Oxygen isotope exchange kinetics between CAI melt and carbon monoxide gas: Implication for CAI formation in the earliest Solar System
Oxygen isotope exchange kinetics between CAI melt and carbon monoxide gas: Implication for CAI formation in the earliest Solar System
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CAI 熔体和一氧化碳气体之间的氧同位素交换动力学：对最早太阳系中 CAI 形成的影响
DOI：
10.1016/j.gca.2022.09.006
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发表时间：
2022
影响因子：
5
通讯作者：
Yurimoto Hisayoshi
中科院分区：
文献类型：
--
作者：
Yamamoto Daiki;Kawasaki Noriyuki;Tachibana Shogo;Kamibayashi Michiru;Yurimoto Hisayoshi
粗粒火成岩富钙铝包裹体（CAIs）被认为经历了气体熔融氧同位素交换过程中的前体熔融事件。因此，它们的氧同位素变化将保存有关最早太阳系高温过程的信息。我们在1420 °C和1460 °C下在0.1、0.5和1 Pa的CO气体分压下实验性地确定CAI模拟熔体与一氧化碳（CO）气体之间的氧同位素交换动力学，以理解CO气体对氧同位素交换的作用。我们观察到的氧同位素分带内的反应样品，通过在熔体表面的氧同位素交换反应和氧在熔体中的扩散形成的。分区配置文件进行了拟合，使用三维球形扩散模型与随时间变化的表面浓度。CO分子碰撞的氧同位素交换效率为1.33 × 10 ~（-4），远小于H_2O分子碰撞的氧同位素交换效率（0.28）。研究结果表明，氧的扩散系数与CAI熔体与H_2O的氧同位素交换实验结果基本一致，表明在CAI熔体中的扩散物种是O_2 ~-，而与周围环境无关。（3）CO和H2O气体表明反应速率按（3）、（2）和（1）的顺序降低。反应（1）的快速同位素交换表明，在岩浆CAIs的熔融和结晶过程中，H_2O和CO的氧同位素组成应已达到平衡。H2O和CO都以相同的方向改变熔融CAI的氧同位素组成，尽管反应（2）控制CAI熔体与周围气体之间的同位素交换时间尺度。我们的数据表明，具有均匀氧同位素组成的黄长石的B型CAIs应该在太阳原行星盘中的黄长石液相线（约1400 °C）以上的PH 2> 100 Pa下加热2-3天。
Coarse-grained igneous calcium-aluminum-rich inclusions (CAIs) are suggested to have experienced gas–melt isotope exchange of oxygen during the melting events of their precursors. Therefore, their oxygen isotope variation would preserve information about the high-temperature processes in the earliest Solar System. We experimentally determined oxygen isotope exchange kinetics between CAI analog melt and carbon monoxide (CO) gas at 1420 °C and 1460 °C under CO gas partial pressures of 0.1, 0.5, and 1 Pa to understand the role of CO gas on the oxygen isotope exchange. We observed oxygen isotope zoning profiles inside the reacted samples that formed through the oxygen isotope exchange reaction at the melt surface and oxygen diffusion in the melt. The zoning profiles were fitted using a three-dimensional spherical diffusion model with time-dependent surface concentration. The oxygen isotope exchange efficiency for colliding CO molecules is estimated to be ∼3.3 × 10–4, which is much smaller than that for H2O (0.28). The oxygen diffusion coefficient obtained in this study is similar to that obtained in the oxygen isotope exchange experiments between the CAI melt and H2O, suggesting that the diffusion species in the melt is O2–, despite the surrounding atmospheres.A comparison of the isotope exchange reaction kinetics between (1) CAI melt and CO gas, (2) CAI melt and H2O gas, and (3) CO and H2O gases shows that the reaction rate decreases in the order of (3), (2), and (1). The rapid isotope exchange of the reaction (1) indicates that the oxygen isotopic compositions of H2O and CO should have been equilibrated during the melting and crystallization processes of igneous CAIs. Both H2O and CO change the oxygen isotope compositions of molten CAI in the same direction, although reaction (2) controls the isotope exchange timescale between the CAI melt and surrounding gas. Our dataset demonstrates that type B CAIs having melilite with homogeneous oxygen isotope composition should have been heated for 2–3 days atPH2> 100 Pa above the melilite liquidus (∼1400 °C) in the solar protoplanetary disk.
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影响因子：
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作者：
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DOI：
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DOI：
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DOI：
--
发表时间：
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期刊：
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