Writers : Koohpeyma,Meysam ;Supervisor:M.Ghasemi
Refference : Research Institute for Earth Sciences, Tehran
Publishing Year : 1385

Abstract :

The studied area includes outcrops of Paleo- tethys remnants that occur in the west and southwest of Mashhad and northeastern part of Binalud mountains.
These rocks are composed of metamorphosed pellitic and carbonate rocks, mafic and ultramafic rocks, and granitoids. Shear zones occure along the contact of rock units and within the rock units. They strike northwest-southeast similar to the general structure of area. Foliations in the deformed rocks have northwest- southeast strike with moderate to steep dips. Liniations mostly show west to northwest trend with low to medium plunge. Obtained shear sence from outcrop and thin-sections studies, shows reverse mechanism with dextral component for the shear zones. Deformation mechanisms in ductile shear zones include mechanical twining, recovery, dislocation creep, grain boundary migration recrystalization, and subgrain rotation recrystalization. Regarding these mechanisms, deformation of rocks occurred in green schist metamorphic facies.
Comparison between kinematic analysis of medium scale syn-deformation folds, that have northweat-southeast axis, and kinematic analysis of shear sense obtained from thin-sctions, shows that strain partitioning has occurred during the ductile deformation. Based on field observations and microscopic studies, four main deformational stages are determined:
D1- D2- progresive deformation
D3- deformation
D4- deformation
D1- D2- progresive deformation and it's related structures are synchoronous with main stage of metamorphism in the area. Metamorphic facies (based on metamorphic mineral assemblage) is greenschist to amphibolite. Structures of this stage of deformation include S1 and S2 foliations, L1 and L2 liniations, isoclinal rootless folds, sheath folds, deformed veins, boudins and ductile shear zones. This stage of deformation can be considered as a result of the Early Cimmerian orogenic phase. S2 mylonitic foliation is predominant foliation in the field. Shear zones are mostly ductile to brittle-ductile. D3 deformation is accompanied by retrograde trend of metamorphic conditions and reduction of deformation intensity. Evidences of this stage of deformation are observed as crenulation cleavage and crenulation liniations. D4 deformational stage occurred in a respectly brittle condition and resulted in production of kink bands and reverse faults. Vergence of thes faults mostly are to south and southwest. Contact metamorphism is distingushed with forming of mica mineral and post- tectonic skeleton crystals of garnet and staurolite, andalusit around plutons and static recrystalization of qurtz grain forming S2 foliation. Considering to granites ages and folding of mylonitic foliation around the plutons, it is supposed that the intrusion time is syn to post early Cimmerian regional metamorphism.

Subject List : Structural analysis