R Jamali Ashtiani; Hassanzadeh J; M Rahgoshay; A Sharifi
Abstract
The Sanandaj-Sirjan zone is a NW-SE trending orogenic belt immediately north of the Zagros suture, which represents the former position of the Neotethys Ocean. This zone includes a Pan-African basement similar to the various terranes to the north in Central Iran. The crystalline basement is nonconformably ...
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The Sanandaj-Sirjan zone is a NW-SE trending orogenic belt immediately north of the Zagros suture, which represents the former position of the Neotethys Ocean. This zone includes a Pan-African basement similar to the various terranes to the north in Central Iran. The crystalline basement is nonconformably overlain by the Paleozoic-Triassic platform sediments, which in turn are unconformably covered by sedimentary and volcanic strata of the Jurassic arc. The Cretaceous carbonates overlie the older rocks with a regional angular unconformity. The Chadegan high-P metamorphic complex exposed along the upper Zayanderoud and consists of quartz schists, amphibolites, gneisses, marbles and eclogites, and is nonconformably underlain by the fossiliferous Permian carbonates, suggesting a Pre-Permian age. In this paper we present new data including whole rock major and trace element compositions, mineral chemistry and radiogenic isotope data for the selected metabasites. The high field strength element (HFSE) abundances and Sr-Nd-Hf ratios suggest tholeiitic compositions with distinct within plate affinity rather than MORB. We also present new 206Pb/238U zircon age of 568.0 ± 5.3 Ma for a crosscutting orthogneiss reconfirming the Late Neoproterozoic age for the granitic protolith. We conclude that previously presented Ar-Ar ages for white-micas in eclogites and gneisses are indicative of metamorphic crystallization due to the regional plutonic arc activity. A comparison is made with the well-investigated Menderes Massif in Turkey where an orthogneiss-metabsite association with similar age and chemistry makes extensive exposures. We also conclude that this rock complex is extended from Zayanderoud to Khoy and beyond to the Menderes Massif and discuss the connection with the final amalgamation tectonics of the Gondwana near the beginning of the Cambrian Period.
F Kozekoulani; M Rahgoshay; H Shafaii Moghadam
Abstract
Intrusive rocks from SW Salmas include mafic-intermediate and acidic rocks, which occur in the border of Sanandaj-Sirjan and Urmia-Dokhtar zones in Northwest of Iran. The mafic-intermediate rocks comprise metadiorite and metagabbros that are the oldest rocks in the region. The acidic rocks include metagranite ...
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Intrusive rocks from SW Salmas include mafic-intermediate and acidic rocks, which occur in the border of Sanandaj-Sirjan and Urmia-Dokhtar zones in Northwest of Iran. The mafic-intermediate rocks comprise metadiorite and metagabbros that are the oldest rocks in the region. The acidic rocks include metagranite and metagranodiorite. These rocks have intruded into the Precambrian metamorphosed volcanic-sedimentary rocks. U-Pb zircon dating of the Salmas metagranite and metagranodiric rocks yielded age ranges of 565±2/7 Ma to 567±2/4 Ma (Ediacaran-Early Cambrian). Zircons have inherited cores. Zircon Hf isotope data (and Hf model ages) indicate that these rocks are not juvenile mantle melt derived but instead are products of juvenile melts interaction with old Mesoproterozoic continental crust. Furthermore, zircon δ18O values suggest contribution of continental crustal rocks during generation of the Salmas rocks. The Salmas Cadomian rocks are coeval with other similar-aged metagranites and gneisses from Central Iran, Sanandaj-Sirjan zone and Alborz Mountains. All these dispersed basement rocks are suggested to be fragments of the Neoproterozoic-early Cambrian magmatism of northern margin of Gondwana.
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.
