Rapid Timescales for Magma Ocean Crystallization on the Howardite-Eucrite-Diogenite Parent Body

Abstract

Asteroid 4 Vesta has long been postulated as the source for the howardite-eucrite-diogenite (HED) achondrite meteorites. Here we show that Al-free diogenite meteorites record variability in the mass-independent abundance of 26 Mg (26 Mg*) that is correlated with their mineral chemistry. This suggests that these meteorites captured the Mg-isotopic evolution of a large-scale differentiating magma body with increasing 27 Al/ 24 Mg during the lifespan of the short-lived 26 Al nuclide (t 1/2 ∼ 730,000 yr). Thus, diogenites and eucrites represent crystallization products of a large-scale magma ocean associated with the differentiation and magmatic evolution of the HED parent body. The 26 Mg* composition of the most primitive diogenites requires onset of the magma ocean crystallization within 0.6 −0.4 +0.5 Myr of solar system formation. Moreover, 26 Mg* variations among diogenites and eucrites imply that near complete solidification of the HED parent body occurred within the following 2-3 Myr. Thermal models predict that such rapid cooling and magma ocean crystallization could only occur on small asteroids (<100 km), implying that 4 Vesta is not the source of the HED meteorites.

Mineralogy of V-type asteroids as a constraining tool of their past history

“…Despite the recent results from the Dawn mission that strengthened this linkage (see e.g., de McSween et al 2011McSween et al , 2013, it is still questioned by some authors (see, e.g., Schiller et al, 2011;Wasson, 2013). We also aim to analyze this genetic linkage.…”

“…But, this linkage was early questioned (Wasson and Wetherill, 1979). Indeed, recently there are some authors still questioning this linkage (see, e.g., Schiller et al, 2011;Wasson, 2013). In one hand, Schiller et al (2011) discuss that the 26 Mg n variations in eucrites and diogenites imply that near complete solidification of the HED parent body occurred in a short timescale of 2-3 Myr.…”

“…Indeed, recently there are some authors still questioning this linkage (see, e.g., Schiller et al, 2011;Wasson, 2013). In one hand, Schiller et al (2011) discuss that the 26 Mg n variations in eucrites and diogenites imply that near complete solidification of the HED parent body occurred in a short timescale of 2-3 Myr. According to thermal Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/pss models, the latter rapid cooling and magma ocean crystallization could only take place in small asteroids with a dimension inferior to 100 km.…”

“…It is also foreseen to test the genetic linkages between V-type asteroids and HED meteorites, which was recently questioned by some authors (Schiller et al, 2011;Wasson, 2013). The paper is organized as follows: in Section 2, we describe the application of adapted Hapke's bidirectional reflectance model to the spectral deconvolution of the selected asteroids and meteorites; in Section 3, we justify the model parameterization and provide a basic description of the data selected; in Section 4, we discuss the performance of the described model on laboratorial samples, HED meteorites and V-type asteroids, we report an analysis of their mineralogies and we discuss the genetic relationship between V-type asteroids and HED meteorites; in Section 5, we stress out the outlines of this paper.…”

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

“…HEDs are likely derived from the Vestoids, a family of small asteroids orbitally related to Vesta that bridge the gap between Vesta and meteorite-delivering resonances (Burbine et al, 2001). Although the connection between HED meteorites and asteroid 4 Vesta is not universally accepted (e.g., Schiller et al, 2011), recent results from the Dawn spacecraft mission, which arrived at 4 Vesta in July 2011, have somewhat reinforced this hypothesis (Russell et al, 2012).…”