Olivine-rich achondrites from Vesta and the missing mantle problem

Abstract

Mantles of rocky planets are dominantly composed of olivine and its high-pressure polymorphs, according to seismic data of Earth’s interior, the mineralogy of natural samples, and modelling results. The missing mantle problem represents the paucity of olivine-rich material among meteorite samples and remote observation of asteroids, given how common differentiated planetesimals were in the early Solar System. Here we report the discovery of new olivine-rich meteorites that have asteroidal origins and are related to V-type asteroids or vestoids. Northwest Africa 12217, 12319, and 12562 are dunites and lherzolite cumulates that have siderophile element abundances consistent with origins on highly differentiated asteroidal bodies that experienced core formation, and with trace element and oxygen and chromium isotopic compositions associated with the howardite-eucrite-diogenite meteorites. These meteorites represent a step towards the end of the shortage of olivine-rich material, allowing for full examination of differentiation processes acting on planetesimals in the earliest epoch of the Solar System.

53Mn‐53Cr chronology and ε54Cr‐Δ17O genealogy of Erg Chech 002: The oldest andesite in the solar system

“…If the 26 Al- 26 Mg chondrule ages date melt formation in the chondrules, then the EC 002 crystallization age and the core formation ages in the magmatic iron meteorite parent bodies either predate or (Gattacceca et al, 2021;Greenwood et al, 2005Greenwood et al, , 2012Scott et al, 2009;Vaci et al, 2021;Zhang et al, 2019) are at the earlier side of the chondrule formation interval defined by the 26 Al- 26 Mg studies of chondrules in unequilibrated ordinary chondrites (e.g., Pape et al, 2019;Siron et al, 2021Siron et al, , 2022. For comparison, the second oldest felsic igneous rock, NWA 11119 (Srinivasan et al, 2018), previously constrained the silica-rich volcanism in the early solar system within the first 2.5-3.5 million years of the solar system history, which is after the peak of the chondrule formation interval (e.g., Pape et al, 2019;Siron et al, 2021Siron et al, , 2022.…”

“…(2021), the unbrecciated anomalous eucrite EET 92023 is mineralogically quite different from EC 002 in several aspects, most notably the prevalence of highly sodic plagioclase and lower FeO/MnO ratios in pyroxenes. The ungrouped achondrites NWA 12217, NWA 12562, and NWA 12319 are reported to be sourced from a fully differentiated parent body that is likely to be a V‐type asteroid or vestoid (Vaci et al., 2021). The heavier Δ 17 O composition of NWA 12217 compared to NWA 12562 and NWA 12319 and main group normal HEDs is explained as having been influenced by mixing with an ordinary chondrite component (Vaci et al., 2021), possibly by an impact event.…”

“…The ungrouped achondrites NWA 12217, NWA 12562, and NWA 12319 are reported to be sourced from a fully differentiated parent body that is likely to be a V‐type asteroid or vestoid (Vaci et al., 2021). The heavier Δ 17 O composition of NWA 12217 compared to NWA 12562 and NWA 12319 and main group normal HEDs is explained as having been influenced by mixing with an ordinary chondrite component (Vaci et al., 2021), possibly by an impact event. If EC 002 is sourced from the same vestoid reservoir as these achondrites, then the Δ 17 O composition of EC 002, which is similar to that of NWA 12217, would also require addition of a higher Δ 17 O and ε 54 Cr component to form EC 002 (Fig.…”

“…Δ 17 O diagram showing EC 002, NWA 12217, 12319, and 12562 in relation to other achondrite groups and anomalous HEDs (Gattacceca et al., 2021; Greenwood et al., 2005, 2012; Scott et al., 2009; Vaci et al., 2021; Zhang et al., 2019). TFL = terrestrial fractionation line.…”

Characterization of achondritic cosmic spherules from the Widerøefjellet micrometeorite collection (Sør Rondane Mountains, East Antarctica)

“…Such anomalous eucrites may indicate that 4-Vesta remained isotopically heterogeneous due to incomplete melting (Wiechert et al, 2004), or may alternatively suggest the existence of several asteroids with mineralogical compositions similar to that of 4-Vesta but distinct oxygen isotope compositions and differentiation histories (Scott et al, 2009;Hublet et al, 2017). Second, olivine-rich achondrites have been associated with the HED-group based on oxygen and chromium isotope systematics, extending the inventory of materials and mineralogies linked to this group (Vaci et al, 2021). Despite these limitations, the combined use of element and oxygen isotope data are considered suitable parameters for the identification of the parent body of the differentiated micrometeoroids, provided that the mineralogical control is understood (Cordier et al, 2012).…”