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

国际钻探中心在加纳的博苏姆特维湖撞击构造(1.07 Ma，直径~10.5公里)和美国地质勘探局(USGS)在弗吉尼亚州切萨皮克湾撞击构造(35 Ma，直径~80公里)中成功地开展了两个岩心钻探项目。这两个保存完好的陨石坑只属于四个已知的陨石坑，与微玻璃陨石和玻璃陨石散布的油田有关。该提案侧重于源自这些撞击事件的熔融产品。我们对玻璃尖晶石、微玻璃陨石、角砾岩中的玻璃碎屑和一种极其罕见的玻璃产品--玻璃碎片进行的地球化学和矿物学研究，旨在鉴定前驱体材料和玻璃的化学均一化程度(TEM-EDX，LAICP-MS)；限制产生不同类型熔体的过程；解开混合过程、高温化学和蒸气羽流中的氧化还原条件(使用EELS测定铁的价态)；解释撞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，并提供工具来区分微玻璃陨石和火山玻璃球体-这一点对于解释太古宙球体层具有特别重要的意义。

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.