Seismic Anisotropy beneath the Incipient Okavango Rift: Implications for Rifting Initiation

Abstract

This study represents the first shear-wave splitting investigation of the Okavango rift zone (ORZ), an incipient continental rift belonging to the East African rift system in northern Botswana. Analysis of broadband seismic data recorded along a 750 km long profile of 22 stations traversing the ORZ and adjacent Congo and Kalahari cratons and several Precambrian orogenic zones reveals dominantly NE-SW fast orientations, which are parallel to both the absolute plate motion direction (based on the NNR-NUVEL-1A model) and the trend of most tectonic boundaries, including that of the ORZ. Spatial coherence analysis of the splitting parameters and correspondence between the observed fast orientations and the trend of tectonic features indicate that the main source of observed anisotropy is most likely in the upper asthenosphere, probably due to simple shear associated with the relative movement of the lithosphere against the asthenosphere. The presence of consistently rift-parallel fast orientations and normal splitting times in the ORZ and most parts of southern Africa implies that neither an upper mantle plume nor small-scale convection is the dominant source for rift initiation and development. The first shear-wave splitting measurements in the vicinity of the ORZ favor a model in which continental rifting develops in response to intra-plate relative movement of continental blocks along zones of weakness produced by ancient tectonic events.

Department(s)

Geosciences and Geological and Petroleum Engineering

Research Center/Lab(s)

Center for High Performance Computing Research

Keywords and Phrases

Anisotropy; Geologic Models; Seismology; Shear Flow; Structural Geology; Tectonics; Absolute Plate Motions; Continental Blocks; Continental Rifting; Rift Zones; Seismic Anisotropy; Shear Wave Splitting; Small-Scale Convection; Tectonic Boundaries; Shear Waves; Orogeny; Plate Motion; Rift Zone; Rifting; S-Wave; Seismic Anisotropy; Seismic Data; Tectonics; Wave Splitting; Botswana; Congo Craton; East African Rift; Kalahari Craton; Okavango Rift Zone

Geographic Coverage

Botswana

International Standard Serial Number (ISSN)

0012-821X

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2015 Elsevier, All rights reserved.

Publication Date

01 Nov 2015

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