Complicated pressure–temperature path recorded in the eucrite Padvarninkai

Abstract

High‐pressure minerals in the eucrite Padvarninkai were investigated. Parts of anorthitic plagioclase and tridymite in the host rock of Padvarninkai vitrified, indicating that the shock pressure was 22–27 GPa. Tissintite, coesite, and a majorite‐bearing garnet occurred in the shock‐melt veins of Padvarninkai as high‐pressure minerals. Tissintite, kyanite, corundum, and dense plagioclase have occurred in the anorthitic plagioclase grains. The anorthitic plagioclase was melted and tissintite crystallized from the melt after the crystallization of kyanite and corundum. The residual melt became dense plagioclase by quenching. Tridymite has also melted and coesite crystallized from the melt. The formation of tissintite and coesite indicates that the shock pressure recorded in the veins was 2–13 GPa. The temperature increased drastically in the veins (>˜3000 K) compared with the host rock (<˜800 K). Parts of the tissintite and coesite became, respectively, amorphous (or anorthite) and quartz. Two different impact events may be recorded in Padvarninkai: The first impact event brecciated a part of the host rock, and the second impact event induced the melting of the brecciated portion, resulting in the formation of shock‐melt veins where the conditions are a high temperature and a relatively low pressure. In the veins, tissintite and coesite formed first, and parts of them underwent a back‐transformation due to a long cooling time.

Natural and experimental high-pressure, shock-produced terrestrial and extraterrestrial materials

“…If the low-pressure and high-temperature conditions are prolonged, the back transformation of a high-pressure mineral occurs, which underestimates the shock pressure (Kimura et al 2004;Hu and Sharp 2017;Miyahara et al 2019). However, a back-transformation mechanism of a high-pressure mineral and its kinetics have not been deeply investigated except for a few works (Ming et al 1991;Fukimoto et al 2020;Miyahara et al 2021). We must work on these issues to trace a pressure-temperature-time path recorded in a shock-melt vein or melt-pocket as future work.…”

Pressure–temperature–time controls on shock vein formation within the Steen River impact structure

“…Her knowledge of and enthusiasm for Steen River facilitated this work, and we dedicate this paper to her memory. Fredriksson et al, 1963;Fritz et al, 2017;Gillet & El Goresy, 2013;Miyahara et al, 2021;Sharp et al, 2015;Sharp & DeCarli, 2006;Stöffler et al, 1991). The terrestrial in situ examples provide valuable information on the spatial distribution of shock veins within impact structures, as well as their pressure-temperature-time (P-T-t) context within the impact process, constraints that remain elusive for meteorite-hosted shock veins.…”

“…Additionally, they have been recognized ex situ within lithic clasts from suevites in two terrestrial impact structures: Ries, Germany (Stähle et al., 2008, 2022) and Xiuyan, China (Yin et al., 2021). Shock melt veins were first recognized and are best known in meteorites, where they are a relatively common feature (e.g., Barnes, 1939; Fredriksson et al., 1963; Fritz et al., 2017; Gillet & El Goresy, 2013; Miyahara et al., 2021; Sharp et al., 2015; Sharp & DeCarli, 2006; Stöffler et al., 1991). The terrestrial in situ examples provide valuable information on the spatial distribution of shock veins within impact structures, as well as their pressure–temperature–time ( P – T – t ) context within the impact process, constraints that remain elusive for meteorite‐hosted shock veins.…”

Modeling the pressure–temperature–time evolution of in situ shock veins: A terrestrial case study from Vredefort

“…Terrestrial ex situ (allochthonous) shock veins have also been described in lithic clasts from suevites in the Ries (Stähle et al., 2008) and Xiuyan (Yin et al., 2021) impact structures. In addition, shock veins are a relatively common feature in many types of meteorites and were first described from meteorites (e.g., Fredriksson et al., 1963; Fritz et al., 2017; Gillet & El Goresy, 2013; Miyahara et al., 2021; Sharp & DeCarli, 2006; Stöffler et al., 1991). In this respect, we believe that the so‐far rare terrestrial examples provide an important link to the more prolific examples of shock veins known from meteorites, especially given that geological context is provided by the in situ versus displaced setting.…”