جستجوی مقالات مرتبط با کلیدواژه « میلونیتی شدن » در نشریات گروه « زمین شناسی »

Ayrakan granitoid pluton with 12 km2 area cropped out in the northeast of Mohammad Abad Kooreh Gaz village from Khur o Biabank County and in the farthest NE end of Jandagh-Arousan Metamorphic-Igneous belt. The main part of this granitoid pluton consists of porphyroidic biotite granites. A few leucocrate aplitic granite dikes and apophyse as a late magmatic phase cut porphyroidic biotite granites. Both type of the rocks, suffered intensively plastic (mylonitisation) and brittle (catclastic or fragmentation) deformations. Porphyroidic biotite granites are supposed to show more intensive mylonitization. Based on geochemical characteristics, isotopic ratios of 87Sr/86Sri, 143Nd/144Ndi and εNd, Ayrakan mylonitized porphyroidic biotite granites and aplitic granites are belonging to peralumious S-type granites. , 87Sr/86Sri (0.712714 and 0.712490), 143Nd/144Ndi (0.5115227 and 0.511581), associated with negative εNd (-8.19 and -7.13) for porphyroidic biotite granites and aplitic granites, respectively, indicate that they are originated from melting of metapelitic lower crust. Based on, Zircon U-Pb dating, porphyroidic biotite granites and aplitic granites have 545±11 and 537±3.8 Ma age, respectively. These values confirm the earlier dating results (549±15 Ma age). Therefore, Ayrakan granitoids certainly are part of the basement and Iranian Gondwanan terrains with the Late Neoproterozoic-Early Cambrian age

Extensive mylonitic fabrics are observed in the north Golpayegan metamorphic rocks in the Sanandaj-Sirjan zone. Earlier researchers did not present any evidence for the relative timing of mylonitic fabrics development. In this paper, the relation between folding and metamorphism events and formation of shear zones in the north Golpayegan are documented. The evidence is systematically presented at the microscopic, outcrop (mesoscopic) and map scales in order to study the relative timing of mylonitization event. The evidence at the microscopic scale indicates that the mylonitization occurred after the first stage amphibolite facies high-grade metamorphism, synchronous with the second stage greenschist facies retrograde metamorphism. The evidence at the microscopic and outcrop scales are compatible with each other and show the mylonitization event during the second stage (D2) folding, coeval with the greenschist facies metamorphism. Transposition of mylonitic foliations on the limbs of the second-generation microscopic and mesoscopic folds is documented. At the map scale, concordance of stretching lineations with second-generation fold axes, and folding of mylonitic foliations during the third stage of deformation also indicate mylonitization event during second stage (D2) deformation. Through a correlation of the isotopic ages, an Early Paleocene age is proposed for the mylonitization during D2 event in the north Golpayegan.

Bon-Dono Gneisses are exposed in the core of Tutak anticline, 200 km NE of Shiraz. Tutak metamorphic complex or the host rock of these gneisses is part of Sanandaj- Sirjan Metamorphic Belt. Field studies have shown that: (1) the age of protoplast of Tutak complex is Upper to Lower Paleozoic. It is comprised of various micaschists, amphibolites, marbles and greenschist. They are metamorphosed in a pre-Upper Jurassic metamorphic event. (2) Tutak complex had been invaded later by a granitic body. Previous regional metamorphic rocks had been subjected to a contact metamorphism resulted from this intrusive magma. (3) This granitic body had been subjected to mylonitization in a shear zone and converted to the so-called Bon-Dono Gneiss. Field, petrographic and geochemical studies all indicate magmatic nature of original protolith of so- called Bon-Dono gneisses.