Sh Eghtesadi; M Shokati Amghani
Abstract
Modelingof bouguer gravity anomaly and tsunami warning due to Makran subduction zone (case study: Beris region)
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Modelingof bouguer gravity anomaly and tsunami warning due to Makran subduction zone (case study: Beris region)
M Mirzaei Souzani; A Shahidi; R Ramezani; F Alizadeh Sevari
Abstract
In order to survey the extensional forces dominated in central Alborz since Late Triassic (Norian) to Middle Jurassic (Early-Bajocian), synsedimentary normal and strike-slip fault systems in Balladeh valley which contains significant distribution of Shemshak Group have been studied. Analysis of σ3 ...
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In order to survey the extensional forces dominated in central Alborz since Late Triassic (Norian) to Middle Jurassic (Early-Bajocian), synsedimentary normal and strike-slip fault systems in Balladeh valley which contains significant distribution of Shemshak Group have been studied. Analysis of σ3 orientation for 404 fault planes in 35 normal fault systems, show two major extension directions at NNE (020°) and NE (070°) trends during sedimentation of Shemshak Group. Also, the presence of a minor extension direction trending WNW (300°) which is coincident with extension direction of synsedimentary strike-slip fault systems implies the existence of transtentional basins in the Shemshak basin at that time. The southward movement of southern edge of Eurasia (from latitude of 30° to 15°) and its clockwise rotation for some 40°-50° during Triassic-Jurassic periods led to domination of N-S extension in early times of Shemshak Group sedimentation, and as soon as the Eurasian plate rotated, the extension direction was changed into a NE-SW trend. These separated records of paleostress axis trends are also due to the high sedimentation rates and subsidence in Norian-Rhaetian and Toarcian-Aalenian during Shemshak Group sedimentation. The minor extension trending WNW-ESE (278°-307°) is due to σ2/σ3 permutation between N-S σ3 direction of stress tensor and its σ2 axis. Low values of Φ (less than 0.4) generally correspond to situation characterized by σ2/σ3 permutation; therefor it causes multidirectional extension in extensional stress regimes. About 80 percent of sites which show WNW-ESE paleostress extension trend have low Φ values. This issue explains σ2/σ3 permutation of N-S major extension trend. The areas of mentioned stations and also those ones with strike-slip fault systems σ3 directions of which are directed WNW-ESE had high basin crustal anisotropy.
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.
