Reconstruction of deformation and metamorphism history in the Bultaq shear zone (Central part of Sanandaj-Sirjan zone)


1 Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran

2 دانشگاه اصفهان- دانشکده علوم - گروه زمین شناسی


The Bultaq shear zone is located 185 km north-west of Isfahan. The study area is a part of the Sanandaj–Sirjan zone, which is affected by ductile and brittle–ductile deformation and consists of slate, schist(garnet-muscovite schist, enriched quartz-muscovite schist and biotite-muscovite schist), amphibolite marble, metavolcanic, andesite and tuff. There are several duplex structures and thrusts with NW-SE-trend and NE dip in the Bultaq shear zone. This shear zone is parallel to the Zagros Organic thrust. Also, boudinage structures geometric analysis, mesoscopic scale asymmetric folds, microscopic studies of S-C, S-Ć cleavages and σ- type porphyroclast confirmed right-lateral strike-slip movement. These fabrics show right rounded cuts in region in some parts. Mylonitic foliations were used to calculate elongation (e) and stretch (s) in this area. The microstructures were formed under green schist to amphibolite facies conditions. The metamorphic rocks have been formed in a Barrovian metamorphism type (medium temperature - pressure) and affected by three metamorphic and deformation phases. The metamorphic phases include dynamothermal, dynamic and retrograde and the deformation phases are D1, D2 and D3.