Water-rich basalts at mid-ocean-ridge cold spots

Abstract

Although water is only present in trace amounts in the suboceanic upper mantle, it is thought to play a significant role in affecting mantle viscosity, melting and the generation of crust at mid-ocean ridges. The concentration of water in oceanic basalts1,2 has been observed to stay below 0.2 wt%, except for water-rich basalts sampled near hotspots and generated by ‘wet’ mantle plumes3,4,5. Here, however, we report unusually high water content in basaltic glasses from a cold region of the mid-ocean-ridge system in the equatorial Atlantic Ocean. These basalts are sodium-rich, having been generated by low degrees of melting of the mantle, and contain unusually high ratios of light versus heavy rare-earth elements, implying the presence of garnet in the melting region. We infer that water-rich basalts from such regions of thermal minima derive from low degrees of ‘wet’ melting greater than 60 km deep in the mantle, with minor dilution by melts produced by shallower ‘dry’ melting—a view supported by numerical modelling. We therefore conclude that oceanic basalts are water-rich not only near hotspots, but also at ‘cold spots’.

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Figure 1: Distribution of Na8 and (H2O)8 in MORB glasses along the axis of the Mid-Atlantic Ridge from Iceland to the Equator.
Figure 2: Geometry of the passive-flow model.
Figure 3: Multibeam topography of the eastern Romanche ridge–transform intersection and predicted melt production beneath the ERRS.
Figure 4: Relationships between melt parameters predicted for MOR melting regimes and values obtained from the basalts sampled along the ERRS axis (Supplementary Table).

References

  1. 1

    Danyushevsky, L. V. The effect of small amounts of H2O on crystallisation of mid-ocean ridge and backarc basin magmas. J. Volcanol. Geotherm. Res. 110, 265–280 (2001)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Michael, P. J. The concentration, behavior and storage of H2O in the suboceanic upper mantle — Implications for mantle metasomatism. Geochim. Cosmochim. Acta 52, 555–566 (1988)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Nichols, A. R. L., Carroll, M. R. & Hoskuldsson, A. Is the Iceland hot spot also wet? Evidence from the water contents of undegassed submarine and subglacial pillow basalts. Earth Planet. Sci. Lett. 202, 77–87 (2002)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Asimow, P. D., Dixon, J. E. & Langmuir, C. H. A hydrous melting and fractionation model for mid-ocean ridge basalts: Application to the Mid-Atlantic Ridge near the Azores. Geochem. Geophys. Geosyst. 5, Q01E16, doi:10.1029/2003GC000568 (2004)

    Article  Google Scholar 

  5. 5

    Dixon, J. E. & Clague, D. A. Volatiles in basaltic glasses from Loihi Seamount, Hawaii; evidence for a relatively dry plume component. J. Petrol. 42, 627–654 (2001)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Dixon, J. E. & Stolper, E. M. An experimental study of water and carbon dioxide solubilities in mid-ocean ridge basaltic liquids. 2. Applications to degassing. J. Petrol. 36, 1633–1646 (1995)

    CAS  Google Scholar 

  7. 7

    Klein, E. M. & Langmuir, C. H. Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness. J. Geophys. Res. 92, 8089–8115 (1987)

    ADS  CAS  Article  Google Scholar 

  8. 8

    Taylor, B. & Martinez, F. Back-arc basin basalt systematics. Earth Planet. Sci. Lett. 210, 481–497 (2003)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Schilling, J. G. Azores mantle blob: The rare-earth evidence. Earth Planet. Sci. Lett. 24, 103–105 (1975)

    ADS  Article  Google Scholar 

  10. 10

    Bonatti, E. Not so hot “hot spots” in the oceanic mantle. Science 250, 107–111 (1990)

    ADS  Article  Google Scholar 

  11. 11

    Bonatti, E., Seyler, M. & Sushevskaya, N. A cold suboceanic mantle belt at the Earth's equator. Science 261, 315–320 (1993)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Schilling, J. G. et al. Thermal structure of the mantle beneath the equatorial mid-Atlantic ridge—Inferences from the spatial variation of dredged basalt glass compositions. J. Geophys. Res. 100, 10057–10076 (1995)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Bonatti, E. et al. Steady-state creation of crust-free lithosphere at cold spots in mid-ocean ridges. Geology 29, 979–982 (2001)

    ADS  Article  Google Scholar 

  14. 14

    Fox, P. J. & Gallo, D. The tectonics of ridge transform intersections. Tectonophysics 104, 204–242 (1984)

    ADS  Article  Google Scholar 

  15. 15

    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)

    ADS  CAS  Article  Google Scholar 

  16. 16

    Braun, M. G., Hirth, G. & Parmentier, E. M. The effect of deep damp melting on mantle flow and melt generation beneath mid-ocean ridges. Earth Planet. Sci. Lett. 176, 339–356 (2000)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Asimow, P. D. & Langmuir, C. H. The importance of water to oceanic mantle melting regimes. Nature 421, 815–820 (2003)

    ADS  CAS  Article  Google Scholar 

  18. 18

    Katz, R. F., Spiegelman, M. & Langmuir, C. H. A new parameterization of hydrous mantle melting. Geochem. Geophys. Geosyst. 4, 1073, doi:10.1029/2002GC000433 (2003)

    ADS  Article  Google Scholar 

  19. 19

    Gast, P. Trace element fractionations and the origin of tholeiitic and alkaline magma types. Geochim. Cosmochim. Acta 32, 1057–1086 (1968)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Shen, Y. & Forsyth, D. W. Geochemical constraints on initial and final depths of melting beneath mid-ocean ridges. J. Geophys. Res. 100, 2211–2237 (1995)

    ADS  CAS  Article  Google Scholar 

  21. 21

    Hellebrand, E., Snow, J. E., Dick, H. J. B. & Hofmann, A. W. Coupled major and trace elements as indicators of the extent of melting in mid-ocean-ridge peridotites. Nature 410, 677–681 (2001)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Ellam, R. M. Lithospheric thickness as a control on basalt geochemistry. Geology 20, 153–156 (1992)

    ADS  Article  Google Scholar 

  23. 23

    McKenzie, D. & O'Nions, R. K. Partial melt distributions from inversion of rare earth element concentrations. J. Petrol. 32, 1021–1091 (1991)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Hellebrand, E., Snow, J. E., Hoppe, P. & Hofmann, A. W. Garnet-field melting and late-stage refertilization in “residual” abyssal peridotites from the central Indian ridge. J. Petrol. 43, 2305–2338 (2002)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Christie, D. M., West, B. P., Pyle, D. G. & Hanan, B. B. Chaotic topography, mantle flow and mantle migration in the Australian-Antarctic discordance. Nature 394, 637–644 (1998)

    ADS  CAS  Article  Google Scholar 

  26. 26

    Michael, P. J. et al. Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge, Arctic Ocean. Nature 423, 956–961 (2003)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Ottolini, L., Bottazzi, P., Zanetti, A. & Vannucci, R. Determination of hydrogen in silicates by secondary ion mass spectrometry. Analyst 120, 1309–1314 (1995)

    ADS  CAS  Article  Google Scholar 

  28. 28

    Phipps Morgan, J. & Forsyth, D. W. Three-dimensional flow and temperature perturbations due to a transform offset: Effects on oceanic crustal and upper mantle structure. J. Geophys. Res. 93, 2955–2966 (1988)

    ADS  Article  Google Scholar 

  29. 29

    DeMets, C., Gordon, R. G., Argus, D. F. & Stein, S. Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions. Geophys. Res. Lett. 21, 2191–2194 (1994)

    ADS  Article  Google Scholar 

  30. 30

    Anders, E. & Grevesse, N. Abundances of the elements: Meteoritic and solar. Geochim. Cosmochim. Acta 53, 197–214 (1989)

    ADS  CAS  Article  Google Scholar 

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Acknowledgements

We thank D. Brunelli for comments, and D. W. Forsyth for providing programs for temperature calculations. This work was supported by the Italian Consiglio Nazionale Ricerche, the US National Science Foundation and the EUROMARGINS programme.

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Correspondence to Enrico Bonatti.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Table

This table shows average chemical parameters obtained from basaltic glasses sampled along the eastern Romanche Ridge segment. (DOC 42 kb)

Supplementary Discussion

This provides a detailed description of the numerical modelling used. (DOC 2770 kb)

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Ligi, M., Bonatti, E., Cipriani, A. et al. Water-rich basalts at mid-ocean-ridge cold spots. Nature 434, 66–69 (2005). https://doi.org/10.1038/nature03264

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