Oral Sessions (Day1, Day2, Day3)
Oral Sessions
- Day 2, May 20（Thu.） 10:40-11:00 Room C (Zoom)
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2C-O8-1040 PDF
53Mn-53Cr dating, and carbon- and oxygen-isotope measurement of carbonate minerals in carbonaceous chondrites using Secondary Ion Mass Spectrometry (SIMS)
Secondary Ion Mass Spectrometry (SIMS) has widely been applied to geochemistry and cosmochemistry. We have utilized SIMS to analyze carbonate minerals in carbonaceous chondrites (CCs) to try to understand the evolution of water-rich asteroids and water-rock interaction (aqueous alteration) in such asteroids.
Recently, we analyzed oxygen and carbon isotopic compositions of carbonates the Tagish Lake meteorite. We found that the carbonates in Tagish Lake are consistently enriched in 13C by ~7 % compared to terrestrial carbonates. The observed 13C-rich compositions are similar to that of 67P/Churyumov-Gerasimenko, a Jupiter-family comet. In addition, the H2O/CO2 ratio of Tagish Lake is consistent with those of comets. Thus, we concluded that the Tagish Lake parent asteroid formed in the cold, outer solar system but was transported to the current orbit in the inner solar system owing to the gravity of giant planets.
We also measured 53Mn-53Cr radiometric ages of carbonates in CCs. We used a Mn- and Cr-bearing carbonate as a standard material to minimize an analytical bias caused by the matrix effect. The obtained formation ages of carbonates are 4,563 Myr ago, indicating that the aqueous alteration in CCs was induced by 26Al decay (half-life: 0.7 Myr). We are still trying to produce a carbonate standard with more homogeneous Mn and Cr concentrations and small amounts of Fe to acquire more accurate 53Mn-53Cr ages.