Late Cenozoic tectonics and denudation in the Central Kenya Rift: quantification of long-term denudation rates

Abstract

Long-term average denudation rates were calculated for the last 3.4 million 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 chronology, and a detailed digital topographic database allow reconstruction of the idealized uneroded plateau surface for an area of 710 km 2. The reconstruction refers to the time when the plateau came into existence (3.4-2.6 Ma) due to widespread deposition of ashflow tuffs and subsequent faulting. The reconstruction of this palaeosurface is based on erosional surface remnants occurring within the present plateau surface. Relict surfaces elements were determined by analyzing the present digital surface representation and geological information within a Geographical Information System (GIS). After generating digital elevation models of the present and palaeosurfaces, long-term denudation rates were calculated using the elevation difference method. About 80% of the study area are characterized by denudation rates between 0 (relict parts) and 20 m per one million years (m/Ma). For deeply eroded plateau regions denudation reaches 80–100 m/Ma. These rates are comparable to denudation rates which are known from other studies in similar settings. The GIS-based approach provides spatially high-resolution denudation rates allowing for further regional analysis of factors controlling spatial variations in sediment supply to the rift basin.