3D effects of sharp boundaries at the borders of the African and Pacific Superplumes: Observation and modeling

To, Akiko; Romanowicz, Barbara; Capdeville, Yann; Takeuchi, Nozomu

doi:10.1016/j.epsl.2005.01.037

Cited by 127 publications

(101 citation statements)

References 26 publications

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“…Using a material with higher bulk modulus than ambient mantle is crucial in generating stable, steep-edged, high-elevation chemical structures [Tan and Gurnis, 2007]. Seismic waveform studies have found steep edges in several parts of LLSVPs [Ni et al, 2002;To et al, 2005;Wang and Wen, 2007;He and Wen, 2009]. The high elevation of LLSVPs suggests that they are nearly neutrally buoyant.…”

Section: Discussionmentioning

confidence: 99%

On the location of plumes and lateral movement of thermochemical structures with high bulk modulus in the 3-D compressible mantle

Tan

Leng

Zhong

et al. 2011

Geochem. Geophys. Geosyst.

110

102

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[1] The two large low shear velocity provinces (LLSVPs) at the base of the lower mantle are prominent features in all shear wave tomography models. Various lines of evidence suggest that the LLSVPs are thermochemical and are stable on the order of hundreds of million years. Hot spots and large igneous province eruption sites tend to cluster around the edges of LLSVPs. With 3-D global spherical dynamic models, we investigate the location of plumes and lateral movement of chemical structures, which are composed of dense, high bulk modulus material. With reasonable values of bulk modulus and density anomalies, we find that the anomalous material forms dome-like structures with steep edges, which can survive for billions of years before being entrained. We find that more plumes occur near the edges, rather than on top, of the chemical domes. Moreover, plumes near the edges of domes have higher temperatures than those atop the domes. We find that the location of the downwelling region (subduction) controls the direction and speed of the lateral movement of domes. Domes tend to move away from subduction zones. The domes could remain relatively stationary when distant from subduction but would migrate rapidly when a new subduction zone initiates above. Generally, we find that a segment of a dome edge can be stationary for 200 million years, while other segments have rapid lateral movement. In the presence of time-dependent subduction, the computations suggest that maintaining the lateral fixity of the LLSVPs at the core-mantle boundary for longer than hundreds of million years is a challenge.

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Section: Discussionmentioning

confidence: 99%

On the location of plumes and lateral movement of thermochemical structures with high bulk modulus in the 3-D compressible mantle

Tan

Leng

Zhong

et al. 2011

Geochem. Geophys. Geosyst.

110

102

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“…5aA); they have found both a sharp change in isotropic velocities (Ni et al 2005;To et al 2005;Sun et al 2009) as well as anisotropy (Cottaar & Romanowicz 2013). Our vote map (Fig.…”

Section: Comparison With Regional Seismic Studiesmentioning

confidence: 99%

“…Burke et al 2008;Lekic et al 2012) and in detailed waveform modeling studies of shear waves reflecting and diffracting at the core-mantle boundary (CMB; e.g. Wen et al 2001;To et al 2005;He et al 2006;Takeuchi et al 2008). Sharp changes across LLSVP boundaries are also seen in seismic anisotropy (Wang & Wen 2007a;Cottaar & Romanowicz 2013;Lynner & Long 2014) and compressional wave speed (Frost & Rost 2014).…”

Section: Introductionmentioning

confidence: 99%

Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

138

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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“…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. As revealed by detailed waveform analyses at several locations, boundaries of large low shear-wave velocity provinces (LLSVPs) might however be very sharp (e.g., Ni et al 2005;To et al 2005). Similarly, synthetic single harmonic patterns for planetary mantle heterogeneity, for example for the CMB conditions that prevailed during the paleo dynamo of Mars, are oversimplified.…”

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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3D effects of sharp boundaries at the borders of the African and Pacific Superplumes: Observation and modeling

Cited by 127 publications

References 26 publications

On the location of plumes and lateral movement of thermochemical structures with high bulk modulus in the 3-D compressible mantle

On the location of plumes and lateral movement of thermochemical structures with high bulk modulus in the 3-D compressible mantle

Morphology of seismically slow lower-mantle structures

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

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