Mineralogy and genesis of serpentine group minerals in serpentinites of the Baft ophiolite mélange in Kerman province

Three types of serpentine polymorphs (lizardite, chrysotile and antigorite) are found in serpentinites from the Baft ophiolite mélange which are different in the textural features and chemical compositions. Lizardite is seen as layered structures that set in the matrix of peridotites, while antigorite is formed in veins or sheared zones as blade crystals and chrysotile develops as shiny and golden fibers in small cracks. The studied peridotites, based on degree of serpentinization, can be divided into three subdivisions including relatively serpentinized peridotites (up to 50 vol. % serpentinization), mainly serpentinized peridotites (50-90 vol. % serpentinization) and completely serpentinized peridotites (90-100 vol. % serpentinization). We suggested three models for serpentinization of olivine in this area. First model contains serpentinization of olivine grain boundaries with unaltered centers. The process has developed in relatively serpentinized peridotites. Second model includes redeveloping serpentinization of inherited olivine grains from the first model and third model contains complete serpentinization of olivine grains. Second and third models have been developed in mainly and completely serpentinized peridotites. It seems that involved lizardite and chrysotile are the result of static alteration in an ocean floor like environment, while interpenetrative-blade antigorites have been produced by dynamic metamorphism. Production of antigorite can be related to subduction of Nain-Baft oceanic crust or it can be related to obduction of serpentinized pridotites in other times, it is possible that lizardite and chrysotile have formed before closure of Nain-Baft Small Ocean.