GRAVITY ANALYSIS OF THE CRUSTAL STRUCTURE WITHIN THE TENDAHO GRABEN, CENTRAL AFAR, ETHIOPIA

The Afar region of Ethiopia lies at a triple junction where northern section of the East African Rift System, the Red Sea rift and Aden rift meet. Within the Afar region, the Red Sea and Aden rifts are propagating from the ocean onto thinned continental crust. The Red Sea propagator is within the Tendaho Graben, occurs in the central Afar and ends near Aseyta. The Tendaho Graben which formed approximately 1.8 Ma ago, is approximately up to 60 km wide, is filled with lacustrine sediments and basalt flows, and bounded by basaltic and rhyolitic flows. Despite the numerous geological studies of the Tendaho graben, there have been few studies of the subsurface crustal structures. To aid in determining the region's crustal structure, a detailed gravity, magnetic and broadband seismic study has been undertaken. Detailed gravity data were collected using differential GPS methods along all available roads at intervals between 0.5 and 1 km to supplement the available gravity data. Preliminary analysis of the gravity data including the construction of anomaly and 2-D models indicates that the youngest sections of the rift has the thickest lacustrine sediments (1.6 km) but is defined by a Bouguer gravity maximum caused by a series of dense mafic dikes extending into the basement. This regional gravity maximum which is thought to define the location of the Red Sea propagator extends to Aseyta where it ends. When combined with a detailed total-field magnetic measurements and analysis, and geochronology data, the gravity data are interpreted that the Tendaho graben represents a slowing down of the current rifting and that the current extension in the Afar is taken up further to the east. Future work will be to construct two and three-dimensional models and to collect additional data to further define the crustal structure of the region.