Presentation Information
[PPS03-P17]Revisiting nucleosynthetic Cr-isotopic data for HED meteorites
*Nao Nakanishi1, Makiko K. Haba1, Tetsuya Yokoyama1 (1.Institute of Science Tokyo)
Keywords:
54Cr,eucrite,diogenite,Vesta
Recent isotopic measurements of meteorites have revealed that the building blocks of individual meteorite parent bodies originated from materials with diverse isotopic compositions. These variabilities reflect the heterogeneous distribution of nuclides synthesized in different stellar environments prior to the birth of the Solar System. Isotopic heterogeneity of non-carbonaceous (NC) meteorites is one of the important topics of cosmochemistry because it relates to building material compositions of rocky planets in the inner Solar System, including Mercury, Venus, Earth, and Mars. Schiller et al. [1] found a positive correlation between 48Ca/44Ca ratios of achondrites and terrestrial samples and the masses of their parent bodies. They suggested that isotopic composition of the inner disk evolved over time through the addition of inward-drifting dust with CI-like composition from the outer Solar System. However, modeling the isotopic evolution in the early Solar System is still difficult because the accretion (age and location) and migration of asteroids and planets are unclear.
To address these issues, this study focuses on isotopic compositions of Howardite-Eucrite-Diogenite (HED) meteorites, the largest group of achondrites, which are considered to originate from Vesta (e.g., [2], [3]). Vesta was accreted in the early stage of disk evolution compared to chondrite parent bodies. The accretion ages were estimated to be ≦1 Ma after CAI formation (e.g., [4], [5]). This early accretion suggests that HED meteorites may record the isotopic evolution during the early stages of disk evolution. Compilation of published data shows that HED meteorites exhibit relatively large isotopic variations in some nucleosynthetic isotope systems, such as Zn, Ca, and Cr, compared to other NC meteorites (e.g., [6]). These isotopic variations may reflect modification of Vesta through the addition of outer solar system materials, or alternatively, may indicate the derivation from a parent body distinct from Vesta. However, some of the data were obtained approximately two decades ago. Given recent advances in high-precision isotope analysis, it is necessary to re-evaluate the reported nucleosynthetic isotope variations in HED meteorites to assess whether the reported variations are robust.
As a first step, we focus on Cr isotope system and analyze HED meteorites in this study. Samples around 5 mg of eucrites (Camel Donga and NWA 2988) and diogenite (Tatahouine) were digested with a mixture of acids (HNO3, HF, and HCl). The Cr was purified using a three-step column chemistry procedure combining an extraction chromatographic resin (DGA-n, Eichrom) and two types of cation exchange resins (AG50W-X8 and AG50W-X12, Bio-Rad). The Cr isotope ratios were measured by TIMS (Triton Plus, Thermo Sci).
The three samples exhibit homogeneous ε54Cr, ranging from -0.71 ± 0.04 to -0.60 ± 0.04. These values fall within the previously reported range (-1 to -0.4 [e.g., 7]) and are consistent with the most abundant range of reported HED data (-0.8 to -0.6). Further discussion based on additional Cr isotope data for HED meteorites will be presented at the meeting.
References: [1] Schiller et al. (2018) Nature, 33 555(7697), 507. [2] Drake (2001) MAPS, 36, 501. [3] McCord et al. (1970) Science, 168, 1445. [4] Sugiura and Fujiya (2014) MAPS, 49, 772. [5] Schiller et al. (2011) ApJL, 740, L22. [6] Valdes et al. (2021) Chem. Geol., 581, 120396. [7] Trinquier et al. (2009) Science, 324(5925), 374.
To address these issues, this study focuses on isotopic compositions of Howardite-Eucrite-Diogenite (HED) meteorites, the largest group of achondrites, which are considered to originate from Vesta (e.g., [2], [3]). Vesta was accreted in the early stage of disk evolution compared to chondrite parent bodies. The accretion ages were estimated to be ≦1 Ma after CAI formation (e.g., [4], [5]). This early accretion suggests that HED meteorites may record the isotopic evolution during the early stages of disk evolution. Compilation of published data shows that HED meteorites exhibit relatively large isotopic variations in some nucleosynthetic isotope systems, such as Zn, Ca, and Cr, compared to other NC meteorites (e.g., [6]). These isotopic variations may reflect modification of Vesta through the addition of outer solar system materials, or alternatively, may indicate the derivation from a parent body distinct from Vesta. However, some of the data were obtained approximately two decades ago. Given recent advances in high-precision isotope analysis, it is necessary to re-evaluate the reported nucleosynthetic isotope variations in HED meteorites to assess whether the reported variations are robust.
As a first step, we focus on Cr isotope system and analyze HED meteorites in this study. Samples around 5 mg of eucrites (Camel Donga and NWA 2988) and diogenite (Tatahouine) were digested with a mixture of acids (HNO3, HF, and HCl). The Cr was purified using a three-step column chemistry procedure combining an extraction chromatographic resin (DGA-n, Eichrom) and two types of cation exchange resins (AG50W-X8 and AG50W-X12, Bio-Rad). The Cr isotope ratios were measured by TIMS (Triton Plus, Thermo Sci).
The three samples exhibit homogeneous ε54Cr, ranging from -0.71 ± 0.04 to -0.60 ± 0.04. These values fall within the previously reported range (-1 to -0.4 [e.g., 7]) and are consistent with the most abundant range of reported HED data (-0.8 to -0.6). Further discussion based on additional Cr isotope data for HED meteorites will be presented at the meeting.
References: [1] Schiller et al. (2018) Nature, 33 555(7697), 507. [2] Drake (2001) MAPS, 36, 501. [3] McCord et al. (1970) Science, 168, 1445. [4] Sugiura and Fujiya (2014) MAPS, 49, 772. [5] Schiller et al. (2011) ApJL, 740, L22. [6] Valdes et al. (2021) Chem. Geol., 581, 120396. [7] Trinquier et al. (2009) Science, 324(5925), 374.