Seismic Evidence of Partial Melt Within a Possibly Ubiquitous Low-Velocity Layer at the Base of the Mantle

Revenaugh, J.; Meyer, Robert P.

doi:10.1126/science.277.5326.670

Cited by 168 publications

(124 citation statements)

References 20 publications

(3 reference statements)

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“…Seismic data indicate that it has a thickness of 5 -40 km and P and S wave velocity reductions of the order of 5 -30%, suggesting a possible partial melting [Garnero and Helmberger, 1995;Mori and Helmberger, 1995;Williams and Garnero, 1996;Revenaugh and Meyer, 1997;Vidale and Hedlin, 1998;Wen and Helmberger, 1998]. …”

Section: Ultralow-velocity Zonementioning

confidence: 99%

Small‐scale convection in the D″ layer

Solomatov

Moresi

2002

J. Geophys. Res.

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[1] Small-scale convection has been suggested as a possible explanation for seismic heterogeneities in the D 00 layer of the Earth's mantle. Recently developed scaling laws for convection with realistic viscosities allow quantitative assessment of this hypothesis. Large temperature and viscosity contrasts across the thermal boundary layer at the core-mantle boundary suggest that small-scale convection starts at the bottom of the thermal boundary layer and propagates upward before the thermal boundary layer as a whole becomes unstable. The convection boundary is likely to become a chemical boundary as a result of mixing within the convective layer. This implies that the D 00 discontinuity can represent both convective and chemical boundary and that the presence or absence of small-scale convection can be responsible for the observed intermittent nature of the D 00 discontinuity. Most lateral heterogeneities in the D 00 layer are concentrated near the convection boundary, consistent with seismic data. The length scale of lateral temperature variations, the topography of the core-mantle boundary, and the viscosity of the D 00 layer are in agreement with observational constraints. The thickness of the secondary thermal boundary layer formed at the bottom of the convective layer is similar to the thickness of the ultralow-velocity zone. The magnitude of lateral variations in temperature can only marginally be responsible for lateral variations in seismic velocities. Variations in the topography of the convection boundary and chemical heterogeneities are likely to be more important factors. A large seismic velocity drop in the ultralow-velocity zone cannot be explained by thermal effects alone and must be caused by other factors such as partial melting.

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Section: Ultralow-velocity Zonementioning

confidence: 99%

Small‐scale convection in the D″ layer

Solomatov

Moresi

2002

J. Geophys. Res.

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“…There are several proposed explanations for low velocities in ULVZs. Probably the most often-quoted hypothesis is the presence of partial melt [Williams and Garnero, 1996;Revenaugh and Meyer , 1997;Helmberger et al, 1998;Vidale and Hedlin, 1998;Williams et al, 1998;Zerr et al, 1998;Berryman, 2000;Wen, 2000;Ross et al, 2004]. However, variations in chemical composition on the mantle side of the CMB [Manga and Jeanloz , 1996;Stutzmann et al, 2000], "sediments" of finite rigidity collecting on the top of the outer core [Buffett et al, 2000;Rost and Revenaugh, 2001], and a gradient in the mantle-core transition (rather than the traditional sharp CMB) [Garnero and Jeanloz , 2000a, b] have also been proposed, singly and in combination.…”

Section: Introductionmentioning

confidence: 99%

“…They include precursors and postcursors in stacks of short period and broad band ScP [Vidale and Benz , 1992;Garnero and Vidale, 1999;Castle and van der Hilst, 2000;Reasoner and Revenaugh, 2000;Persh et al, 2001;Revenaugh, 2001, 2003], ScS [Avants et al, 2006], and PcP [Mori and Helmberger , 1995;Kohler et al, 1997;Revenaugh and Meyer , 1997;Havens and Revenaugh, 2001;Persh et al, 2001;Ross et al, 2004]; scattered precursors to PKP [Vidale and Hedlin, 1998;Wen and Helmberger , 1998a;Thomas et al, 1999;Wen, 2000;Ni and Helmberger , 2001;Niu and Wen, 2001], and SKS [Stutzmann et al, 2000]; and travel time and waveform anomalies in PKPdf and…”

Section: Introductionmentioning

confidence: 99%

Seismic and gravitational studies of melting in the mantle's thermal boundary layers

Ark¹,

Emily²

2007

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“…However, other studies have argued for the existence of a very thin (ca. 1 km) ubiquitous global layer of partial melt away from ULVZ based on the analysis of high-frequency seismic waves (Revenaugh and Meyer, 1997;Ross et al, 2004). Studies with somewhat lower effective resolutions (≈3 km), on the other hand, failed to find a similar ubiquitous signal along the CMB (Persh et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…The uncertainties for the temperature of the CMB as well as the deep mantle solidus are likely large enough to to permit this scenario, though some (e.g., Boehler, 2000) have argued that the core may be too cool, and the solidus too high to allow for this possibility. In its simplest form, this would lead to ubiquitous melting of the lowermost mantle where the geotherm intersects the solidus just above the CMB (Revenaugh and Meyer, 1997), or be concentrated by localized processes, e.g., magma chamber-like heat pumps (Morse, 2001). Others (e.g., Helffrich and Kaneshima, 2004) have argued that the solidus must be an upper bound on core temperature, because the distribution of partial melting that would occur cannot be consistent with the observed seismic heterogeneity in D".…”

Section: Introductionmentioning

confidence: 99%

Some dynamical consequences of partial melting in Earth’s deep mantle

Hernlund

Tackley

2007

Physics of the Earth and Planetary Interiors

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We use regional scale numerical models of mantle convection to investigate the simple hypothesis that seismically anomalous thin patches of Earth's lowermost mantle, termed "ultralow-velocity zones" or ULVZ, are derived from partial melting of ordinary mantle. The models span the lower 500 km of Earth's mantle, employ both temperature and meltingrelated contributions to buoyancy, and include a cold randomly moving downwelling introduced from above to maintain a thermal boundary layer. Partial melting of ordinary mantle introduces a ubiquitous partially molten layer above an isothermal core-mantle boundary as a consequence of its isothermal and isobaric conditions, although it naturally develops variations in thickness greater than two orders of magnitude, with the thickest portions occurring at the base of upwelling plumes and a thin layer elsewhere. We find that only a dense partially molten mixture produces partial melt distributions that are compatible with seismic observations of ULVZ, however, if such a melt percolates downward a dense basal liquid layer accumulates above the core-mantle boundary. The apparent requirement of a volumetrically dense and non-percolating melt phase in the lowermost mantle presents serious problems for the hypothesis that ULVZ arise from melting of ordinary mantle, and suggests that such features likely form as a consequence of more complex processes. Furthermore, these considerations suggest that the solidus of ordinary mantle is a reasonable upper bound on the present day temperature of the CMB.

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Seismic Evidence of Partial Melt Within a Possibly Ubiquitous Low-Velocity Layer at the Base of the Mantle

Abstract: However, the partitioning of the waveforms in our data set increases the variance of the observations, currently limiting the ability of this approach to resolve lateral variations in scattering strength.

Cited by 168 publications

References 20 publications

Small‐scale convection in the D″ layer

Small‐scale convection in the D″ layer

Seismic and gravitational studies of melting in the mantle's thermal boundary layers

Some dynamical consequences of partial melting in Earth’s deep mantle

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