Variations in initial 26Al/27Al ratios among fine-grained Ca-Al-rich inclusions from reduced CV chondrites
Variations in initial 26Al/27Al ratios among fine-grained Ca-Al-rich inclusions from reduced CV chondrites
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DOI：
10.1016/j.gca.2020.03.045
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发表时间：
2020-06-15
影响因子：
5
通讯作者：
Yurimoto, Hisayoshi
中科院分区：
文献类型：
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作者：
Kawasaki, Noriyuki;Wada, Sohei;Yurimoto, Hisayoshi
碳质球粒陨石（CV chondrites）中的富钙铝细粒包体（FGIs）被认为是直接由太阳星云气体凝结形成的。通过使用二次离子质谱仪进行原位铝 - 镁同位素测量，获得了来自还原性碳质球粒陨石埃弗拉莫夫卡（Efremovka）、维加拉诺（Vigarano）、蒂尔山07007（Thiel Mountains 07007）以及西北非8613（Northwest Africa 8613）的7个富钙铝细粒包体的铝 - 镁矿物等时线。7个富钙铝细粒包体的矿物等时线斜率在初始铝 - 26/铝 - 27比值（(Al - 26/Al - 27)(0)）上呈现出具有统计学意义的变化，范围从(5.19 ± 0.17)×10⁻⁵到(3.35 ± 0.21)×10⁻⁵，这对应着0.44 ± 0.07百万年的相对年龄跨度。富钙铝细粒包体的(Al - 26/Al - 27)(0)推断上限与通过对碳质球粒陨石中钙铝包体（CAIs）进行全岩铝 - 镁等时线研究确定的太阳系(Al - 26/Al - 27)(0)（约为5.2×10⁻⁵）相同。矿物等时线的截距，即富钙铝细粒包体形成时的初始镁 - 26/镁 - 24比值，与太阳组成的星云气体的镁同位素演化路径一致。富钙铝细粒包体的(Al - 26/Al - 27)(0)观测到的变化与通过熔化和凝固形成的碳质球粒陨石中粗粒火成钙铝包体（约为5.2×10⁻⁵到约为4.2×10⁻⁵）的变化基本相似。如果铝 - 26在形成区域均匀分布，那么我们的数据表明，钙铝包体形成的凝结和熔化热过程是同时发生的，并且在太阳系形成之初至少持续了约0.4百万年。或者，(Al - 26/Al - 27)(0)观测到的变化也表明铝 - 26在形成区域可能是非均匀分布的，对应着至少3.4×10⁻⁵ < (Al - 26/Al - 27)(0) < 5.2×10⁻⁵的范围。（C）2020爱思唯尔有限公司。保留所有权利。
Fine-grained Ca-Al-rich inclusions (FGIs) in CV chondrites are suggested to be condensates formed directly from the solar nebular gas. Al-Mg mineral isochrons of seven FGIs from reduced CV chondrites Efremovka, Vigarano, Thiel Mountains 07007, and Northwest Africa 8613 were obtained via in situ Al-Mg isotope measurements using secondary ion mass spectrometry. The slopes of the mineral isochrons for seven FGIs exhibit statistically significant variations in initial Al-26/Al-27 ratios, (Al-26/Al-27)(0), ranging from (5.19 +/- 0.17) to (3.35 +/- 0.21) x 10(-5), which correspond to a relative age spread of 0.44 +/- 0.07 Myr. Inferred upper limit of (Al-26/Al-27)(0) for the FGIs is identical to the Solar System (Al-26/Al-27)(0) of similar to 5.2 x 10(-5) as determined by whole-rock Al-Mg isochron studies for CAIs in CV chondrites. The intercepts of the mineral isochrons, the initial Mg-26/Mg-24 ratios the FGIs formed with, are consistent with Mg-isotope evolution path of a solar-composition nebular gas. The observed variations in (Al-26/Al-27)(0) for FGIs are essentially similar to those (similar to 5.2 to similar to 4.2 x 10(-5)) for coarse-grained, igneous CAIs of CV chondrites that are formed by melting and solidification. If Al-26 was distributed homogeneously in the forming region, then our data indicate that thermal processes of condensation and melting for CAI formation occurred contemporaneously and continued for at least similar to 0.4 Myr at the very beginning of the Solar System. Alternatively, the observed variations in (Al-26/Al-27)(0) also indicate the possibility of heterogeneous distributions of Al-26 in the forming region, corresponding to a range of over at least 3.4 x 10(-5) < (Al-26/Al-27)(0) < 5.2 x 10(-5). (C) 2020 Elsevier Ltd. All rights reserved.