A New Source of Basaltic Meteorites Inferred from Northwest Africa 011

Abstract

Eucrites are a class of basaltic meteorites that share common mineralogical, isotopic, and chemical properties and are thought to have been derived from the same parent body, possibly asteroid 4 Vesta. The texture, mineralogy, and noble gas data of the recently recovered meteorite, Northwest Africa (NWA) 011, are similar to those of basaltic eucrites. However, the oxygen isotopic composition of NWA011 is different from that of other eucrites, indicating that NWA011 may be derived from a different parent body. The presence of basaltic meteorites with variable oxygen isotopic composition suggests the occurrence of multiple basaltic meteorite parent bodies, perhaps similar to 4 Vesta, in the early solar system.

Oxygen isotopic constraints on the origin and parent bodies of eucrites, diogenites, and howardites

“…NWA 011 is unshocked and unbrecciated (Fig. 6c), though it appears to be a recrystallized impact breccia Yamaguchi et al, 2002). Like most eucrites, NWA 011 has pyroxenes with equilibrated Fe/Mg ratios.…”

“…Although the mineralogy and major element composition of NWA 011 resemble those of the noncumulate eucrites, Yamaguchi et al (2002) and Floss et al (2005) inferred from its unique oxygen isotopic composition (∆ 17 O is -1.6‰ cf. -0.2‰ in HEDs) that it formed on a separate parent body.…”

40Ar/39Ar impact ages and time–temperature argon diffusion history of the Bunburra Rockhole anomalous basaltic achondrite

“…A distinct Δ 17 O value suggests that the Bunburra achondrite either belongs to a unique parent body not previously sampled before, or originated from an isotopically unequilibrated part of 4 Vesta. Yamaguchi et al (2002) and others (e.g., Scott et al, 2009), suggested that the latter hypothesis is less likely as the complete melting and differentiation of the parent body should have resulted in complete oxygen homogenisation.…”

“…In addition to the 'normal' eucrites, a minority of anomalous basaltic achondrites (eleven specimens discovered so far, such as NWA 011 and Ibitira; Yamaguchi et al (2002)) have major element compositions similar to other eucrites, but distinct trace element concentrations and, most importantly Δ 17 O values, significantly departing from the HED-type eucrite meteorites. Due to their distinct Δ 17 O signatures, these anomalous basaltic achondrites have been proposed to: (1) belong to distinct parent bodies, similar in nature, but unrelated to 4 Vesta, (2) originate from 4 Vesta but from a region where the parent body did not undergo complete oxygen homogenisation (Scott et al, 2009;Yamaguchi et al, 2002), and (3) originate from Vesta, but prior to or during impact ejection had their oxygen composition modified by an impactor 'contaminant' or late veneers (Greenwood et al, 2013).…”

“…Due to their distinct Δ 17 O signatures, these anomalous basaltic achondrites have been proposed to: (1) belong to distinct parent bodies, similar in nature, but unrelated to 4 Vesta, (2) originate from 4 Vesta but from a region where the parent body did not undergo complete oxygen homogenisation (Scott et al, 2009;Yamaguchi et al, 2002), and (3) originate from Vesta, but prior to or during impact ejection had their oxygen composition modified by an impactor 'contaminant' or late veneers (Greenwood et al, 2013).…”