High-pressure minerals in eucrite suggest a small source crater on Vesta

Abstract

High-pressure minerals in meteorites are important records of shock events that have affected the surfaces of planets and asteroids. A widespread distribution of impact craters has been observed on the Vestan surface. However, very few high-pressure minerals have been discovered in Howardite-Eucrite-Diogenite (HED) meteorites. Here we present the first evidence of tissintite, vacancy-rich clinopyroxene, and super-silicic garnet in the eucrite Northwest Africa (NWA) 8003. Combined with coesite and stishovite, the presence of these high-pressure minerals and their chemical compositions reveal that solidification of melt veins in NWA 8003 began at a pressure of >~10 GPa and ceased when the pressure dropped to <~8.5 GPa. The shock temperature in the melt veins exceeded 1900 °C. Simulation results show that shock events that create impact craters of ~3 km in diameter (subject to a factor of 2 uncertainty) are associated with sufficiently high pressures to account for the occurrence of the high-pressure minerals observed in NWA 8003. This indicates that HED meteorites containing similar high-pressure minerals should be observed more frequently than previously thought.

Shock‐induced phase transformation of anorthitic plagioclase in the eucrite meteorite Northwest Africa 2650

“…It has also been observed in the shocked eucrite NWA 8003 (Pang et al. ). Recently, tissintite has been synthesized with starting material of natural labradorite (Rucks et al.…”

“…Pang et al. ). The vacancy‐rich clinopyroxene is the predominant phase in simple shock melt veins and occurs at the margin of the zoned shock melt veins.…”

“…Tissintite is a recently found mineral with a composition of anorthitic plagioclase and a crystal structure of C2/c clinopyroxene (Ma et al 2015). It has also been observed in the shocked eucrite NWA 8003 (Pang et al 2016). Recently, tissintite has been synthesized with starting material of natural labradorite (Rucks et al 2018).…”

“…In addition, tissintite has also been observed in the shocked eucrite Northwest Africa 8003 (Pang et al. ). The recent high‐pressure experimental investigations of plagioclase (e.g., Kubo et al.…”

“…Recently, tissintite and st€ offlerite, two high-pressure polymorphs of labrodorite, have been found in shocked Martian meteorites (Walton et al 2014;Ma et al 2015;Tschauner and Ma 2017;Sharp et al 2019). In addition, tissintite has also been observed in the shocked eucrite Northwest Africa 8003 (Pang et al 2016). The recent high-pressure experimental investigations of plagioclase (e.g., Kubo et al 2010;Jaret et al 2015;Rucks et al 2018;Sims et al 2019) and the observations of different plagioclase polymorphs in shocked samples have improved our understanding of the phase transformation behaviors, mechanisms, and conditions of anorthitic plagioclase.…”