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.
Highlights
Hyper-velocity collisions between celestial bodies create impact craters on the surfaces of planets and asteroids and may result in the formation of high-pressure minerals[1,2]
1,700 HED meteorites have been identified in the meteorite collections; high-pressure minerals have only been reported in one shocked eucrite[18]
Tissintite, vacancy-rich clinopyroxene, and super-silicic garnet are reported in HED meteorites for the first time
Summary
Hyper-velocity collisions between celestial bodies create impact craters on the surfaces of planets and asteroids and may result in the formation of high-pressure minerals[1,2]. Many high-pressure minerals have been observed in shocked meteorites[3,4,5,6,7], samples returned by the Apollo missions[8], and in terrestrial impact structures[9], indicating that widespread and intense dynamic events have occurred on both planets and asteroids These minerals provide important clues that allow us to constrain the prevailing Pressure-Temperature-time (P-T-t ) conditions characterizing these shock events, the sizes and velocities of the impactors, and the size scale of the source impact craters[3,4,5,6,7,10,11,12,13]. The high-pressure minerals tissintite, vacancy-rich clinopyroxene, and super-silicic garnet are observed in the shocked eucrite Northwest Africa (NWA) 8003 in addition to coesite and stishovite The discovery of these high-pressure minerals provides important constraints on the P-T-t conditions of shock metamorphism in HED meteorites. We further estimate the possible sizes of the impact craters from which HED meteorites with high-pressure minerals might have originated
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