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

Abstract

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.

Demagnetization of Ordinary Chondrites under Hydrostatic Pressure up to 1.8 GPa

“…Laboratory shock experiments are characterized by the difficulty in calibrating shock pressure, and possible mechanical damages of investigated samples (e.g. Fuller et al, 1974;Bezaeva et al, 2016a;Badyukov et al, 2018). Static pressure experiments allow better pressure calibration and are essentially non-destructive for samples.…”

Rock magnetism of ejected basaltic boulders from Lonar crater, India: Implications for the existence of a short‐lived impact‐generated weak magnetic field

“…Finally, occurrence of maskelynite in a few of the Lonar ejected basaltic boulders (Kieffer et al 1976;Nayak 1993;Misra et al 2007) suggests that these boulders experienced a maximum shock pressure between 25-30 GPa (cf. Badyukov et al 2018).…”

“…This study has importance because these basalt fragments were ejected by the highest shock pressure from close to the impact point (cf. Melosh 1989), which could be between 25-28 GPa as indicated by the presence of maskelynite-bearing basaltic boulders within the ejecta (Kieffer et al 1976;also p. 63 in French 1998;Badyukov et al 2018).…”