Structure of the Ethiopian lithosphere; xenolith evidence in the main Ethiopian Rift

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doi: 10.1016/j.gca.2005.03.043
Authors:Rooney, Tyrone O.; Furman, T.; Yirgu, G.; Ayalew, D.
Author Affiliations:Primary:
Pennsylvanian State University, Department of Geosciences, University Park, PA, United States
Addis Ababa University, Ethiopia
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 69(15), p.3889-3910. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:2005
Note:In English. 101 refs.; illus., incl. 1 plate, 6 tables, sketch map
Summary:The lithospheric and sublithospheric processes associated with the transition from continental to oceanic magmatism during continental rifting are poorly understood, but may be investigated in the central Main Ethiopian Rift (MER) using Quaternary xenolith-bearing basalts. Explosive eruptions in the Debre Zeyit (Bishoftu) and Butajira regions, offset 20 km to the west of the contemporaneous main rift axis, host Al-augite, norite and lherzolite xenoliths, xenocrysts and megacrysts. Al-augite xenoliths and megacrysts derived from pressures up to 10 kb are the dominant inclusion in these recent basalts, which were generated as small degree partial melts of fertile peridotite between 15 and 25 kb. Neither the xenoliths nor the host basalts exhibit signs of carbonatitic or hydrous (amphibole + phlogopite) metasomatism, suggesting that infiltration of silicate melts resulting in pervasive Al-augite dyking/veining dominates the regional lithospheric mantle. Recent geophysical evidence has indicated that such veining/dyking is pervasive and segmented, supporting the connection of these Al-augite dykes/veins to the formation of a proto ridge axis. Al-augite xenoliths and megacrysts have been reported in other continental rift settings, suggesting that silicate melt metasomatism resulting in Al-augite dykes/veins is a fundamental processes attendant to continental rift development. Abstract Copyright (2005) Elsevier, B.V.
Subjects:Basalts; Cenozoic; Characterization; Continental crust; Crust; Dikes; Eruptions; Flood basalts; Geochemistry; Geologic barometry; Geologic thermometry; ICP mass spectra; Igneous rocks; Inclusions; Intrusions; Large igneous provinces; Lava; Lherzolite; Lithosphere; Mafic composition; Major elements; Mantle; Mass spectra; Megacrysts; Melts; Metasomatism; Mineral composition; Peridotites; Petrography; Plate tectonics; Plutonic rocks; Pressure; Quaternary; Rift zones; Rifting; Silicate melts; Spectra; Trace elements; Ultramafics; Upper mantle; Veins; Volcanic rocks; Volcanism; Xenoliths; Addis Ababa Ethiopia; Africa; East Africa; Ethiopia; Ethiopian Rift; Bishoftu Ethiopia; Butajira Ethiopia; Debre Zeyit Ethiopia
Coordinates:N090300 N090300 E0384200 E0384200
Abstract Numbers:05M/3309
Record ID:2006035972
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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