A proposal funded by the NSF Continental Dynamics Program   6/01/2002

PROJECT SUMMARY
The  dynamic  processes of strain localization, magmatic modification of the crust, and lithospheric heating can be constrained by studies of magmatic continental rifts at the point of break-up.    Although recent progress has been made in understanding the kinematics of continental lithosphere deformation, we lack a geologically consistent perspective and a clear understanding  of  the mechanisms by which the continental lithosphere deforms, the manner in which strain is partitioned (spatially and temporally),  and  the  timing,  composition,  spatial distribution and melting depth of rift-related magmas. These processes control the fundamental architecture of margins and hence the location and magnitude of resources and geologic hazards, and are best studied by a suite of nested and multidisciplinary investigations at various scales. We  will carry out  seismic  experiments,  integrated with geochemical, gravity and structural studies,  to  study  lithospheric  structure  in  one of the rare areas where the transition from continental  rifting  to  incipient  spreading  is  captured  -  the main  Ethiopian  Rift  (MER).    In  the MER the along-axis transition to initial seafloor spreading provides a spatial proxy for temporal variability.  Both continental [fault-dominated]  end-members  and  oceanic  [magma-dominated] rift end-members are well studied; but the transitional stage is not understood. We will document this  critical  transition  from  continental  to oceanic rifting.  Our specific objectives are: (1) to determine detailed crust and mantle structure across and along a transitional rift segment and (2) to understand magmagenesis beneath and within the rift.  We will document the mechanisms by which the East African continental rift propagates and evolves through Ethiopia into Afar and and the Red Sea oceanic rift.  We will obtain crustal P- and S-velocity cross-sections that can be interpreted  for  lithology  across  the  Ethiopian  rift  at  10°N  where  active  magmatic  centers  first appear; and along-strike to the north to study the transition into fully magmatic rifting.  We will interpret existing and new gravity data in light of our new seismic data, and use geochemical data to constrain the physical state of the upper mantle and magmatic inputs to the crust.

US-EAGLE is fully integrated with the funded UK-EAGLE initiative.    Scientists  at Leicester, Leeds and London, have been awarded UK funds to carry out a refraction profile across the Ethiopian rift in January 2003, coupled with local seismicity studies and teleseismic recording.   NSF-CD  funding  will allow us to shoot and record a complementary orthogonal along-axis wide-angle profile; and to shoot fan shots into these linear arrays and the local seismic network to provide a measure of 3D coverage. Together these seismological experiments form a nested, multi-scale seismic image of the Ethiopian rift and plume, and are coupled with geochemical and petrological and gravity studies,  and  structural,  thermochronological and additional gravity studies.  This full range of techniques, though funded by different agencies,  is  bringing  many  individual  scientists  and  different  institutional  capabilities  to  the comprehensive study of a single natural laboratory, in the true spirit of a CD project. Our  multi-disciplinary  project  enables  observation  and  interpretation  at  several  spatial scales.  At  a  ~10  km  scale,  we  will  explore  shallow  magma  chambers  with  seismic  and geochemical studies, constrained by gravity modelling and observation of faults, dikes and local seismicity.  At the crustal scale, our 400-km-long profiles along and across the rift will define crustal thickness and magmatic crustal inputs, the latter further constrained by basalt geochemistry.    At  the  largest  scale,  teleseismic  imaging around the rift will be coupled with our geochemistry to constrain depth to asthenosphere, and potentially  the mantle plume to the core-mantle boundary.
 

For maps, cross-sections and other figures, and for more detailed text, click here
 

Participation by Institution:
USA:        Stanford                    Simon Klemperer
                UT El Paso                Randy Keller & Steve Harder
                Penn State                 Tanya Furman & Andy Nyblade
                SW Missouri State     Kevin Mickus
UK:         Leicester                    Peter Maguire, Aftab Khan
                RHUL (London)        Cindy Ebinger, Mary Fowler
                Leeds                        Graham Stuart, Mike Kendall
                Edinburgh                   Kathy Whaler
Ethiopia:
Addis Ababa University (AAU)      Telahun Mammo, Gezahegn Yirgu, Dereje Ayalew,
                                                      Bekele Abebe, Abera Alemu
Geophysical Observatory of AAU   Laike Asfaw, Atalay Ayele
Ethiopian Geological Survey            Ketema Tadesse, Berhanu Bekele
Petroleum Operations Department   Abiy Hunegnaw, Ketsela Tadesse

Participation by Methodology:
Controlled source seismology
  Simon Klemperer, Randy Keller, Steve Harder, Peter Maguire, Aftab Khan, Telahun Mammo, Laike Asfaw, Ketema Tadesse, Ketsela Tadesse
Teleseismic recording and Local seismicity:
  Andy Nyblade, Graham Stuart, Mike Kendall; Cindy Ebinger, Mary Fowler, Laike Asfaw, Atalay Ayele
Geochemistry and magma genesis
  Tanya Furman, Gezahegn Yirgu, Dereje Ayalew
Gravity analysis, Structural analysis
  Kevin Mickus, Cindy Ebinger, Berhanu Bekele, Abera Alemu, Abiy Hunegnaw, Bekele Abebe
 
 
 

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