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Journal: 

PETROLOGY

Issue Info: 
  • Year: 

    2021
  • Volume: 

    12
  • Issue: 

    2
  • Pages: 

    125-148
Measures: 
  • Citations: 

    0
  • Views: 

    64
  • Downloads: 

    5
Abstract: 

Anarak ophiolite, belonging to Paleozoic, formed along with the tectonic evolution of the Paleo-Tethys Ocean, consisting of meta-peridotites of mantle and crust, cumulate rocks, massive gabbros, pillow lava, basic and ultrabasic dikes, rodingite and listwanite covered all by schist and marble units. The olistolithic patches of Anarak ophiolite have commonly exposed in Sebarz schist, within the sole of Chah-Gorbeh complex. Olistoliths composed of listwanite, meta-mafic, serpentinite and meta-peridotite olistoliths varying from centimeter to several hundred meters in size. The results of electron microprobe analyses show that the fundamental rock-forming minerals of the listwanitized olistoliths are chromian spinel and pyroxene, secondary minerals including calcite, garnet, tremolite, chlorite, magnetite and opaque minerals. Meta-mafic olistoliths composed of chromian spinel, sphene, epidote, chlorite and opaque minerals. Serpentinized olistoliths consist of chromian spinel, magnetite, tremolite, talc and chlorite. It also shows that the meta-peridotite olistoliths composed of chromian spinel, chrome-bearing magnetite, chlorite, calcite, garnet and antigorite. Based on the geochemical analyses, Cr# in the listwanite patches, meta-mafic, serpentinite and meta-peridotite olistoliths are 87. 40-97. 92, 49. 38-51. 89, 49. 22-60. 05 and 29. 76-55. 97 respectively with very low amount of TiO2. The different in chemical composition of minerals in the North Anarak complex shows different petrogenesis for ophiolitic olistoliths suggests characteristic of the MORB and/or supra-subduction zone.

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Issue Info: 
  • Year: 

    2009
  • Volume: 

    1
  • Issue: 

    3
  • Pages: 

    59-72
Measures: 
  • Citations: 

    0
  • Views: 

    1069
  • Downloads: 

    0
Abstract: 

Gorgan metamorphic complex located with the length of 110 km and with of 2 to 10km parallel to general E-W direction of eastern Alborz. Shear zone was detected extensively in the region which some of them contain considerable olistolith fragments. By studying the kinematics and geometry, this zone is divided in to 3 kinds:1- Mehdi-Rajah Shear zone in northern part2- Reverse shear zones of the southern part of Gorgan Metamorphic Complex3- Naharkhoran-Toskestan Shear zones in Eastern partMehdi-Rajeh shear zone with slow slope towards the south which by field and laboratory studies considered to be Khazar fault with reverse mechanism.Southern shear zones with different distances with the direction of roughly east-west with the slope of N-NW and begins from Niala shear zone and continue to Deraznoo. All this shear zones are reverse.Naharkhoran-Toskestan shear zone in the east with steep slope from Naharkhoran towards Toskestan. With respect to the studies in the field, shear zones of eastern part to Gorgan metamorphic complex connected to the shear zones of southern part.The previous studies on Gorgan metamorphic complex showed that folds and faults of the region formed simultaneously with the placement of Gorgan metamorphic complex the mechanism of shear zone have a close relation with explored structures in the region and it seems that these zones formed simultaneously with placement of Gorgan metamorphic complex in the northern margin of Iran.

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Journal: 

SEDIMENTARY FACIES

Issue Info: 
  • Year: 

    2019
  • Volume: 

    11
  • Issue: 

    2
  • Pages: 

    250-271
Measures: 
  • Citations: 

    0
  • Views: 

    536
  • Downloads: 

    0
Abstract: 

Introduction Coral fossils of Jamal Formation Bagh-e-Vang member in Bagh-e-Vang and Shesh-Angosht stratigraphic sections (Tabas area of East-Central Iran) have been investigated in this research. Except the studies by Flü gel (e. g.; 1964, 1968, 1972, 1995) and Ezaki (1991) Permian corals are poorly known from Iran. The Jamal Formation was firstly introduced by Stö cklin et al. (1965) for the Permian rocks of east central Iran consisting mainly of limestone and dolomite in Shotori and Shirgesht Mountain ranges of the Tabas Block. With 293 to 473 m thickness (Stö cklin et al., 1965; Ruttner et al., 1968; Leven and Vaziri Mohaddam, 2004), its succession confined unconformably upon eroded surface of siliciclastic rocks belonging to the Carboniferous Sardar Formation and is conformably overlain by the Lower Triassic Sorkh Shale Formation (Partoazar et al., 2014). Jamal Formation in the studied sections is divided into 2 members, Bagh-e-Vang and Cherty Limestone member. The first one which is the main subject of the current research consists of shale and fossiliferous limestone with a siliciclastic rock unit of conglomerate and sandstone at the base, which is overlaid on the green shales of the Sardar Formation. The member is overlaid by cherty limestone of the Jamal Formation through a conglomeratic horizon. This study discuss paleontologically and paleobiogeographically the new material collected from the Jamal Formation in the mentioned localities, Bagh-e-Vang (coordinates of N33° 58′ 27″ and E56° 47′ 33″ ) on the southwestern flank of the Bagh-e-Vang Mountain and Shesh-Angosht (coordinates of N33° 59′ 15″ and E56° 46′ 50″ ) on the western flank of the SheshAngosht Mountain, at the north of Tabas. Materials and methods Beside the lithostratigraphical studies in the field, we looked the whole succession of the Bagh-e-Vang member to investigate the coral contents. Totally more than 350 specimens of in situ and float solitary and colonial corals have been collected bed by bed. The specimens were immersed in cold water for one week for study to remove the soft sediment particles attached to them with a special brush. Subsequently, the descriptive characteristics of the specimens included external features such as overall shape, length, diameter, diameter, base and calyx diameter, presence or absence of transverse and longitudinal bands, preservation and wall thickness, rejuvenation, columella and its diameter and depth of calyx were recorded in the respective tables and photographed from various positions with a Canon XD60 camera. In addition, coral fossils serially sectioned in the transverse and longitudinal directions according to the size and conditions of the study. They were studied under normal light (PPl) binocular microscope with a magnification of 5. In the thin section studies, coral diameter, dissepimentarium thickness, number of dissepiment rows, their size and slope, types of dissepiments, central structure, number, shape and thickness of septa as well as their types (Alar septa, cardinal septa, etc. ), granule, fossula, tabularium and their number in cm, tabular diameter, type of wall, its thickness and ornamentation, central area diameter and septotheca were investigated. The final determination is carried out based on the proper literatures such as Flü gel (1964, 1972, 1990), Ezaki (1991), Flü gel & Hubmann (1993), Fedorowski (2010), Berkowski (2012), Kossavaya et al. (2012), Somerville et al. (2012). Discussion and conclusion The stratigraphic interval in which all examined tabulate corals occur represents the lowest ca. 60 m part (= Bagh-e Vang Member in Partoazar, 1995), where carbonate facies are sandy to marly and contain interlayers of sandstone, shale, and olistolith. The Bagh-e-Vang member was dated by various taxa. These results are as follows: Bolorian ( = Kungurian; fusulinids; Leven and Vaziri Mohaddam, 2004), Yakhtashian ( = Artinskian) to Bolorian (fusulinids; Arefifad, 2006), Artinskian to Kungurian (bryozoans; Ernst et al., 2006), Bolorian to early Kubergandinian (= early Roadian; fusulinids; Leven and Gorgij, 2011), and Sakmarian to Kungurian (conodonts; Voulo, 2014). Taking these information into consideration, the age of corals examined herein is best constrained as late early Permian. The Tabas Block forms the Central-East Iranian Microcontinent with the Yazd and Lut blocks, whose paleogeographic position is interpreted to have been part of northern margin of Gondwana during early Permian time (e. g. Berberian and King, 1981; Ruban et al., 2007). It is concluded that, therefore, habitat of the Jamal coral assemblage was on the southern shelves of the Paleotethys. The coral assemblage of the Bagh-e-Vang member comprises 27 genera, 2 subgenera, 35 species, and 6 subspecies belong to 20 families of solitary and cerioid-fasiculate colonial Rugosa and Tabulata corals. This fauna is similar to Early Permain (Sakmarian – Kungurian) assemblages of the Cimmerian blocks. They are categorized into two distinct Waagenophyllum and Cyathaxonia fauna; although the Cyathaxonian forms with more diversity and abundance are dominant in the studied sequences. The Fasciculat and cerioid colonial genera of the Waagenophyllum fauna approve the shallow warm water tropical realms of the Tethys Ocean, however the small solitary Cyathaxonia fauna mostly tends to cool-temperate antitropical, antiequatorial or bipolar realms of the northern and southern hemispheres in the Permian (Wang et al., 2013). It means the Cyathaxonia fauna of the Bagh-e-Vang member are comparable with the Pri-Gonwanan realm and the Waagenophyllum fauna are similar to those from North and South China in the tropical realm. Consequently, the Early Permian coral fauna in the Bagh-e-Vang member suggests a complex paleobiogeographic pattern consist of tropical Waagenophyllum and cool-temperate Cyathaxonia fauna.

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