Fault control on patterns of Quaternary monogenetic vents in the Ethiopian Rift between Omo and Tendaho

Abstract

Field and remote sensing data are used to examine the distribution of volcanism and fault geometry in the Ethiopian Rift between Omo-Chew Bahir rift and Tendaho graben during the Quaternary and evaluate their influence on the location and shape of individual vents as well as the development of alignments. The results of remote sensing, and field study of the total (2214) cone populations reveal that monogenetic vent alignments and the long axes of elongate cones are parallel to and spatially linked with mapped normal faults. This is consistent with the overall sub- latitudinal extension direction in the Quaternary deduced from fault slip analysis and earthquake focal mechanism solutions. Out of the rift axis, pre-existing faults were apparently reactivated and acted as conduits for magmatism to reach the surface, and hence vent clustering. On regional scales, vent clusters are located in Quaternary volcanic fields along the rift axis and in zones of reactivation of pre-Tertiary structures. Sixty two percent of the vents in the study area are part of nine regional vent alignments that vary in length from 48 to 68 km. On sub-regional scales, twelve clusters ranging in length from 10 to 30 km have been mapped. Locally, field structural data show that individual vents and short vent alignments, up to 10 km in length, occur along and adjacent to faults, particularly along fault segments, intersections, and bifurcations. The long axes of elongate volcanic cones also have trends generally parallel to the local faults.