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Title:
The Afar Depression: Was There a Triple Junction Above the Mantle Plume?
Authors:
Ebinger, C.; Wolfenden, E.; Yirgu, G.; Ayalew, D.; Eagles, G.; Gloaguen, R.; Tiberi, C.; Rowland, J. R.; Deino, A.; Tesfaye, A.; Tesfaye, S.
Affiliation:
AA(Royal Holloway, U of London, Department of Geology, Egham, TW20 0EX United Kingdom ; ), AB(Royal Holloway, U of London, Department of Geology, Egham, TW20 0EX United Kingdom ; ), AC(Addis Ababa University, Department of Geology and Geophysics, Addis Ababa, A1 Ethiopia ; ), AD(Addis Ababa University, Department of Geology and Geophysics, Addis Ababa, A1 Ethiopia ; ), AE(AWI Polar and Marine Research, Postfach 120161, Bremerhaven, D-27515 Germany ; ), AF(Royal Holloway, U of London, Department of Geology, Egham, TW20 0EX United Kingdom ; ), AG(Royal Holloway, U of London, Department of Geology, Egham, TW20 0EX United Kingdom ; ), AH(University of Auckland, Department of Geology, Auckland, A1 New Zealand ; ), AI(Berkeley Geochronology Center, 2255 Ridge Road, Berkeley, CA 94709 United States ; ), AJ(Addis Ababa University, Department of Geology and Geophysics, Addis Ababa, A1 Ethiopia ; ), AK(Lincoln University, Department of Geology, Jefferson City, MO 63017 United States ; )
Publication:
American Geophysical Union, Fall Meeting 2002, abstract #S11A-1129
Publication Date:
12/2002
Origin:
AGU
AGU Keywords:
8109 Continental tectonics: extensional (0905), 8121 Dynamics, convection currents and mantle plumes, 8155 Plate motions: general, 8434 Magma migration
Abstract Copyright:
(c) 2002: American Geophysical Union
Bibliographic Code:
2002AGUFM.S11A1129E

Abstract

The Red Sea - Gulf of Aden- Main Ethiopian rift systems (Afar Depression) have served as the textbook example of a R-R-R triple junction zone which formed above a mantle plume (Ethiopia-Yemen flood basalt province, 31-28 Ma). Recent work has documented the onset and propagation of seafloor along the length of the Gulf of Aden and Red Sea arms, but the timing of continental rifting had been poorly constrained. Our aims were to constrain the timing of rift initiation in each arm of the rift near the proposed Oligocene triple junction and to re-assess models for break-up above a mantle plume. Although much of the early history of rifting is deeply buried by Pliocene-Recent lavas, erosional dissection of the rift margins provides windows into the early rift history. Along the southernmost Red Sea, faults commonly marked by eruptive centers initiated at about 26 Ma, coincident with rifting along the easternmost Gulf of Aden. New data from the rift immediately south of the southernmost Red Sea basin (ca.10N) constrain the earliest rift sequences in the northern Main Ethiopian rift (MER). Field and Ar-Ar data from sequences overlying the pre-rift flood basalts show that extension in the northern MER commenced at 12-10 Ma when the two rift systems were finally linked. The active zone of extension and magmatism in the southern Red Sea and eastern Gulf of Aden, however, had migrated east and north, respectively. Summarising, rifting in southern Ethiopia had commenced by 16-18 Ma, and had propagated northward to cut across Oligo-Miocene rift structures of the Red Sea and Gulf of Aden by 10 Ma, consistent with plate kinematic data. A triple junction could have developed only during the past 10 My, long after flood basaltic magmatism. Inverse models of gravity data predict a significant step (2-4 km) in the Moho where the youthful, less extended MER breaks into the Afar Depression. Project EAGLE (UK-US-Ethiopia) is now acquiring seismic data across and along this zone to evaluate mechanisms for rift segmentation and propagation prior to breakup.
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