RESUMO
Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher δ18O, Δ17O, and ε54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10's of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.
Assuntos
Meteoroides , Sistema Solar , ÁguaRESUMO
BACKGROUND: Chromium isotopes have been used to trace geochemical and cosmochemical processes in the past. However, the presence of multivalent Cr species has made it difficult to isolate Cr from geological samples, particularly for samples with a low Cr mass fraction. RESULTS: Here, a simple three-step ion exchange chromatography procedure is presented to separate Cr from various sample matrices, ranging from ultramafic to felsic rocks. Throughout each of the column chromatography step, 1 mL of cation exchange resin AG50W-X8 (200-400 mesh) was used as the stationary phase and oxalic acid as a chelating agent, was used in addition to the inorganic acids. This method yielded high recoveries of Cr [93 ± 8% (2SD, N = 7)] regardless of the lithology. The total procedural blank of Cr was <0.5 ng. We also developed a double spike-total evaporation-thermal ionization mass spectrometry (DS-TE-TIMS) technique that significantly reduced sample consumption to â¼20 ng of Cr per each measurement of mass-dependent 53Cr/52Cr. SIGNIFICANCE: This study achieved a 2SD external precision of 0.02 for the analysis of NIST NBS3112a and of 0.01-0.07 for the geological samples. This study enabled high-precision Cr isotope analysis in geological samples with various matrix and Cr compositions using relatively small sample volumes.
RESUMO
Nickel isotope ratios have traditionally been used as an important tracer in cosmochemistry, and recently, it has gained attention in geochemistry, biochemistry, and environmental sciences with the development of MC-ICP-MS. Purification of Ni before isotope measurement is mandatory for obtaining precise data, which has been commonly achieved with ion-exchange chromatography, employing dimethylglyoxime (DMG) as a chelating agent for Ni. However, it has been pointed out that the use of DMG can adversely affect the isotope measurement due to insufficient Ni recovery and mass bias during measurement caused by the remaining DMG. Ni isolation procedures without the usage of DMG were innovated, but they have disadvantages such as the necessity of complex separation methods, high Ni blank, and matrix-dependent Ni recovery. Here, we present a simple Ni isolation procedure without using DMG but with the aid of oxalic acid along with common inorganic acids, achieving near-complete recovery of Ni with low blanks [0.7 ± 0.3 ng (2SD, n = 4)] only using three ion exchange column steps. To validate our method and strengthen the Ni isotope database of reference materials, 60Ni/58Ni of 20 geological reference materials, covering wide matrix compositions, were measured by MC-ICP-MS using the double-spike method. The results have shown that high recovery of Ni, independent of the sample matrix elements was achieved (98 ± 4%) and the 60Ni/58Ni was measured with a 2SD of 0.006-0.084 from samples containing 100-200 ng Ni.