title: Discovery of natural MgSiO3 tetragonal garnet in a shocked chondritic meteorite.
abstract: MgSiO3 tetragonal garnet, which is the last of the missing phases of experimentally predicted high-pressure polymorphs of pyroxene, has been discovered in a shocked meteorite. The garnet is formed from low-Ca pyroxene in the host rock through a solid-state transformation at 17 to 20 GPa and 1900° to 2000°C. On the basis of the degree of cation ordering in its crystal structure, which can be deduced from electron diffraction intensities, the cooling rate of the shock-induced melt veins from ~2000°C was estimated to be higher than 10(3)°C/s. This cooling rate sets the upper bound for the shock-temperature increase in the bulk meteorite at ~900°C.
authors.affiliation: Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Kochi 783-8502, Japan.
authors.forename: Naotaka
authors.initials: N
authors.lastname: Tomioka
authors.affiliation: Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashihiroshima, Hiroshima 739-8526, Japan.
authors.forename: Masaaki
authors.identifier: 0000-0002-4404-9813
authors.initials: M
authors.lastname: Miyahara
authors.affiliation: Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Kochi 783-8502, Japan.
authors.forename: Motoo
authors.identifier: 0000-0001-5686-0243
authors.initials: M
authors.lastname: Ito
mesh_terms: D019110:Meteoroids; D046529:Microscopy, Electron, Transmission; D008903:Minerals / Q000032:analysis / Q000737:chemistry*; D008962:Models, Theoretical; D014961:X-Ray Diffraction
chemical_list: D008903:Minerals; C092478:pyroxene
keywords: Deep Earth’s minerals; Garnet; High pressure; Shock metamorphism; Transmission electron microscopy; meteorites