16:30 〜 17:00
[SGL22-04] 二次イオン質量分析計を用いた高精度・局所マグネシウム同位体分析法の改良と地球外物質への応用
★招待講演
キーワード：二次イオン質量分析計、Al-Mg年代、初期太陽系、コンドルール
Secondary Ion Mass spectrometry (SIMS) is a powerful tool for revealing the timescale of geological and cosmochemical events recorded in small (µm to tens of µm) solids. Short-lived radionuclides such as Aluminum-26 (26Al), which decays to 26Mg with a half-life of 0.7 million years (Myr), have been widely used to decipher the formation timescale of early Solar System solids. However, the precision and accuracy are not yet enough to conclude the earliest history of the Solar System evolution, causing some discrepancies among the community [e.g., 1-4].
Here we improved the precision and accuracy of SIMS 26Al-26Mg analysis for plagioclase and Al-rich glass, to better understand the formation timescale of asteroidal seeds, called chondrules. To do so, we developed analytical methods using the multi-collector SIMS CAMECA IMS 1280 equipped with the radio-frequency plasma ion source at the University of Wisconsin-Madison [5-9]. The improved methods were then applied to a total of 46 chondrules from the pristine ordinary and carbonaceous chondrites. The uncertainties (2σ) on the determined chondrule formation ages are improved as typically ±0.1–0.2 Myr. The calculated relative formation ages of the 46 chondrules range from 1.74 (± 0.11) to 2.76 (−0.23/+0.30) Myr after the formation of Ca-Al-rich inclusions (CAIs), which are the oldest solids in the Solar System [5-7]. Our new data reveal a systematic age difference in chondrules from different types of chondrites. That is, the formation ages of chondrules from ordinary chondrites (1.7–2.2 Myr after CAI formation) are systematically order than those of the majority of chondrules from carbonaceous chondrites (2.2–2.8 Myr after CAI formation). Considering the difference in formation regions of chondrules from ordinary and carbonaceous chondrites, our high-precision 26Al-26Mg isotope data indicate a temporal shift of chondrule generation from the inner to outer Solar System. The discrete chondrule-formation events in the different disk regions reflect a time difference in the growth and orbital evolution of planetesimals with the first 4 Myr of the Solar System [6]. In this meeting, I will introduce the modification of the detection system for high-precision 26Al-26Mg analyses [5-7] and, if time is available, the difficulty of accurate Mg isotope analyses using SIMS [8,9].
[1] Kita et al. (2000) GCA 64, 3913-3922. [2] Villeneuve et al. (2009) Science 325,985-988. [3] Pape et al. (2019) GCA 244, 416-436. [4] Piralla et al. (2023) Icarus 394, 15427. [5] Siron et al. (2021) GCA 293, 103-126. [6] Fukuda et al. (2022) GCA 322, 194-226. [7] Siron et al. (2022) GCA 324, 312-345. [8] Fukuda et al. (2020) Chem. Geol. 540, 119482. [9] Fukuda et al. (2021) GCA 293, 544-574.
Here we improved the precision and accuracy of SIMS 26Al-26Mg analysis for plagioclase and Al-rich glass, to better understand the formation timescale of asteroidal seeds, called chondrules. To do so, we developed analytical methods using the multi-collector SIMS CAMECA IMS 1280 equipped with the radio-frequency plasma ion source at the University of Wisconsin-Madison [5-9]. The improved methods were then applied to a total of 46 chondrules from the pristine ordinary and carbonaceous chondrites. The uncertainties (2σ) on the determined chondrule formation ages are improved as typically ±0.1–0.2 Myr. The calculated relative formation ages of the 46 chondrules range from 1.74 (± 0.11) to 2.76 (−0.23/+0.30) Myr after the formation of Ca-Al-rich inclusions (CAIs), which are the oldest solids in the Solar System [5-7]. Our new data reveal a systematic age difference in chondrules from different types of chondrites. That is, the formation ages of chondrules from ordinary chondrites (1.7–2.2 Myr after CAI formation) are systematically order than those of the majority of chondrules from carbonaceous chondrites (2.2–2.8 Myr after CAI formation). Considering the difference in formation regions of chondrules from ordinary and carbonaceous chondrites, our high-precision 26Al-26Mg isotope data indicate a temporal shift of chondrule generation from the inner to outer Solar System. The discrete chondrule-formation events in the different disk regions reflect a time difference in the growth and orbital evolution of planetesimals with the first 4 Myr of the Solar System [6]. In this meeting, I will introduce the modification of the detection system for high-precision 26Al-26Mg analyses [5-7] and, if time is available, the difficulty of accurate Mg isotope analyses using SIMS [8,9].
[1] Kita et al. (2000) GCA 64, 3913-3922. [2] Villeneuve et al. (2009) Science 325,985-988. [3] Pape et al. (2019) GCA 244, 416-436. [4] Piralla et al. (2023) Icarus 394, 15427. [5] Siron et al. (2021) GCA 293, 103-126. [6] Fukuda et al. (2022) GCA 322, 194-226. [7] Siron et al. (2022) GCA 324, 312-345. [8] Fukuda et al. (2020) Chem. Geol. 540, 119482. [9] Fukuda et al. (2021) GCA 293, 544-574.