Journal of Conference Abstracts

P_n Tomography of the Tanzania Craton and Adjoining Rifted Mobile Belts, East Africa

Richard A Brazier (brazier@geosc.psu.edu)¹, Andrew A Nyblade (andy@geosc.psu.edu)², Charles A Langston (cal@geosc.psu.edu)³ & Thomas J Owens (owens@tigger.seis.sc.edu)⁴

¹431 Deike Bldg, Penn State University, University Park, PA 16802., US

²440 Deike Bldg, Penn State University, University Park, PA 16802., US

³445 Deike Bldg, Penn State University, University Park, PA 16802., US

⁴Dept of Geological Sciences, University of South Carolina, Columbia, SC, 29208, US

Uppermost mantle velocities (P_n) beneath areas of Cenozoic rifting and uplift in Tanzania, East Africa have been investigated to ascertain the extent to which the mantle lithosphere has been modified. Some 10,000 Pn travel times from 1200 local and regional earthquakes recorded by the Tanzania broadband seismic experiment and other stations operating in East Africa during the past few decades have been inverted for P wave velocity structure. Uppermost mantle velocities beneath the Archean Tanzania Craton, which lies in the center of the East African Plateau, are between 8.00 and 8.05 km/s. These velocities lie within the lower end of the range of velocities observed in other Archean cratons and thus do not necessarily a broad modification of the uppermost mantle across the interior of the East African Plateau. A narrow (50 km wide) zone of lower P_n velocities (7.90-7.95 km/s) is found beneath the terminus of the Eastern Branch of the rift system in northeastern Tanzania. This low velocity region is situated directly south of the Kenya Rift along the boundary between the Tanzania Craton and Mozambique belt, and it is spatially correlated with major rift faults and seismicity. P_n velocities of 7.9-7.95 km/s, compared to velocities of 8-8.05 km/s found in the craton, indicate slightly elevated upper mantle temperatures beneath the rift, consistent with recent temperature and pressure estimates from mantle xenoliths. P_n velocities of 8.00-8.05 km/s are found beneath the Ubendian Belt to the southwest of the craton in the vicinity of the Rukwa Rift, however, limited model resolution allows for the possibility that P_n velocities beneath the Rukwa Rift could be lower than that.