Early Structural Development of the Okavango Rift Zone, NW Botswana

Abstract

Aeromagnetic and gravity data collected across the Okavango rift zone, northwest Botswana are used to map the distribution of faults, provide insights into the two-dimensional shallow subsurface geometry of the rift, and evaluate models for basin formation as well as the role of pre-existing basement fabric on the development of this nascent continental rift. The structural fabric (fold axes and foliation) of the Proterozoic basement terrane is clearly imaged on both gravity and magnetic maps. The strike of rift-related faults (030-050⁰ in the north and 060-070⁰ in the south) parallels fold axes and the prominent foliation directions of the basement rocks. These pre-existing fabrics and structures represent a significant strength anisotropy that controlled the orientation of younger brittle faults within the stress regime present during initiation of this rift. Northwest dipping faults consistently exhibit greater displacements than southeast dipping faults, suggesting a developing half-graben geometry for this rift zone. However, the absence of fully developed half-grabens along this rift zone suggests that the border fault system is not fully developed consistent with the infancy of rifting. Three en-echelon northeast trending depocenters coincide with structural grabens that define the Okavango rift zone. Along the southeastern boundary of the rift, developing border faults define a 50 km wide zone of subsidence within a larger 150 km wide zone of extension forming a rift-in-rift structure. We infer from this observation that the localization of strain resulting from extension is occurring mostly along the southeastern boundary where the border fault system is being initiated, underscoring the important role of border faults in accommodating strain even during this early stage of rift development. We conclude that incipient rift zones may provide critical insights into the development of rift basins during the earliest stages of continental rifting.

Department(s)

Geosciences and Geological and Petroleum Engineering

Sponsor(s)

Petroleum Research Fund
National Science Foundation (U.S.)

Keywords and Phrases

Okavango Rift Zone; Embryonic Rift; Faults; Potential Field Methods

Geographic Coverage

Northwest Botswana

International Standard Serial Number (ISSN)

0899-5362

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2007 Elsevier, All rights reserved.

Publication Date

01 Jun 2007

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