On the temporal evolution of long‐wavelength mantle structure of the <scp>E</scp>arth since the early <scp>P</scp>aleozoic

Zhong, Shijie; Rudolph, M. L.

doi:10.1002/2015gc005782

Cited by 48 publications

(66 citation statements)

References 55 publications

(165 reference statements)

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“…Moreover, the prediction is consistent with deformation on the eastern boundary of the Perm Anomaly and the presence of high seismic velocity structures to the east of the Perm Anomaly that also reveal anisotropy in SKS–SKKS splitting measurements18. Together with seismic observations18 and previous models13141516, our results challenge the long-term fixity and rigidity of deep-mantle thermochemical structures.…”

Section: Resultssupporting

confidence: 89%

“…1). Visual comparison suggests the reference model better fits the long-wavelength shape than similar models16. The edges of the model LLSVPs tend to be hotter than their interior (Fig.…”

Section: Resultsmentioning

confidence: 95%

“…This concept has been used to build a model of absolute motion of tectonic plates over the Phanerozoic (past 540 Myr)8, under the assumptions that LLSVPs are fixed9 and non-deforming10 through time. However, numerical models suggest that the influence of sinking slabs1112 should result in LLSVP deformation and motion13141516 over hundreds of million years. Additionally, measurements of differential splitting of SKS and SKKS seismic phases reveal anisotropy along the boundary of the African LLSVP17 and along the eastern boundary of the Perm Anomaly18, suggesting deformation is occurring on the edges of these structures.…”

mentioning

confidence: 99%

“…Finally, while SKS phases passing along the edge of LLSVPs suggest gradients in shear velocity that are too large to be explained by thermal variations alone1920, how chemically distinct LLSVPs are from the rest of the mantle remains unclear21. Previous studies have shown that the largest-scale structure of the lower mantle results from past subduction history11121315162223, without quantifying the geographic match between predicted and tomographic structures or the motion of individual thermochemical structures. Although some geodynamic models2324 produce a Perm-like anomaly linked to the African LLSVP, its tectonic origin remains to be explained.…”

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confidence: 99%

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Origin and evolution of the deep thermochemical structure beneath Eurasia

et al. 2017

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A unique structure in the Earth's lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia. It seismologically resembles the large low-shear velocity provinces (LLSVPs) under Africa and the Pacific, but is much smaller. This challenges the current understanding of the evolution of the plate–mantle system in which plumes rise from the edges of the two LLSVPs, spatially fixed in time. New models of mantle flow over the last 230 million years reproduce the present-day structure of the lower mantle, and show a Perm-like anomaly. The anomaly formed in isolation within a closed subduction network ∼22,000 km in circumference prior to 150 million years ago before migrating ∼1,500 km westward at an average rate of 1 cm year−1, indicating a greater mobility of deep mantle structures than previously recognized. We hypothesize that the mobile Perm Anomaly could be linked to the Emeishan volcanics, in contrast to the previously proposed Siberian Traps.

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Section: Resultssupporting

confidence: 89%

“…1). Visual comparison suggests the reference model better fits the long-wavelength shape than similar models16. The edges of the model LLSVPs tend to be hotter than their interior (Fig.…”

Section: Resultsmentioning

confidence: 95%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Origin and evolution of the deep thermochemical structure beneath Eurasia

et al. 2017

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“…Bower et al 2013;Zhong & Rudolph 2015). We analyse the geographic distributions and morphologies of both slow and fast clusters in order to qualitatively assess to what extent sinking slabs may control the varied morphology of lower-mantle slow structures (e.g.…”

Section: Geodynamic Implicationsmentioning

confidence: 99%

Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

141

147

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S U M M A R YLarge low shear velocity provinces (LLSVPs), whose origin and dynamic implication remain enigmatic, dominate the lowermost mantle. For decades, seismologists have created increasingly detailed pictures of the LLSVPs through tomographic models constructed with different modeling methodologies, data sets, parametrizations and regularizations. Here, we extend the cluster analysis methodology of Lekic et al., to classify seismic mantle structure in five recent global shear wave speed (V S ) tomographic models into three groups. By restricting the analysis to moving depth windows of the radial profiles of V S , we assess the vertical extent of features. We also show that three clusters are better than two (or four) when representing the entire lower mantle, as the boundaries of the three clusters more closely follow regions of high lateral V S gradients. Qualitatively, we relate the anomalously slow cluster to the LLSVPs, the anomalously fast cluster to slab material entering the lower mantle and the neutral cluster to 'background' lower mantle material. We obtain compatible results by repeating the analysis on recent global P-wave speed (V P ) models, although we find less agreement across V P models. We systematically show that the clustering results, even in detail, agree remarkably well with a wide range of local waveform studies. This suggests that the two LLSVPs consist of multiple internal anomalies with a wide variety of morphologies, including shallowly to steeply sloping, and even overhanging, boundaries. Additionally, there are indications of previously unrecognized meso-scale features, which, like the Perm anomaly, are separated from the two main LLSVPs beneath the Pacific and Africa. The observed wide variety of structure size and morphology offers a challenge to recreate in geodynamic models; potentially, the variety can result from various degrees of mixing of several compositionally distinct components. Finally, we obtain new, much larger estimates of the volume/mass occupied by LLSVPs-8.0 per cent ±0.9 (μ ± 1σ ) of whole mantle volume and 9.1 per cent ±1.0 (μ ± 1σ ) of whole mantle mass-and discuss implications for associating the LLSVPs with the hidden reservoir enriched in heat producing elements.

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Mantle control of the geodynamo: Consequences of top‐down regulation

Olson

2016

Geochem. Geophys. Geosyst.

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The mantle global circulation, including deep subduction and lower mantle superplumes, exerts first‐order controls on the evolution of the core, the history of the geodynamo, and the structure of the geomagnetic field. Mantle global circulation models that include realistic plate motions, deep subduction, and compositional heterogeneity similar to the observed large low seismic velocity provinces in the lower mantle predict that the present‐day global average heat flux at the core‐mantle boundary (CMB) exceeds 85 mW m−2. This is sufficient to drive the present‐day geodynamo by thermochemical convection and implies a very young inner core, with inner core nucleation between 400 and 1100 Ma. The mantle global circulation also generates spatially heterogeneous heat flux at the CMB, with peak‐to‐peak lateral variations exceeding 100 mW m−2. Such extreme lateral variability in CMB heat flux, in conjunction with the high thermal conductivity of the core, implies that the liquid outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces. Numerical dynamo simulations show how this pattern of heterogeneous boundary heat flux affects flow in the outer core, producing localized circulation patterns beneath the CMB tied to the mantle heterogeneity and long‐lived deviations from axial symmetry in the geomagnetic field.

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On the temporal evolution of long‐wavelength mantle structure of the Earth since the early Paleozoic

Cited by 48 publications

References 55 publications

Origin and evolution of the deep thermochemical structure beneath Eurasia

Origin and evolution of the deep thermochemical structure beneath Eurasia

Morphology of seismically slow lower-mantle structures

Mantle control of the geodynamo: Consequences of top‐down regulation

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