Mineralogical and geochemical studies of impact melt products from the Chesapeake Bay impact structure

美国地质勘探局和ICDP对弗吉尼亚州35 Ma历史、约85 km大小的潜艇切萨皮克湾撞击构造进行钻探。这个陨石坑是北美玻璃陨石散布场和始新世上部沉积物中相关微玻璃陨石的来源。本建议侧重于撞击熔融产物（熔融岩石、撞击角砾岩内的玻璃弹/颗粒、玻璃陨石、微玻璃陨石、微晶陨石），这些产物产生于不同的成坑阶段。所有命名的岩性都应该出现在切萨皮克陨石坑内、周围或远处的不同地质环境中。这提供了一个独特的机会来研究迄今为止各种熔体起源的不受约束的不同机制，深入了解蒸汽羽流中发生的过程（混合，高温化学，氧化还原条件），推导出撞击玻璃的不同冷却路径，并开发工具来区分微玻璃陨石和火山玻璃球。为了实现这一目标，我们打算通过矿物学和地球化学技术来表征熔体和目标岩性，通过地球化学和同位素指纹识别来识别撞击玻璃的前体岩石。（Rb-Sr、Sm-Nd、REE，TIMS和LA-ICP-MS技术），通过一种新的互补方法结合直接耦合的挥发性气体分析系统（DEGAS）来确定挥发物含量和氧化还原状态在透射电子显微镜（TEM）上用电子能量损失谱（EELS）进行。

USGS and ICDP perform a drilling project into the 35 Ma old, ~85-km-sized submarine Chesapeake Bay impact structure, Virginia. This crater is source to the North American tektite strewn field and related microtektites in upper Eocene sediments. This proposal focuses on impact melt products (melt rocks, glass bombs/particles within impact breccias, tektites, microtektites, microkrystites) that originate during different stages of cratering. All named lithologies are supposed to occur at different geological settings in, around, or far off the Chesapeake crater. This gives a unique opportunity to ¿ study the so far rather unconstrained different mechanisms for the origin of the various melts, ¿ get insight into processes taking place in the vapor plume (mixing, high-temperature chemistry, redox conditions), ¿ derive the different cooling paths of impact glasses, and ¿ develop tools to distinguish microtektites from volcanic glass spherules. To reach this goals we intend to ¿ characterize melt and target lithologies by mineralogical and geochemical techniques, ¿ identify precursor rocks of impact glasses by geochemical and isotopic fingerprinting (Rb-Sr, Sm-Nd, REE with TIMS and LA-ICP-MS techniques), ¿ determine volatile content and redox state by a novel complementary approach combining a Directly coupled Evolved Gas Analysing System (DEGAS) with Electron Energy Loss Spectroscopy (EELS) on a transmission electron microscope (TEM).