E Moosavi; M Mohajjel
Abstract
Two main metamorphic events have occurred within Muteh- Golpayegan metamorphic core complexes (including eastern and western complexes) in the Sanandaj-Sirjan zone. Some grain-scale deformations were also happened in relation to these metamorphisms which have produced various deformation microstructures. ...
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Two main metamorphic events have occurred within Muteh- Golpayegan metamorphic core complexes (including eastern and western complexes) in the Sanandaj-Sirjan zone. Some grain-scale deformations were also happened in relation to these metamorphisms which have produced various deformation microstructures. Microfaults are among the microstructures that were formed during brittle conditions. Bulging recrystallization of quartz and rarely feldspar grains, and bookshelf structure of fragmented feldspar porphyroclasts indicate various deformation and formation of shear zones under low-temperature conditions in the eastern complex. Polygonal granoblastic texture of polycrystalline quartz porphyroclasts documents post-mylonitization annealing at medium- grade conditions in shear zones of eastern complex. Chessboard pattern quartz subgrains propose high-grade metamorphic conditions during the first deformation. However, their undulatory extinction reveals low-grade conditions for the second deformation. Polygonal granoblastic texture of chevron folded feldspar grains also accurately supports these conditions during the two mentioned deformations. In general, considering deformation microstructures and conditions, three stages of recrystallization are respectively recognizable in the Muteh-Golpayegan metamorphic complexes including: 1- high-grade static recrystallization subsequent to early metamorphic event, 2- dynamic recrystallization and related mylonitization under low-grade to locally medium-grade conditions, 3-post-mylonitization static recrystallization in medium-grade conditions. The north Golpayegan intrusive bodies can be considered as the heat source for annealing in the western complex but the cause of annealing is not evident in the eastern complex.
E Moosavi; M Mohajjel; N Rashidnejad-Omran
Abstract
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 ...
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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.
E Moosavi; M Mohajjel
Abstract
The North Esfajerd ductile shear zone is exposed in NE Golpaygan in the Sanandaj-Sirjan zone. The shear sense indicators are observed in the both outcrop and microscopic scales in this shear zone. These indicators are representing a NW striking dextral shear. The dynamic analysis and outcrop- scale indicators ...
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The North Esfajerd ductile shear zone is exposed in NE Golpaygan in the Sanandaj-Sirjan zone. The shear sense indicators are observed in the both outcrop and microscopic scales in this shear zone. These indicators are representing a NW striking dextral shear. The dynamic analysis and outcrop- scale indicators of extension direction exhibit a NW extension sub-parallel to the dextral shear and a compression perpendicular to it. The relative simultaneity and parallelism between North Esfajerd ductile shear zone and North Varzaneh thrust shear zone propose the partitioning of strain components in a transpressional deformation. Regarding the geochronologic data and the angular unconformity between the middle Cretaceous and Eocene rock units, the transpressional deformation and its related mylonitization occurred during the Laramide orogeny in late Cretaceous-Paleocene. The gently dipping mylonitic foliations with dextral shear imply an incompatibility between geometry and kinematics in the North Esfajerd ductile shear zone. However, the kinematic and dynamic characteristics of the North Esfajerd ductile shear zone are accommodated with lateral extrusion of material in a dextral domain.
Parallelism between the trends of dominant stretching lineations and the second generation large scale fold axes document that the major mylonitization in the North Esfajerd shear zone occurred during the second generation deformation. These mylonitic fabrics were folded due to the third generation deformation. Two generations of crenulation cleavages, respectively in relation to two refolding events, can be recognized in this shear zone. One of the refolding events with type III interference patterns (coaxial refolding) occurred during the second stage deformation in the late Cretaceous- Paleocene interval, caused the formation of the North Esfajerd shear zone, and can be observed in an outcrop scale. The other has emerged during the third stage of deformation, probably in the post Paleocene-pre Miocene interval, folded the North Esfajerd shear zone and formed the type II (boomerang shape) interference pattern in a map scale.
