The Phase Boundary Between α- and β-Mg
            <sub>2</sub>
            SiO
            <sub>4</sub>
            Determined by in Situ X-ray Observation

Morishima, H.; Kato, T.; Suto, Minoru; Ohtani, Eiji; Urakawa, Satoru; Utsumi, Wataru; Shimomura, Osamu; Kikegawa, Takumi

doi:10.1126/science.265.5176.1202

Cited by 215 publications

(96 citation statements)

References 9 publications

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“…Possibly the pressure and temperature range of thermodynamic stability of wadsleyite occurred only after the third reverberation, thus reducing growth times to Ϸ350 ns, which then implies even faster growth rates. Because no other high-pressure phase has been clearly identified in our experiment, it is also possible that the observed wadsleyite crystallized from shock-induced melt or transformation of higher-pressure polymorphs such as ringwoodite upon release from the shock state as the pressures decreased down to the 14-to 16-GPa range (29). In this range of pressure, temperature may have been too low to induce complete back-transformation, while any record of higherpressure polymorphs may have been lost.…”

Section: Discussionmentioning

confidence: 98%

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Tschauner

Asimow

Kostandova

et al. 2009

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

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We observed micrometer-sized grains of wadsleyite, a high-pressure phase of (Mg,Fe) 2SiO4, in the recovery products of a shock experiment. We infer these grains crystallized from shock-generated melt over a time interval of <1 s, the maximum time over which our experiment reached and sustained pressure sufficient to stabilize this phase. This rapid crystal growth rate (Ϸ1 m/s) suggests that, contrary to the conclusions of previous studies of the occurrence of high-pressure phases in shock-melt veins in strongly shocked meteorites, the growth of high-pressure phases from the melt during shock events is not diffusion-controlled. Another process, such as microturbulent transport, must be active in the crystal growth process. This result implies that the times necessary to crystallize the high-pressure phases in shocked meteorites may correspond to shock pressure durations achieved on impacts between objects 1-5 m in diameter and not, as previously inferred, Ϸ1-5 km in diameter. These results may also provide another pathway for syntheses, via shock recovery, of some high-value, high-pressure phases.meteorite ͉ recovery ͉ high-pressure phases ͉ planetesimal growth ͉ shock experiments A number of high-pressure silicate phases that stably occur only in the Earth's deep interior have documented natural occurrences, most commonly within shock-induced melt veins in L-and H-chondrites and Martian meteorites, notably the highly shocked (S6) Peace River, Tenham, Sixiangkou, and Yamato 791384 meteorites. Such phases include lingunite (the highpressure polymorph of NaAlSi 3 O 8 in the hollandite structure) (1, 2); stishovite and poststishovite silica phases (3-5); wadsleyite (6) and ringwoodite (7), the high-pressure polymorphs of (Mg,Fe) 2 SiO 4 in a spinelloid (wadsleyite) and the spinel structure (ringwoodite), respectively; and (Mg,Fe)SiO 3 in the garnet [majorite (8, 9)], ilmenite [akimotoite (10)], and arguably the perovskite structure (11,12). Pressures of formation have been estimated from static synthesis experiments of such phases and range up to 26 GPa (12-16). However, only stishovite has been recovered from shock experiments with very rapid quench and only in small amounts (17)(18)(19). None of the other dense silicate phases (wadsleyite, ringwoodite, majorite, lingunite, akimotoite, or perovskite) has been recovered from shock experiments conducted up to megabar pressures (20). These negative laboratory results in combination with observations of texture and paragenesis of high-pressure silicate polymorphs in meteorites have been used to infer the durations of shock-induced highpressure, high-temperature conditions to be on the order of seconds to minutes (15,(21)(22)(23)(24). In particular, this conclusion has been based on the grain size of these minerals (15), the width of lamellae within partly converted phases (21,22), and diffusion profiles of trace or major elements across phase boundaries (23, 24) between high-pressure minerals occurring within shockinduced melt veins of meteorites. Seconds-to minutes-lo...

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Section: Discussionmentioning

confidence: 98%

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Tschauner

Asimow

Kostandova

et al. 2009

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

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“…The relationship between load and sample pressure was calibrated by using the following phase transformations for the 18 mm assembly: Bi (2.55 and 7.7 GPa) at room temperature and SiO 2 (quartzcoesite) at 3.2 GPa and 1200°C (Akaogi et al, 1995). Furthermore, it was calibrated by using the following phase transformations for the 14 mm assembly: Bi and ZnTe (6, 9.6, and 12 GPa) at room temperature (Kusaba et al, 1993), SiO 2 (coesite-stishovite) at 9.4 GPa and 1300°C (Zhang et al, 1996), and Mg 2 SiO 4 (olivine-wadsleyite) at 14.0-15.1 GPa and 1300-1600°C (Morishima et al, 1994). In each experiment, pressure was applied first.…”

Section: Experimental Methodsmentioning

confidence: 99%

Morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the deep upper mantle

Matsukage

Hashimoto

Nishihara

2017

Journal of Mineralogical and Petrological Sciences

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The morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the basaltic part of a subducting slab were investigated based on experimental constraints for the dihedral angles. We measured the dihedral angles in the eclogite-H 2 O system at a temperature of 1000°C and at pressures ranging from 4 to 16 GPa. The dihedral angle of hydrous liquid versus garnet-garnet (θ GG-L ) increased with increasing pressure from 46°at 4 GPa to 66°at 12 GPa, although it showed a weak decreasing trend at pressures higher than 12 GPa. The dihedral angle of hydrous liquid versus clinopyroxene-clinopyroxene (θ CC-L ) was almost constant with increasing pressure (61 and 59°at 4 and 10 GPa, respectively). The dihedral angle of hydrous liquid versus garnet-clinopyroxene (θ GC-L ) was 73-76°at 4-10 GPa, and it was always higher than θ GG-L and θ CC-L . By applying the morphological stability criteria for liquid in a system with two solid phases (garnet and clinopyroxene) and bond percolation theory for a three-dimensional lattice of tetracoordination, we found that the hydrous liquid was isolated at the grain edges and corners of eclogite minerals in the cold slab under a wide range of pressure conditions of the upper mantle from 4-14 GPa when the grain size of garnet was equal to that of clinopyroxene. Thus, basaltic crust containing hydrous liquid droplets may carry water to the lowermost upper mantle and the mantle transition zone when the slab is cold.

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“…A 14/8-mm assembly (octahedron length/truncation length) was used for each experiment, consisting of a MgO-based octahedral pressure medium with a stepped graphite heater, MgO and/or BN spacers and pyrophyllite gaskets. Dry experiments in the system MgO-SiO 2 are -among others-the base of the P calibration of the multi-anvil experiments where the α−β transition curve of the study of Morishima et al (1994) has been taken as reference (13.6 GPa -1,200°C). In some experiments, the pressure was calculated using the (Mg,Fe) 2 SiO 4 phase relations (see Frost and Dolejs, 2007).…”

Section: Multi-anvil Synthesesmentioning

confidence: 99%

Water and Iron effect on the P-T-x coordinates of the 410-km discontinuity in the Earth upper mantle

Deon

Koch‐Müller

Rhede

et al. 2010

Contrib Mineral Petrol

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We performed multi-anvil experiments in the system MgO-SiO 2 ± H 2 O at 13.0-13.7 GPa and 1,025-1,300°C and in the system MgO-FeO-SiO 2 ± H 2 O, under reducing conditions, at 11.0-12.7 GPa and 1200°C, to depict the effect of H 2 O on the P-T-x coordinates of the 410-km discontinuity, i.e. the olivine-wadsleyite phase boundary. The charges were investigated with where wad-ring and ol-ring coexist, we observe, however, an unexpected broadening of the loops with a shift to higher iron contents. In total the stability field of hydrous wad expands in both directions, to lower and higher pressures. Fe 3+ concentrations as determined by EELS are very low and are expected to play no role in the broadening of the loops.

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The Phase Boundary Between α- and β-Mg ₂ SiO ₄ Determined by in Situ X-ray Observation

Cited by 215 publications

References 9 publications

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the deep upper mantle

Water and Iron effect on the P-T-x coordinates of the 410-km discontinuity in the Earth upper mantle

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The Phase Boundary Between α- and β-Mg 2 SiO 4 Determined by in Situ X-ray Observation

Cited by 215 publications

References 9 publications

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the deep upper mantle

Water and Iron effect on the P-T-x coordinates of the 410-km discontinuity in the Earth upper mantle

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The Phase Boundary Between α- and β-Mg ₂ SiO ₄ Determined by in Situ X-ray Observation