Multiple shock events recorded in the Northwest Africa 2139 LL6 chondrite: Implications for collisional histories of the LL chondrite parent body
Multiple shock events recorded in the Northwest Africa 2139 LL6 chondrite: Implications for collisional histories of the LL chondrite parent body
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DOI：
10.1111/maps.13768
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发表时间：
2021-11
影响因子：
2.2
通讯作者：
A. Takenouchi;H. Sumino;Karin Shimodate;A. Yamaguchi
中科院分区：
文献类型：
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作者：
A. Takenouchi;H. Sumino;Karin Shimodate;A. Yamaguchi
LL彗星经历了多次冲击事件，然而，每次冲击事件和它们的时间的关系很少被研究。为了证明每种冲击结构和冲击年代学之间的关系，我们使用从西北非洲（NWA）2139 LL 6球粒陨石的同一芯片中取样的等分试样进行了岩石学和年代学（40 Ar/39 Ar和I-Ar年龄）研究。40 Ar/39 Ar研究和岩石学观察表明，NWA 2139在4.17 ± 0.10Ga之前至少记录了3次撞击事件，形成了复杂的角砾岩结构、硅酸盐变暗和厚的冲击脉。4.17 ± 0.10Ga发生了一次强烈的加热事件，使粗脉重结晶，裂纹愈合。然后，在<3.9Ga发生了一次弱震事件。结合其它LL球粒陨石的40 Ar/39 Ar数据，支持LL球粒陨石母体可能在1.7Ga发生裂解，且大部分裂解可能发生在3.8- 4.2Ga。
LL chondrites have experienced multiple shock events; however, the relations of each shock event and their timing have rarely been investigated. To demonstrate the relations between each shock texture and shock chronological ages, we conducted both petrological and chronological (40Ar/39Ar and I‐Xe ages) studies using aliquots subsampled from the same chip of the Northwest Africa (NWA) 2139 LL6 chondrite. Our 40Ar/39Ar studies and petrological observation reveal that NWA 2139 recorded at least three impact events before 4.17 ± 0.10 Ga, thus resulting in a complex brecciated texture, silicate darkening, and thick shock veins. An intense heating event occurred at 4.17 ± 0.10 Ga, which recrystallized the thick veins and healing cracks. Then, a weak shock event occurred at <3.9 Ga. Combined with 40Ar/39Ar data of other LL chondritic materials, this study supports that the LL chondrite parent body was possibly broken up by 1.7 Ga, and that most of the breakup likely occurred within 3.8–4.2 Ga.