319 ISSN 0016-8521, Geotectonics, 2017, Vol. 51, No. 3, pp. 319–330. © Pleiades Publishing, Inc., 2017. Deformation Condition Determination and Strain Analysis: Application of Microstructural and Microthermometry Study of the Zamanabad Shear Zone (East of Iran) 1 S. Abbasi*, M. R. Heyhat, E. Gholami, and M. H. Zarrinkoub Department of Geology, University of Birjand, Birjand, Iran *e-mail: s.abbasi@birjand.ac.ir Received June 14, 2016 Abstract⎯Microstructural analysis and microthermometry are useful methods for determining the deforma- tion evolution. To address this issue, rheological behavior of quartz, feldspar and calcite in veins and host rocks during deformation, are presented in the mylonite zone of the dextral reverse Zamanabad Shear Zone (ZSZ), in northern part of Sistan Suture Zone (SSZ), in east of Iran. Microstructure evidences revealed two evolution stages of high and low temperature deformation. Quartz microstructures in the ZSZ show abundant evidences for early high-temperature plastic deformation (e.g. Bulging recrystallization (BLG)) which are as microstructures with SW directed ductile shearing in the central parts of the ZSZ. This shear zone shows progressively decreasing strain away from the central of shear zone toward the wall. High-temperature micro- structures are overprinted partly or completely during shearing by the later low-temperature deformation (e.g. Pressure solution, fractures, veinlets). Microstructural observations of veins (quartz and calcite) con- firms the results of microstructures in the host rock, as quartz veins occurred from peak metamorphic con- ditions (<400°C) and then in lower P–T conditions have been formed calcite veins (~250°C). According to microthermometric studies, two primary f luid groups are observed in quartz veins: (1) f luids trapped during peak deformation conditions, with higher-salinity, They were initially trapped at ~300–400°C, (2) smaller fluids by trapping of low-salinity inclusions at ~240–180°C that related to subsequent phases of shear zone exhumation in lower deep. Microthermometry results and microstructural analysis indicate deformation under lower greenschist facies conditions for the ZSZ, and then exhumation of the early of high-temperature rocks within regime of ductile-brittle transition to brittle. Keywords: Zamanabad Shear Zone, microstructure, microthermometry, exhumation DOI: 10.1134/S0016852117030025 INTRODUCTION Sistan Suture Zone (SSZ) of eastern Iran has spread as a north-south belt with a length of more than 700 kilometers along the margin of Lut and Afghan blocks (Fig. 1) [6, 10, 41, 53, 61, 73]. This zone records a remnant of oceanic lithosphere (Sistan Ocean), fly- sch-facies sediments, volcanic and volcanoclastic rocks, and molasse-facies sediments from the Creta- ceous to Quaternary [1, 6, 53]. The presence of Nehbandan fault system in the border of SSZ and Lut block has caused severe defor- mation of rock units in the margin and inside the SSZ. Nehbandan fault system with dextral strike-slip mech- anism and the general of N–S trend has splays in northern and southern parts. The northern splays of this fault have shifted towards the west and in southern part has shifted towards the East. Birjand ophiolite with an E–W trend is one of the northern isolated splays in north part of SSZ [27]. The relationship between various rock contacts in this ophiolitic com- plex is obscured by intense brittle and ductile shearing during mélange formation [71, 72]. Deformation of the Earth’s crust and mantle is often powerfully localized in such shear zones [9, 25, 36, 37, 49, 50, 54, 55]. Ductile shear zones localize deformation in much of the Earth, except the upper few kilometers in which frictional processes is domi- nated [49]. An important part of understanding the evolution of this ductile shear zones is associated with studying thin sections and interpretation of micro- structure of deformed rocks and exhumed in their width and length that can offer information about the stress changes, strain rate, temperature and the mech- anism of deformation over time [3, 12, 22, 29–31, 40, 59, 60, 62, 67]. The study and interpretation of micro- structures in minerals such as quartz, feldspar and cal- cite can be very useful due to their abundance in the earth’s crust and recording plastic intracrystalline 1 The article is published in the original.