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Magma-assisted rifting in Ethiopia

Abstract

The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick continental lithosphere1,2. However, Buck1 has proposed that lithospheric heating by mantle upwelling and related magma production could promote lithospheric rupture at much lower stresses. Such models of mechanical versus magma-assisted extension can be tested, because they predict different temporal and spatial patterns of crustal and upper-mantle structure. Changes in plate deformation produce strain-enhanced crystal alignment and increased melt production within the upper mantle, both of which can cause seismic anisotropy3. The Northern Ethiopian Rift is an ideal place to test break-up models because it formed in cratonic lithosphere with minor far-field plate stresses4,5. Here we present evidence of seismic anisotropy in the upper mantle of this rift zone using observations of shear-wave splitting. Our observations, together with recent geological data, indicate a strong component of melt-induced anisotropy with only minor crustal stretching, supporting the magma-assisted rifting model in this area of initially cold, thick continental lithosphere.

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Figure 1: SKS splitting results in the region of the Northern Ethiopian Rift.
Figure 2: Shear-wave splitting parameters, φ (top panels) and δt (bottom panels), as a function of distance perpendicular to the rift (NW to SE) (left panels) and distance along the rift moving from the SW to the NE (right panels).

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Acknowledgements

We thank the EAGLE working group6 and especially L. Asfaw and A. Ayele for help with the EAGLE experiment. We thank SEIS-UK for equipment and technical support. We also thank M. Savage, R. Huismans, T. Furman, R. Buck and E. Calais for comments on the manuscipt and A. Parr for help with the data processing. Funding was provided by NERC-UK grants.

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Correspondence to J.-M. Kendall.

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Supplementary information

Supplementary Figure 1a

Examples of SKS splitting at one of the BB stations, GEWE, and one of the rift valley stations, E48. (PDF 173 kb)

Supplementary Figure 1b

Examples of SKS splitting at one of the BB stations, GEWE, and one of the rift valley stations, E48. (PDF 209 kb)

Supplementary Table 1

List of events used in shear-wave splitting analysis. Last column indicates phase used in splitting analysis. (PDF 21 kb)

Supplementary Table 2

Summary of splitting parameters obtained for each station. (PDF 26 kb)

Supplementary Figure and Table Legends

Legends to accompany the above. (DOC 22 kb)

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Kendall, JM., Stuart, G., Ebinger, C. et al. Magma-assisted rifting in Ethiopia. Nature 433, 146–148 (2005). https://doi.org/10.1038/nature03161

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