A narrow, mid‐mantle plume below southern Africa

Sun, Daoyuan; Helmberger, Donald V.; Gurnis, Michael

doi:10.1029/2009gl042339

Cited by 23 publications

(26 citation statements)

References 27 publications

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“…A variety of studies have suggested that the LLSVPs are both thermally and chemically distinct features, but seismic studies have given inconclusive answers on the net density of the LLSVP (Koelemeijer et al, 2017;Lau et al, 2017), which is consistent with geodynamic models suggesting a balance between chemical and thermal forces (Tan & Gurnis, 2007). A more detailed review of the sharp edges of the LLSVP can be found in Text S1 in the supporting information (Davaille, 1999;French & Romanowicz, 2015;Garnero & McNamara, 2008;Grand, 2002;Ishii & Tromp, 1999;Lau et al, 2017;Masters et al, 2000;Montelli et al, 2006Montelli et al, , 2004Ritsema et al, 1998;Sun et al, 2010;Tan & Gurnis, 2005, 2007Trampert et al, 2004;Wang & Wen, 2007). Thus, relatively steep ray paths (such as SKS) can be used to define local boundary sharpness and small features such as ULVZs using the SPdKS arrival.…”

Section: Introductionmentioning

confidence: 56%

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Sun

Helmberger

Lai

et al. 2019

Geophysical Research Letters

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At the core‐mantle boundary, most observed ultralow velocity zones (ULVZs) cluster along the edges of the large low shear velocity provinces (LLSVPs) and provide key information on the composition, dynamics, and evolution of the lower mantle. However, their detailed structure near slab‐like structures beneath the mid‐Pacific remains particularly challenging because of the lack of station coverage. While most studies of ULVZs concentrate on SKS‐complexity, here we report on the multipathing of ScS, which expands the sampling for ULVZs. We find the strongest multipathing along a ULVZ patch located just south of Hawaii and the far northeastern edge of the LLSVP, in a zone ~200 km in width and extending 600 km southward. The anomalous ScS travel times and distorted Sdiff waveforms further reveal patches interrupted by observed enhanced D″ indicative of slab‐debris influence on the complexity of the northeastern boundary of the mid‐Pacific LLSVP.

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Section: Introductionmentioning

confidence: 56%

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Sun

Helmberger

Lai

et al. 2019

Geophysical Research Letters

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“…These weak plumes are more easily deflected by large-scale mantle flow, more likely blocked by the 660 km discontinuity, and less likely to reach the surface and produce hot spots. An example of one such weak plume atop the African LLSVP that has not penetrated to the surface has been imaged recently [Sun et al, 2010]. When internal heating due to enriched material is incorporated, we found that even higher percentages (67%) of strong plumes are near the edges of chemical domes, due to more heat available from the domes.…”

Section: Discussionmentioning

confidence: 71%

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.

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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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“…Large low shear velocity provinces (LLSVPs) are arguably the largest discrete structures in the mantle. Seismic and mineral physics data suggest LLSVPs are thermochemically distinct from the surrounding material [e.g., Dziewonski et al , 2010; Helmberger and Ni , 2005; Sun et al , 2009, 2010; Wang and Wen , 2007] and geodynamic models suggest plausible scenarios for their formation [e.g., Garnero and McNamara , 2008; McNamara and Zhong , 2004; Schubert et al , 2004; Tan and Gurnis , 2005]. For example, given observed variations of δ V S and δ V P within the African LLSVP, and if the density anomaly at a given temperature is equal or greater than ambient, then K S must be larger than that of ambient mantle to maintain neutral buoyancy [e.g., Tan and Gurnis , 2005, 2007].…”

Section: Discussionmentioning

confidence: 99%

Spin crossover equation of state and sound velocities of (Mg_0.65Fe_0.35)O ferropericlase to 140 GPa

et al. 2012

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[1] We have determined the elastic and vibrational properties of periclase-structured (Mg 0.65 Fe 0.35 )O ("FP35"), a composition representative of deep mantle "pyrolite" or chondrite-pyroxenite models, from nuclear resonant inelastic x-ray scattering (NRIXS) and x-ray diffraction (XRD) measurements in diamond-anvil cells at 300 K. Combining with in situ XRD measurements, the Debye sound velocity of FP35 was determined from the low-energy region of the partial phonon density of states (DOS) obtained from NRIXS measurements in the pressure range of 70 to 140 GPa. In order to obtain an accurate description of the equation of state (EOS) for FP35, separate XRD measurements were performed up to 126 GPa at 300 K. A new spin crossover EOS was introduced and applied to the full P-V data set, resulting in a zero-pressure volume V 0 = 77.24 AE 0.17 Å 3 , bulk modulus K 0 = 159 AE 8 GPa and its pressure-derivative K′ 0 = 4.12 AE 0.42 for high-spin FP35 and K 0,LS = 72.9 AE 1.3 Å 3 , K 0,LS = 182 AE 17 GPa with K′ 0,LS fixed to 4 for low-spin FP35. The high-spin to low-spin transition occurs at 64 AE 3 GPa. Using the spin crossover EOS and Debye sound velocity, we derived the shear (V S ) and compressional (V P ) velocities for FP35. Comparing our data with previous results on (Mg,Fe)O at similar pressures, we find that the addition of iron decreases both V P and V S , while elevating their ratio (V P /V S ). Small amounts (<10%) of low-spin FP35 mixed with silicates could explain moderate reductions in wave speeds near the core mantle boundary (CMB), while a larger amount of FP35 near the CMB would not allow a large structure to maintain neutral buoyancy.

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A narrow, mid‐mantle plume below southern Africa

Cited by 23 publications

References 27 publications

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

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

Spin crossover equation of state and sound velocities of (Mg_0.65Fe_0.35)O ferropericlase to 140 GPa

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A narrow, mid‐mantle plume below southern Africa

Cited by 23 publications

References 27 publications

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

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

Spin crossover equation of state and sound velocities of (Mg0.65Fe0.35)O ferropericlase to 140 GPa

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Spin crossover equation of state and sound velocities of (Mg_0.65Fe_0.35)O ferropericlase to 140 GPa