Experimental shock metamorphism of terrestrial basalts: Agglutinate‐like particle formation, petrology, and magnetism

Hypervelocity impacts occur on bodies throughout our solar system, and play an important role in altering the mineralogy, texture, and magnetic properties in target rocks at nanometer to planetary scales. Here we present the results of hypervelocity impact experiments conducted using a two-stage light-gas gun with 5 mm spherical copper projectiles accelerated toward basalt targets with ~6 km s−1 impact velocities. Four different types of magnetite- and titanomagnetite-bearing basalts were used as targets for seven independent experiments. These laboratory impacts resulted in the formation of agglutinate-like particles similar in texture to lunar agglutinates, which are an important fraction of lunar soil. Materials recovered from the impacts were examined using a suite of complementary techniques, including optical and scanning electron microscopy, micro-Raman spectroscopy, and high- and low-temperature magnetometry, to investigate the texture, chemistry, and magnetic properties of newly formed agglutinate-like particles and were compared to unshocked basaltic parent materials. The use of Cu-projectiles, rather than Fe- and Ni-projectiles, avoids magnetic contamination in the final shock products and enables a clearer view of the magnetic properties of impact-generated agglutinates. Agglutinate-like particles show shock features, such as melting and planar deformation features, and demonstrate shock-induced magnetic hardening (two- to seven-fold increases in the coercivity of remanence Bcr compared to the initial target materials) and decreases in low-field magnetic susceptibility and saturation magnetization. © The Meteoritical Society, 2017. Russian Science Foundation, RSF: 17-17-01279 Rochester Academy of Science, RAS Acknowledgments—We thank the anonymous reviewer for the review and constructive suggestions and Prof. Oliver Tschauner for useful suggestions and the editorial handling, which helped to improve the manuscript. The work is supported by Act 211 Government of the Russian Federation, agreement no. 02.A03.21.0006 and is performed according to the Russian Government Program of Competitive Growth of Kazan Federal University. We gratefully acknowledge support by the U.S. National Science Foundation IRM Visiting Fellowship to N.S.B. D.D.B. was supported by Program no. 7P of Presidium RAS and a Russian Science Foundation Grant 17-17-01279. D.D.B. acknowledges the staff at the Center of Microscopy and Nanotechnology of the University of Oulu (Finland) for assistance with some aspects of electron microprobe and SEM works.