Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Melt-rich channel observed at the lithosphere–asthenosphere boundary


The lithosphere–asthenosphere boundary (LAB) separates rigid oceanic plates from the underlying warm ductile asthenosphere. Although a viscosity decrease beneath this boundary is essential for plate tectonics, a consensus on its origin remains elusive. Seismic studies identify a prominent velocity discontinuity at depths thought to coincide with the LAB but disagree on its cause1,2,3,4,5, generally invoking either partial melting6 or a mantle dehydration boundary7 as explanations. Here we use sea-floor magnetotelluric data to image the electrical conductivity of the LAB beneath the edge of the Cocos plate at the Middle America trench offshore of Nicaragua. Underneath the resistive oceanic lithosphere, the magnetotelluric data reveal a high-conductivity layer confined to depths of 45 to 70 kilometres. Because partial melts are stable at these depths in a warm damp mantle8, we interpret the conductor to be a partially molten layer capped by an impermeable frozen lid that is the base of the lithosphere. A conductivity anisotropy parallel to plate motion indicates that this melt has been sheared into flow-aligned tube-like structures9. We infer that the LAB beneath young plates consists of a thin, partially molten, channel of low viscosity that acts to decouple the overlying brittle lithosphere from the deeper convecting mantle. Because this boundary layer has the potential to behave as a lubricant to plate motion, its proximity to the trench may have implications for subduction dynamics.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Regional tectonic map and location of the magnetotelluric survey.
Figure 2: Resistivity model obtained from anisotropic inversion of the sea-floor magnetotelluric data.
Figure 3: High asthenosphere conductivity explained by a thin partially molten layer.


  1. Rychert, C. A. & Shearer, P. M. A global view of the lithosphere-asthenosphere boundary. Science 324, 495–498 (2009)

    CAS  ADS  Article  Google Scholar 

  2. Schmerr, N. The Gutenberg discontinuity: melt at the lithosphere-asthenosphere boundary. Science 335, 1480–1483 (2012)

    CAS  ADS  Article  Google Scholar 

  3. Bagley, B. & Revenaugh, J. Upper mantle seismic shear discontinuities of the Pacific. J. Geophys. Res.. 113, B12301, (2008)

    ADS  Article  Google Scholar 

  4. Nettles, M. & Dziewoński, A. M. Radially anisotropic shear velocity structure of the upper mantle globally and beneath North America. J. Geophys. Res.. 113, B02303, (2008)

  5. Kawakatsu, H. et al. Seismic evidence for sharp lithosphere-asthenosphere boundaries of oceanic plates. Science 324, 499–502 (2009)

    CAS  ADS  Article  Google Scholar 

  6. Anderson, D. L. & Sammis, C. Partial melting in the upper mantle. Phys. Earth Planet. Inter. 3, 41–50 (1970)

    CAS  ADS  Article  Google Scholar 

  7. Karato, S. & Jung, H. Water, partial melting and the origin of the seismic low velocity and high attenuation zone in the upper mantle. Earth Planet. Sci. Lett. 157, 193–207 (1998)

    CAS  ADS  Article  Google Scholar 

  8. Hirschmann, M. M. Partial melt in the oceanic low velocity zone. Phys. Earth Planet. Inter. 179, 60–71 (2010)

    CAS  ADS  Article  Google Scholar 

  9. Caricchi, L., Gaillard, F., Mecklenburgh, J. & Le Trong, E. Experimental determination of electrical conductivity during deformation of melt-bearing olivine aggregates: implications for electrical anisotropy in the oceanic low velocity zone. Earth Planet. Sci. Lett. 302, 81–94 (2011)

    CAS  ADS  Article  Google Scholar 

  10. Ni, H., Keppler, H. & Behrens, H. Electrical conductivity of hydrous basaltic melts: implications for partial melting in the upper mantle. Contrib. Mineral. Petrol. 162, 637–650 (2011)

    CAS  ADS  Article  Google Scholar 

  11. Poe, B. T., Romano, C., Nestola, F. & Smyth, J. R. Electrical conductivity anisotropy of dry and hydrous olivine at 8GPa. Phys. Earth Planet. Inter. 181, 103–111 (2010)

    CAS  ADS  Article  Google Scholar 

  12. Key, K., Constable, S., Matsuno, T., Evans, R. L. & Myer, D. Electromagnetic detection of plate hydration due to bending faults at the Middle America Trench. Earth Planet. Sci. Lett. 351–352, 45–53 (2012)

    ADS  Article  Google Scholar 

  13. deGroot-Hedlin, C. & Constable, S. Occam’s inversion to generate smooth, two-dimensional models from magnetotelluric data. Geophysics 55, 1613–1624 (1990)

    ADS  Article  Google Scholar 

  14. Key, K. & Ovall, J. A parallel goal-oriented adaptive finite element method for 2.5-D electromagnetic modelling. Geophys. J. Int. 186, 137–154 (2011)

    ADS  Article  Google Scholar 

  15. Cox, C. S., Constable, S. C., Chave, A. D. & Webb, S. C. Controlled-source electromagnetic sounding of the oceanic lithosphere. Nature 320, 52–54 (1986)

    ADS  Article  Google Scholar 

  16. Hirschmann, M. M., Tenner, T., Aubaud, C. & Withers, A. C. Dehydration melting of nominally anhydrous mantle: the primacy of partitioning. Phys. Earth Planet. Inter. 176, 54–68 (2009)

    CAS  ADS  Article  Google Scholar 

  17. Stein, C. A. & Stein, S. A model for the global variation in oceanic depth and heat flow with lithospheric age. Nature 359, 123–129 (1992)

    ADS  Article  Google Scholar 

  18. Hirth, G. & Kohlstedt, D. L. Water in the oceanic upper mantle: implications for rheology, melt extraction and the evolution of the lithosphere. Earth Planet. Sci. Lett. 144, 93–108 (1996)

    CAS  ADS  Article  Google Scholar 

  19. Mierdel, K., Keppler, H., Smyth, J. R. & Langenhorst, F. Water solubility in aluminous orthopyroxene and the origin of Earth’s asthenosphere. Science 315, 364–368 (2007)

    CAS  ADS  Article  Google Scholar 

  20. Evans, R. L. et al. Geophysical evidence from the MELT area for compositional controls on oceanic plates. Nature 437, 249–252 (2005)

    CAS  ADS  Article  Google Scholar 

  21. Baba, K., Chave, A. D., Evans, R. L., Hirth, G. & Mackie, R. L. Mantle dynamics beneath the East Pacific Rise at 17°S: insights from the Mantle Electromagnetic and Tomography (MELT) experiment. J. Geophys. Res.. 111, B02101, (2006)

    ADS  Google Scholar 

  22. Ballmer, M. D., van Hunen, J., Ito, G., Tackley, P. J. & Bianco, T. A. Non-hotspot volcano chains originating from small-scale sublithospheric convection. Geophys. Res. Lett.. 34, L23310, (2007)

    ADS  Article  Google Scholar 

  23. Zhu, W., Gaetani, G. A., Fusseis, F., Montesi, L. G. J. & De Carlo, F. Microtomography of partially molten rocks: three-dimensional melt distribution in mantle peridotite. Science 332, 88–91 (2011)

    CAS  ADS  Article  Google Scholar 

  24. Katz, R. F. Magma dynamics with the enthalpy method: benchmark solutions and magmatic focusing at mid-ocean ridges. J. Petrol. 49, 2099–2121 (2008)

    CAS  ADS  Article  Google Scholar 

  25. Kohlstedt, D. L. & Holtzman, B. K. Shearing melt out of the Earth: an experimentalist’s perspective on the influence of deformation on melt extraction. Annu. Rev. Earth Planet. Sci. 37, 561–593 (2009)

    CAS  ADS  Article  Google Scholar 

  26. Höink, T., Jellinek, A. M. & Lenardic, A. Viscous coupling at the lithosphere-asthenosphere boundary. Geochem. Geophys. Geosyst. 12, Q0AK02 (2011)

    Article  Google Scholar 

  27. Takei, Y. & Holtzman, B. K. Viscous constitutive relations of solid-liquid composites in terms of grain boundary contiguity: 1. Grain boundary diffusion control model. J. Geophys. Res.. 114, B06205, (2009)

    ADS  Google Scholar 

  28. Matsuno, T. et al. Upper mantle electrical resistivity structure beneath the central Mariana subduction system. Geochem. Geophys. Geosyst. 11, Q09003 (2010)

    ADS  Article  Google Scholar 

  29. Egbert, G. D. Robust multiple-station magnetotelluric data processing. Geophys. J. Int. 130, 475–496 (1997)

    ADS  Article  Google Scholar 

  30. Hayes, G. P., Wald, D. J. & Johnson, R. L. Slab1.0: A three-dimensional model of global subduction zone geometries. J. Geophys. Res.. 117, B01302, (2012)

    ADS  Article  Google Scholar 

Download references


We thank the captain (M. Stein) and crew of R/V Melville and the governments of Nicaragua and Costa Rica for permission to work in their exclusive economic zones. The following are thanked for their participation in the research cruise: C. Armerding, C. Berger, E. Carruthers, B. Cohen, J. Elsenbeck, T. Matsuno, D. Myer, A. Orange, J. Perez, K. Shadle, J. Souders, K. Weitemeyer, B. Wheelock and S. Zipper; J. Lemire and A. Jacobs are thanked for their efforts with cruise planning, mobilization and demobilization. We thank B. Wheelock and D. Hasterok for discussions. This work was supported by the National Science Foundation (grants OCE-08411141 and OCE-0840894) and the Seafloor Electromagnetic Methods Consortium at Scripps Institution of Oceanography.

Author information

Authors and Affiliations



K.K., R.L.E. and S.C. conceived the survey. K.K. and S.C. collected the data. S.N. and S.C. processed the data. S.N. analysed and inverted the data. S.N. and K.K. developed the interpretation and wrote the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to S. Naif.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Figures

This file contains Supplementary Figures 1-4. (PDF 2672 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Naif, S., Key, K., Constable, S. et al. Melt-rich channel observed at the lithosphere–asthenosphere boundary. Nature 495, 356–359 (2013).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing