The effects of 10 to >160 GPa shock on the magnetic properties of basalt and diabase

Abstract

Hypervelocity impacts within the solar system affect both the magnetic remanence and bulk magnetic properties of planetary materials. Spherical shock experiments are a novel way to simulate shock events that enable materials to reach high shock pressures with a variable pressure profile across a single sample (ranging between ∼10 and >160 GPa). Here we present spherical shock experiments on basaltic lava flow and diabase dike samples from the Osler Volcanic Group whose ferromagnetic mineralogy is dominated by pseudo‐single‐domain (titano)magnetite. Our experiments reveal shock‐induced changes in rock magnetic properties including a significant increase in remanent coercivity. Electron and magnetic force microscopy support the interpretation that this coercivity increase is the result of grain fracturing and associated domain wall pinning in multidomain grains. We introduce a method to discriminate between mechanical and thermal effects of shock on magnetic properties. Our approach involves conducting vacuum‐heating experiments on untreated specimens and comparing the hysteresis properties of heated and shocked specimens. First‐order reversal curve (FORC) experiments on untreated, heated, and shocked specimens demonstrate that shock and heating effects are fundamentally different for these samples: shock has a magnetic hardening effect that does not alter the intrinsic shape of FORC distributions, while heating alters the magnetic mineralogy as evident from significant changes in the shape of FORC contours. These experiments contextualize paleomagnetic and rock magnetic data of naturally shocked materials from terrestrial and extraterrestrial impact craters.

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

“…This shock‐induced enhanced coercivity is consistent with previous findings (e.g., Bezaeva et al. and references therein), and may be due to domain wall pinning, microcracking, and/or fragmentation of magnetic grains (Bezaeva et al. ).…”

“… and references therein), and may be due to domain wall pinning, microcracking, and/or fragmentation of magnetic grains (Bezaeva et al. ). On the other hand, we cannot exclude that new SD grains have nucleated independently from the melt while primary volcanic oxides have not been entrained in the melt or been fully melted.…”

“…; Bezaeva et al. ) and is likely to be linked to shock‐induced microfracturing of Tmt grains, the creation of defects, and dislocations in Tmt crystal structures, as well as domain wall pinning (Lindquist et al. ).…”

“…; Bezaeva et al. ). This is exemplified by the lunar regolith where the concentration of agglutinates and the magnetic properties are well correlated (Rochette et al.…”

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

“…Hypervelocity impact events are widespread phenomena throughout the solar system and the interest in understanding shock demagnetization of crustal material has increased significantly in the last decade (e.g., Bezaeva et al, 2016;Gattacceca et al, 2007;Louzada et al, 2011;Reznik et al, 2016;Tikoo et al, 2015). This interest results from the observation that magnetic anomaly lows are ubiquitous phenomena of many impact structures on Earth and Mars (e.g., Acuña et al, 1999;Pilkington & Grieve, 1992).…”