Establishing the link between the Chesapeake Bay impact structure and the North American tektite strewn field: The Sr‐Nd isotopic evidence
Establishing the link between the Chesapeake Bay impact structure and the North American tektite strewn field: The Sr‐Nd isotopic evidence
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DOI：
10.1111/j.1945-5100.2006.tb00985.x
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发表时间：
2006-05
影响因子：
2.2
通讯作者：
A. Deutsch;C. Koeberl
中科院分区：
文献类型：
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作者：
A. Deutsch;C. Koeberl
摘要：切萨皮克湾撞击结构距今约 35 Ma，此前曾被认为是北美玻璃陨石 (NAT) 的可能源坑。在这里，我们报告了主要和微量元素数据，以及目标岩性、火山口填充角砾岩和切萨皮克湾撞击结构的撞击后沉积物的钻芯和露头样品的第一批 Sr-Nd 同位素数据。松散沉积物的年龄为白垩纪至中始新世，∍Srt = 35.7 Ma，范围为+54至+272，∍Ndt = 35.7 Ma，范围为-6.5至-10.8；来自花岗岩基底的一个样本，TNdCHUR 模型年龄为 1.36 Ga，得出 ∍Srt = 35.7 Ma（+188）和 ∍Ndt = 35.7 Ma（−5.7）。埃克斯莫尔角砾岩（火山口填充物）可以解释为测量的目标沉积物和花岗岩的混合物，加上尚未确定的成分。 Chickahominy 地层的撞击后沉积物的 TNdCHUR 模型年龄略高，约为 1.55 Ga，表明一些较旧材料的贡献。新分析的贝二铁矿具有以下同位素参数：+104 至 +119 (∍Srt = 35.7 Ma)、−5.7 (∍Ndt = 35.7 Ma)、0.47 Ga (TSrUR) 和 1.15 Ga (TNdCHUR)，这与之前发布的 NAT 散布场样本数据非常一致。解释深海钻探项目 (DSDP) 站点 612 玻陨石同位素特征所需的具有高放射性 Sr 同位素组成的目标岩石并不在分析的样品组中。根据新的同位素数据，我们排除了 NA 玻璃陨石和 Popigai 陨石坑之间的任何关系，尽管它们的年龄相同，误差在 2s̀ 以内。然而，切萨皮克湾结构现在显然被限制为北美玻璃陨石的源坑，尽管目前的数据集显然不包括对玻璃陨石成分有贡献的所有目标岩性。
Abstract— The Chesapeake Bay impact structure, which is about 35 Ma old, has previously been proposed as the possible source crater of the North American tektites (NAT). Here we report major and trace element data as well as the first Sr‐Nd isotope data for drill core and outcrop samples of target lithologies, crater fill breccias, and post‐impact sediments of the Chesapeake Bay impact structure. The unconsolidated sediments, Cretaceous to middle Eocene in age, have ∍Srt = 35.7 Ma of +54 to +272, and ∍Ndt = 35.7 Ma ranging from −6.5 to −10.8; one sample from the granitic basement with a TNdCHUR model age of 1.36 Ga yielded an ∍Srt = 35.7 Ma of +188 and an ∍Ndt = 35.7 Ma of −5.7. The Exmore breccia (crater fill) can be explained as a mix of the measured target sediments and the granite, plus an as‐yet undetermined component. The post‐impact sediments of the Chickahominy formation have slightly higher TNdCHUR model ages of about 1.55 Ga, indicating a contribution of some older materials. Newly analyzed bediasites have the following isotope parameters: +104 to +119 (∍Srt = 35.7 Ma), −5.7 (∍Ndt = 35.7 Ma), 0.47 Ga (TSrUR), and 1.15 Ga (TNdCHUR), which is in excellent agreement with previously published data for samples of the NAT strewn field. Target rocks with highly radiogenic Sr isotopic composition, as required for explaining the isotopic characteristics of Deep Sea Drilling Project (DSDP) site 612 tektites, were not among the analyzed sample suite. Based on the new isotope data, we exclude any relation between the NA tektites and the Popigai impact crater, although they have identical ages within 2s̀ errors. The Chesapeake Bay structure, however, is now clearly constrained as the source crater for the North American tektites, although the present data set obviously does not include all target lithologies that have contributed to the composition of the tektites.