COUPLED AEROMAGNETIC AND SRTM (DEM) DATA INVESTIGATIONS OF FAULT GROWTH PATTERNS IN INCIPIENT RIFT ZONES

Digital Elevation Models (DEMs) extracted from the Shuttle Radar Topography Mission (SRTM) are coupled with high resolution aeromagnetic data to investigate fault development during the early stages of continental extension in the Okavango Rift Zone (ORZ), NW Botswana. Aeromagnetic data provide information on fault morphology at depth within the basement, while the SRTM data provide morphological information on surface ruptures associated with these faults. Our results suggest that the ORZ preexisting tectonic fabric of the basement strongly influences the overall geometry of the rifted basins and facilitated the growth and propagation of faults. Fault systems at different stages of development in the ORZ typically display an en-échelon distribution of small right stepping segments ~ 3-25 km in length. Nascent fault systems are characterized by soft linkages, where the overlapping fault segments are linked by ductile strain zones between them. More mature fault systems are characterized by hard linkages, where overlapping fault segments are linked directly by touching of fault surfaces. ORZ is not defined by a well developed border fault system. However, the existing fault system can develop into a main master or border fault for this rift system as evidenced by linkage in two ways: (1) linkage of short individual segments (3-25 km long) to form a single fault (~100-325 km long; second order linkage); and (2) simultaneous linkage of fault segments (~100-325 km long) by development of transfer faults (first order linkage). Paleoclimatic studies suggest that the ORZ is < 40,000 years old and aeromagnetic data reveal that the faults are as long as 325 km. Thus, the propagation of the rift faults is relatively fast, probably due to the strong influence of the pre-existing fabric.