THE YERER-TULLU-WELLEL VOLCANOTECTONIC LINEAMENT - A TRANSTENSIONAL STRUCTURE IN CENTRAL ETHIOPIA AND THE ASSOCIATED MAGMATIC ACTIVITY

An east-west trending structure in central Ethiopia, the Yerer Tullu-W ellel volcanotectonic lineament, intersects the Main Ethiopian Rift an d lies between latitudes 8 degrees 20'N and 9 degrees 05'N. Interpreta tion of Landsat images, calibrated by field study, indicates the relat ive chronology of the observed fracture systems (northeast-southwest, east-west, north-south and northwest-southeast). Along this structure there are several central volcanoes concentrated along the latitude of 8 degrees 45'N. Most of these volcanoes have basic lava flows at thei r base with acid dome, plug, and/or pyroclastic deposits as their evol ved end members. The chemistry of these volcanic rocks shows a progres sive decrease in alkalinity and silica undersaturation from western ar eas towards the rift margin. Radiometric ages of these volcanoes range from 12 Ma to Recent and indicate that the volcanic activity shifted eastward in time. The central volcanoes are usually located at the int ersections of the above described fracture systems. The role of the tr anstensional Yerer Tullu-Wellel volcanotectonic lineament since Late M iocene times is discussed within the geodynamic evolution of the Main Ethiopian Rift. (C) 1998 Elsevier Science Limited.