Early stages of core segregation recorded by Fe isotopes in an asteroidal mantle

Abstract

Available online xxxx Editor: B. Marty Keywords: iron isotopes achondrite ureilite coreUreilite meteorites are achondrites that are debris of the mantle of a now disrupted differentiated asteroid rich in carbon. They provide a unique opportunity to study the differentiation processes of such a body. We analyzed the iron isotopic compositions of 30 samples from the Ureilite Parent Body (UPB) including 29 unbrecciated ureilites and one ureilitic trachyandesite (ALM-A) which is at present the sole large crustal sample of the UPB. The δ 56 Fe of the whole rocks fall within a restricted range, from 0.01 to 0.11h, with an average of +0.056 ± 0.008h, which is significantly higher than that of chondrites.We show that this difference can be ascribed to the segregation of S-rich metallic melts at low degrees of melting at a temperature close to the Fe-FeS eutectic, and certainly before the onset of the melting of the silicates (<1100 • C), in agreement with the marked S depletions, and the siderophile element abundances of the ureilites. These results point to an efficient segregation of S-rich metallic melts during the differentiation of small terrestrial bodies.

Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

“…Fe 265 of the ureilites, that is significantly higher than that of chondrites (Barrat et al, 2015); it is in agreement with 266 the marked S-depletions and the siderophile element abundances of the ureilites (e.g., Warren et al, 2006); 267 this step would not have had an impact on the incompatible trace element distributions which are neither 268 chalcophile nor siderophile. After core segregation, the ureilite precursors would have displayed flat REE 269 patterns, but their incompatible trace element abundances were likely to have been higher than that of CIs, 270 probably close to 2 x CI, as suggested by the Sc abundances (Fig.…”

“…The UPB was definitely C-rich, but was 84 isotopically distinct from the carbonaceous chondrites (Yamakawa et al, 2010; Warren, 2011). However, it 85 contained enough 26 Al to be heated by the decay of this isotope, which allowed the segregation of S-rich 86 metallic melts (e.g., Warren et al, 2006; Rankenburg et al, 2008; Budde et al, 2015), more likely before the 87 onset of silicate melting (Barrat et al, 2015). Subsequent extraction of silicate melts is demonstrated by the 88 presence of feldspar-rich rock debris in ureilitic breccias (e.g., Ikeda et al, 2000; Cohen et al, 2004; 89 Bischoff et al, 2014), but the melting experienced by the UPB was more limited than in other early bodies, 90 such as the angrite parent body or Vesta, where magma oceans homogenized the O isotope compositions 91 (Greenwood et al, 2005 (Yamakawa et al, 2010; Goodrich et al, 2010, Bischoff et al, 2014 Budde et al, 2015).…”

The Stubenberg meteorite—An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field

“…After homogenizing 0.5 g of interior material, a 200 mg whole-rock sample of fragments and splinters was analyzed for major and trace element concentrations by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma sector field mass spectrometry (ICP-SFMS) following the procedure described by Barrat et al (2012Barrat et al ( , 2015Barrat et al ( , 2016. Cosmogenic radionuclide concentrations were analyzed by means of nondestructive high purity germanium (HPGe) gamma spectroscopy in the underground laboratories at the Laboratori Nazionali del Gran Sasso and at the Max-Planck-Institut f€ ur Kernphysik in Heidelberg (Arpesella 1996;Heusser et al 2015), and bulk oxygen isotope composition was analyzed by laser fluorination in combination with gas source mass spectrometry (Sharp 1990 Pack et al 2016).…”

Origin of mass‐independent oxygen isotope variation among ureilites: Clues from chondrites and primitive achondrites

“…Ureilites are widely regarded as mantle residues, or restites, from which feldspar-rich magma (Ringwood 1960;Cohen et al 2004;Bischoff et al 2014), and sulfur-rich iron melt Rankenberg et al 2008;Barrat et al 2015) have been removed. These losses are reflected in the bulk chemistry of ureilites, which is broadly chondritic with strong depletions of plagiophile elements (Na, Ca, and Al) and incompatible lithophile trace elements including light rare earth elements, and variable small depletions of siderophile elements (Mittlefehldt et al 1998).…”

“…; Barrat et al. ) have been removed. These losses are reflected in the bulk chemistry of ureilites, which is broadly chondritic with strong depletions of plagiophile elements (Na, Ca, and Al) and incompatible lithophile trace elements including light rare earth elements, and variable small depletions of siderophile elements (Mittlefehldt et al.…”