Developing a Holocene Tephrostratigraphy for Ethiopia

Crynodeb

Explosive eruptions occurred throughout the Ethiopian Rift Valley during the Quaternary, depositing tephras that have provided crucial chronology for archaeological sites in eastern Africa. However, Holocene tephras are largely unstudied and the recent volcanic history of Ethiopia remains poorly constrained.The first < 17 ka regional tephrostratigraphy is presented here, constructed using sediments from seven Ethiopian lakes: Ashenge and Hayk (Ethiopian Highlands), Dendi and Hora (Yerer-Tullu Wellel Volcano Tectonic Lineament,YTVL) and Awassa, Tilo and Chamo (central Main Ethiopian Rift, CMER). A database of 2100 major and trace element single grain glass analyses will aidthe future identification of these tephras at proximal and distal locations. Peralkaline rhyolitic tephras are dominant throughout the Ethiopian Rift. Tephras are more differentiated in the central Main Ethiopian Rift than those deposited in northern Ethiopia. The uniquely phonolitic-trachytic Dendi tephrasare derived from volcanoes on the rift shoulders, where magma evolved under high pressure. Archives from the Ethiopian Highlands record < 17 ka distal volcanism from seven unknown volcanic centres in the Afar Rift. Eruptions occurred every <1000 years between 15:3&#x100000;1:6 cal. ka BP. Different tephras were deposited in lakes Ashenge and Hayk, and they were not dispersed towards lakes further south. Tephras erupted from centres in the CMER are recorded in the Awassa, Tiloand Chamo archives. Glass compositions are indistinguishable from recent Corbetti eruptives. During < 10 ka, eruptions from Corbetti occurred every< 800 years and 6 eruptions were highly explosive. Two tephras are correlated between Tilo and Chamo (170 km SW of Tilo). However, eruptions from Corbettiare not recorded in archives from Ashenge, Hayk and Dendi.These findings demonstrate the potential for further study to construct a comprehensive tephra framework, enabling assessment of regional volcanic hazards. Further geochemical characterisation of regional volcanoes will constrain the sources of these tephras and their petrogenesis

Dyddiad Dyfarnu	22 Medi 2016
Iaith wreiddiol	Saesneg
Sefydliad Dyfarnu	Prifysgol Aberystwyth
Noddwyr	Natural Environment Research Council
Goruchwyliwr	Henry Lamb (Goruchwylydd) & Nicholas Pearce (Goruchwylydd)