Collaborative Research: US-EAGLE (Ethiopia-Afar Grand Lithospheric Experiment): Modification of Lithospheric Structure During Continental Break-up

0207764

Furman

The architecture of continental margins in terms of how they are created is not well understood because most of the previous work has been on successfully rifted margins after rifting is complete. Both continental (fault dominated) end-members and oceanic (magma dominated) rift end-members are well studied, but the transitional stage is not understood. This project will document this critical transition from continental to oceanic rifting. The PIs 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. 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. The PIs will obtain crustal P-and S-velocity cross-sections that can be interpreted for lithology across the Ethiopian rift at 10 deg. N where active magmatic centers first appear, and along-strike to the north to study the transition into fully magmatic rifting. They will interpret existing and new gravity data in light of their new seismic data, and use geochemical data to constrain the physical state of the upper mantle and magmatic inputs to the crust.

The project (US - EAGLE) is fully integrated with the already funded UK - EAGLE initiative. Scientists at Leicester, Leeds and London, have been awarded UK funds to carry out a single refraction profile across the Ethiopian rift in January 2003, coupled with local seismicity studies and teleseismic recording. The US - EAGLE PIs will shoot and record a complementary orthogonal along-axis wide-angle profile; and will 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. The seismic studies will be coupled with geochemical and petrological and gravity studies (US), and structural, thermochronological, magnetotelluric and additional gravity studies (UK).