Petrology of Impact Breccias from Manson Drill Cores

钻进K-T边界年龄Manson撞击构造中心峰区的岩心遇到了三个主要的撞击角砾岩。最浅的是沉积碎屑角砾岩，含有罕见的结晶、熔融或震荡碎屑。这是由玻璃状基质的结晶碎屑角砾岩和砂质基质的结晶碎屑角砾岩构成的。冲击变质和冲击熔融物质在两种结晶角砾岩中都很常见。这项研究将调查新钻井遇到的这些角砾岩和相关角砾岩的岩石学，并将建立它们的侵位和随后的变形模式。它将由爱荷华州大学的人员与爱荷华州自然资源部-地质调查局(IDNR-GSB)联合进行。这项研究承诺加强对曼森遗址的陨石坑过程的了解，并提供有关可能已被并入世界K-T边界沉积物的喷射物的性质的信息。本研究中使用的薄片将从分配给IDNR-GBS的岩芯中切割出来，并进行岩石学检查，以确定碎屑的类型、大小、形状以及基质材料的性质。光学隐蔽的碎屑和基质材料将使用扫描电子显微镜-能谱仪和X射线衍射仪进行鉴定。碎屑和基质丰度随深度的变化将通过点计数来量化。电子探针分析将被用来表征矿物和玻璃相组成随深度的变化。这些数据将使用IBM-PD2计算机上运行的标准软件进行存储、处理和图形显示。当它被汇编时，它将提供给其他曼森研究人员。

Cores drilled into the central peak region of the K-T boundary-age Manson impact structure have encountered three major impact breccias. The shallowest is a sedimentary clast breccia with rare crystalline, melted or shocked clasts. This is underlain by a crystalline clast breccia with a glassy matrix followed by a crystalline clast breccia with a sandy matrix. Shock-metamorphosed and shock-melted materials are common in both crystalline breccias. This study will investigate the petrology of these breccias and related breccias encountered by new drilling, and will develop models for their emplacement and subsequent deformation. It will be conducted by University of Iowa personnel in conjunction with the Iowa Department of Natural Resources-Geological Survey Bureau (IDNR-GSB). This study promises to enhance understanding of cratering processes at the Manson site as well as provide information about the nature of ejecta that may have been incorporated into K-T boundary sediments worldwide. Thin-sections used in this study will be cut from core allocated to the IDNR- GBS and petrographically examined to determine clast types, sizes, and shapes as well as the nature of matrix materials. Optically obscure clasts and matrix materials will be identified using SEM- EDS and XRD techniques. Changes in clast and matrix abundances with depth will be quantified by point-counting. Electron microprobe analysis will be used to characterize changes in mineral and glass phase compositions with depth. These data will be stored, manipulated and graphically displayed using standard soft- ware running on IBM-PD2 computers. It will be made available to other Manson researchers when it is compiled.