Seismic anisotropy beneath the incipient Okavango rift: Implications for rifting initiation

Citation data:

Earth and Planetary Science Letters, ISSN: 0012-821X, Vol: 430, Page: 1-8

Publication Year:
2015
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Repository URL:
https://works.bepress.com/kelly-liu/73; http://scholarsmine.mst.edu/geosci_geo_peteng_facwork/410
DOI:
10.1016/j.epsl.2015.08.009
Author(s):
Yu, Youqiang; Gao, Stephen S.; Moidaki, Moikwathai; Reed, Cory A.; Liu, Kelly H.
Publisher(s):
Elsevier BV; Elsevier
Tags:
Earth and Planetary Sciences; 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 Data; Wave Splitting; Botswana; Congo Craton; East African Rift; Kalahari Craton; Okavango Rift Zone; 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; Geology; Numerical Analysis and Scientific Computing
article description
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.