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Off-rift volcanism in rift zones determined by crustal unloading

Nature Geoscience volume 7, pages 297–300 (2014)Cite this article

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Abstract

When continents are stretched over a long period of time, deep elongated rift valleys form at Earth’s surface and zones of ponded magma, centred beneath the rift, form at the crust–mantle boundary1,2. Ascending magma sometimes erupts within the rift valley3,4 or, counterintuitively, at volcanic fields away from the rift valley that are offset by tens of kilometres from the source of magma at depth5,6,7,8. The controls on the distribution of this off-rift volcanism are unclear. Here we use a numerical model of magmatic dyke propagation during rifting to investigate why some dykes reach the surface outside the rift valley, whereas others are confined to the valley. We find that the location of magmatism is governed by the competition between tectonic stretching and gravitational unloading pressure, caused by crustal thinning and faulting along the rift borders. When gravitational unloading dominates over tectonic stretching forces, dykes ascending from the ponded magma are steered towards the rift sides, eventually causing off-rift eruptions. Our model also predicts the formation of stacked magma sills in the lower crust above the magma-ponding zone, as well as the along-rift propagation of shallow dykes during rifting events, consistent with observations of magmatism and volcanism in rift zones globally. We conclude that rift topography-induced stress changes provide a fundamental control on the transfer of magma from depth to the surface.

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Figure 1: Examples of off-rift volcanism.
Figure 2: Set-up for the numerical experiments.
Figure 3: Numerical simulations.
Figure 4: Summary of the numerical results.

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Acknowledgements

C. Pagli is acknowledged for extracting the SRTM DEM for the CdPs. The work was financially supported by the ERC StG project N. 240583 CCMP-POMPEI. V.A. acknowledges the PRIN 2009 project.

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Authors and Affiliations

  1. GFZ German Centre for Geosciences, Section 2.1, Telegrafenberg 14473 Potsdam, Germany,

    Francesco Maccaferri & Eleonora Rivalta

  2. Institute of Geophysics, University of Hamburg, Bundesstr. 55 20146, Hamburg, Germany,

    Francesco Maccaferri & Eleonora Rivalta

  3. National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK

    Derek Keir

  4. Dipartimento di Scienze, University of Roma Tre, L. S.L. Murialdo, 1 00146, Roma, Italy,

    Valerio Acocella

Authors
  1. Francesco Maccaferri
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  3. Derek Keir
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  4. Valerio Acocella
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Contributions

F.M. and E.R. planned the paper, the numerical experiments and formulated the analytical modelling. F.M. implemented and ran the BE code. D.K. and V.A. compared the numerical results with natural cases. D.K. made Fig. 1 with input from V.A. F.M. made Figs 2–4 with input from E.R. All authors discussed the results and contributed to writing the manuscript.

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Correspondence to Francesco Maccaferri.

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Maccaferri, F., Rivalta, E., Keir, D. et al. Off-rift volcanism in rift zones determined by crustal unloading. Nature Geosci 7, 297–300 (2014). https://doi.org/10.1038/ngeo2110

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