Mantle transition zone structure and upper mantle S velocity variations beneath Ethiopia: Evidence for a broad, deep-seated thermal anomaly

被引:58
作者
Benoit, Margaret H.
Nyblade, Andrew A.
Owens, Thomas J.
Stuart, Graham
机构
[1] Penn State Univ, Dept Geosci, University Pk, PA 16801 USA
[2] Univ S Carolina, Dept Geol Sci, Columbia, SC 29201 USA
[3] Univ Leeds, Sch Earth & Environm, Leeds LS2 9JT, W Yorkshire, England
关键词
Ethiopia; Afar; mantle plume; superplume; seismology : mantle (1212,1213,8124); tectonophysics : dynamics of lithosphere and mantle : general (1213); tectonophysics : dynamics : convection currents; and mantle plumes;
D O I
10.1029/2006GC001398
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
[1] Ethiopia has been subjected to widespread Cenozoic volcanism, rifting, and uplift associated with the Afar hot spot. The hot spot tectonism has been attributed to one or more thermal upwellings in the mantle, for example, starting thermal plumes and superplumes. We investigate the origin of the hot spot by imaging the S wave velocity structure of the upper mantle beneath Ethiopia using travel time tomography and by examining relief on transition zone discontinuities using receiver function stacks. The tomographic images reveal an elongated low-velocity region that is wide (> 500 km) and extends deep into the upper mantle (> 400 km). The anomaly is aligned with the Afar Depression and Main Ethiopian Rift in the uppermost mantle, but its center shifts westward with depth. The 410 km discontinuity is not well imaged, but the 660 km discontinuity is shallower than normal by similar to 20 - 30 km beneath most of Ethiopia, but it is at a normal depth beneath Djibouti and the northwestern edge of the Ethiopian Plateau. The tomographic results combined with a shallow 660 km discontinuity indicate that upper mantle temperatures are elevated by similar to 300 K and that the thermal anomaly is broad (> 500 km wide) and extends to depths >= 660 km. The dimensions of the thermal anomaly are not consistent with a starting thermal plume but are consistent with a flux of excess heat coming from the lower mantle. Such a broad thermal upwelling could be part of the African Superplume found in the lower mantle beneath southern Africa.
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页数:16
相关论文
共 59 条
[1]  
AYALEW D, 2002, GEOPHYS J, V36, P409
[2]   A brief Oligocene period of flood volcanism in Yemen: Implications for the duration and rate of continental flood volcanism at the Afro-Arabian triple junction [J].
Baker, J ;
Snee, L ;
Menzies, M .
EARTH AND PLANETARY SCIENCE LETTERS, 1996, 138 (1-4) :39-55
[3]   Upper-mantle seismic structure in a region of incipient continental breakup: northern Ethiopian rift [J].
Bastow, ID ;
Stuart, GW ;
Kendall, JM ;
Ebinger, CJ .
GEOPHYSICAL JOURNAL INTERNATIONAL, 2005, 162 (02) :479-493
[4]   Upper mantle P-wave speed variations beneath Ethiopia and the origin of the Afar hotspot [J].
Benoit, MH ;
Nyblade, AA ;
VanDecar, JC .
GEOLOGY, 2006, 34 (05) :329-332
[5]   PHASE-TRANSITION CLAPEYRON SLOPES AND TRANSITION ZONE SEISMIC DISCONTINUITY TOPOGRAPHY [J].
BINA, CR ;
HELFFRICH, G .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 1994, 99 (B8) :15853-15860
[6]   UPPER-MANTLE STRUCTURE OF THE NORTHERN CASCADIA SUBDUCTION ZONE [J].
BOSTOCK, MG ;
VANDECAR, JC .
CANADIAN JOURNAL OF EARTH SCIENCES, 1995, 32 (01) :1-12
[7]  
Burke K, 1996, S AFR J GEOL, V99, P341
[8]  
CHERNET T, 1999, ACTA VULCANOL, V11, P21
[9]   Global-scale analysis of the mantle Pds phases [J].
Chevrot, S ;
Vinnik, L ;
Montagner, JP .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 1999, 104 (B9) :20203-20219
[10]  
COULIE E, 2003, EARTH PLANET SC LETT, V200, P292