Dereje Ayalew

By Dereje Ayalew, David Pyle and David Ferguson

We report field observation, textural description (thin section and scanning electron microscope (SEM)) and mineral chemistry (backscattered electron imaging and dispersive X-ray analysis) for rhyolitic obsidian lavas from previously under described effusive Badi volcano, central Afar within the Ethiopian rift. These rhyolitic obsidian lavas are compositionally homogeneous and contain well developed flow bands. Textural analysis is undertaken to understand the formation of flow band, and to draw inferences on the mechanism of emplacement of this silicic volcano. Flow band arises from variable vesicularity (i.e., alternating domains of vesicular, light glass and non-vesicular, brown glass). Such textural heterogeneities have been developed during distinct cooling and degassing of the melt in the conduit.

Part of the book: Progress in Volcanology

By Dereje Ayalew and Bekele Abebe

The presented paper described in detail the mineralogy of silicic peralkaline eruptives from Kone volcano within the Ethiopian rift system, which is formed predominantly by rhyolite with some small occurrence of trachyte. The majority of eruptive rocks in the Kone volcanic area are phenocryst-poor. The studied rocks contain alkali feldspars (anorthoclase and sanidine), quartz, clinopyroxene (hedenbergite), aenigmatite and olivine (fayalite), accompanied by rare Fe-To oxides (ilmenite) and apatite. All these minerals are described in detail. These data are very interesting for all researchers, who study similar eruptive rocks.

Part of the book: Mineralogy