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Episodic kinematics in continental rifts modulated by changes in mantle melt fraction

Nature volume 547, pages 8488 (06 July 2017) | Download Citation


Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres1, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6–15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres.

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This paper is part of a wider project funded through the New Zealand Marsden Fund, the Earthquake Commission, and Victoria University of Wellington graduate scholarships. J.D.P.M. was supported by the National Research Foundation of Singapore (award NRF-NRFF2013-04) at the Earth Observatory of Singapore.

Author information


  1. Institute of Geophysics, Victoria University of Wellington, Wellington, New Zealand

    • Simon Lamb
    • , Euan Smith
    •  & Tim Stern
  2. Earth Observatory of Singapore, Nanyang Technological University, Singapore

    • James D. P. Moore


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S.L. led the research, carried out the kinematic and flexural analysis, developed the mantle force model and wrote the manuscript. J.D.P.M. developed the viscous flow finite-element models. E.S. calculated horizontal and vertical continuous GPS velocities and their uncertainties. T.S. provided advice and help with all aspects of the study. All authors commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Simon Lamb.

Reviewer Information Nature thanks C. Beaumont, E. Calais and C. Faccenna for their contribution to the peer review of this work.

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