Original paper

Whole rock and relict igneous clinopyroxene geochemistry of ophiolite-related amphibolites from NW Iran Implications for protolith nature

Moazzen, Mohssen; Oberhänsli, Roland

Abstract

Whole rock samples and relict igneous clinopyroxenes in ophiolite-related amphibolites in the Khoy area, from the NW Iran were analysed by XRF and electron probe micro-analyser respectively. Chemistry of clinopyroxene along with whole rock chemistry indicate an alkaline parental magma, formed likely in an oceanic island setting. A fractionation trend of clinopyroxenes on the "pyroxene quadrilateral" is similar to those from alkaline magmas. This trend is controlled by enstatite replacement by ferrosilite during fractional crystallization. The study of variation of major elements in clinopyroxene show that with fractionation increasing (XFe), Si, Ti, Mn and Altotal increase while AlIV content decreases. The studied clinopyroxenes crystallized at moderate oxygen fugacity and the parental alkaline magma was not strongly evolved due to oxidation and was formed more likely as a seamount.

Keywords

alkaline basaltrelict igneous pyroxenesophioliteamphibolitefractionation trendkhoyiran