Deep structure of the Baringo Rift Basin (central Kenya) from three-dimensional magnetotelluric imaging: Implications for rift evolution

Three-dimensional modeling of data: from 31 vertical electrical and 24 magn etotelluric soundings collected in the Baringo-Bogoria Basin (central Kenya Rift Valley) shows a thick succession of well-defined tectonostratigraphic units beneath the Recent deposits of the Marigat-Loboi Plain. They include from top to bottom, a sedimentary basin, similar to 1.5 km thick, controll ed by N-S and N140 degrees structural trends, and a thick homogeneous resis tive layer related to the bottom of the basin, overlying a conductive struc ture, which cannot be clearly correlated with the Proterozoic basement. It is suggested that the resistive layer correlates with the mid-Miocene plate au-type flood phonolites which flowed over the early Kenya Rift during a ma jor volcanic activity period. The conductive structure overlain by these la va flows could be a sedimentary basin developed during the initial phase of rifting, during the Oligocene-Miocene. The absence of a significant gravit y low associated with this deep basin suggests a zone of dense intrusion de eper than 5-10 km, not discernible with the magnetotelluric data but requir ed to explain the gravity anomalies. The recognition of a deeply buried sed imentary succession lying between 4 and 8 km beneath the lower Miocene volc anic series of the Baringo valley would provide new insights into the regio nal volcano-sedimentary stratigraphic succession and the rift development o f the Kerio and Baringo Basins.