Geophysical project in Ethiopia studies continental breakup

Abstract

As continental rift zones evolve to sea floor spreading, they do so through progressive episodes of lithospheric stretching, heating, and magmatism, yet the actual process of continental breakup is poorly understood. The East African Rift system in northeastern Ethiopia is central to our understanding of this process, as it lies at the transition between continental and oceanic rifting [Ebinger and Casey, 2001]. We are exploring the kinematics and dynamics of continental breakup through the Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE), which aims to probe the crust and upper mantle structure between the Main Ethiopian (continental) and Afar (ocean spreading) rifts, a region providing an ideal laboratory to examine the process of breakup as it is occurring. EAGLE is a multidisciplinary study centered around the most advanced seismic project yet undertaken in Africa (Figure l). Our study follows the Kenya Rift International Seismic Project [e.g., KRISP Working Group, 1995],and capitalizes on the IRIS/PASSCAL broadband seismic array [Nyblade and Langston, 2002], providing a telescoping view of the East African Rift within this suspected plume province.

Mantle transition zone variations beneath the Ethiopian Rift and Afar: Chemical heterogeneity within a hot mantle?

“…[8] We utilize teleseismic (m b > 5.8) earthquake data recorded by EAGLE [Maguire et al, 2003] and EBSE [Nyblade and Langston, 2002] temporary broadband seismological stations plus permanent stations FURI and ATD ( Figure 1 and Figure S1 in the auxiliary material).…”

Magma-assisted rifting in Ethiopia

“…1). Structural, geochemical and seismic data indicate that magmatic segments are zones of intense dyke injection and magmatic intrusion 6,7,19 , with many dyke-fed mafic lavas sourced within the asthenosphere 26 . En Figure 2 Shear-wave splitting parameters, f (top panels) and dt (bottom panels), as a function of distance perpendicular to the rift (NW to SE) (left panels) and distance along the rift moving from the SW to the NE (right panels).…”

“…1) constitutes the northern part of the East African Rift system and forms one arm of a triple junction that formed on or near a mantle plume. Our study region is transitional between continental and incipient oceanic, with strain localized to ,20-km-wide zones of dyking, faulting and volcanism 6,7 . It is an ideal place to study magmatism and plate rupture, because up to 25% of the crust is extruded lava or intrusive magma 7,8 and mantle lithosphere is thin (,50 km) beneath the rift valley 9 .…”

“…It is an ideal place to study magmatism and plate rupture, because up to 25% of the crust is extruded lava or intrusive magma 7,8 and mantle lithosphere is thin (,50 km) beneath the rift valley 9 . Seismic data were acquired in three phases of the EAGLE project 6 , two of which were designed to record passive seismicity. In phase I, 29 broad-band seismometers were deployed for 16 months with a nominal station spacing of 40 km and covering a 250 km £ 350 km region centred on the transitional part of the rift (Fig.…”

“…The data we analysed were collected as part of the EAGLE project (Ethiopian Afar Geophysical Lithospheric Experiment), an international multi-institutional experiment designed to investigate rifting processes in Ethiopia 6 . The Miocene-Recent Ethiopian Rift (Fig.…”