Presentation Information
[PPS12-P14]Constraining the origin of Chromium isotopic variations in carbonaceous chondrites
*Ayumi Shirahata1, Tetsuya Yokoyama1, Ryuso Kitadai1 (1.Department of Earth and Planetary Sciences, Institute of Science Tokyo)
Keywords:
carbonaceous chondrites,chromium isotopes
Nucleosynthetic isotope anomalies observed in primitive meteorites result from the heterogeneous distribution of presolar grains synthesized in diverse stellar environments and preserved within the protoplanetary disk. These anomalies serve as crucial tracers for understanding the origin and early evolution of Solar System materials. Chromium (Cr) isotopes have been identified as effective tracers, particularly in the context of distinguishing between carbonaceous (CC) and non-carbonaceous (NC) reservoirs. This distinction is attributed to their inherited compositional differences between these reservoirs [1]. Sequential acid leaching experiments on carbonaceous chondrites have revealed larger 54Cr isotope anomalies than those observed in bulk samples. While this technique allows for the isolation of mineral phases with varying acid resistance to constrain the carrier phases of Cr isotope anomalies, the actual nature of the isotopic end-members within carbonaceous chondrites remains poorly understood [2].
In this study, to further constrain the carrier phases of Cr isotope anomalies, we performed sequential acid leaching on bulk samples and insoluble organic matter-rich residue (IOMR) separated from the carbonaceous chondrites Tagish Lake (C2-ung) and Murchison (CM2). The Cr isotope compositions of individual samples were measured with thermal ionization mass spectrometry (TIMS). The Cr isotope data of the leaching fractions define a negative linear correlation between 53Cr/52Cr and 54Cr/52Cr ratios. This observation indicates the presence of two distinct components in carbonaceous chondrites: one characterized by high 53Cr/52Cr and low 54Cr/52Cr, and another by low 53Cr/52Cr and high 54Cr/52Cr. Notably, one of the IOMR leaching fractions of Tagish Lake yielded the lowest 53Cr/52Cr ratio reported to date in sequential leaching studies. To identify the endmember responsible for the negative correlation, we corrected for the radiogenic contribution from the decay of 53Mn to 53Cr and determined the regression line between corrected 53Cr/52Cr and 54Cr/52Cr. A comparison of our results with nucleosynthetic models of supernovae indicates that the materials carrying 54Cr excesses in the Solar System are likely to have been produced in the He/C zone of a 25 Msun, Z = 0.02 Type II supernova.
References: [1] Zhu et al. (2021). Geochimica et Cosmochimica Acta, 301, 158-186. [2] Yamakawa, and Yin. (2014). Meteoritics and Planetary Science, 49(11), 2118-2127.
In this study, to further constrain the carrier phases of Cr isotope anomalies, we performed sequential acid leaching on bulk samples and insoluble organic matter-rich residue (IOMR) separated from the carbonaceous chondrites Tagish Lake (C2-ung) and Murchison (CM2). The Cr isotope compositions of individual samples were measured with thermal ionization mass spectrometry (TIMS). The Cr isotope data of the leaching fractions define a negative linear correlation between 53Cr/52Cr and 54Cr/52Cr ratios. This observation indicates the presence of two distinct components in carbonaceous chondrites: one characterized by high 53Cr/52Cr and low 54Cr/52Cr, and another by low 53Cr/52Cr and high 54Cr/52Cr. Notably, one of the IOMR leaching fractions of Tagish Lake yielded the lowest 53Cr/52Cr ratio reported to date in sequential leaching studies. To identify the endmember responsible for the negative correlation, we corrected for the radiogenic contribution from the decay of 53Mn to 53Cr and determined the regression line between corrected 53Cr/52Cr and 54Cr/52Cr. A comparison of our results with nucleosynthetic models of supernovae indicates that the materials carrying 54Cr excesses in the Solar System are likely to have been produced in the He/C zone of a 25 Msun, Z = 0.02 Type II supernova.
References: [1] Zhu et al. (2021). Geochimica et Cosmochimica Acta, 301, 158-186. [2] Yamakawa, and Yin. (2014). Meteoritics and Planetary Science, 49(11), 2118-2127.