HR: 1330h
AN: T43B-07    [Abstracts]
TI: Structural Evolution of the Incipient Okavango Rift Zone, NW Botswana
AU: * Atekwana, E A
EM: atekwana@umr.edu
AF: Department of Geological Sciences and Engineering, 125 McNutt Hall University of Missouri-Rolla, Rolla, MO 65409
AU: Kinabo, B D
EM: bdk6x2@umr.edu
AF: Department of Geological Sciences and Engineering, 125 McNutt Hall University of Missouri-Rolla, Rolla, MO 65409
AU: Modisi, M P
EM: modisimp@mopipi.ub.bw
AF: Department of Geology, University of Botswana, Private Bag 0022, Gaborone, Botswana
AU: Hogan, J P
EM: jhogan@umr.edu
AF: Department of Geological Sciences and Engineering, 125 McNutt Hall University of Missouri-Rolla, Rolla, MO 65409
AU: Wheaton, D D
EM: ddwhc8@umr.edu
AF: Department of Geological Sciences and Engineering, 125 McNutt Hall University of Missouri-Rolla, Rolla, MO 65409
AB: Studies of the East African Rift System (EARS) and other continental rifts have significantly improved our understanding of rifting processes; however, we particularly lack studies of the embryonic stages of rift creation. The Okavango Rift Zone (ORZ), NW Botswana is one of few places worldwide where one can study the early stages of continental extension prior to the accumulation of significant amounts of sediments, volcanism, and multiphase deformation that obscure the investigation of these early time processes in more evolved continental rift zones. In this study, gravity and aeromagnetic data have been used to examine the initiation and development of the nascent ORZ. The Okavango basin in NW Botswana is located at the southern tip of the southwestern branch of the EARS. The rift is hosted within the Proterozoic fold and thrust belt of the Ghanzi-Chobe formation. Our objectives include (1) assessing the role of pre-existing structures on the development of rift faults and basin architecture, (2) Examining fault linkage patterns and boarder fault development, and (3) determining the shallow subsurface basin geometry. Aeromagnetic data from the ORZ suggest two main structural trends: 1) northeast-southwest (030- 070o) and 2) northwest - southeast (290 - 320o). The 030- 070o structures occur within the rift zone and throughout the surrounding basement. They form the main bounding fault system of this incipient rift. The NE - SW orientations of rift faults mirror the fold axes and foliation of the basement rocks, suggesting that the basement fabric played an important role in localizing the development of faults within the stress regime present during the initiation of this rift. Additionally, the greatest throw (~400- ~700 m) occurs along the Kunyere (NW dipping) and Tsau faults (SE dipping), defining a full graben as observed on gravity models. This differs from the half-graben model typical of most continental rift zones. Thus, it appears the basin geometry was strongly influenced by the position of these pre-existing faults. Evidence of fault linkage is seen along some of the faults. Linked segments of faults are well defined and some are > 200 km long. We suggest from this result that fault linkage and propagation occurred very early and prior to significant basin development. We conclude that basement fabric seems to be a controlling factor at least in the early stages of basin architecture and structural evolution of ORZ.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 1219 Local gravity anomalies and crustal structure
DE: 1517 Magnetic anomaly modeling
SC: Tectonophysics [T]
MN: 2005 Joint Assembly