Cluster analysis of global lower mantle tomography: A new class of structure and implications for chemical heterogeneity

Lekić, V.; Cottaar, Sanne; Dziewoński, Adam M.; Romanowicz, Barbara

doi:10.1016/j.epsl.2012.09.014

Cited by 306 publications

(362 citation statements)

References 60 publications

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“…In previous work, Lekic et al (2012) applied cluster analysis on the whole lower-mantle V S profiles, and showed that the resulting geographic distribution of clusters was dominated by structure near the CMB. In contrast, in this study, we seek to map how the geographic extent of the LLSVPs varies with height above the CMB; therefore, we apply k-means cluster analysis of all V S profiles in 1124 S. Cottaar and V. Lekic restricted depth ranges using a sliding window.…”

Section: Cluster Analysismentioning

confidence: 99%

“…When applied to profiles of the entire lower mantle, k-means clustering of five recent tomographic models (Mégnin & Romanowicz 2000;Houser et al 2008;Kustowski et al 2008;Simmons et al 2010;Ritsema et al 2011) retrieves the geographic extents of the LLSVPs, as well as the LLSVP-like, but geographically isolated meso-scale structure called the Perm anomaly (Lekic et al 2012).…”

Section: Cluster Analysismentioning

confidence: 99%

“…In seeking to describe the dominant dichotomy of the lowermost mantle-that between the LLSVP and non-LLSVP regions- Lekic et al (2012) set the number of clusters (N) to two. In this study, we relax this assumption and seek to quantitatively determine the N most appropriate for classifying V S variations in the entire lower mantle.…”

Section: Number Of Clustersmentioning

confidence: 99%

“…This is seen both in global tomographic models (e.g. 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).…”

Section: Introductionmentioning

confidence: 99%

“…Here, we study the morphology and volume of the LLSVPs in the lower mantle as suggested by cluster analysis across five recent whole-mantle tomographic models, in order to identify common features. Lekic et al (2012) applied cluster analysis to radial profiles of the entire lower mantle. This led to the discovery of a meso-scale slow feature beneath Perm, Russia, which is separated from the African and Pacific LLSVPs.…”

Section: Introductionmentioning

confidence: 99%

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Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

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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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Section: Cluster Analysismentioning

confidence: 99%

Section: Cluster Analysismentioning

confidence: 99%

Section: Number Of Clustersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

Self Cite

141

147

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BurnMan: A lower mantle mineral physics toolkit

Cottaar

Heister

Rose

et al. 2014

Geochem. Geophys. Geosyst.

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108

100

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We present BurnMan, an open-source mineral physics toolbox to determine elastic properties for specified compositions in the lower mantle by solving an Equation of State (EoS). The toolbox, written in Python, can be used to evaluate seismic velocities of new mineral physics data or geodynamic models, and as the forward model in inversions for mantle composition. The user can define the composition from a list of minerals provided for the lower mantle or easily include their own. BurnMan provides choices in methodology, both for the EoS and for the multiphase averaging scheme. The results can be visually or quantitatively compared to observed seismic models. Example user scripts show how to go through these steps. This paper includes several examples realized with BurnMan: First, we benchmark the computations to check for correctness. Second, we exemplify two pitfalls in EoS modeling: using a different EoS than the one used to derive the mineral physical parameters or using an incorrect averaging scheme. Both pitfalls have led to incorrect conclusions on lower mantle composition and temperature in the literature. We further illustrate that fitting elastic velocities separately or jointly leads to different Mg/Si ratios for the lower mantle. However, we find that, within mineral physical uncertainties, a pyrolitic composition can match PREM very well. Finally, we find that uncertainties on specific input parameters result in a considerable amount of variation in both magnitude and gradient of the seismic velocities.

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Lithospheric structure across the California Continental Borderland from receiver functions

Reeves

Lekić

Schmerr

et al. 2015

Geochem Geophys Geosyst

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Due to its complex history of deformation, the California Continental Borderland provides an interesting geological setting for studying how the oceanic and continental lithosphere responds to deformation. We map variations in present-day lithospheric structure across the region using Ps and Sp receiver functions at permanent stations of the Southern California Seismic Network as well as ocean bottom seismometer (OBS) data gathered by the Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE), which enhances coverage of the borderland and provides first direct constraints on the structure of the Pacific plate west of the Patton Escarpment. Noisiness of OBS data makes strict handpicking and bandpass filtering necessary in order to obtain interpretable receiver functions. Using H-j and common-conversion point stacking, we find pronounced lithospheric differences across structural blocks, which we interpret as indicating that the Outer Borderland has been translated with little to no internal deformation, while the Inner Borderland underwent significant lithospheric thinning, most likely related to accommodating the 90 clockwise rotation of the Western Transverse Range block. West of the Patton Escarpment, we find that the transition to typical oceanic crustal thickness takes place over a lateral distance of 50 km. We detect an oceanic seismic lithosphere-asthenosphere transition at 58 km depth west of the Patton Escarpment, consistent with only weak age-dependence of the depth to the seismic lithosphereasthenosphere transition. Sp common-conversion point stacks confirm wholesale lithospheric thinning of the Inner Borderland and suggest the presence of a slab fragment beneath the Outer Borderland.

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Cluster analysis of global lower mantle tomography: A new class of structure and implications for chemical heterogeneity

Cited by 306 publications

References 60 publications

Morphology of seismically slow lower-mantle structures

Morphology of seismically slow lower-mantle structures

BurnMan: A lower mantle mineral physics toolkit

Lithospheric structure across the California Continental Borderland from receiver functions

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