Mineralogical and geochemical studies of impact melt products from the Chesapeake Bay and the Lake Bosumtwi impact structures (ICDP)

ICDP在加纳Bosumtwi湖冲击构造（1.07 Ma， Ø~10.5 km）和美国地质调查局（USGS）在弗吉尼亚州切萨皮克湾冲击构造（35 Ma， Ø~80 km）进行了两个成功的岩心钻探项目。这两个保存完好的陨石坑都属于仅有的四个已知的与微陨石和布满陨石的地区有关的陨石坑。本提案的重点是源自这些撞击事件的熔体产物。我们对角砾岩中的微晶岩、微晶岩、玻璃碎片和极为罕见的玻璃制品回退球进行了地球化学和矿物学研究，目的是：●鉴定玻璃的前驱体物质和化学均质化程度（TEM-EDX, LAICP-MS）；●限制产生不同类型熔体的工艺；•解开混合过程、高温化学和蒸汽羽流中的氧化还原条件（使用EELS测定铁的价态）；●解读冲击玻璃的不同冷却路径。我们的新数据有助于更好地理解陨石坑，作为数值模拟的输入参数，并提供区分微陨石和火山玻璃球的工具——这是解释太古代球体层的一个特别相关的点。

ICDP performed two successful core drilling projects into (i) the Lake Bosumtwi impact structure (1.07 Ma old, Ø~10.5 km), Ghana, and (ii) together with USGS, the Chesapeake Bay impact structure, Virginia (35 Ma, Ø~80 km). Both excellently preserved craters belong to only four known craters associated with microtektite and tektite strewn fields. This proposal focuses on melt products that originated in these impact events. Our geochemical and mineralogical studies on tektites, microtektites, glass shards in breccias and fallback spherules, an extremely rare glass product, aim at ● Identification of precursor materials and degree of chemical homogenization of glasses (TEM-EDX, LAICP-MS); ● Constraining processes that yield different types of melts; ● Unraveling mixing processes, high-temperature chemistry and redox conditions in vapor plume (using EELS for valence state determination of iron); ● Deciphering the different cooling paths of impact glasses. Our new data contribute to a better understanding of cratering, serve as input parameters for numerical modeling and provide tools to distinguish microtektites from volcanic glass spherules – a point of particular relevance for the interpretation of Archean spherule layers.