Effect of dynamic melting on acoustic velocities in a partially molten peridotite
TL;DR: In this paper, it was shown that the softening of elastic modulus is controlled by the pressure dependence of melt fraction, ∂F/∂P, and not the percentage of melt present.
About: This article is published in Physics of the Earth and Planetary Interiors.The article was published on 2013-09-01 and is currently open access. It has received 18 citations till now. The article focuses on the topics: Shear modulus & Elastic modulus.
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TL;DR: In situ ultrasonic velocity measurements on a series of partially molten samples are reported, providing direct compressional and shear wave velocities and constrain attenuation as a function of melt fraction, showingantle partial melting appears to be a viable origin for the low-velocity zone.
Abstract: The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 01 to 40 volume % of basalt, under conditions relevant to the LVZ Our measurements provide direct compressional (VP) and shear (VS) wave velocities and constrain attenuation as a function of melt fraction Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~02% In contrast, the presence of volatile elements appears necessary to explaining the extremely high VP/VS values observed in some local areas The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere
98 citations
Cites background from "Effect of dynamic melting on acoust..."
...Because of experimental difficulties, the dynamic interaction between partial melts and the solid matrix under relevant mantle conditions (pressures at several gigapascals) has only begun to be explored (21)....
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01 Dec 2016
TL;DR: In this article, the authors report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the low velocity zone (LVZ).
Abstract: The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (VP) and shear (VS) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high VP/VS values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere.
66 citations
TL;DR: A new model for seismic velocity reductions is presented that accounts for the anomalous compressibility of silicate melt, rendering compressional wave velocities more sensitive to melt fraction and distribution than previous estimates.
Abstract: Low seismic velocity regions in the mantle and crust are commonly attributed to the presence of silicate melts. Determining melt volume and geometric distribution is fundamental to understanding planetary dynamics. We present a new model for seismic velocity reductions that accounts for the anomalous compressibility of silicate melt, rendering compressional wave velocities more sensitive to melt fraction and distribution than previous estimates. Forward modeling predicts comparable velocity reductions for compressional and shear waves for partially molten mantle, and for low velocity regions associated with the lithosphere-asthenosphere boundary (LAB), melt present at <5% distributed in near-textural equilibrium. These findings reconcile seismic observations for the LAB regionally and locally and favor models of strong coupling across the LAB rather than melt channeling due to shear deformation.
34 citations
Cites result from "Effect of dynamic melting on acoust..."
...Note that NFDmodel results are consistent with experiments showing that RSP is close to unity at the onset of melting of peridotite (27, 28)....
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18 citations
Cites background from "Effect of dynamic melting on acoust..."
...…with the location where extensive partial melting is both expected (Kelley et al., 2006) and indicated by the seismic velocity structure (Wei et al., 2015; Wiens et al., 2008), thus favoring the mechanisms involving partial melt (Budiansky & O'Connell, 1980; Li & Weidner, 2013; Schmeling, 1985)....
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...Furthermore, Li and Weidner (2013) suggested that when seismic waves travel though a partially molten region, the stress perturbation will change melt fraction through a solid‐liquid phase change and thus cause bulk attenuation....
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TL;DR: Recent studies suggest that the asthenosphere may play a more active role as the source of the heat and magma responsible for intraplate volcanoes and may have a major impact on plate tectonics and the pattern of mantle flow.
Abstract: The asthenosphere—derived from the Greek asthenēs, meaning weak—is the uppermost part of Earth's mantle, right below the tectonic plates that make up the solid lithosphere. First proposed by Barrell 100 years ago (1), the asthenosphere has traditionally been viewed as a passive region that decouples the moving tectonic plates from the mantle and provides magmas to the global spreading ridge system. Recent studies suggest that the asthenosphere may play a more active role as the source of the heat and magma responsible for intraplate volcanoes. Furthermore, it may have a major impact on plate tectonics and the pattern of mantle flow.
13 citations
References
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TL;DR: The article ''On the Equilibrium of Heterogeneous Substances'', which was published in ''Transactions of the Connecticut Academy of Arts and Sciences'', vol. 3 (1874-78), pp. 108-248 and 343-524 as mentioned in this paper
Abstract: Review of the article ''On the Equilibrium of Heterogeneous Substances'', which was published in ''Transactions of the Connecticut Academy of Arts and Sciences'', vol. 3 (1874-78), pp. 108-248 and 343-524.
1,728 citations
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954 citations
"Effect of dynamic melting on acoust..." refers background in this paper
...Anderson (1989) and Jackson (2007) discuss the role of volume changing phase transformations on attenuation of elastic waves....
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Book•
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01 Jan 1989
TL;DR: Theory of the Earth as mentioned in this paper is a theory of the origin, composition, evolution, and evolution of the entire Earth from the perspective of geology, petrology, mineralogy, geochemistry, geodesy, and seismology.
Abstract: The maturing of the Earth sciences has led to a fragmentation into subdisciplines which speak imperfectly to one another. Some of these subdisciplines are field geology, petrology, mineralogy, geochemistry, geodesy and seismology, and these in turn are split into even finer units. The science has also expanded to include the planets and even the cosmos. The practitioners in each of these fields tend to view the Earth in a completely different way. Discoveries in one field diffuse only slowly into the consciousness of a specialist in another. In spite of the fact that there is only one Earth, there are probably more Theories of the Earth than there are of astronomy, particle physics or cell biology where there are uncountable samples of each object. Even where there is cross-talk among disciplines, it is usually as noisy as static. Too often, one discipline's unproven assumptions or dogmas are treated as firm boundary conditions for a theoretician in a slightly overlapping area. The data of each subdiscipline are usually consistent with a range of hypotheses. The possibilities can be narrowed considerably as more and more diverse data are brought to bear on a particular problem. The questions of origin, composition and evolution of the Earth require input from astronomy, cosmochemistry, meteoritics, planetology, geology, petrology, mineralogy, crystallography, materials science and seismology, at a minimum. To a student of the Earth, these are artificial divisions, however necessary they are to make progress on a given front.
In Theory of the Earth I attempt to assemble the bits and pieces from a variety of disciplines which are relevant to an understanding of the Earth. Rocks and magmas are our most direct source of information about the interior, but they are biased toward the properties of the crust and shallow mantle. Seismology is our best source of information about the deep interior; however, the interpretation of seismic data for purposes other than purely structural requires input from solid-state physics and experimental petrology. Although this is not a book about seismology, it uses seismology in a variety of ways.
The "Theory of the Earth" developed here differs in many respects from conventional views. Petrologists' models for the Earth's interior usually focus on the composition of mantle samples contained in basalts and kimberlites. The simplest hypothesis based on these samples is that the observed basalts and peridotites bear a complementary relation to one another, that peridotites are the source of basalts or the residue after their removal, and that the whole mantle is identical in composition to the inferred chemistry of the upper mantle and the basalt source region. The mantle is therefore homogeneous in composition, and thus all parts of the mantle eventually rise to the surface to provide basalts. Subducted slabs experience no barrier in falling through the mantle to the core-mantle boundary.
891 citations
TL;DR: The effective elastic moduli of a fluid-saturated solid containing thin cracks depend on the degree of interconnection between the cracks as mentioned in this paper, which can be estimated from the crack geometry or permeability.
Abstract: The effective elastic moduli of a fluid-saturated solid containing thin cracks depend on the degree of interconnection between the cracks. Three separate regimes may be identified: (1) dry (drained), in which fluid in cracks can flow out of bulk regions of compression, (2) saturated isobaric, in which fluid may flow from one crack to another but no bulk flow takes place, and (3) saturated isolated, in which there is no communication of fluid between cracks. Transitions between these cases involve fluid flow, resulting in dissipation of energy. Relaxation of shear stresses in viscous fluid inclusions also results in dissipation. Viscoelastic moduli are derived, by using a self-consistent approximation, that describe the complete range of behavior. There are two characteristic frequencies near which dissipation is largest and the moduli change rapidly with frequency. The first corresponds to fluid flow between cracks, and its value can be estimated from the crack geometry or permeability. The second corresponds to the relaxation of shear stress in an isolated viscous fluid inclusion; its value may also be estimated. Variations of crack geometry result in a distribution of characteristic frequencies and cause Q to be relatively constant over many decades of frequency. Fluid flow between cracks accounts for attenuation of seismic waves in water-saturated rocks and attenuation observed in laboratory measurements on water-saturated rocks and partially molten aggregates. Attenuation in a partially molten upper mantle is probably due to fluid flow between cracks, although grain boundary relaxation in an unmelted upper mantle could also account for the seismic low-velocity zone. Grain boundary relaxation in the mantle may cause the long-term shear modulus to be around 20% less than that measured from seismic observations.
835 citations
"Effect of dynamic melting on acoust..." refers background in this paper
...…on descriptions of pore geometry and fluid distribution in defining different regimes such as drained, saturated isobaric and saturated isolated (O’Connell and Budiansky, 1977); where fluid can flow out of the bulk; can communicate between pores; and cannot communicate between pores…...
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...The propagation of stress waves in fluid-bearing rocks have been studied both experimentally and theoretically for decades (Anderson and Sammis, 1970; Jackson et al., 2004; Mavko et al., 1979; Mavko and Nur, 1979; O’Connell and Budiansky, 1977)....
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...These models focus on descriptions of pore geometry and fluid distribution in defining different regimes such as drained, saturated isobaric and saturated isolated (O’Connell and Budiansky, 1977); where fluid can flow out of the bulk; can communicate between pores; and cannot communicate between pores respectively....
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...A few mechanisms such as regional flow (Mavko and Nur, 1975), viscous (shear) relaxation (Walsh, 1969), stress-induced flow (O’Connell and Budiansky, 1977) or melt-squirt (Mavko and Nur, 1975) were proposed to describe the dynamic of fluid under stress waves....
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Book•
01 Jan 2007
TL;DR: In this article, Seismology and Structure of the Earth Volume 2: Mineral Physics Volume 3: Physical Geodesy Volume 4: Earthquake SEismology Volume 5: Geomagnetism Volume 6: Crustal and Lithosphere Dynamics Volume 7: Mantle Dynamics Volume 8: Core Dynamics Volume 9: Evolution of Earth Volume 10: Planets and Moons Volume 11: Index Volume
Abstract: Volume 1: Seismology and Structure of the Earth Volume 2: Mineral Physics Volume 3: Physical Geodesy Volume 4: Earthquake Seismology Volume 5: Geomagnetism Volume 6: Crustal and Lithosphere Dynamics Volume 7: Mantle Dynamics Volume 8: Core Dynamics Volume 9: Evolution of the Earth Volume 10: Planets and Moons Volume 11: Index Volume
562 citations