Expedition 364 Chicxulub: Chicxulub Peak Ring Formation

墨西哥的希克苏鲁伯陨石坑是独一无二的。它是唯一已知的与大灭绝事件直接相关的陆地撞击结构，也是唯一一个具有全球喷射层的陆地撞击。在地球上三个最大的撞击结构中，希克苏鲁伯是保存最完好的。希克苏鲁伯也是唯一已知的具有完整、明确地形“峰环”的陆地撞击结构。希克苏鲁伯在K-Pg大灭绝中的作用及其特殊的保存状态使其成为研究地球和其他行星上大型撞击坑形成以及对地球环境和生态的重大影响的重要自然实验室。我们对撞击过程的理解远未完成，尽管经过了30多年的激烈辩论，我们仍在努力回答这个问题，即为什么这次撞击如此具有灾难性。探险队364号是第一个钻入完整地形峰环的洞，也是第一个穿透希克苏鲁伯陨石坑近海部分的洞。峰环是指在类地行星上的大型撞击盆地中，从火山口底部伸出来的一圈小山，它们的形成机制和形成它们的岩石的性质都没有达成共识。地球物理数据表明，希克苏鲁伯的峰环是由低速度和低密度的岩石形成的，对此的一种解释是，它们高度断裂和多孔。撞击后，峰环立即被淹没在水下，并位于一个厚厚的热熔岩池附近。因此，我们预计在峰环内会有强烈的热液活动。这种活动可能为外来生命形式提供了一个生态位，就像海洋中的热液喷口系统一样。钻探峰环将确定形成它的岩石的起源、岩性和物理状态，使我们能够区分峰环形成的竞争模型，并记录热液系统和任何相关的微生物学。撞击发生后，当地的海洋很可能立即变得贫瘠。我们将使用岩心通过撞击后的沉积物来检查海洋的重新定植，包括：哪些生物群首先恢复（底栖动物，鞭毛藻，专家与通才），以及恢复正常状态需要多长时间？拟议的钻探直接有助于IODP的目标：深层生物圈和海底海洋与环境变化、过程和影响，特别是希克苏鲁伯引起的环境和生物扰动。

The Chicxulub impact crater, Mexico, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event, and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic "peak ring". Chicxulub's role in the K-Pg mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets, and the effects of large impacts on the Earth's environment and ecology. Our understanding of the impact process is far from complete and, despite over 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic.Expedition 364 is the first drill hole into an intact topographic peak ring, and the first to penetrate the offshore portion of the Chicxulub crater. Peak rings are a ring of hills that protrude through the crater floor within large impact basins on the terrestrial planets, and there is no consensual agreement on either their formational mechanism or the nature of the rocks that form them. Geophysical data indicate that the peak ring at Chicxulub is formed from rocks that have a low velocity and density, and one explanation for this is that they are highly fractured and porous. Immediately after impact the peak ring was submerged under water, and located adjacent to a thick pool of hot melt rocks. Hence, we would expect intense hydrothermal activity within the peak ring. This activity may have provided a niche for exotic life forms, in a similar way that hydrothermal vent systems do in the oceans. Drilling the peak ring will determine the origin, lithology, and physical state of the rocks that form it, allow us to distinguish between competing models of peak-ring formation, as well as document the hydrothermal systems and any associated microbiology. Immediately after impact the ocean is, locally, likely to have been sterile. We will use core through the post-impact sediments to examine the recolonization of the ocean, including: what biota came back first (benthic, dinoflagellates, specialists vs generalists), and how long did it take to return to normal conditions? The proposed drilling directly contributes to IODP goals in the: Deep Biosphere and the Subseafloor Ocean and Environmental Change, Processes and Effects, in particular the environmental and biological perturbations caused by Chicxulub.