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Seismic Anisotropy and Mantle Dynamics Beneath the Malawi Rift Zone, East Africa
Tectonics
  • Cory A. Reed
  • Kelly H. Liu, Missouri University of Science and Technology
  • Youqiang Yu
  • Stephen S. Gao, Missouri University of Science and Technology
Abstract

SKS, SKKS, and PKS splitting parameters measured at 34 seismic stations that we deployed in the vicinity of the Cenozoic Malawi Rift Zone (MRZ) of the East African Rift System demonstrate systematic spatial variations with an average splitting time of 1.0 ± 0.3 s. The overall NE-SW fast orientations are consistent with absolute plate motion (APM) models of the African Plate constructed under the assumption of no-net rotation of the global lithosphere and are inconsistent with predicted APM directions from models employing a fixed hot spot reference frame. They also depart considerably from the trend of most of the major tectonic features. These observations, together with the results of anisotropy depth estimation using the spatial coherency of the splitting parameters, suggest a mostly asthenospheric origin of the observed azimuthal anisotropy. The single-layered anisotropy observed at 30 and two-layered anisotropy observed at 4 of the 34 stations can be explained by APM-related simple shear within the rheologically transitional layer between the lithosphere and asthenosphere, as well as by the horizontal deflection of asthenospheric flow along the southern and western edges of a continental block with relatively thick lithosphere revealed by previous seismic tomography and receiver function investigations. This first regional-scale shear wave splitting investigation of the MRZ suggests the absence of rifting-related active mantle upwelling or small-scale mantle convection and supports a passive-rifting process for the MRZ.

Department(s)
Geosciences and Geological and Petroleum Engineering
Geographic Coverage
East Africa
Document Type
Article - Journal
Document Version
Final Version
File Type
text
Language(s)
English
Rights
© 2017 Blackwell Publishing Ltd, All rights reserved.
Publication Date
7-1-2017
Disciplines
Citation Information
Cory A. Reed, Kelly H. Liu, Youqiang Yu and Stephen S. Gao. "Seismic Anisotropy and Mantle Dynamics Beneath the Malawi Rift Zone, East Africa" Tectonics Vol. 36 Iss. 7 (2017) p. 1338 - 1351 ISSN: 0278-7407
Available at: http://works.bepress.com/kelly-liu/108/