ABSTRACT Serpentinizedperidotites are a part of the coloured mélange complex in the Salmas area. The serpentinization degree of peridotites is variable. Mesh and bastite textures (pseudomorphic textures after olivine and pyroxene respectively) are the dominant textures in these rocks. According to the textural and petrographical studies and XRD analyses, lizardite and low abundant chrysotile are the main serpentine polymorphs in the serpentinizedperidotites. On the basis of mineral chemistry, the composition of serpentines from different textures (mesh or bastite) is variable and depends on the composition of the primary mineral. Presence of lizardite and absence of antigorite in the Salmasserpentinizedperidotites indicate that the serpentinization of peridotites has occurred under low temperature conditions (lower than 200°C). Petrographic studies show that serpentinization of the Salmasperidotites has occurred during several stages. Hydration of olivine and pyroxene (ortho-and clinopyroxene) was the first and main stage. After the main stage of serpentinization, SiO 2 -rich fluids affected the serpentines and talc was formed at the rim of serpentine. Late chrysotile veins crosscut the serpentinite in various directions. Finally, serpentinites were affected by CO 2 rich fluids which lead to formation of low abundant carbonate minerals. KEYWORD Lizardite, chrysotile, serpentinite, serpentinized peridotite, Salmas INTRODUCTION erpentinization is one of the important processes in geology, which results in fundamental changes to the petrophysical[1, 2] geochemical [3] and rheological [4,5,6] of the oceanic crust and peridotites. Serpentinization can occur in different tectonic settings such as mid-ocean ridge [7, 8], subduction zone [9,10] and the mantle wedge [11]. Study of textures formed during serpentinization provides useful information on evolution of serpentinized *Corresponding Author: Masoumeh Ahangari E-mail: m.ahangari@urmia.ac.ir Telephone Number: 09143484115 peridotites. For instance, serpentinization due to expansion, rock-fluid interaction and deformation is usually accompanied by formation of different veins and veinlets. The study of such veins with different textures in the serpentinized peridotites can reveal the history of the rocks during serpentinization e.g.[12,13].The recent studies have highlighted the importance of serpentinites in geodynamics of the subduction zones [14,17]. These rocks contain ~13% water, which are the main water carrier of the subducting lithosphere into the mantle[18]. We have studied the serpentinizedperidotites from the Salmas area in NW Iran in this contribution. Using petrological and textural features along with chemistry of the studied rocks, different phases affected the rocks during serpentinization are determined. This can be used to decipher the evolutionary history of these rocks in this part of the earth crust. Geological Setting The study area is located at the south of Salmas town in west Azerbaijan province of NW Iran (Fig. 1a). This area is located at the junction of the Sanandaj-Sirjan and the Central Iran geological zones [19]. However, the geological position of the study area, in the geology of Iran is not certain and different researchers have attributed it to different zones [20,21,22,23]. Rocks types outcropped in this area cover a wide variety including different types of metamorphic, igneous and sedimentary rocks ranging in age from Precambrian to Quaternary (Fig. 1b). The "Coloured Mélange" complex of the area is a mixture of serpentinized ultramafic rocks, mafic rocks (gabbro, diabase and basalt), diorite and andesite and metamorphic rocks including greenschist and amphibolite (with diorite and gabbro protolith). Deep ocean sedimentary rocks of pelagic limestone and radiolarian cherts are other constituents of the "Coloured Mélange". This complex is bounded by faults. The stratigrphical relations of this complex with the other rock units of the area are not clear. The time of formation of he mélange is considered to be Upper Cretaceous to Paleocene [24]. Serpentinization of peridotites from the Salmas area,NW Iran; textural and mineralogical studies Masoumeh Ahangari *1 , Mohssen Moazzen 2 and Robab Hajialioghli 3 1 Department of Geology, Faculty of Sciences, Urmia University 2 Department of Earth Sciences, Faculty of Natural Sciences, University of Tabriz, Doctor of Petrology 3 Department of Earth Sciences, Faculty of Natural Sciences, University of Tabriz S