Origin of the pleonaste-bearing mafic–ultramafic rocks from the Armutlu peninsula, NW Turkey

Authors : Mutlu ÖZKAN, Ömer Faruk ÇELİK

Pages : 167-190

View : 15 | Download : 6

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :Al-rich spinels were rarely reported compared to Cr-spinels, which were mostly observed in ophiolitic rocks. Pleonaste [insert ignore into journalissuearticles values(Mg, Fe 2+ );Al 2 O 4 ], which is an Al-rich spinel, was observed in the ophiolitic mafic-ultramafic rocks tectonically located in the Early Cretaceous accretionary complex, at the eastern part of the Armutlu peninsula, NW Turkey. The ophiolitic mafic-ultramafic rocks have cumulate character, and most of them are represented by peridotite and pyroxenite. Pleonaste was observed in pyroxenites and gabbros of the ophiolitic rocks. Pyroxenites consist mainly of clinopyroxene + orthopyroxene + amphibole ± olivine + spinel. Gabbros are composed of clinopyroxene + orthopyroxene + amphibole + plagioclase + spinel. Pleonaste in these rocks lies parallel to the magmatic layers and is distinguished by its emerald greenish color under the microscope. Pleonastes have high Al 2 O 3 insert ignore into journalissuearticles values(59.65-62.24 wt.%); and low Cr 2 O 3 insert ignore into journalissuearticles values(0.05-1.32 wt.%); contents with Mg# and Fe 3+ # ranging from 54.23 to 59.77 and 3.83 to 4.28, respectively. Petrographical observations and the pressure?temperature insert ignore into journalissuearticles values(P-T); pseudosection modelling suggest that pleonaste in the mafic-ultramafic rocks from the study area crystallized during magmatic processes. Presence of amphibole and Ca-rich insert ignore into journalissuearticles values(An % 85-88); plagioclase in these rocks suggests that the ophiolitic rocks, located in the Early Cretaceous accretionary complex at the eastern part of Armutlu peninsula, formed from an arc-related hydrous magma source.
Keywords : Cumulate, ophiolite, pseudosection models, pyroxenite, spinel