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A tree of Indo-African mantle plumes imaged by seismic tomography

Nature Geoscience volume 14, pages 612–619 (2021)Cite this article

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Abstract

Mantle plumes were conceived as thin, vertical conduits in which buoyant, hot rock from the lowermost mantle rises to Earth’s surface, manifesting as hotspot-type volcanism far from plate boundaries. Spatially correlated with hotspots are two vast provinces of slow seismic wave propagation in the lowermost mantle, probably representing the heat reservoirs that feed plumes. Imaging plume conduits has proved difficult because most are located beneath the non-instrumented oceans, and they may be thin. Here we combine new seismological datasets to resolve mantle upwelling across all depths and length scales, centred on Africa and the Indian and Southern oceans. Using seismic waves that sample the deepest mantle extensively, we show that mantle upwellings are arranged in a tree-like structure. From a central, compact trunk below ~1,500 km depth, three branches tilt outwards and up towards various Indo-Austral hotspots. We propose that each tilting branch represents an alignment of vertically rising blobs or proto-plumes, which detached in a linear staggered sequence from their underlying low-velocity corridor at the core–mantle boundary. Once a blob reaches the viscosity discontinuity between lower and upper mantle, it spawns a ‘classical’ plume-head/plume-tail sequence.

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Fig. 1: The RHUM–RUM experiment instrumented the southwestern Indian Ocean with 57 broadband OBSs and 35 broadband land seismometers.
Fig. 2: East–west cross sections through La Réunion and South Africa, showing the contributions of three tomography datasets to resolving whole-mantle structure.
Fig. 3: 3D rendering of slow P-velocity anomalies in model RROx-19.
Fig. 4: 3D rendering of seismically slow regions in the lower mantle, presumed to be upwelling.
Fig. 5: Interpreted evolution of a tilted mid-mantle upwelling underlain by a low-velocity CMB corridor.

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Data availability

All data used in this study are freely retrievable from international data centres that support the ‘web service’ protocol of the International Federation of Digital Seismograph Networks. We used the obspyDMT software of Hosseini and Sigloch56 to retrieve and pre-process all the waveforms used in this study. Our tomography model and the models compared with in this paper are freely available through the ‘SubMachine’ tomography web portal: http://submachine.earth.ox.ac.uk/ (where the user can select models, depths and other parameters).

Code availability

The software used for tomographic inversion is available upon request from the corresponding author. It was customized from the software freely available at https://www.geoazur.fr/GLOBALSEIS/Soft.html.

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Acknowledgements

RHUM–RUM was funded by Deutsche Forschungsgemeinschaft in Germany (grants SI1538/2-1, SI1538/3-1 and SI1538/4-1 and ship grant R/V Meteor cruise 101) and by Agence Nationale de la Recherche in France (project ANR-11-BS56-0013). Additional supports came from Centre National de la Recherche Scientifique–Institut National des Sciences de l’Univers (CNRS–INSU), Terres Australes et Antarctiques Françaises (TAAF), Institut Polaire Paul Emile Victor (IPEV), University of La Réunion and Alfred Wegener Institut (AWI). OBSs were provided by DEPAS (Deutsche Geräte-Pool für Amphibische Seismologie, Bremerhaven), GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel and INSU-IPGP (Institut National des Sciences de l’Univers - Institut de Physique du Globe de Paris). M.T. was funded by the NERC DTP in Environmental Research award NE/L002612/1 and a St. Edmund Hall RCUK Partnership award. K.S. acknowledges additional funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013/ under REA grant agreement no. PCIG14-GA-2013-631104 ‘RHUM–RUM’ and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement 639003 ‘DEEP TIME’). K.H. acknowledges support by The Alan Turing Institute under the EPSRC grant EP/N510129/1. We thank M. Wysession for sharing MACOMO data. This is IPGP contribution 4097.

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Authors and Affiliations

  1. Department of Earth Sciences, University of Oxford, Oxford, UK

    Maria Tsekhmistrenko, Karin Sigloch & Kasra Hosseini

  2. Geophysics Section, Dublin Institute of Advanced Studies, Dublin, Ireland

    Maria Tsekhmistrenko

  3. Université Côte d’Azur, Géoazur, CNRS, UMR 7329, Sophia Antipolis Cedex, France

    Karin Sigloch

  4. The Alan Turing Institute, British Library, London, UK

    Kasra Hosseini

  5. Université de Paris, Institut de physique du globe de Paris, CNRS, UMR 7154, Paris, France

    Guilhem Barruol

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  1. Maria Tsekhmistrenko
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Contributions

M.T. analysed the RHUM–RUM body-wave data, modelled their sensitivities and developed the 3D visualization techniques. K.H. analysed the P-diffracted data and computed sensitivity kernels. M.T. and K.H. jointly integrated the datasets into a global-scale tomographic model. K.S. designed the tomography studies and acted as the primary academic adviser to M.T. and K.H. G.B. and K.S. designed the RHUM–RUM experiment and led the acquisition of its data. All authors contributed to writing this manuscript.

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Correspondence to Maria Tsekhmistrenko.

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Peer review information Nature Geoscience thanks Alistair Boyce, Jeroen Ritsema 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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Extended data

Extended Data Fig. 1 East-west, thick-slice cross-section through Réunion and South Africa: comparison of our model (top) with other published tomography models.

View and 3-D visualisation are the same as in Figs. 2 and 3. Colour bar refers to dVp/Vp in % for P-velocity models and dVs/Vs for S-velocity models. Orange line on the CMB outlines the ‘Plume Generation Zone’ proposed by Burke et al. (ref. 4), a convenient visual guide for model comparison. Top row: three global P-wave tomographies, by Hosseini et al. 2019 (DETOX-P323); Obayashi et al. 2014 (GAP-P474); Houser et al. 2006 (HMSL-P0675). Middle and bottom row: 6 global S-velocity models, by Montelli et al. 2006 (PRI-S0570); Moulik et al. 2016 (S363ANI + M76); Ritsema et al. 2011 (S40RTS77); Auer 2014 (savani78), French and Romanowicz 2014 (SEMUCB-WM179), Lu and Grand 2016 (TX201580).

Extended Data Fig. 2 Tomography result and resolution test for two thin vertical plume conduits observed in the upper mantle slight southwest of La Réunion and offshore southernmost Madagascar.

Top row, left: Joint tomography model (ISC, Pdiff, RHUM-RUM P) at 200 km depth (map outcrop extending from 11ºS/45ºE to 26ºS/65ºE). Purple dots are RHUM-RUM OBS locations. The dominant feature is the sharp, SW-NE-trending contrast between slow (red) anomalies around the Réunion hotspot and its asthenospheric flows towards the Central Indian Ridge (which runs N-S along the easternmost edge of the map), versus the fast (blue) anomalies of the Mascarene basin’s old, thick lithosphere. Top right: Cross-section through the two slow conduits. Its location is marked in the previous map by a black line and coloured dots. (Due to their three-dimensional, moderately tilting geometries, the conduits are more clearly apparent as such in the 3-D thick-slice rendering of Fig. 3.) Second row: Cross-sections of resolution test input and output, consisting of two vertical columns of 150 km diameter in the observed locations, from the surface to 700 km depth. Rows 3-6: Resolution test input and output at 150, 300, 500 and 700 km depth. The Réunion column is more difficult to recover than the Madagascar column because it falls into a gap between OBS stations.

Extended Data Fig. 3 Whole mantle cross-section striking north-south through Réunion; the view is from the east.

Left panel shows a 2-D section; right panel shows the same section supplemented by low-velocity isosurfaces rendered in a 1000-km thick great-circle slice (shaded blue in the globe inset). Same rendering styles as in Fig. 2. This perspective shows most clearly the absence of Réunion plume tail into the lowermost mantle. Long-dashed purple line marks the interpreted cusp of the LLVP, as in Fig. 3. Bull’s-eye marks the area where the Kerguelen mid-mantle branch emerges toward the viewer.

Extended Data Fig. 4 Model comparison of seismically slow anomalies extending up to 500 km above the CMB (2400-2900 km depth).

The same 4 P-velocity and 6 S-velocity models are rendered as in Extended Data Fig. 1. Visualization style of five nested, slow velocity isosurfaces is the same as in Figs. 2, 3, and Extended Data Fig. 1. The orange line at the CMB outlines the Plume Generation Zone proposed by ref. 4. Southwestward away from the LLVP’s core (reddest area), in direction of 7 o’clock, DETOX-P3 and all six S-wave models show a bulge towards Bouvet hotspot. This observation is consistent with the existence of a fully developed CMB corridor towards Bouvet, which would be recovered only as such a vestigial bulge (see targeted resolution test Extended Data Fig. 5) by our tomography, and presumably by others.

Extended Data Fig. 5 Seismic resolvability of three slow corridors at the CMB.

Left: the resolution test input consists of three corridor-like, slow anomalies diverging from the LLVP centre under South Africa. Its geometries are idealised from lowermost mantle structure imaged by RROx-19. As in the tomography, corridors are ~700 km wide and 500 km ‘high’ above the CMB. The white column shows the location of Bouvet. Right: the results of this test confirm that the Southern Indian Ocean and East African corridors can be recovered well, while a Bouvet corridor would not be resolvable in our model, except for remnant southeastward bulging, away from the LLVP’s core. Such a bulge is actually observed by all S-wave tomographies in Extended Data Fig. 4, and by P-wave model DETOX-P3. Hence the presence of a fully developed CMB corridor towards Bouvet is consistent with currently available data.

Extended Data Fig. 6 Thick-slice cross-section through Afar, South Africa, and Bouvet (see globe inset): comparison of our model (top) with other published tomography models.

Same 3-D visualisation and same models rendered as in Supplementary Fig. 1. Colour bar refers to dVp/Vp in % for P-velocity models and dVs/Vs for S-velocity models. Orange line on the CMB outlines the ‘Plume Generation Zone’ proposed by Burke et al. (ref. 4).

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Tsekhmistrenko, M., Sigloch, K., Hosseini, K. et al. A tree of Indo-African mantle plumes imaged by seismic tomography. Nat. Geosci. 14, 612–619 (2021). https://doi.org/10.1038/s41561-021-00762-9

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  • DOI: https://doi.org/10.1038/s41561-021-00762-9

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