Petrology
Mahin Hashemi; Nahid Shabanian; Alireza Davoudian; Hossein Azizi
Abstract
Estimation of temperature- pressure deformation path for metamorphic rocks experiencing a complex deformation history commonly rely on the relationship between successive metamorphic assemblages and different microstructures that remain. However, by changing the temperature-pressure conditions, metamorphic ...
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Estimation of temperature- pressure deformation path for metamorphic rocks experiencing a complex deformation history commonly rely on the relationship between successive metamorphic assemblages and different microstructures that remain. However, by changing the temperature-pressure conditions, metamorphic minerals with a microstructure, which are specific to those conditions, can be chemically re-equilibrate. Mylonitic paragneisses around the lake of Zayandehrood Dam, have range low-grade to medium-grade mylonites. According to petrographic and microstructural studies, we define at least three stages of metamorphism and deformation. The first stage metamorphism (the earliest recognizable metamorphic stage) took place during eclogite facies conditions. At this stage, high pressure minerals such as rutile, phengite, garnet and alkali-feldspar formed that enclosed in garnet or feldspar, and or located in matrix. These hosted garnets and feldspars based on the evidence of petrography formed at the amphibolite facies condition. Eventually a retrograde metamorphism took place in the lower green schist facies condition, That's evidence includes the sericitization of some feldspars, the chloritization of some biotite, and the formation of cholorite and quartz in and around some garnets. contemporaneous whit these retrograde processes, there is evidence of a relatively high temperature to low temperature deformation microstructure. The combination of evidences of metamorphism and deformation results is that these rocks have risen from relatively high depths, which during the rising stages undergone the various metamorphism condition, and many deformations have affected on this collection.
