GEOPHYSICAL CHARACTERIZATION OF THE OKAVANGO RIFT ZONE (ORZ), NW BOTSWANA: PROVIDING INTERNATIONAL RESEARCH EXPERIENCE FOR STUDENTS

Our NSF-IRES project is designed to partner US students with peers from the University of Botswana to conduct field-based research focused on investigating the interplay between neotectonics and surficial processes due to rifting. We have investigated two grabens within the Okavango Rift Zone (ORZ) in NW Botswana, the Lake Ngami graben and the Mababe depression. Students investigated the detailed 2-D structure of the developing juvenile border fault system using electrical resistivity, controlled source audio magnetotelluric (CSAMT), magnetic, and gravity techniques. Geomorphologic expression of these faults is very subtle with fault scarps <~ 5-12 m high. The resistivity sections show faults as steeply dipping anomalies characterized by sharp lateral resistivity contrasts cutting basement rocks. The grabens are characterized by low resistivities (< 5 Ohm.m) suggesting the presence of silts and clays or saline water. Faults on the CSAMT profiles appear as conductive anomalies suggesting possible channeling of fluids from the Okavango delta into the Lake Ngami graben. The Mababe fault was mapped and found to exist in the subsurface dipping in the northwesterly direction with little surface expression. The sediments in the graben only reach 600 to 800 meters deep with little basement features indicating very young rifting processes.