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  • Title: Ultrafast olivine-ringwoodite transformation during shock compression.
    Author: Okuchi T, Seto Y, Tomioka N, Matsuoka T, Albertazzi B, Hartley NJ, Inubushi Y, Katagiri K, Kodama R, Pikuz TA, Purevjav N, Miyanishi K, Sato T, Sekine T, Sueda K, Tanaka KA, Tange Y, Togashi T, Umeda Y, Yabuuchi T, Yabashi M, Ozaki N.
    Journal: Nat Commun; 2021 Jul 14; 12(1):4305. PubMed ID: 34262045.
    Abstract:
    Meteorites from interplanetary space often include high-pressure polymorphs of their constituent minerals, which provide records of past hypervelocity collisions. These collisions were expected to occur between kilometre-sized asteroids, generating transient high-pressure states lasting for several seconds to facilitate mineral transformations across the relevant phase boundaries. However, their mechanisms in such a short timescale were never experimentally evaluated and remained speculative. Here, we show a nanosecond transformation mechanism yielding ringwoodite, which is the most typical high-pressure mineral in meteorites. An olivine crystal was shock-compressed by a focused high-power laser pulse, and the transformation was time-resolved by femtosecond diffractometry using an X-ray free electron laser. Our results show the formation of ringwoodite through a faster, diffusionless process, suggesting that ringwoodite can form from collisions between much smaller bodies, such as metre to submetre-sized asteroids, at common relative velocities. Even nominally unshocked meteorites could therefore contain signatures of high-pressure states from past collisions.
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