Heterogeneous crust and upper mantle across southern Kenya and the relationship to surface deformation as inferred from magnetotelluric imaging

摘要

We have used magnetotelluric data imaging to determine the resistivity structure across southern Kenya and our results suggest the presence of a buckled blocky or segmented lithosphere across the region. Prominent steep conductive zones at the Oloololo (OLO) escarpment and eastern rift margin allow us to subdivide the region into three crustal domains. West of OLO, a bow-shaped conductor underlies a 10 km thick resistive upper crustal unit spatially correlating with an exposed Archaean greenstone belt. Between OLO and the eastern rift margin are found steeply dipping alternating conductive and resistive zones that appear buckled. East of this belt are found prominent, 5 to 20 km deep, subhorizontal conductors atop steep resistive blocks with flanking conductors. The main steep features in the crust appear to extend below the seismic Moho and thus suggest the presence of anomalously thick crust across the region. A 50 km-wide and 4–8 km deep w-shaped (double half-graben) structure is suggested at the position of the Kenyan rift. We show that our inferred lateral zoning is consistent with collocated gravity and seismic measurements. We propose a link between the deep resistivity heterogeneity and surface deformation pattern in the area.