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

Abstract

Three‐dimensional modeling of data from 31 vertical electrical and 24 magnetotelluric 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, ∼1.5 km thick, controlled by N‐S and N140° structural trends, and a thick homogeneous resistive layer related to the bottom of the basin, overlying a conductive structure, which cannot be clearly correlated with the Proterozoic basement. It is suggested that the resistive layer correlates with the mid‐Miocene plateau‐type flood phonolites which flowed over the early Kenya Rift during a major volcanic activity period. The conductive structure overlain by these lava flows could be a sedimentary basin developed during the initial phase of rifting, during the Oligocene‐Miocene. The absence of a significant gravity low associated with this deep basin suggests a zone of dense intrusion deeper than 5–10 km, not discernible with the magnetotelluric data but required to explain the gravity anomalies. The recognition of a deeply buried sedimentary succession lying between 4 and 8 km beneath the lower Miocene volcanic series of the Baringo valley would provide new insights into the regional volcano‐sedimentary stratigraphie succession and the rift development of the Kerio and Baringo Basins.