caa a22 4500 477064647 CHVBK 20180405111409.0 cr unu---uuuuu 170330e19960601xx s 000 0 eng 10.1007/BF02422243 doi (NATIONALLICENCE)springer-10.1007/BF02422243 Wolde B. Department of Geology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia aut Spatial and temporal variations in the compositions of Upper Miocene to Recent basic lavas in the northern main Ethiopian rift: Implications for the causes of Cenozoic magmatism in Ethiopia [Elektronische Daten] [B. Wolde] The rate of lithospheric extension has previously been suggested as the most important factor governing the compositions of magmas generated in the Cenozoic Ethiopian volcanic province (CEVP). However, the distribution and chemistry of volcanic rocks extending from the western plateau margin at Addis Ababa to the rift floor in Nazret, northern sector of the main Ethiopian rift (MER), suggest that transitional magmatism in the region may have been triggered by an increase in the amount of lithospheric extension in the Early Pliocene. The rocks occur across an area of variable crustal thickness and show a general age progression from Upper Miocene (≤9 Ma) to Recent toward the rift. Alkalic basalts are extensive in the western part of the rift and along its margin but are found only locally within the rift, whereas transitional basalts are found within the rift only. Both types of basalts appear to have been derived from a common mantle source. In contrast, alkalic and transitional basalts on the Ethiopian plateau are mutually exclusive in terms of their spatial distribution, but exhibit a compositional contiguity which suggests that transitional magmas on the plateau formed at the expense of alkalic magmas, i.e. by equilibration of alkalic magmas at relatively shallow depth. The alkalic basalts bear clear record of a decrease in the degree of partial melting with time, suggesting that magmatism on the plateau was possibly triggered by a transient thermal anomaly. Springer-Verlag GmbH & Co KG, 1996 Main Ethiopian rift nationallicence Transitional basalt magmatism nationallicence Lithospheric extension nationallicence Plateau magmatism nationallicence Thermal anomaly nationallicence Geologische Rundschau Springer-Verlag 85/2(1996-06-01), 380-389 0016-7835 85:2<380 1996 85 531 https://doi.org/10.1007/BF02422243 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF02422243 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Wolde B. Department of Geology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia aut NATIONALLICENCE 773 0- Geologische Rundschau Springer-Verlag 85/2(1996-06-01), 380-389 0016-7835 85:2<380 1996 85 531 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer