Investigations on amphibole origin in olivine-bearing hornblende gabbros from NW of Salmas; NW Iran

Amphiboles in olivine-bearing hornblende- gabbros from NW of Salmas were crystallized in various textures including oikocryst and interstitial textures in the matrix, outer part of reaction rims around olivine, and at the rim and cleavages of clinopyroxene. On the basis of petrographical and textural studies, amphiboles were formed later than the other minerals in the olivine-bearing hornblende- gabbros. The REE and trace element composition of amphiboles from two different textures including interstitial and matrix amphiboles (group one) and amphiboles after clinopyroxenes (group two), indicate that the studied amphiboles were formed by either crystallization of interstitial melt/fluid or interaction of interstitial melt/fluid with early crystalized minerals such as clinopyroxene and plagioclase. Hence, according to the textural and mineralogical data and trace element composition of amphiboles, olivine-bearing hornblende- gabbros were crystallized at least at two stages. The first stage include fractional crystallization and formation of olivine, clinopyroxene and plagioclase and the second stage was interaction of the relict melt/fluid with early crystalized minerals, specially clinopyroxene and plagioclase and formation of amphibole