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Assembly of the basal mantle structure beneath Africa

An Author Correction to this article was published on 27 May 2022

This article has been updated

Abstract

Plate tectonics shapes Earth’s surface, and is linked to motions within its deep interior1,2. Cold oceanic lithosphere sinks into the mantle, and hot mantle plumes rise from the deep Earth, leading to volcanism3,4. Volcanic eruptions over the past 320 million years have been linked to two large structures at the base of the mantle presently under Africa and the Pacific Ocean5,6. This has led to the hypothesis that these basal mantle structures have been stationary over geological time7,8, in contrast to observations and models suggesting that tectonic plates9,10, subduction zones11,12,13,14 and mantle plumes15,16 have been mobile, and that basal mantle structures are presently deforming17,18. Here we reconstruct mantle flow from one billion years ago to the present day to show that the history of volcanism is statistically as consistent with mobile basal mantle structures as with fixed ones. In our reconstructions, cold lithosphere sank deep into the African hemisphere between 740 and 500 million years ago, and from 400 million years ago the structure beneath Africa progressively assembled, pushed by peri-Gondwana slabs, to become a coherent structure as recently as 60 million years ago. Our mantle flow models suggest that basal mantle structures are mobile, and aggregate and disperse over time, similarly to continents at Earth’s surface9. Our models also predict the presence of continental material in the mantle beneath Africa, consistent with geochemical data19,20.

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Fig. 1: Structure of the lower mantle and volcanic eruption locations from 320 Ma to the present day.
Fig. 2: Distributions of distances between basal mantle structures and reconstructed eruption locations.
Fig. 3: Match of model basal mantle structures to volcanic eruption locations and tomographic models.
Fig. 4: Dynamic assembly of the African basal mantle structure and predicted continental crust in the deep Earth.

Data availability

Data generated for this study are available at https://doi.org/10.5281/zenodo.6031641Source data are provided with this paper.

Code availability

The code used to compute the mantle flow models is available at https://github.com/EarthByte/citcoms. Figure 1 was created with the Generic Mapping Tools82 (GMT6) which is open-source software licensed under the GNU Lesser General Public License. Key Python scripts to compute the results shown in Figs. 2, 3 are available at https://doi.org/10.5281/zenodo.6031641. Figures 2, 3 were produced with the open-source Python library Matplotlib83, and Fig. 4 was created with ParaView67, which is shared openly under the 3-Clause BSD License.

Change history

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Acknowledgements

N.F. and Ö.F.B. were supported by Australian Research Council grant LP170100863 (industry partner: De Beers). S.E.W. was supported by National Natural Science Foundation of China grant 41972237 and by Australian Research Council grants DP180102280 and DP200100966. A.S.M. was supported by the Deep Carbon Observatory and the Richard Lounsbery Foundation. This research was supported by the Australian Government’s National Collaborative Research Infrastructure Strategy (NCRIS), with access to computational resources provided by the National Computational Infrastructure (NCI) through the National Computational Merit Allocation Scheme and through the University of Wollongong (UOW).

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Contributions

N.F.: conceptualization, methodology, software, validation, formal analysis, investigation, writing of the original draft, and visualization. Ö.F.B.: methodology, software, formal analysis, review and editing of the paper, and visualization. S.E.W.: methodology, software, and review and editing of the paper. A.S.M.: resources and review and editing of the paper.

Corresponding author

Correspondence to Nicolas Flament.

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Extended data figures and tables

Extended Data Fig. 1 Temporal distribution of considered volcanic eruptions.

Histograms showing the number of volcanic eruptions as a function of age. a, Back to 320 Ma. b, Back to 640 Ma. The number of volcanic eruptions over the considered period for each database is given in brackets. Databases: J18 (ref. 40) and T18 (ref. 41).

Extended Data Fig. 2 Location of volcanic eruptions from 320 Ma in different reconstructions.

High-velocity (white) and low-velocity (grey) regions revealed by k-means cluster analysis between 1,000 km and 2,800 km depth for seismic tomographic model Savani26, and location of volcanic eruptions (diamonds, J18, ref. 40) and kimberlites (circles, T18, ref. 41) reconstructed at their time of eruption and shown at present day using tectonic reconstruction M16 (ref. 44; a), tectonic reconstruction Y19 (ref. 45; b), tectonic reconstruction M21 (ref. 10; c), and tectonic reconstruction M21-NNR without net rotation (no net rotation or ‘NNR’) (d). In ad, the brown lines are present-day coastlines Symbols are coloured by age. Robinson projection at Earth’s surface.

Extended Data Fig. 3 Spatial match of lower mantle structure between mantle flow and tomographic models with respect to tomographic model Savani, and distance to hot basal mantle structures from Savani.

a, Intersection of mantle structure revealed by k-means cluster analysis between 1,000 km and 2,800 km for tomographic model Savani26 and mantle flow model cases 1–9 as indicated. Orange (true positive) indicates high-temperature model regions and low-velocity tomographic regions, grey (true negative) indicates low-temperature model regions and high-velocity tomographic regions, green (false positive) indicates high-temperature model regions and high-velocity tomographic regions and blue (false negative) indicates low-temperature regions and low-velocity tomographic regions. b, As in a but for tomographic model Savani and other tomographic models as indicated. Orange (true positive) indicates low-velocity regions for both models, grey (true negative) indicates high-velocity regions for both models, green (false positive) indicates high-velocity regions for Savani and low-velocity regions for other models and blue (false negative) indicates low-velocity regions for Savani and high-velocity regions for other models. c, Angular distance (AD) to the edge or interior (as indicated) of LLSVPs (delineated by a red contour) as derived by k-means cluster analysis of tomographic model Savani between 1,000 km and 2,800 km depth. In a and b, the white lines indicate a value of five (solid) and a value of one (dotted) in a vote map for low-velocity regions in S-wave tomographic models42. Present-day coastlines are shown in black in ac. Robinson projection at Earth’s surface.

Extended Data Fig. 4 Distributions of distances between basal mantle structures and volcanic eruption locations.

Sample empirical distribution functions (EDFs; blue lines) showing the cumulative probability of minimum angular distances between volcanic eruption locations (J18 and T18) and the closest BMS for the last 320 Myr. Grey lines are a series of 1,000 random EDFs each consisting of points in random locations with the same temporal distribution as in the sample EDF. a, For S-wave tomographic models as indicated. b, For mantle flow models cases 1–22 as indicated.

Extended Data Fig. 5 Match between volcanic eruption locations, tomographic models and mantle flow models for different tectonic reconstructions.

a, Fractional area fa of the surface of cluster maps covered by slow (in tomography) or hot (in flow models, averaged over 320 Myr) BMSs. b, Spatial match \(\overline{{\rm{Acc}}}\) between present-day BMSs for a given case and LLSVPs imaged by tomographic models. c, Time-averaged median of minimum angular distances \(\widetilde{\theta }\) between BMSs and volcanic eruption locations from 320 Ma. d, Fraction fs of random EDFs compared to which the sample EDF passes a statistical test. In ad, the first four rows show results for tomographic models (stationary LLSVPs) and different tectonic reconstructions as indicated, and the fifth and last row shows results for a series of mantle flow models (mobile BMSs) based on different tectonic reconstructions as indicated. NNR, no-net-rotation reference frame; MFM, mantle flow model. Tectonic reconstructions: M16, ref. 44; Y19, ref. 45; M21, ref. 10. The horizontal lines denote reference cases. The grey shadings in ac highlight the range of results for tomographic models.

Source data

Extended Data Fig. 6 Match of model basal mantle structures to volcanic eruption locations and tomographic models: structure interiors and over 640 Myr.

ad, Match to BMS interiors. a, Fractional area fa of the surface of cluster maps covered by slow (in tomography) or hot (in flow models, averaged over 320 Myr) BMSs. b, Spatial match \(\overline{{\rm{Acc}}}\) between present-day BMSs for a given case and LLSVPs imaged by tomographic models. c, Time-averaged median of minimum angular distances \(\widetilde{\theta }\) between BMSs and volcanic eruption locations from 320 Ma, considering distances to be zero within BMSs and positive outwards from their edges. d, Fraction fs of random EDFs compared to which the sample EDF passes a statistical test. eh, Match to BMS edges over 640 Myr. e, Fractional area fa of the surface of cluster maps covered by hot (in flow models, averaged over 640 Myr) or slow (in tomography) BMSs. f, Same as b. g, Time-averaged median of minimum angular distances \(\widetilde{\theta }\) between BMSs and volcanic eruption locations from 640 Ma. h, Same as d. In g, h, open symbols denote results for reconstruction M21 as opposed to M21-NNR. In ah, the first row shows results for a series of tomographic models (stationary LLSVPs), and subsequent rows show results for mantle flow models (mobile BMSs) across which parameters are varied as indicated. BL, basal layer; T1–T7, tomographic models 1–7; C1–C12, mantle flow model cases 1–12. The horizontal lines denote reference cases. The grey shadings in ac, eg highlight the range of results for tomographic models.

Source data

Extended Data Fig. 7 Match of model basal mantle structures to volcanic eruption locations and tomographic models: varying model parameters and African hemisphere.

ad, Match for varied model parameters as indicated. a, Fractional area fa of the surface of cluster maps covered by slow (in tomography) or hot (in flow models, averaged over 320 Myr) BMSs. b, Spatial match \(\overline{{\rm{Acc}}}\) between present-day BMSs for a given case and LLSVPs imaged by tomographic models. c, Time-averaged median of minimum angular distances \(\widetilde{\theta }\) between BMSs and volcanic eruption locations from 320 Ma. d, Fraction fs of random EDFs compared to which the sample EDF passes a statistical test. eh, Match in the African hemisphere. e, Same as a but for different model cases. f, Global spatial match \(\overline{{\rm{Acc}}}\) between present-day BMSs for a given case and LLSVPs imaged by tomographic models. g, Time-averaged median of minimum angular distances \(\widetilde{\theta }\) between BMSs and volcanic eruption locations in the African hemisphere (within 10,000 km of a point located at 0° N, 11° E; ref. 47) from 320 Ma. h, For points within the African hemisphere, fraction fs of random EDFs compared to which the sample EDF passes a statistical test. In ah, the first row shows results for a series of tomographic models (stationary LLSVPs), and subsequent rows show results for mantle flow models (mobile BMSs) across which parameters are varied as indicated. C1–C22, mantle flow model cases 1–22; T1–T7, tomographic models 1–7; ISD, initial slab depth; PCD, phase change depth; BL, basal layer. The horizontal lines denote reference cases. The grey shadings in ac, eg highlight the range of results for tomographic models.

Source data

Extended Data Fig. 8 Snapshots of tectonic reconstruction and synthetic seafloor ages.

af, Location of tectonic blocks for tectonic reconstruction M21-NNR10 in the no-net-rotation frame with synthetic seafloor ages62. Snapshots are shown at: 740 Ma (a), 550 Ma (b), 400 Ma (c), 250 Ma (d), 100 Ma (e), 0 Ma (f). The reconstructed subduction zones are shown as black lines with triangles on the overriding plate, reconstructed mid-oceanic ridges and transform faults are shown in light orange, reconstructed ancient continental interiors are show as light grey polygons with a pattern fill, and present-day coastlines are shown in white in f. The colour scale indicates the palaeo-age of the ocean crust. WGB, west Gondwanan blocks; PTNM, Palaeo-Tethys northern margin; GWM, Gondwana western margin. Robinson projection at Earth’s surface.

Extended Data Fig. 9 Model initial temperature field and present-day temperature and viscosity.

a, b, Initial temperature field for case 7 at 1,000 Ma. a, Temperature at 109 km depth. Reconstructed subduction zones are shown in red, mid-oceanic ridges and transform faults in yellow, and continental blocks in grey. Robinson projection at Earth’s surface. b, Temperature along an equatorial cross-section (green line in a). Numbers above the colour scale indicate non-dimensional temperature, and numbers below the colour scale indicate temperature in kelvin. c, d, Horizontally averaged present-day mantle temperature (c) and viscosity (d). The grey line in d is a viscosity profile adjusted to fit the geoid and post-glacial rebound60.

Extended Data Table 1 Boundary conditions and parameters for mantle flow model cases

Supplementary information

Peer Review File

41586_2022_4538_MOESM2_ESM.mp4

Supplementary Video 1 Structure of the lower mantle and location of volcanic eruptions from 640 Ma to the present day. High-velocity (white) and low-velocity (grey) regions revealed by cluster analysis between 1,000 km and 2,800 km depth for 22 mantle flow model cases and seven tomographic models, and location of volcanic eruptions (diamonds, J18, ref. 40) and kimberlites (circles, T18, ref. 41) reconstructed from 640 Ma in 20-Myr increments. Results are shown starting 40 Myr into models starting after 600 Ma. Locations are shown for eruptions within 10 Myr of the considered age. The black lines indicate a value of (solid) and a value of one (dotted) in a vote map for low-velocity regions in S-wave tomographic models[42]. Symbols are coloured by age.

41586_2022_4538_MOESM3_ESM.mp4

Supplementary Video 2 Evolution of the spatial match of lower mantle structure between mantle flow and tomographic models with respect to tomographic model Savani from 640 Ma to the present day. Intersection of mantle structure revealed by k-means cluster analysis between 1,000 km and 2,800 km for tomographic model Savani[26] and 22 mantle flow model cases and seven tomographic models mantle flow as indicated, since 640 Ma in 20-Myr increments. Results are shown starting 40 Myr into models starting after 600 Ma. Orange (true positive) indicates high-temperature (or low-velocity) regions and low-velocity tomographic regions, grey (true negative) indicates low-temperature (or high-velocity) regions and high-velocity tomographic regions, green (false positive) indicates high-temperature (or low-velocity) regions and high-velocity tomographic regions and blue (false negative) indicates low-temperature (or fast-velocity) regions and low-velocity tomographic regions. The white lines indicate a value of five (solid) and a value of one (dotted) in a vote map for low-velocity regions in S-wave tomographic models[42]. The time-dependent value of \(\overline{{\rm{Acc}}}\) is reported next to each panel.

41586_2022_4538_MOESM4_ESM.mp4

Supplementary Video 3 Evolution of mantle temperature in the African mantle domain from 740 Ma to the present day. Mantle structures 155 K colder than ambient mantle below 300 km depth (coloured by depth with cold colours), and mantle structures 310 K hotter than ambient mantle below 170 km depth (coloured by depth with warm colours) predicted by case 7, shown in 20-Myr increments since 740 Ma for the African mantle domain (the video is centred on the prime meridian, 0° longitude). Reconstructed plate boundaries are shown in cyan and the graticule spacing is 30°.

Supplementary Video 4 Evolution of mantle temperature in the African mantle domain from 740 Ma to the present day. Same as Supplementary Video 3, but for case 4.

Supplementary Video 5 Evolution of mantle temperature in the African mantle domain from 740 Ma to the present day. Same as Supplementary Video 3, but for case 9.

41586_2022_4538_MOESM7_ESM.mp4

Supplementary Video 6 Recycling of continental crust in the African mantle domain from 740 Ma to the present day. Mantle structures 310 K hotter than ambient mantle below 170 km depth (coloured by depth with warm colours), and mantle predicted to consist of at least 5% continental crust (below 170 km depth, coloured by depth with cold colours) shown in 20-Myr increments since 740 Ma for the African mantle domain (the video is centred on the prime meridian, 0° longitude). Reconstructed plate boundaries are shown in cyan and the graticule spacing is 30°.

41586_2022_4538_MOESM8_ESM.mp4

Supplementary Video 7 Recycling of continental crust in the Pacific mantle domain from 740 Ma to the present day. Mantle structures 310 K hotter than ambient mantle below 170 km depth (coloured by depth with warm colours), and mantle predicted to consist of at least 5% continental crust (below 170 km depth, coloured by depth with cold colours) shown in 20-Myr increments since 740 Ma for the Pacific mantle domain (the video is centred on the date line, 180° longitude). Reconstructed plate boundaries are shown in cyan and the graticule spacing is 30°.

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Flament, N., Bodur, Ö.F., Williams, S.E. et al. Assembly of the basal mantle structure beneath Africa. Nature 603, 846–851 (2022). https://doi.org/10.1038/s41586-022-04538-y

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