Synthetic tomography of plume clusters and thermochemical piles

Bull, A. L.; McNamara, A. K.; Ritsema, Jeroen

doi:10.1016/j.epsl.2008.11.018

Cited by 115 publications

(119 citation statements)

References 61 publications

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“…Observational and numerical studies of the lower mantle suggest that the structures and dynamics there are far more complex. First, non-thermal contributions (e.g., compositional, phase changes) perturb the idealized linear seismic-thermal mapping (Bull et al 2009;Deschamps et al 2012;Lay et al 2008;Nakagawa and Tackley 2008;Tackley 2011;Trampert et al 2004). Second, while the spatial resolution inherent to tomographic models in the lowermost mantle (e.g., Lekic et al 2012) exceeds the resolution of the observed core field, strong lateral gradients of shear wave velocities are not captured.…”

Section: Generalmentioning

confidence: 99%

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Amit

Choblet

Olson

et al. 2015

Prog. in Earth and Planet. Sci.

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Mantle control on planetary dynamos is often studied by imposing heterogeneous core-mantle boundary (CMB) heat flux patterns on the outer boundary of numerical dynamo simulations. These patterns typically enter two main categories: Either they are proportional to seismic tomography models of Earth's lowermost mantle to simulate realistic conditions, or they are represented by single spherical harmonics for fundamental physical understanding. However, in reality the dynamics in the lower mantle is much more complicated and these CMB heat flux models are most likely oversimplified. Here we term alternative any CMB heat flux pattern imposed on numerical dynamos that does not fall into these two categories, and instead attempts to account for additional complexity in the lower mantle. We review papers that attempted to explain various dynamo-related observations by imposing alternative CMB heat flux patterns on their dynamo models. For present-day Earth, the alternative patterns reflect non-thermal contributions to seismic anomalies or sharp features not resolved by global tomography models. Time-dependent mantle convection is invoked for capturing past conditions on Earth's CMB. For Mars, alternative patterns account for localized heating by a giant impact or a mantle plume. Recovered geodynamo-related observations include persistent morphological features of present-day core convection and the geomagnetic field as well as the variability in the geomagnetic reversal frequency over the past several hundred Myr. On Mars the models aim at explaining the demise of the paleodynamo or the hemispheric crustal magnetic dichotomy. We report the main results of these studies, discuss their geophysical implications, and speculate on some future prospects.

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Section: Generalmentioning

confidence: 99%

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Amit

Choblet

Olson

et al. 2015

Prog. in Earth and Planet. Sci.

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“…Their results range from shallow-sloping piles (e.g. Bull et al 2009) to steep metastable plumes (e.g. Davaille 1999;Simmons et al 2007;Tan et al 2011;Bower et al 2013).…”

Section: Geodynamic Implicationsmentioning

confidence: 99%

“…Typical scenarios are broad stable piles with low-angle slopes and plumes coming off of ridges (e.g. Bull et al 2009;Zhang et al 2010;Li et al 2014a,b) or metastable piles with steep sides and a buoyancy crossover within the pile (Tan et al 2005;Samuel & Bercovici 2006;Bower et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

135

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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“…7b. However, more appropriately, the geodynamic models should also be "looked at" through a tomography filter (Mégnin et al, 1997;Schuberth et al, 2009;Bull et al 2009).…”

Section: B Steinberger Et Al: Subduction To the Lower Mantle -Compamentioning

confidence: 99%

Subduction to the lower mantle – a comparison between geodynamic and tomographic models

2012

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Abstract. It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000 s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ∼10 20 Pas, and viscosity increases to ∼10 23 Pas in the lower mantle above D " . Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved, presumably because of advances in both plate reconstructions and mantle flow computations. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation -in particular at spherical harmonic degree two -is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 2 ± 0.8 cm yr −1 to achieve a better fit.

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Synthetic tomography of plume clusters and thermochemical piles

Cited by 115 publications

References 61 publications

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Morphology of seismically slow lower-mantle structures

Subduction to the lower mantle – a comparison between geodynamic and tomographic models

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