Petrological aspects of the Bayazeh Paleozoic ophiolite (Central Iran); Implications for Paleo-Tethys subduction

Abstract

The Paleozoic Bayazeh ophiolite is situated in the western part of the Central-East Iranian Microcontinent (CEIM). This ophiolite consists of serpentinized peridotite, metagabbro, metapicrite, serpentinite and amphibole-bearing listwaenite, which are covered by schists and marbles. Serpentinites in the Bayazeh ophiolite are produced by serpentinization of a mantle protolith. The composition of primary chromian spinel cores (with average content of Cr~9.9, Mg~4.3, Ti< 0.01 and Fe3+<0.5 apfu) in the Bayazeh serpentinites suggests an origin from high degrees of partial melting of a depleted harzburgite source in a supra-subduction zone setting. The texture and mineral assemblage of amphibole-bearing listwaenites and their association with serpentinites indicate that the studied listwaenites were generated by prograde metamorphism under upper greenschist to lower amphibolite facies conditions from a carbonated serpentinite. Geochemical characteristics of the Bayazeh metagabbros, indicate high value of large ion lithophile elements, high content of light rare earth elements, low HREE fractionations [e.g. (Gd/ Yb)CN=0.95-1.21], low contents of high-field strength elements and large variation of the LILE/HFSE ratios (e.g. Sr/Sm=47.83-564.67). These compositions are similar to cumulate gabbros and point to a possible role of melts from a lithospheric mantle and effect of fluids derived from the subducted slab in their formation. Mineralogical characteristics (e.g. presence of primary hydrous minerals such as phlogopite up to 10 vol%) and chemical composition of the Bayazeh metapicrites suggest derivation from a metasomatized asthenospheric mantle. Metasomatic enrichment of the mantle source probably occurred by fluids released during subduction of the Paleo-Tethys Ocean beneath the Central Iran. Subduction of the Paleo-Tethys from the Early to the Late Paleozoic is the cause of volatile enrichment and mantle metasomatism in the western part of the Central-East Iranian Microcontinent. © 2019 Edizioni Nuova Cultura. All rights reserved.