Introduction of meta-harzburgites using Contact originated Minerals in the Gishaki ophiolitic area, as a part of Iranian Alpine type ophiolites

In this paper, we investigated two originated metamorphosed harzburgites of the metaperidotite complex from the northern part of the Gishaki area. Harzburgite rocks, as main ultramafic complexes of the studied area, have outcrops in the scattered locations of the area. Harzburgitic units were discriminated using petrography and Raman spectroscopy. There are two meta-harzburgite types based on the metamorphic history of their protholites with different mineralogy types. Normal metamorphosed harzburgites (N-Hz) are metamorphosed via phases of retrograde processes and contact metamorphosed harzburgites (C-Hz) metamorphosed visa some different phases containing contact metamorphism. One of the best clues that are different in these two rock types is Antigorite mineral characteristics. Antigorite polymorphs have structural and chemical sensitive characteristics that can discriminate using Raman spectroscopy. It had certain specific chemical differentiation compared with other serpentine polymorphs especially in Silica and molecular water contents. Reviewed antigorites illustrated general differentiations in themselves so that polymorphs hosted by C-HZ rocks could be considered as a group with typical Contact antigorite by geochemical criteria such as lower molecular water, higher Octahedral content and, higher Silica content. An increase in Si and Fe2+ activities cause incurrences octahedral substitutions as temperature-dependent phenomena in Contact antigorites. Diagrams of Silica versus molecular water contents and octahedral contents clearly distinguished modified antigorites from former antigorite polymorphs. Contact antigorite in the Gishaki serpentinites could be considered as metamorphosed products related to metamorphic aureoles.