X-Ray And Electron Microprobe Analysis Of Some Plagioclases From The Jabal Abu Safiyah Intrusion

Abstract

The Jabal Abu Safiyah is a layered intrusion, which was emplaced within volcanosedimentary rocks. It extends in an arc for about 15 km and displays clear layering. The lower zone plagioclases were studied by electron microprobe and X-ray diffraction techniques to investigate their chemistry and structural state. Cumulus plagioclase forms the dominant phase in all thin sections studied, except in the amphibolized clinopyroxenite. Cumulus plagioclases from the lower zone of the Jabal Abu Safiyah intrusion have a slightly ordered structural state. It is suggested that the structural state of these plagioclases was formed during sub-solidus crystallization at intermediate temperature. The slightly ordered structural state is in good agreement with the petrographic characteristics of the plagioclases studied.