical data, the mafic rocks seems to be formed by melting of metasomatised mantle wedge; whereas felsic rocks are formed by melting of lower crust metabasic rocks as a result of the injection of mantle derived mafic magmas. It can be concluded that the Khunrang intrusive complex was formed in a volcanic arc setting due to subduction of the Neotethys oceanic crust beneath the Central Iranian Micro-continent in the Middle-Jurassic time.
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.
Kh. Allahyari; M. Pourmoafi; M. Khaleatbari-Jafari
Abstract
The extrusive sequence of Kermanshah ophiolite complex are exposed in Tamark and Gashor area, in east of Kermanshah and Harsin, in west of Iran. These lavas are located along the Main Zagros Reverse Fault, which marks the ophiolitic suture zone between the Zagros belt and the Sanandaj-Sirjan zone. These ...
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The extrusive sequence of Kermanshah ophiolite complex are exposed in Tamark and Gashor area, in east of Kermanshah and Harsin, in west of Iran. These lavas are located along the Main Zagros Reverse Fault, which marks the ophiolitic suture zone between the Zagros belt and the Sanandaj-Sirjan zone. These rocks with pillow structures are nominated in Tamark area as basalt to basaltic andesite and in Gashor area as basalt to basaltic trachy-andesite. According to classifications for magmatic series Tamark’s pillows are belong to subalkali series and Gashor’s pillows are belong to alkaline series. In classifications of tectono magmatic patterns, Tamark and Gashor’s basalts respectively are plotted in E-MORB and WPB. These rocks in both of pillows enriched from LILE, LREE and some HFSE and the enriched mantel is the source of the primitive magma. They represent the Neo-Tethyan oceanic lithosphere originally existing between the Arabian and Eurasian continental margins.
H. Nazari; J-F. Ritz; S. Oghbaee
Abstract
Development and evolution of Tethys basins during geological history from the Precambrian to Paleogene has been considered by many geoscientists. The first sign of various basins propagation of Tethys which resulted in separation of supercontinents, ancient lands (such as Eurasia, Gondwana) and ...
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Development and evolution of Tethys basins during geological history from the Precambrian to Paleogene has been considered by many geoscientists. The first sign of various basins propagation of Tethys which resulted in separation of supercontinents, ancient lands (such as Eurasia, Gondwana) and blocks or microplates among them, are found in the Precambrian. One of these old basins in the north of Iran has been called Ortho-Tethys, its evidence can be found in the primary structures of Alborz and its Precambrian units.
Some other researchers believe that the Ordovician and Silurain volcanic series of Iranian Plateau and Alborz were formed after genesis of Early Tethys basin or Paleotethys due to extension-shear system along the Paleo-Tethys between Turan plate and Alborz-Kopet-Dagh belts. By increasing the rate of subsidence in the Permain basin, the dominating marks of extension system between Iranian microcontinents and Arabian plate were recorded, however, the related alkaline volcanic rocks of the Neotethys rifting found in Triassic succesion. In addition, the most important tectonic changes of the Caspian and Black seas occurred in the Triassic time.
Structural upheaval of Tethys basins among blocks and plates, such as Turan in the north Kopet-e-Dagh, Caucasus, Alborz, Sabzevar, Central Iranian micro-continents and Arabian plate in the south is traceable periodically.
The succession of extension and compression tectonic events resulting from opening and closing of such basins during Assynitic–Pan african and Alpine orogenies which sometimes correspond to metamorphic facies from Caldonian and Hercynian orogenies, resulted in tectonic evolution of sedimentary basins in the areas impressed by various orogenies.
Alborz as an extended block in active tectonic zone and impressed by most distinguished geological events in both supercontinents of Eurasia and Gondwana is evolved between two ancient continents. The total of thinning and thickening of Alborz basement during ancient events in comparison to other parts of Iran indicate approximately constant rate and little negative gradients due to thickness decrease of crystalline crust and lower crust towards Caspian basin.
Detachment folding system with uplift of ancient facies in hanging wall of basic fault in north Alborz is one of the apparent features of central part of this structural block that occurred in flower structure. More folding and movement in western part of this fault comparing to eastern part, is another structural feature in the area.
North Alborz , Mosha and Taleghan faults as principal faults appearing in internal part of Central Alborz,wheresomepropagationfaults like the North Tehran and Khazar can be derived from them to the south and north side of Central Alborz.
M. R. Poursoltani; R. Moussavi Harami; Y. Lasemi
Abstract
The KopetDaghBasin of northeast Iran formed in the NeotethysOcean after the closure of Paleotethys in the south of Turan plate. A thick sequence of Jurassic to Miocene sediments has been deposited in this basin without any major break. The siliciclastic Kashafrud Formation ...
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The KopetDaghBasin of northeast Iran formed in the NeotethysOcean after the closure of Paleotethys in the south of Turan plate. A thick sequence of Jurassic to Miocene sediments has been deposited in this basin without any major break. The siliciclastic Kashafrud Formation (Middle Jurassic), overlying unconformably on Triassic rocks and ultrabasic rocks comprises nearly 2 km of turbidite and fluvio-deltaic facies, consists of sandstone, shale and conglomerate. Trace-fossil assemblages are presented in some units with different environments. The most important ichnofossils in this formation are Skolithos, Palaeophycus tabularizes,Belerhaphe, Thalassinoides suevicus, Psilonichnus , Planololites beverleyensis, Rhizocoralium jenese, Scolicia, Conichnus, Lophactenium, Palaeophycus striatus,Taenidium. It is interpreted, based on identified ichnofossils, the Kashafrud Formation may have been deposited in fluvio-deltaic and deep water (turbidity conditions) environment. We hope that these data can help in a better understanding of palaeogeography and tectonic setting of the region during Middle Jurassic.