Abstract
AbstractProjectile–target interactions as a result of a large bolide impact are important issues, as abundant extraterrestrial material has been delivered to the Earth throughout its history. Here, we report results of shock‐recovery experiments with a magnetite‐quartz target rock positioned in an ARMCO iron container. Petrography, synchrotron‐assisted X‐ray powder diffraction, and micro‐chemical analysis confirm the appearance of wüstite, fayalite, and iron in targets subjected to 30 GPa. The newly formed mineral phases occur along shock veins and melt pockets within the magnetite‐quartz aggregates, as well as along intergranular fractures. We suggest that iron melt formed locally at the contact between ARMCO container and target, and intruded the sample causing melt corrosion at the rims of intensely fractured magnetite and quartz. The strongly reducing iron melt, in the form of μm‐sized droplets, caused mainly a diffusion rim of wüstite with minor melt corrosion around magnetite. In contact with quartz, iron reacted to form an iron‐enriched silicate melt, from which fayalite crystallized rapidly as dendritic grains. The temperatures required for these transformations are estimated between 1200 and 1600 °C, indicating extreme local temperature spikes during the 30 GPa shock pressure experiments.
Highlights
Hypervelocity impact events are local but widespread phenomena in our solar system, leading to enormous petrological and mineralogical changes in rocks
Possible structural and phase transformations occurring at the interfacial regions between minerals like magnetite and quartz were not within the scope of our previous studies (Reznik et al 2016a, 2016b; Kontny et al 2018), and we did not concentrate on interactions between the ARMCO iron container and the target rock
A higher abundance of such grains was observed in the 30 GPa sample
Summary
Hypervelocity impact events are local but widespread phenomena in our solar system, leading to enormous petrological and mineralogical changes in rocks. It is an important scientific challenge to reveal impact-related microstructural changes occurring in rocks. Understanding the effect of shock waves on magnetic and structural properties of magnetite (Fe3O4) as one of the most abundant magnetic carriers in impacted rocks is an important objective (e.g., Gattacceca et al 2007). Possible structural and phase transformations occurring at the interfacial regions between minerals like magnetite and quartz were not within the scope of our previous studies (Reznik et al 2016a, 2016b; Kontny et al 2018), and we did not concentrate on interactions between the ARMCO iron container and the target rock. Interactions of projectiles with target rocks are reported from natural impactites, such as Henbury crater in Australia (Ding and Veblen 2004), the Wabar craters in Saudi Arabia (Hamann et al 2013), or Kamil crater in Egypt (D’Orazio et al 2011).
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