Alkaline Rocks and Carbonatites of the World

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Gedemsa (Gadamsa)

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Occurrence number: 
054-00-040
Country: 
Ethiopia
Region: 
Main Ethiopian Rift
Location: 
Longitude: 39.17, Latitude: 8.37

Gedemsa is an 8 km diameter caldera located immediately east of Lake Koka. The geology is clearly depicted on a 1:50,000 geological map of the Nazret-Dera region (Alula et al., 1992). The caldera contains eight pantelleritic and comenditic lava domes a number of which also occur around the caldera. These rocks contain phenocrysts of sanidine, quartz, oligoclase, aegirine-augite and sodic amphibole. There are extensive pantelleritic pumice fall deposits and welded ignimbrites around the caldera with a similar mineralogy to the domes but containing also clasts of basaltic rock.

References: 
ALULA, D., BOCCALETTI, M., GETANEH, A., MAZZUOLI, R., TORTORICI, L. and TRUA, T. 1992. Geological map of the Nazret-Dera region (Main Ethiopian Rift). Consiglio Nazionale delle Ricerche, Ministero degli Esteri, Direzione Generale Cooperazione allo Sviluppo.
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