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Tag: LLSVP

Earth’s mantle heterogeneity theories

Conceptual model sketches for proposed compositional structures of Earth’s mantle, including “Marble cake”, “Thermo-chemical piles”, and “Mid-mantle blobs” theories.

Conceptual model sketches for proposed compositional structures of Earth’s mantle. The “Marble cake” theory emphasises that much of Earth’s mantle is made out of recycled oceanic lithosphere (dark and light) slivers that are preserved throughout the mantle. The “Thermo-chemical piles” theory suggests that intrinsically dense materials may accumulate as piles atop the core–mantle boundary. In particular, the two large low-shear velocity provinces (LLSVPs) in the deep Earth are commonly thought to have resisted mantle mixing due to their thermochemical origin. The “mid-mantle blobs” theory emphasises large, compositionally-different domains that may be located in the mid-mantle of the Earth, with mantle convection being accommodated around them. Red triangles at the surface represent volcanism.

  • Creator: Anna Gülcher
  • This version: 17.12.2022
  • License: Attribution-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
  • Specific citation: These graphics by Anna Gülcher from Gülcher et al. (2021) are available via the open-access s-Ink.org repository.
  • Related reference: Gülcher, A. J. P., Ballmer, M. D., and Tackley, P. J. (2021), Coupled dynamics and evolution of primordial and recycled heterogeneity in Earth’s lower mantle, Solid Earth, 12, 2087–2107, 2021 https://doi.org/10.5194/se-12-2087-2021
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Seismic mantle tomography maps

Surface projected global horizontal seismic S-wave velocity anomaly maps for different mantle depths revealing the two large low shear-wave velocity provinces (LLSVPs).

Surface projected global horizontal seismic S-wave velocity anomaly maps for different mantle depths revealing the two large low shear-wave velocity provinces (LLSVPs) below the Pacific (named Jason) and Africa (named Tuzo). Shown is the S10MEAN model based on Doubrovine et al. (2016) averaging 10 tomography models allowing to compare relative variations in S-wave velocity. The Scientific colour map ‘batlow‘ is used to represent data accurately and to all readers.

  • Creator: Fabio Crameri
  • This version: 31.10.2021
  • License: Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
  • Specific citation: This graphic by Fabio Crameri based on data compiled by Doubrovine et al. (2016) is available via the open-access s-Ink repository.
  • Related references: Doubrovine, P. V., Steinberger, B., and Torsvik, T. H. (2016), A failure to reject: Testing the correlation between large igneous provinces and deep mantle structures with EDF statistics, Geochem. Geophys. Geosyst., 17, 1130– 1163, doi:10.1002/2015GC006044.
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Global-scale mantle flow (sketch)

A sketch outlining the link between the viscous convection within the Earth’s mantle and tectonic surface plate motions.

A sketch outlining the link between the viscous convection within the Earth’s mantle and tectonic surface plate motions, deforming Earth’s surface across wide areas. Shown are the relative positions and motion of some of Earth’s continental (brown) and oceanic plates (blue) captured by the hypothetical cross-section through the middle of the planet. The dynamic link between surface and mantle motion is highlighted by arrows representing first-order material flow direction. This global-scale mantle flow is believed to also affect the shape, position and mobility of large low shear-velocity provinces (LLSVPs; red) at the base of the mantle (yellow) just above the Earth’s core (orange).

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Planetary interior

Comparison of suggested mantle convection in the Earth (mobile-lid mode) and Venus (inefficient short slab mode).

Comparison of suggested mantle convection in Earth and Venus. Mobile-lid mantle convection in the Earth involves most surface plates (dark brown), which are recycled by sinking back into the deep mantle, where large low shear-wave velocity provinces (LLSVPs) exist (whitish). The ongoing plate destruction causes a more heterogeneous mantle and a surface of variable age, with young and thin oceanic plates and old and thick continental plates that remain at the surface. Mantle plumes (light red) tend to occur far away from sinking plates. By contrast, the mode of mantle convection on Venus is suggested to consist of a nearly immobile, mostly stagnant lid, and only localised, short sinking plate portions that are formed by (and thus spatially coincide with) hot mantle upwelling (light red). The resulting surface deformation matches observations from coronae on Venus. The short sinking portions do not, in contrast to Earth, significantly move their tail ends at the surface, which explains the uniformly aged, relatively thick surface plate (dark brown).

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Mantle convection

Illustrative vertical cross-section showing the oceanic plate as part of whole-mantle convection.

The oceanic plate as part of whole-mantle convection. Illustrative vertical cross-section showing the oceanic plate sinking and destructing on its way down into the deep mantle, whereas hot mantle plumes next to large-low-shear-wave-velocity provinces (LLSVPs) form and rise back to the surface forming the process of mantle convection. Resisting whole mantle overturn are only the continental lithosphere, which is light and strong and therefore resists subduction, and the large-low shear-wave velocity provinces (LLSVP), which are chemically heavy features atop the core-mantle boundary. Somewhat passive features in mantle covection are the centre parts of the mantle (in some locations at around 1’000–2’200 km depth) around which the anomalously hot or cold material circles, sometimes called BEAMS, an abbreviation for “bridgmanite-enriched ancient mantle structures“. Thicknesses of individual layers and structures are not perfectly to scale.

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