Numerical models (sleep, 1996,1997) of mantle plumes that consider variations in lithospheric thicknesss suggest that deep cratonic roots influence the flow of hot, bouyant plume material. This process may explain the longlevity of cold, thick cratonic roots and the generation of kimberlites in crtons. We will use these methods to: a) predict the temporal and spatial distribution of adiabatic decompression melting and b) track the diamond/graphite stability field beneath and along the margins of the supeior craton, the world's largest, and the small tanzania craton, working in collaboration with n. Sleep. Initial lithospheric rhickness will be constrained by new and existing seismic, as well as zenolith, gravity, and heat flow data. These results will improve models for mineral exploration, as well as plume processes.

One of the primary processes shaping Earth's surface is the stretching and eventual break-up of continents to create new ocean basins. The processes of stretching and heating of -150 km-thick plates, or layers of rock, are made evident at Earth's surface via earthquakes, volcanoes, hot springs, landslides and rockfalls that occur within and along the margins of narrow, long basins flanked by steep mountain ranges (e.g., East African rift, Gulf of Corinth). Ancient areas of stretching are more difficult to decipher, since the physical processes we wish to understand have since stopped, and competing processes of erosion, sedimentation, and subsidence of the rift zones makes them difficult to image. Finally, studies of continental break-up require an understanding of margins on both sides of ocean basins, which may now be 1000's of km apart (e.g., N. Atlantic). We propose to determine the evolution of continental rifting leading to break-up in the Gulf of Aden, where break-up occurred <20 My ago, and both margins are within a day's shiptime from one another. The short time interval since break-up means that sedimentary strata overlying the stretched, fractured, and heated rock layers of the plate are thin, and we can image clearly using geophysical methods. Our experiment involves the analyses of the travel times of seismic waves through the rock layers of the plates and underlying mantle where rocks are hotter, and where pockets of molten rock may have accumulated. Electronic devices capable of measuring vibrations from earthquakes worldwide (seismometers) will be buried along onshore continuations of profiles across the Gulf of Aden. We intend to use both man-made sound sources generated onboard the French seismic research vessel Marie Dufresne, which will travel along 3 profiles of the Gulf of Aden sending airblasts into the water every 50 metres. Our instruments will also record earthquakes occurring in the Himalayas, the Atlantic mid-ocean ridge, the Mediterranean sea, and the East African rift system. Variations in the arrival times of these sound waves recorded across our array allow us to map out velocity structure of the rocks beneath the array and across the width of the Gulf of Aden. Our aims are to map the geometry of the stretched layers within the plates, as well as their variations in velocity and physical properties. The velocity variations help us detect small variations in temperature and/or composition of the rocks, and help us determine the mechanical properties of the plates as they are stretched. Do the plates come apart along one large fracture, or fault zone, or does the stretching move continually inward to a narrow zone of necking, much like one finds stretching blue tack? Has some of the hot mantle rock which passively rises up to fill the place previously occupied by the plate depressurise and melt to form lavas? Where do these lavas form and rise up? Are these properties continuous along the length of the rift zone, or is the process three-dimensional? All of this information is vitally important to 1) oil explorationists trying to improve predictive models for oil and gas generation and migration 2) planners and government officials who need to evaluate seismic and volcanic hazards in areas of active rifting 3) earth scientists who wish to understand the physical properties of rocks so that we can adequately describe the physics of continental break-up and predict the onset of seafloor spreading. Funds are requested to cover travel to and from Oman to deploy instruments, to download data every 6 weeks (3 months) and every 12 weeks (9 months), plus travel to partner institutions to confer and integrate research results.

Since 20 September, 2005, an ~120 km-long segment of the Red Sea rift system in Ethiopia has been rocked by 31 earthquakes detected on seismometers worldwide. Ashes emanating from long, open fissures at the surface have blanketed a much wider area, displacing ~50,000 people and their livestock. Colleagues from Addis Ababa University report new fault scarps, and new displacements along existing fault scarps; these faults provide direct measures of rates of crustal deformation that can only be inferred from routine monitoring. The active rupture zone is much larger than has been associated with other historic sequences in the Afar depression, and other continental rift zones worldwide, suggesting this linked tectonic-volcanic crisis is a major event. Thus, the Boina seismo-volcanic crisis provides a superb opportunity to record directly the processes of continental breakup leading to the formation of a new ocean basin. Routine seismic, volcanic, and geodetic monitoring provides information on the time-averaged deformation, but misses the sometimes catastrophic discrete events that achieve the tectonic processes. This proposal aims to: 1) establish a seismic monitoring network to measure aftershock sequences and lava movement within the plate; 2) investigate reports of new eruptions and measure gas emissions from vents along the length of the rupturing segment and compare them with earlier baseline measurements from Afar; and 3) use space-based radar images acquired prior to, during, and after the crisis to measure the magnitude and extent of deformation across the region. Simple elastic modelling of seismic and radar interferometry results will allow us to estimate the proportion of tectonic vs magmatic deformation associated with continental rupture. Additionally, our measurements will provide a firm basis for hazard mitigation for the Ethiopian government coping with this catastrophe, supplementing the sparse infrastructure established by our Ethiopian colleagues.