A fresh look at catastrophic impact-cratering: how do melt-bearing impact-deposits form?

当小行星与地球相撞时，它们会冲击地壳，导致目标区域在几秒钟内蒸发，熔化和碎片。大量灼热的熔岩、岩石碎片和尘埃从大气层中喷出，留下直径不到300公里的陨石坑，并使周围的景观布满碎片。这一点，以及随之而来的灾难性的空中爆炸、地震和海啸，破坏了环境、生物群和生态系统。影响改变气候，导致全球大规模灭绝，可以说是对人类最大的自然危害。他们实际上塑造了地球的历史，他们生产钻石和有用的贵金属来源。因此，令人惊讶的是，这一过程的基本方面没有得到理解：直到我们更好地了解在撞击点附近发生了什么，我们才能正确地理解更广泛的影响。幸运的是，最近没有发生大的影响，所以我们的理解必须从对旧产品的法医式调查中拼凑起来。地球上的撞击坑非常重要，因为它们提供了直接接触内部结构、喷出物沉积物、熔融碎片和矿物的机会，这些都是帮助重建极端事件的重要线索。我们将调查如何热的影响，融化是破碎的，并迅速运输到整个景观从影响网站。被称为“suevite”和“冲击熔融角砾岩”的沉积物已被证明是不可估量的有用的，告诉我们很多关于冲击的知识，例如所涉及的惊人的高压。然而，令人惊讶的是，撞击熔化的碎裂和运输仍然是撞击成坑最不了解和有争议的方面之一。长期以来，研究火山的科学家们一直在研究热熔体是如何破裂的，以及由此产生的熔体碎片是如何喷射到整个景观中的。他们已经开发出越来越复杂的实地和实验室方法来分解保存在矿床中的证据。然而，令人遗憾的是，这些方法尚未适用于研究小行星撞击。撞击显然不同于火山（例如，初始温度和压力），但熔体碎裂和迁移必须遵循相同的物理定律。我们建议首次将世界领先的物理火山学家和撞击专家聚集在一起，整合最先进的方法，以提高理解，并引领新一轮的研究，这将改变该领域。聚焦于地球上保存最完好的大型撞击坑，里斯（德国）和其他选定的地点，我们将重新评估撞击熔融轴承岩石，以确定，新鲜的眼睛，他们揭示的过程。我们将从火山调查中采用3种最先进的方法：1.精细的艺术研究，检查内部变化的微妙分层和颗粒大小的粒状岩石，以揭示颗粒是如何运输和沉积从高速地面拥抱密度流; 2。如何在玻璃碎片中的形状和模式的气泡产生的粘弹性熔体破碎-像快速拉伸的奶油冻-可以用来揭示热熔体时，它打破了物理性能;和3.如何保存在灾难性电流沉积物中的方向（使用岩石磁性来提取）可以用来揭示迄今为止隐藏的信息，即撞击坑的斜坡在最初的撞击之后如何变形和转移，直到重力坍塌和冷却的最后阶段。鉴于该领域目前的流动状态，这项工作非常及时，因为它将利用来自火山学的最新实验数据，计算机模拟的影响，2017年地球物理调查（里斯）和2017年钻孔（希克苏鲁布）。从结果中，我们将重建如何热的影响，熔体的行为和移动的发展中的撞击坑消退。这将提高我们对撞击坑如何形成的理解，以及热物质如何在地球上运输，造成巨大的环境破坏。

When asteroids collide with Earth they shock the crust causing the target area to vaporize, melt, and fragment in seconds. Vast quantities of searing-hot melted rock, rock-fragments and dust are ejected through the atmosphere, leaving craters <300 km across and draping the surrounding landscape with debris. This, and the attendant catastrophic air blasts, earthquakes and tsunami, devastate the environment, biota and ecosystems. Impacts change climate, cause global mass-extinctions, and arguably represent the greatest natural hazard to humanity. They have actually shaped Earth history and they produce diamonds and useful sources of precious metals. Its therefore surprising that fundamental aspects of the process are not understood: until we better understand what happens near the point of impact we won't properly understand the wider effects. Luckily there hasn't been a recent large impact, so our understanding has to be pieced together from forensic-style investigations of the products of old ones. Impact craters on Earth are really important as they provide hands-on access to internal structures, the ejecta deposits and the melt-fragments and minerals that yield vital clues to help reconstruct the extreme events. We will investigate how hot impact-melt is fragmented and transported rapidly across the landscape from the impact site. Deposits known as 'suevite' and 'impact-melt breccia' have proved immeasurably useful, telling us much of what we have learned about impacts, e.g the phenomenal high pressures involved. Yet surprisingly impact-melt fragmentation and transport remains one of the least-understood and controversial aspects of impact-cratering. Scientists who study volcanoes have long been tackling how hot melt breaks and how the resultant melt fragments are ejected across the landscape. They have developed increasingly sophisticated field and laboratory approaches to take-apart evidence preserved in deposits. Yet astonishingly such methods have not yet been adapted for the study of asteroid impacts. Impacts clearly differ from volcanoes (e.g. the initial temperatures and pressures) but melt fragmentation and transport must follow the same laws of physics. We propose to bring together, for the first time, world-leading physical volcanologists and impact-specialists, to integrate state-of-art approaches to improve understanding and to spearhead a new wave of research that will transform the field. Focusing on Earth's best-preserved large impact-crater, Ries (Germany) and selected other sites, we will reappraise impact-melt bearing rocks to determine, with fresh eyes, the processes they reveal. We will adapt 3 state-of-art methods from volcano-investigations: 1. the fine-art study of examining internal variations in subtle layering and grain sizes in granular rocks to reveal how the particles were transported and deposited from high-velocity ground-hugging density currents; 2. how the shapes and patterns of bubbles in glass shards produced by the fragmentation of visco-elastic melt - like rapidly-stretched custard - can be used to reveal the physical properties of the hot melt when it broke apart; and 3. how orientations (unpicked using rock-magnetism) preserved in deposits of catastrophic currents can be used to reveal hitherto-hidden information about how the impact-crater slopes morphed and shifted just after the initial impact through to the final stages of gravitational collapse and cooling. The work is very timely given the current state of flux in this field, and because it will draw on the very latest experimental data from volcanology, computer-simulations of impacts, a 2017 geophysical survey (Ries) and 2017 borehole (Chicxulub). From the results we will reconstruct how hot impact-melt behaves and moves as the developing impact-crater subsides. This will improve our understanding of how impact craters are created, and how hot material is transported across the planet, causing immense environmental damage.