Paleogene initiation of the Western Branch of the East African Rift: The uplift history of the Rwenzori Mountains, Western Uganda

Abstract

The two branches of the East African Rift System (EARS) are believed to have initiated diachronously. However, a growing body of work continues to suggest the onset of rifting in the Western Branch occurred in the Palaeogene, coeval to the Eastern Branch. Due to a lack of pre-Miocene stratigraphy, attempts to resolve the geological history of the Western Branch must study the uplift and erosional histories of the modern rift topography. In this study, the rock uplift history of the Rwenzori Mountains, Western Uganda, is resolved to better our understanding of the tectonic history of the Western Branch of the EAR. Through the application of low-temperature thermochronology, -mapping and the modelling of river profiles, we show that rock uplift of the Rwenzori dates back to the Oligocene, with thermal history models suggesting uplift induced exhumation may date back as far as the Eocene. This provides tangible evidence that extension began in the region in the Paleogene, coeval with the Eastern Branch, and not the late Neogene. These results have broad implications for the tectonic evolution of the entire East African Rift System and suggest our current understanding of the region's rift history remains incomplete.

Combined Zircon/Apatite U-Pb and Fission-Track Dating by LA-ICP-MS and Its Geological Applications: An Example from the Egyptian Younger Granites

“…The FT thermochronology is a powerful tool that may be applied to resolve several geological problems in a variety of geological settings [12][13][14][15]. The FT age is calculated by determining the number of spontaneous fission tracks (i.e., formed by daughter nuclides) and the number of U-238 atoms (i.e., parent nuclides) per weight of sample.…”

Exhumation of the passive margin of the DR Congo during pre- and post- Gondwana breakup: Evidence from low-temperature thermochronology, geology and geomorphology

“…In Central Africa, this period is characterized by ubiquitous uplift through ~35 Ma (38-30 Ma) doming and bulging, e.g. the Cameroon Dome (north of the CAAS), and the East African Rift System (Guillocheau et al, 2018;Boone et al, 2019;Jess et al, 2020). This late Eoceneearly Oligocene Central African uplift and consequential denudation is also evidenced in the deep-sea Congo River fan sediments, which after a period of basin starvation show sudden high sedimentation rates (~80 m/Ma) (Anka et al, 2010).…”

Geodynamics of continental rift initiation and evolution

“…Observational constraints on rift controls will help unravel the evolution of lithospheric strength during rifting and break-up through quantifications of crustal and lithospheric thickness, thermal state, and topography. This can include thermochronological dating of fault surfaces and river networks to reveal vertical motion changes 193,194 , joint inversion of seismic, tomographic and satellite data to reveal lithosphere structure 195 , and inversion for lithospheric rheology and temperature structure from topography, gravity, horizontal and vertical surface velocities 196 .…”