LATE CENOZOIC TECTONICS AND DENUDATION IN THE CENTRAL KENYA RIFT - QUANTIFICATION OF LONG-TERM DENUDATION RATES

Long-term average denudation rates were calculated for the last 3.4 mi llion years (Ma) using digital topographic data related to the present surface of the intrarift Bahati-Kinangop Plateau in the Central Kenya Rift. Well established relations between stratigraphy and faulting ch ronology, and a, detailed digital topographic database allow reconstru ction of the idealized uneroded plateau surface for an area of 710 km( 2). The reconstruction refers to the time when the plateau came into e xistence (3.4-2.6 Ma) due to widespread deposition of ashflow tuffs an d subsequent faulting. The reconstruction of this palaeosurface is bas ed on erosional surface remnants occurring within the present plateau surface. Relict surfaces elements were determined by analyzing the pre sent digital surface representation and geological information within a Geographical Information System (GIS). After generating digital elev ation models of the present and palaeosurfaces, long-term denudation r ates were calculated using the elevation difference method. About 80% of the study area are characterized by denudation rates between 0 (rel ict parts) and 20 m per one million years (m/Ma), For deeply eroded pl ateau regions denudation reaches 80-100 m/Ma. These rates are comparab le to denudation rates which are known from other studies in similar s ettings. The GIS-based approach provides spatially high-resolution den udation rates allowing for further regional analysis of factors contro lling spatial variations in sediment supply to the rift basin.