Back‐transformation mechanisms of ringwoodite and majorite in an ordinary chondrite

Fukimoto, Kanta; Miyahara, Masaaki; Sakai, Takeshi; Ohfuji, Hiroaki; Tomioka, Naotaka; Kodama, Yu; Ohtani, Eiji; Yamaguchi, A.

doi:10.1111/maps.13543

Cited by 9 publications

(8 citation statements)

References 40 publications

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“…It has been proposed that the combination of relatively high temperature and low pressures that characterize retrograde events leads to the back-transformation of ringwoodite into wadsleyite (Madon and Poirier 1983;Price et al 1983), or even into olivine, as for example reported for the Mbale and Y-75267 ordinary chondrites (Chen et al 1998;Kimura et al 2004;Hu and Sharp 2017;Fukimoto et al 2020). In order for reverse transformations to occur, however, the shock feature needs to be quenched at relatively slow rates, maintaining high temperatures for a few seconds (Kimura et al 2004;Ohtani et al 2004).…”

Section: Discussionmentioning

confidence: 99%

Apollo 15 regolith breccia provides first natural evidence for olivine incongruent melting

Satta,

Miyahara,

Ozawa

et al. 2022

American Mineralogist

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The Apollo 15 mission has returned various samples of regolith breccias to the Earth -typical lunar rocks lithified by impact events on the Moon's surface. Here we report our observations on shock features recorded in a section of the Apollo Sample 15299. We observe the presence of ferropericlase crystals confined in a shock melt pocket and conclude that their formation is related to a shock-induced incongruent melting of olivine. While predicted by experiments, this phenomenon has never been observed in a natural sample. The incongruent melting of olivine provides an important signature of melting under high-pressure conditions, and allows for estimating the pressure (P)-temperature (T) experienced by the studied sample during the impact event. We infer that the fracture porosity that likely characterized the studied sample prior to the This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Section: Discussionmentioning

confidence: 99%

Apollo 15 regolith breccia provides first natural evidence for olivine incongruent melting

Satta,

Miyahara,

Ozawa

et al. 2022

American Mineralogist

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“…Even if both the high‐pressure and temperature conditions required for the formation of a high‐pressure mineral are achieved, the high‐pressure mineral cannot form if the duration is not sufficiently long (e.g., Kubo et al., 2010). It is also possible that a high‐pressure mineral, which formed during the compression and equilibrium stages once, back‐transforms into its low‐pressure mineral during the subsequent adiabatic decompression stage if the cooling is slow (Fritz et al., 2017; Fukimoto et al., 2020; Hu & Sharp, 2017; Shaw & Walton, 2013).…”

Section: Discussionmentioning

confidence: 99%

Chondrule Flattening by Shock Recovery Experiments on Unequilibrated Chondrites

et al. 2021

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Shock recovery experiments were conducted using ALH‐78084 H3 and Y‐793375 L3 chondrites in the shock pressure range of 11–43 GPa to reproduce shock‐induced melting and chondrule flattening. Shock‐induced melt and chondrule flattening in 15 H3, 23 L3, and 23 LL3 ordinary chondrites were also investigated for comparisons. The shock experiments proved that, at least in unequilibrated ordinary chondrites, shock‐induced melting occurred beyond 11 GPa. The melting occurs at the boundary between chondrule and matrix. The melts included fine‐grained silicate minerals, glasses, and ameba or spherical metallic Fe–Ni or metallic Fe–Ni–iron sulfide with a eutectic texture that coincided with shock‐induced melts in the investigated H/L/LL3 ordinary chondrites. Shock experiments also proved that shock‐induced flattening of chondrules occurs and the flattening degree increases with increasing shock pressure. Considering the shock experiments not only of ordinary chondrites but also of carbonaceous chondrites, the flattening degree is not significantly affected by the density, porosity, and chondrule/matrix ratio of chondrites. The long axes of chondrules in shocked ALH‐78084 H3 and Y‐793375 L3 chondrites have preferred orientations and the degree increases with increasing shock pressure. It is difficult to estimate quantitatively the shock pressure recorded in unequilibrated ordinary chondrites using the empirical formula between the aspect ratio of chondrules and shock pressure. Nevertheless, the investigated L/LL3 ordinary chondrites with shock‐induced melts had higher aspect ratios (median, 1.36) and more strongly preferred orientations than those without shock‐induced melts (median, 1.25).

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“…However, the pyroxene glass also forms during the back‐transformation from majorite to low‐Ca pyroxene (Fukimoto et al. 2020). Not all pyroxene glass is necessarily vitrified bridgmanite.…”

Section: Discussionmentioning

confidence: 99%

“…S4). The back-transformation from ringwoodite to olivine proceeds by an incoherent nucleation and by an interface-controlled growth mechanism; nucleation occurs on the grain boundaries of ringwoodite, and subsequently olivine grains grow (Fukimoto et al 2020). Fine-grained olivine crystal assemblages are expected to be formed in the H chondrites from wadsleyite and/or ringwoodite.…”

Section: Abundance Of High-pressure Polymorphsmentioning

confidence: 99%

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Systematic investigations of high‐pressure polymorphs in shocked ordinary chondrites

Miyahara

Yamaguchi

Saitoh

et al. 2020

Meteorit & Planetary Scien

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Shock-induced melting textures and high-pressure polymorphs in 178 ordinary chondrites of all chemical groups and petrologic types were investigated. The shock-induced melting modes were classified into three types, namely pocket, line, and network. The type of shock-induced melting depends on the petrologic type. The width of the shock-induced melt increased with increasing the petrologic type number. The approximate estimated shock-pressure ranges recorded in and around the shock-induced melts of the H-group ordinary chondrites based on the identified high-pressure polymorphs were as follows: H3, less than 2 GPa; H4-H6, 2-6 GPa. For ordinary chondrites of the L/LL group, the values were as follows: L/LL3, 2-6 GPa; L/LL4, 2-14 GPa; L5: 14-20 GPa; LL5, 2-14 GPa; L6, 17-23 GPa; and LL6, 14-18 GPa. After adopting the estimated shock pressures into the onion shell-structured parent body model, the shock pressure on the surface was much lower than in the interior. One possibility is that the apparent lower shock pressure on the surface is due to spallation during the impact. Considering the features of the high-pressure polymorphs, the major disruption history of the parent bodies is different in each chemical group, although the L/LL chondrite parent bodies may have a similar major disruption history.

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Back‐transformation mechanisms of ringwoodite and majorite in an ordinary chondrite

Cited by 9 publications

References 40 publications

Apollo 15 regolith breccia provides first natural evidence for olivine incongruent melting

Apollo 15 regolith breccia provides first natural evidence for olivine incongruent melting

Chondrule Flattening by Shock Recovery Experiments on Unequilibrated Chondrites

Systematic investigations of high‐pressure polymorphs in shocked ordinary chondrites

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