Introduction to the special issue of Meteoritics & Planetary Science on “Shock metamorphism and high pressure phases in meteorites and terrestrial impactites”

Abstract

Interplanetary collisions of planetary bodies represent a fundamental process that affected all planets and moons of the solar system since its formation. They occur on an extremely wide scale of projectile and target sizes, and with a large range of impact velocities. Hypervelocity collisions result in the propagation of shock waves in the colliding bodies and as a consequence in “shock metamorphism” of the impacted regions. Shock metamorphism of solid rocks and sediments has been identified on all terrestrial planets and moons from which samples are available so far, i.e., Earth, Moon, Mars, and asteroids. Shock waves with an intensity exceeding the Hugoniot elastic limit lead to distinct changes in the constituent minerals of rocks ranging from mechanical deformation to phase transitions such as isotropization and formation of high-pressure phases, and to melting. With increasing pressure, whole rock melting and finally vaporization occurs. This special issue is devoted to the observation and interpretation of these effects on the basis of the current state of research. It covers both natural shock metamorphism and shock wave experiments as well as numerical modeling of shock metamorphism and shock wave physics in general. The last decade has seen important changes in this field: novel techniques in submicrometer-scale structural and chemical analysis, marked improvements in established techniques such as FIB-TEM and EPMA and synchrotron radiation analyses, and an increasing supply of meteorite material have largely increased the number of identified high-pressure minerals that form upon shock metamorphism. In fact, over the past 10 years more such minerals were discovered than in the previous four decades. Novel, ultrafast probes of structural and chemical states during shock experiments promise to reveal some of the fundamental mechanisms that occur during the initial states of shock compression. Efforts in three-dimensional modeling of dynamic stress evolution in polycrystalline aggregates suggest far more complex stress–temperature distribution patterns than conventional hydrocode simulations. This special issue is based on a workshop entitled “Shock metamorphism and high pressure phases in meteorites and terrestrial impactites” which was held on August 6 and 7, 2016, in conjunction with the 79th Annual Meeting of the Meteoritical Society in Berlin, Germany. The conveners were O. Tschauner, T. G. Sharp, and D. Stöffler. Since the date of acceptance of some of the contributions to this Special Issue, further articles about the topic of the Special Issue have been published. In addition, several new high-pressure phases in meteorites and in the Ries impact crater have been accepted by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA). The relevant references are the following: Bindi L. and Xie X. 2017. Shenzhuangite, IMA 2017-018. CNMNC Newsletter No. 38. Mineralogical Magazine 81:1033–1038. Ma C. and Tschauner O. 2017. Zagamiite, IMA 2015-022a. CNMNC Newsletter No. 36. Mineralogical Magazine 81:403–409. Ma C. and Tschauner O. 2017. Chenmingite, IMA 2017-036. CNMNC Newsletter No. 38. Mineralogical Magazine 81:1033–1038. Ma C., Tschauner O., Beckett J. R., Rossman G. R., Prescher C., Prakapenka V. B., Bechtel H. A., and MacDowell A. 2017. Liebermannite, KAlSi3O8, a new shock-metamorphic, high-pressure mineral from the Zagami Martian meteorite. Meteoritics & Planetary Science https://doi.org/10.1111/maps.13000. Tomioka N. and Miyahara M. 2017. High-pressure minerals in shocked meteorites. Meteoritics & Planetary Science 52:2017–2039. Tschauner O., Ma C., Lanzirotti A., and Newville M. 2017. Riesite, a new high pressure polymorph of TiO2 that forms upon shock-release comparison to (Zr,Ti)O2 in pseudotachylites, Goldschmidt Conference 2017, Abstract. Tschauner O. and Ma C. 2017. Stöfflerite, IMA 2017-062. CNMNC Newsletter No. 39. Mineralogical Magazine 81:1279–1286.