New links between the Chicxulub impact structure and the Cretaceous/Tertiary boundary
New links between the Chicxulub impact structure and the Cretaceous/Tertiary boundary
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希克苏鲁伯撞击构造与白垩纪/第三纪边界之间的新联系
DOI：
10.1038/359819a0
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发表时间：
1992
期刊：
影响因子：
64.8
通讯作者：
J. Urrutia‐Fucugauchi
中科院分区：
文献类型：
--
作者：
V. Sharpton;G. B. Dalrymple;L. Marín;G. Ryder;B. Schuraytz;J. Urrutia‐Fucugauchi
墨西哥尤卡坦半岛北方直径200公里的希克苏鲁布结构1 -3已成为白垩纪/第三纪（K/T）边界撞击坑的主要候选者3 -6。与上白垩纪角砾岩和安山岩的神秘出现相关的同心地球物理异常导致Penfield和Camargo 1怀疑该结构是一个埋藏的撞击盆地。最近，在希克苏鲁布角砾岩3中发现了受冲击的石英颗粒，以及希克苏鲁布岩石和K/T玻璃陨石3 -6之间的化学相似性，这些都被认为是希克苏鲁布结构是K/T撞击地点的证据。在这里，我们提出的证据，从核心样本，希克苏鲁布确实是一个K/T源陨石坑，显然可以解释所有的证据，影响全球分布在K/T边界，而不需要同时的多个影响或彗星阵雨。在岩芯中发现的震碎角砾岩碎屑与世界范围内K/T边界喷出物层中发现的震碎岩屑类似7，8。我们研究的希克苏鲁布熔岩含有极高的铱含量（高达13.5份/109），这也与富含铱的K/T边界层一致9。根据40 Ar/<39 Ar分析，我们对这些熔融岩石结晶年龄的最佳估计为65.2 ±0.4（1σ）Myr，与最近公布的平均坪年龄64.98 ± 0.05 Myr非常一致10。此外，这些熔融岩石获得的reversible磁化表明，他们在地磁极性反转的情节冷却。唯一符合40 Ar/<39 Ar约束的事件是29 R时，它包括K/T边界。
THE 200-km-diameter Chicxulub structure1–3 in northern Yucatan, Mexico has emerged as the prime candidate for the Cretaceous/Tertiary (K/T) boundary impact crater3–6. Concentric geophysical anomalies associated with enigmatic occurrences of Upper Cretaceous breccias and andesitic rocks led Penfield and Camargo1 to suspect that this structure was a buried impact basin. More recently, the discovery of shocked quartz grains in a Chicxulub breccia3, and chemical similarities between Chicxulub rocks and K/T tektite-like glasses3–6 have been advanced as evidence that the Chicxulub structure is a K/T impact site. Here we present evidence from core samples that Chicxulub is indeed a K/T source crater, and can apparently account for all the evidence of impact distributed globally at the K/T boundary without the need for simultaneous multiple impacts or comet showers. Shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the K/T boundary ejecta layer7,8. The Chicxulub melt rocks that we studied contain anomalously high levels of iridium (up to 13.5 parts per 109), also consistent with the iridium-enriched K/T boundary layer9. Our best estimate of the crystallization age of these melt rocks, as determined by 40Ar/<39Ar analyses, is 65.2 ±0.4 (1σ) Myr, in good agreement with the mean plateau age of 64.98 ± 0.05 Myr recently reported10. Furthermore, these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity. The only such episode consistent with 40Ar/<39Ar constraints is chron 29R, which includes the K/T boundary.