152 130 Years of Research in the Turkana Basin, Kenya: Insights into Earth, Climate, and Life in Eastern Africa

Tuesday, 24 September 2024
8:00 AM - 12:00 PM
Ballroom A&B

THE DYNAMICS OF THE EAST AFRICAN RIFT SYSTEM WITHIN THE TURKANA BASIN REGION

Paper number: 152-4
Program: Technical Sessions
Time: 9:00 AM – 9:20 AM

Authors

Abstract

The East African Rift System (EARS) formed diachronously over a large, low shear wave velocity province beneath the lithosphere. The roles of deeper mantle dynamics, thermo-mechanical weakening of the lithosphere, and gravitational body forces in the evolution of the EARS remain enigmatic. By integrating numerical modeling with the long-term thermal evolution of the crust and the current thermo-mechanical structure of the mantle, we explore the geodynamic mechanisms responsible for the EARS development since the Oligocene.

Using a model estimate of continuous strain rates through time, we quantitatively reconstructed body force estimates during the Oligocene. We simulated the temporal evolution of global mantle flow from backward mantle convection to 30 Ma, using present-day mantle and lithospheric density variations inferred from seismic models. These inputs, including body force distributions and asthenosphere temperatures, were used in 4-D thermo-mechanical models to evaluate lithospheric evolution in the EARS. Our simulations were validated by comparing predicted pressure-temperature-time paths with the Oligocene to recent tectono-thermal evolution of the African crust, as recorded by low-temperature thermochronology.

Our results indicate that the primary driving forces for lithospheric evolution in the EARS include gravitational body forces acting on the 3-D lithospheric structure, as well as traction fields and temperature changes associated with mantle convection. Over time, gravitational potential energy differences, linked to the development of dynamic topography, have become increasingly significant. Temperature evolution linked to plume activity has profoundly influenced the rheology and development of the plate boundary system. Furthermore, our models explain the observed northward rift-parallel seismic anisotropy beneath the EARS at present.

Building on this foundation, we introduce landscape evolution modeling, incorporating climate models from 30 Ma to the present. We aim to match sediment volumes in the extensional basins and compare drainage patterns in the model simulations with paleocurrent measurements. This integrated approach aims to elucidate the interactions between tectonics, climate, and surface processes, providing a new understanding of the EARS evolution and its environmental implications.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-405374

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