Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

Abstract

Seafloor spreading centres show a regular along-axis segmentation thought to be produced by a segmented magma supply in the passively upwelling mantle1,2. On the other hand, continental rifts are segmented by large offset normal faults, and many lack magmatism. It is unclear how, when and where the ubiquitous segmented melt zones are emplaced during the continental rupture process. Between 14 September and 4 October 2005, 163 earthquakes (magnitudes greater than 3.9) and a volcanic eruption occurred within the 60-km-long Dabbahu magmatic segment of the Afar rift, a nascent seafloor spreading centre in stretched continental lithosphere3,4. Here we present a three-dimensional deformation field for the Dabbahu rifting episode derived from satellite radar data, which shows that the entire segment ruptured, making it the largest to have occurred on land in the era of satellite geodesy. Simple elastic modelling shows that the magmatic segment opened by up to 8 m, yet seismic rupture can account for only 8 per cent of the observed deformation. Magma was injected along a dyke between depths of 2 and 9 km, corresponding to a total intrusion volume of 2.5 km3. Much of the magma appears to have originated from shallow chambers beneath Dabbahu and Gabho volcanoes at the northern end of the segment, where an explosive fissural eruption occurred on 26 September 2005. Although comparable in magnitude to the ten year (1975–84) Krafla events in Iceland5, seismic data suggest that most of the Dabbahu dyke intrusion occurred in less than a week. Thus, magma intrusion via dyking, rather than segmented normal faulting, maintains and probably initiated the along-axis segmentation along this sector of the Nubia–Arabia plate boundary.

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Figure 1: Coloured and shaded relief map for northern Afar, and study area.
Figure 2: Satellite radar data spanning the 2005 Dabbahu rifting event produced using data from ESA's Envisat satellite.
Figure 3: Observed and modelled three-dimensional deformation field of the 2005 Dabbahu rifting episode.

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Acknowledgements

Staff at Addis Ababa University, especially L. M. Asfaw, are thanked for their rapid response to the Dabbahu crisis, as are the Ethiopian Air Force for helicopter support. C. Oppenheimer, T. Kidane, A. Philpotts, D. Ayalew, G. Orsi and A. Asrat provided field reports and initial volcanological observations. This report benefited from discussions with B. Parsons, E. Calais, R. Buck, L. Asfaw, C. Wicks and J. Cann. Our work was supported by an NERC urgency grant, Addis Ababa University, the Ministry of Capacity Building of the Ethiopian Federal Government, and the Afar Regional Government. SAR data were provided quickly by the European Space Agency. T.J.W. is funded by a Royal Society University Research Fellowship. Author Contributions T.J.W., C.E., G.Y. and A.A. planned the project; T.J.W. and J.B. processed, analysed and modelled the radar data; A.S., D.K. and A.A. analysed seismic data; G.Y. and C.E. provided petrological and tectonic context; and T.J.W., C.E., D.K. and J.B. wrote the paper.

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Correspondence to Tim J. Wright.

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Supplementary Notes

This file contains Supplementary Figures 1–6, Supplementary Tables 1–3 and Supplementary Methods. (DOC 4287 kb)

Supplementary Figure 7

This is a full resolution jpeg of Supplementary Figure 1 showing the wrapped, geocoded interferograms used in this study. KML descriptor files are available at http://www.earth.ox.ac.uk/~timw/dabbahu/, so the images can be viewed in Google Earth. Ascending. (PDF 396 kb)

Supplementary Figure 8

This is a full resolution jpeg of Supplementary Figure 2 showing the wrapped, geocoded interferograms used in this study. KML descriptor files are available at http://www.earth.ox.ac.uk/~timw/dabbahu/, so the images can be viewed in Google Earth. Descending. (PDF 496 kb)

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Wright, T., Ebinger, C., Biggs, J. et al. Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode. Nature 442, 291–294 (2006). https://doi.org/10.1038/nature04978

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