THE ROLE OF ASCENDING FLUIDS IN WEAKENING THE CRUST DURING THE INITIAL STAGES OF RIFTING, EXAMPLE FROM OKAVANGO RIFT ZONE, EARS

Fluids and their migration play an essential role in localizing the nucleation and evolution of continental rift by weakening and modifying the lithosphere. A gravity and magnetic analysis in the Okavango Rift Zone in the Southwestern branch of the EARS showed how fluids can weaken the continental lithosphere, leading to extensional strain localization and initiating continental rifting. An aeromagnetic analysis that included a 3D inversion of the data was used to map the Curie point depth (CPD), and these depths were used in conjunction with geothermal modeling to indicate that there are shallow CPD values beneath the Okavango Rift and high heat flow values within the rift zone. These shallow depths and high heat flow values are interpreted to be caused by fluid flow in the continental lithosphere. Gravity modeling has also indicated that the Okavango Rift Zone is associated with a thinned crust with lower lithospheric and upper mantle densities consistent with the aeromagnetic analysis. These lithospheric thickness and physical property results have been confirmed by seismic tomography and magnetotelluric models and have interpreted their results that the Okavango Rift Zone is associated with lithospheric fluids that are important in initiating and continuing the rifting process. The role of lithospheric fluids in rift initiation has become increasingly recognized, especially in other segments of the EARS that are in different stages of their rift evolution, including the Natron and Magadi basins of the Tanzanian Divergent Zone in the Eastern Branch of the EARS and the Eastern Branch of the EARS in southern Kenya and northern Tanzania.