A. Kamali; H. Pirooj; F. Nemati; A. Ameri; M. Fadaeyan
Abstract
The studied area is located in southern part of the Torghabeh quadrangle, 90 km SE of Mashad city. The rocks of the investigated area are alkaline basalt and trachy andesite. The major minerals are plagioclase and pyroxene, minor amounts of olivine. The accessory minerals are rutile, titanite and apatite. ...
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The studied area is located in southern part of the Torghabeh quadrangle, 90 km SE of Mashad city. The rocks of the investigated area are alkaline basalt and trachy andesite. The major minerals are plagioclase and pyroxene, minor amounts of olivine. The accessory minerals are rutile, titanite and apatite. The major texture is hiyalomicroporphyry. The nature of magma by various diagrams show that the generated magms are alkaline.The linear trends between Rb/Sr, K/Nb, in the rocks of the study area can show mixing of two sources from mantle astenosphere and lithosphere. Also positive anomaly of Pb and enrichment in LREE, in the studied samples may indicate crustal contamination. The low SiO2, high Mg and also negative Nb anomaly suggest strong role of crustal contamination in the petrogenesis of the studied rocks. The tectonic environment studies shows that these rocks are within plate basalts. Regarding the presence of coral fossil in the associated carbonate rocks and sand stone facies which belong to Devonian age it can be concluded that volcanic rocks of the study area are produed as a Caledonian eruption and shallow depth environment.
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.
