Formation and collapse of ejecta plumes from large meteorite impact - a case study at the Ries crater, Germany

该项目旨在更好地了解与不断演变的撞击坑和蒸汽羽中撞击角砾岩形成有关的神秘和极其动态的过程，以及它们在撞击坑内外的分布模式。我们选择了一种创新的双管齐下的调查方法。这包括对从里斯撞击构造内部到外部沿剖面钻探的冲击角砾岩进行全面和比较的岩石学（包括纹理）分析，以及可以追踪物质从原始目标地层到最终沉积地点运动的数值模拟。在FBN 1973、Enkingen、Otting和Wörnitzostheim岩心样品上收集了模态、晶粒尺寸、颗粒形状和取向数据，以及矿物学组成和结构观测，取得了重大进展。迄今为止的数值模拟表明，在苏韦特陨石坑和周围结构中观测到的撞击熔体数量与模拟的熔体体积不符。此外，我们的模拟结果也不能证实传统的假设，即撞击角砾岩是由撞击蒸汽羽流的沉降物形成的。因此，陨石坑内的过程，如沿着陨石坑底部的地涌，具有更重要的意义。我们的模型的另一个结果是，在火山口内部必须形成一个广泛的熔池。由于这与地球物理和钻井观测结果不一致，因此需要一种新的方法来解决这个问题。我们申请将项目延期1年，目的是完成岩相结构数据采集，作为数据合成的前提条件，并建立一个撞击后质量传递的数值模型，该模型是由火山喷发-岩浆类型的爆炸和与之相关的陨坑内外硫化钾沉积引起的。

This project aims at obtaining better understanding of the enigmatic and extremely dynamic processes related to formation of impact breccias within the evolving impact crater and vapour plume, and their mode(s) of distribution within and outside of the crater. An innovative two-prong investigative approach has been chosen. This comprises comprehensive and comparative petrographic (including textural) analysis of impact breccias drilled along a profile from the interior to the exterior of the Ries impact structure, as well as numerical modeling which allows to trace movement of material from the original target stratigraphy to its final place of deposition. Significant progress has been made with collection of modal, grain size, particle shape and orientation data, and mineralogical composition and textural observations from the groundmass of suevite, on samples from the FBN 1973, Enkingen, Otting and Wörnitzostheim drill cores. Numerical modeling has so far indicated that the amount of impact melt observed in crater suevite and surroundings of the structure does not satisfy the modeled melt volume. Also, the traditional hypothesis that suevitic impact breccias develop by fallout from an impact vapor plume can not be confirmed with our modeling results. Within-crater processes, such as ground-surge along the crater floor, thus attains enhanced significance. A further outcome of our modeling is that an extensive melt pool must develop within the crater interior. As this is not consistent with geophysical and drilling observations, a new approach to solve this problem is required. We apply for a 1-year extension of this project in order to complete petrographic-textural data acquisition as a prerequisite for data synthesis, and to develop a numerical model for post-impact mass transfer caused by phreato-magmatic type of explosions and related deposition of suevite inside and outside of the crater.