Fault growth and propagation during incipient continental rifting: Insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango Rift Zone, northwest Botswana

Abstract

Digital Elevation Models (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data and high‐resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the Okavango Rift Zone (ORZ), northwest Botswana. Significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the rift graben. Faults in the center of the rift either lack topographic expressions or are interpreted to have become inactive, or have large throws and small scarp heights indicating waning activity. Faults on the outer margins of the rift exhibit either (1) large throws or significant scarp heights and are considered older and active or (2) throws and scarp heights that are in closer agreement and are considered young and active. Fault linkages between major fault systems through a process of “fault piracy” have combined to establish an immature border fault for the ORZ. Thus, in addition to growing in length (by along‐axis linkage of segments), the rift is also growing in width (by transferring motion to younger faults along the outer margins while abandoning older faults in the middle). Finally, utilization of preexisting zones of weakness allowed the development of very long faults (>100 km) at a very early stage of continental rifting, explaining the apparent paradox between the fault length versus throw for this young rift. This study clearly demonstrates that the integration of the SRTM DEM and aeromagnetic data provides a 3‐D view of the faults and fault systems, providing new insight into fault growth and propagation during the nascent stages of continental rifting.

The time scales of continental rifting: Implications for global processes

“…The plate is thick and comparatively strong, and the stress accumulation required to cause fault slip may take 10 3 -10 5 a, based on sparse paleo-trenching studies (e.g., Zielke and Strecker, 2009;Machette et al, 1998). All or large parts of long border-fault systems that develop very early in basin evolution slip in large magnitude earthquakes (e.g., Kinabo et al, 2008;Craig et al, 2011), and intrabasinal faulting may also be seismogenic (e.g., Biggs et al, 2011). The interseismic cycle is barely detectable with GPS, suggesting that nearly all strain occurs during rifting episodes.…”

Geomorphic Landforms and Tectonism Along the Eastern Margin of the Okavango Rift Zone, North Western Botswana as Deduced from Geophysical Data in the Area

“…The development of the ORZ is thought to be taking place within a large structural depression known as the Makgadikgadi-OkavangoZambezi basin (MOZ) and is characterized by northeasterly trending folds and faults of the Ghanzi-Chobe belt (Cooke, 1984). The strike of the main bounding rift-related faults is 030 -050 o in the north and 060 -070 o in the south (Kinabo et al, 2007;2008). The orientation of the faults on the surface is influenced by pre-existing faults and folds of the basement rocks Kinabo et al, 2007;2008).…”

“…In addition, comparison of the throw on the basement surface with the throw on the topographic fault scarp demonstrates many of the faults have extended histories. Most of the faults suggest evidence for multiple episodes of faulting with concomitant sedimentation along the down thrown block and erosion of the fault scarps (Kinabo et al, 2008).…”

“…The strike of the main bounding rift-related faults is 030 -050 o in the north and 060 -070 o in the south (Kinabo et al, 2007;2008). The orientation of the faults on the surface is influenced by pre-existing faults and folds of the basement rocks Kinabo et al, 2007;2008). The MOZ basin comprised of both alluvial fan deposits and deeper palaeo-lake sediments in structural depressions or sub-basins Shaw and Nash 1998).…”

“…It occurs in an intercratonic zone between the Congo craton to the northwest and the Kalahari craton (consisting of the Zimbabwe and Kaapvaal cratons) to the www.intechopen.com Geomorphic Landforms and Tectonic Controls Along the Eastern Margin of the Okavango Rift Zone, North Western Botswana as Deduced From Geophysical Data in the Area 171 east-southeast (e.g., Kinabo et al, 2007;2008). The development of the ORZ is thought to be taking place within a large structural depression known as the Makgadikgadi-OkavangoZambezi basin (MOZ) and is characterized by northeasterly trending folds and faults of the Ghanzi-Chobe belt (Cooke, 1984).…”