Chromespinel and Magnetite as Indicators for Recognition of Genesis and History of Serpentinites in Baft Ophiolite Mélange (Kerman Province in Iran)

Baft ophiolite mélange is a part of Naein-Baft ophiolite (southeast of Kerman province in Iran). Serpentinites from Baft ophiolite mélange contain different types of spinels such as chromite, chromespinel, ferritchromite and magnetite which can reveal different stages of evolution in host serpentinites. The compositions of Baft chromites show that they belong to podiform chromitites that may have crystallized from boninitic magmas. It seems that the Baft chromitite ores initially have been formed in a primary ophiolitic complex within dunitic envelopes; In the next stage, due to serpentinization of the peridotites and ascending of the resulted serpentinite, the studied deposits have been emplaced along the shear zones of the Baft ophiolitic melange. The compositions of primary Cr-spinels show that the Baft ophiolite has been formed in a suprasubduction zone in an arc/back-arc environment and the host rocks represent serpentinized Alpine type mantle residual peridotites. These studies suggest that the first serpentinization has taken place in an ocean floor environment and in this stage, mesh-textured serpentinites formed under static conditions. Then, the main serpentinization occurs and Cr-spinels have progressively replaced by ferritchromite rims, probably due to regional metamorphism. It seems that in the studied area, flare-textured serpentinites have passed higher temperature and pressure, and their formation can be related to dynamic evolutions such as subduction of Naein-Baft oceanic slab beneath the central Iranian microcontinent. Probably, the formation of magnetite fibers (type II) have accompanied by deformation process, while idiomorphic magnetites (type I) have produced from the passing Fe-rich fluids.