In situ study of the mechanism of formation of pressure-densified Sio2 glasses

El’kin, F. S.; Brazhkin, V. V.; Khvostantsev, L. G.; Tsiok, O. B.; Lyapin, A. G.

doi:10.1134/1.1485264

Cited by 65 publications

(38 citation statements)

References 32 publications

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“…2). Our results for SiO 2 glass along with those of previous studies (17)(18)(19)(20)(21)(22)(23)(24) indicate that the velocity-pressure trends in SiO 2 glass can be interpreted as a gradual transition from four-to sixfold coordination of Si below 40 GPa, predominantly sixfold coordination from 40 to 140 GPa, and a transition from sixfold to a higher coordination state above 140 GPa (16) (Fig. 2).…”

Section: Resultssupporting

confidence: 65%

Evidence of denser MgSiO₃glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Murakami

Bass

2011

Proc. Natl. Acad. Sci. U.S.A.

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Ultralow velocity zones are the largest seismic anomalies in the mantle, with 10-30% seismic velocity reduction observed in thin layers less than 20-40 km thick, just above the Earth's core-mantle boundary (CMB). The presence of silicate melts, possibly a remnant of a deep magma ocean in the early Earth, have been proposed to explain ultralow velocity zones. It is, however, still an open question as to whether such silicate melts are gravitationally stable at the pressure conditions above the CMB. Fe enrichment is usually invoked to explain why melts would remain at the CMB, but this has not been substantiated experimentally. Here we report in situ high-pressure acoustic velocity measurements that suggest a new transformation to a denser structure of MgSiO 3 glass at pressures close to those of the CMB. The result suggests that MgSiO 3 melt is likely to become denser than crystalline MgSiO 3 above the CMB. The presence of negatively buoyant and gravitationally stable silicate melts at the bottom of the mantle, would provide a mechanism for observed ultralow seismic velocities above the CMB without enrichment of Fe in the melt. An ultradense melt phase and its geochemical inventory would be isolated from overlying convective flow over geologic time.dynamics | early Earth evolution | high-pressure experiment | sound velocity measurement | pressure-induced polymorphism T he buoyancy relations between silicate melts and crystals in a deep terrestrial magma ocean are the primary constraints on the possible chemical stratification of Earth's interior (1, 2). The nature of silicate melts under high-pressure conditions is therefore critically important for elucidating the formation and differentiation of the Earth through massive primordial melting of the proto-Earth. Extensive melting of the proto-Earth and the formation of a deep magma ocean, induced by massive planetesimal collisions and possibly encompassing an entire planet, facilitated metal-silicate (core-mantle) segregation, with the subsequent fractional crystallization of silicate melt leading to chemical and gravitational equilibrium (3-6). Because of the high compressibility of melts, a density crossover between crystals and coexisting magmas is expected in the course of fractional crystallization in a deep magma ocean, which would enhance chemical differentiation and could result in a stratified structure of the Earth's interior (7,8). The possible presence of dense, gravitationally stable magmas deep within the Earth at pressures above 100 gigapascals (GPa) has thus been proposed as a consequence of partial melting and a remnant of a deep magma ocean (9, 10), which might explain the observation of anomalously ultralow seismic velocities (ULVZ) above the core-mantle boundary (CMB) (11). However, the behavior of silicate melts under such extreme pressures is poorly understood, and it is still an open question as to whether a density crossover between silicate melt and coexisting mantle phases occurs in the D′′ region above the CMB (approximately 2,900 km dep...

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Section: Resultssupporting

confidence: 65%

Evidence of denser MgSiO₃glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Murakami

Bass

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…It is obvious that with another increase in pressure to P $ 1 Mbar (the stability region of an a-PbO 2 structure type), the coordination number in glassy silica should slightly rise [98] and approach eight at P $ 2-3 Mbar (the stability region of a pyrite-like structure of crystalline silica). This state of the [90]. These data are evidence for the two transitions: between the ordinary glass and densified rigid network state of glass with a small increase of coordination (the gray regions correspond to the direct and reverse transitions) and between densified state of glass and six-fold coordinated phase (nonhatched regions).…”

Section: A Silicamentioning

confidence: 77%

“…By using a strain gauge technique, direct in situ measurements of the relative volume of the glass in a wide range of pressures (0-10 GPa) and temperatures (30-730 K) have been conducted (see Fig. 2) [90]. It has been found that at increased temperatures and pressures of 4-8 GPa, the a-SiO 2 glass undergoes a transformation accompanied by moderate volume changes of 2-7%, depending on the pressure.…”

Section: A Silicamentioning

confidence: 99%

Multiple Amorphous–Amorphous Transitions

Loerting

Бражкин

Morishita

2009

Advances in Chemical Physics

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“…There is serious evidence that this behavior is inherent for many fluids. For example, experimental studies show that amorphous SiO 2 [117] and liquid AsS [118] undergoes two pressure-induced transformations. Two liquid-liquid transitions have been observed in simulations of systems of particles interacting via a spherical potential with two repulsive steps and one attractive step [24] and with one repulsive and one attractive step.…”

Section: Multiplicity Of the Liquid-liquid Transitions Of Watermentioning

confidence: 99%

Multiple Phases of Liquid Water

2008

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The history of the study of the anomalies of liquid water, from the 17th century up to the present, is reviewed and the current view on the origin of these anomalies is summarized. The hypothesis of the multiple liquid-liquid transitions of water in the supercooled region is consistent with the available experimental and simulation data and provides physical explanation of water behavior in a wide thermodynamic range. The general character of the liquid-liquid transitions of fluids is discussed and the remaining questions are formulated.

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In situ study of the mechanism of formation of pressure-densified Sio2 glasses

Cited by 65 publications

References 32 publications

Evidence of denser MgSiO₃glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Evidence of denser MgSiO₃glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Multiple Amorphous–Amorphous Transitions

Multiple Phases of Liquid Water

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In situ study of the mechanism of formation of pressure-densified Sio2 glasses

Cited by 65 publications

References 32 publications

Evidence of denser MgSiO3glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Evidence of denser MgSiO3glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Multiple Amorphous–Amorphous Transitions

Multiple Phases of Liquid Water

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Product

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Evidence of denser MgSiO₃glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

Evidence of denser MgSiO₃glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean