Constraining exhumation and erosion along Lake Tanganyika to assess landscape evolution in rifts

Continental rifting leads to the formation of economic resources and deposits, influences the distribution and evolution of plants and animals through changes in topography and habitats, and impacts global climate by volcanic outgassing of carbon dioxide. The East African Rift serves as a modern example for many of these processes. However, even in this modern setting, the timing and rates of development of the mountains and valleys that characterize the rift remain poorly understood.

Lake Tanganyika is the largest lake within the East African Rift, but the age of the lake and the timing of uplift of the adjacent mountains are debated. This debate, in turn, impedes understanding of the timing of rift evolution, rates of erosion and sedimentation, and the pulse of speciation and diversification of the organisms living in the lake and watersheds.

The project’s goal is to constrain the timing of rift initiation and fault magnitude along the Lake Tanganyika portion of the rift to understand how rifts grow, the timing of lake formation and variation in erosion and sedimentation rates. This project will also produce maps of nearshore habitats along the lake, providing critical decision-making information for NGO’s, such as the Nature Conservancy, and local scientific units, that are actively considering the location of protected areas around the lake.

Finally, this project will initiate new collaborations among the US and international researchers and both present and future research and teaching will benefit from cross-fertilization of ideas, methods, and means of analysis developed during this project.

This project involves creating a spatially extensive analysis of exhumation and denudation along the Lake Tanganyika (LT) rift to infer timing of rift initiation, model erosion and denudation, and explore the role of tectonic exhumation and denudation on watershed morphology. The specific objectives of this research are to 1) use low-temperature thermochronology (apatite fission-track and apatite (U-Th-Sm)/He analysis) to determine timing, rate and magnitude of tectonic exhumation along discrete footwall blocks of the LT rift; 2) use cosmogenic nuclide analysis (10Be) of quartz-bearing sediment to determine catchment-wide denudation rates of catchments that drain footwall blocks of varying size and tectonic style; and 3) analyze variation in river and catchment characteristics, using well-established quantitative tools, along the targeted footwall uplifts of contrasting tectonic style to examine transient changes in watershed geomorphology and footwall uplift induced by faulting and/or surface processes.

Using the combined datasets, the researchers will test different hypotheses on the timing of rifting in the LT portion of the EAR, and test various models of normal fault growth, linkage, and controls on erosion and delivery of sediment (rates, texture and composition) to the basin sink.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.