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Oceanic crustal flow in Iceland observed using seismic anisotropy

Nature Geoscience volume 14, pages 168–173 (2021)Cite this article

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Abstract

Understanding accretion and deformation processes at mid-ocean ridges is crucial as they control the resulting oceanic crustal structure, which covers two-thirds of Earth’s surface. The most common tool for observing such dynamic processes within the Earth is seismic anisotropy. Iceland, which is uplifted by a convective mantle plume and has an active spreading ridge system exposed above sea level, offers a unique opportunity for studying this phenomenon. Here we use a high-resolution dataset of Love and Rayleigh wave speeds to constrain the seismic anisotropy in the Icelandic crust. We show that seismic anisotropy in the lower crust is controlled by crystal preferred orientation, providing a direct observation of lower crustal flow. Furthermore, since shear is needed to align the crystals, our results reveal that crustal flow cannot be a simple translation of mass and requires internal deformation. This finding suggests that crustal flow plays an important role in oceanic crustal accretion and deformation where thick, hot oceanic crust is formed, such as at volcanic rifted margins and where there are mantle plume–ridge interactions.

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Fig. 1: Crustal thickness in Iceland and ray path coverage.
Fig. 2: Path average ξ from phase velocity dispersion curves.
Fig. 3: Radial anisotropy models for TPL and olivine LPO.
Fig. 4: ξ versus azimuth at different depths.

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Data availability

Seismic data from the HOTSPOT (https://doi.org/10.7914/SN/XD_1996) network, the Cambridge University network in Iceland (https://doi.org/10.7914/SN/Z7_2010) and the station BORG from the GSN network (https://doi.org/10.7914/SN/II) can be freely accessed on the Incorporated Research Institutions for Seismology website (http://service.iris.edu/fdsnws/dataselect/1/). Data from the IMAGE project by GFZ (stations KEF, SUH, HOV) and from BGS (stations FAL1, FAL 3) are available from those institutions and were used under license for the current study: for data requests from GFZ or BGS, please contact those organizations directly. All seismic noise cross correlations used in this work are freely available at https://doi.org/10.6084/m9.figshare.13228211.

Code availability

All software used in this work is freely available online. MSNoise, a Python package for computing cross correlations, is available at http://www.msnoise.org/. ts-PWS, a software package for computing the time-scale phase-weighted stack, is available at https://github.com/sergiventosa/ts-PWS. SURF96, software for surface wave analysis, is available at http://www.eas.slu.edu/eqc/eqc_cps/.

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Acknowledgements

A number of seismometers were borrowed from the Natural Environment Research Council (NERC) SEIS-UK facility (loans 914, 968 and 1071). The work was funded by research grants from the NERC to R.S.W. (numbers NE/H025006/1, NE/F011407/1, NE/M017427/1) and the European Community’s Seventh Framework Program grant no. 308377 (FUTUREVOLC) to R.S.W. The IMAGE project received funding from the European Union’s Seventh Program for research, technological development and demonstration under grant agreement number 608553. Stations for the IMAGE project were provided by the Geophysical Instrument Pool of Potsdam (GFZ). Work undertaken in this study was financially supported by studentships from the NERC and Shell. We thank B. Brandsdóttir, S. Steinþórsson and all those who assisted with fieldwork in Iceland. The British Geological Survey (BGS) kindly provided additional data from their seismometers in northeast Iceland. S.P. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie Grant Agreement 790203.

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Authors and Affiliations

  1. Department of Earth Sciences, Bullard Laboratories, University of Cambridge, Cambridge, UK

    Omry Volk, Robert S. White, Simone Pilia, John Maclennan & Nicholas Rawlinson

  2. GeoForschungsZentrum Potsdam, Potsdam, Germany

    Robert G. Green

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Contributions

O.V., N.R., R.S.W. and R.G.G. have participated in collecting the data in the field. O.V., S.P. and R.G.G. performed the data processing. J.M. assisted in the interpretation of the results. The manuscript was written by O.V., N.R. and R.S.W. with all authors contributing towards discussing and interpreting the results and refining the paper.

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Correspondence to Omry Volk.

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Peer review information Stefan Lachowycz. Nature Geoscience thanks Harro Schmeling, James Gaherty and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Stefan Lachowycz.

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Volk, O., White, R.S., Pilia, S. et al. Oceanic crustal flow in Iceland observed using seismic anisotropy. Nat. Geosci. 14, 168–173 (2021). https://doi.org/10.1038/s41561-021-00702-7

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