Abstract
Most of the Earth's crust is created along 60,000 km of mid-ocean ridge system. Here, tectonic plates spread apart and, in doing so, gradually build up stress. This stress is released during rifting episodes, when bursts of magmatic activity lead to the injection of vertical sheets of magma — termed dykes — into the crust. Only 2% of the global mid-ocean ridge system is above sea level, so making direct observations of the rifting process is difficult. However, geodetic and seismic observations exist from spreading centres in Afar (East Africa) and Iceland that are exposed at the land surface. Rifting episodes are rare, but the few that have been well observed at these sites have operated with remarkably similar mechanisms. Specifically, magma is supplied to the crust in an intermittent manner, and is stored at multiple positions and depths. It then laterally intrudes in dykes within the brittle upper crust. Depending on the availability of magma, multiple magma centres can interact during one rifting episode. If we are to forecast large eruptions at spreading centres, rifting-cycle models will need to fully incorporate realistic crust and mantle properties, as well as the dynamic transport of magma.
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Acknowledgements
Our work is supported by NERC grants NE/D008611/1, NE/D01039X/1 and NE/E007414/1, NSF grants EAR-0635789 and EAR-0613651, a NERC-COMET+ studentship to I.J.H., and a Royal Society University Research Fellowship to T.J.W. Authors in Iceland were supported by the Icelandic Research Fund (through Volcano Anatomy project) and the University of Iceland Research Fund. We are grateful to Janet Key and Bob White for providing seismicity data for Askja, and to the numerous scientists involved in the countless field experiments in Afar and Iceland that have collected the data sets described here. The manuscript was improved by thoughtful comments from Bob White and Falk Amelung. The Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET+) is part of the UK National Environment Research Council's National Centre for Earth Observation.
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T.J.W. and F.S. planned and wrote the article with input from all other authors. Previously unpublished seismic data from Krafla were collected and analysed by P.E. and B.B. Also, D.K., R.P., B.B. and T.W. constructed Fig. 1; B.B., M.B., C.P. and I.J.H. collated data from Dabbahu and Krafla to build Figs 2 and 3; I.J.H. and T.W. conducted a new analysis of InSAR data to make Fig. 4; R.P. and C.P. created Fig. 5; T.J.W. and F.S. designed Fig. 6 with input from other authors.
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Wright, T., Sigmundsson, F., Pagli, C. et al. Geophysical constraints on the dynamics of spreading centres from rifting episodes on land. Nature Geosci 5, 242–250 (2012). https://doi.org/10.1038/ngeo1428
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