Can Scanned Cathodoluminescence (SEM-CL) of Quartz Silt be Applied to Provenance Studies of Mudstones? A Feasibility Study

石英粉砂的扫描阴极发光 (SEM-CL) 能否应用于泥岩的物源研究？

• 批准号: 0073995
• 负责人: Juergen Schieber
• 金额: $ 10.5万
• 依托单位: University of Texas at Arlington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-09-01 至 2002-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0073995&HistoricalAwards=false
• 关键词: Scanned; Cathodoluminescence; SEM; CL; Quartz

0073995SchieberMost of recorded earth history is contained in mudstones and shales, fine-grained sediments derived from weathering and erosion of continental landmasses. Yet, mudstones are the least understood sedimentary rock type, and extracting information from them is difficult. A basic task in the study of sediments is the determination of provenance, meaning how the constituents of a rock originated and got to their site of deposition. Whereas we have quite sophisticated ways of doing this for sandstones, the fine grain size of mudstones has long defied efforts to decipher their history in detail.Clay minerals, the dominant constituent of mudstones, are unfortunately chemically labile and altered substantially during burial and diagenesis. As a consequence, it is very difficult to determine after the fact what the original clay minerals were and where they came from. Detrital quartz grains are second in abundance, and are chemically and mechanically very resistant. In principle they would be the ideal component to examine for a well-preserved provenance record, but in the past they only showed limited promise for provenance studies.The recent development of scanning cathodoluminescence (SEM-CL) allows us to observe previously unrecognized textural features in quartz grains. Its application to principal source rocks (plutonic, volcanic, metamorphic) of sediments strongly suggests that quartz grains that originate under different conditions can be differentiated through textural features visible under SEMCL. This has created new opportunities for the in depth examination of sedimentary particles. Because it allows the examination of small particles, such as quartz silt grains, it has potential for the provenance study of mudstones. Examination of quartz silt in Late Devonian mudstones by SEM-CL shows that textures related to metamorphic, plutonic, and volcanic quartz are still recognizable, and that it is very likely that SEM-CL could become an important tool in the study of mudstones.This study is the first step in a systematic study of source rock related SEM-CL features. We want to developing criteria by which to differentiate metamorphic, plutonic, and volcanic quartz grains on the basis of SEM-CL features, and then examine how reliably these features are retained trough soil forming and sedimentary processes. There is very good potential that once there is a solid foundation for the application of this technique, SEM-CL will become a very important tool in the study of all kinds of quartz bearing sedimentary rocks. Because the sedimentary record is so strongly dominated by mudstones, understanding where its quartz component originates will contribute greatly to a sensible interpretation of the geologic record. Our catalog of SEM-CL features in metamorphic, plutonic, and volcanic quartz should also stimulate research by igneous and metamorphic petrologists into processes and causes behind these features, and lead to new insights into the origin of igneous and metamorphic rocks. Because the observed SEM-CL features reflect fundamental processes that occur during the formation of igneous and metamorphic rocks, the results from this study should also be applicable to the study of rocks from other worlds. Specifically, they may provide new ways of interpreting quartz grains that will in all likelihood be retrieved from Mars in the near future.

0073995Schieber 大多数有记录的地球历史都包含在泥岩和页岩中，这些细粒沉积物源自大陆陆地的风化和侵蚀。 然而，泥岩是人们了解最少的沉积岩类型，从中提取信息很困难。 沉积物研究的一项基本任务是确定来源，即岩石的成分如何起源并到达沉积地点。 虽然我们对砂岩有相当复杂的方法，但泥岩的细粒度长期以来一直难以详细破译其历史。不幸的是，粘土矿物是泥岩的主要成分，化学性质不稳定，在埋藏和成岩作用过程中会发生很大的变化。 因此，事后很难确定原始粘土矿物是什么以及它们来自哪里。碎屑石英颗粒的丰度位居第二，并且具有很强的化学和机械抵抗力。 原则上，它们是检查保存完好的起源记录的理想组件，但在过去，它们在起源研究方面的前景有限。扫描阴极发光 (SEM-CL) 的最新发展使我们能够观察石英颗粒中以前未被识别的纹理特征。 其在沉积物主要烃源岩（火成岩、火山岩、变质岩）中的应用有力地表明，不同条件下形成的石英颗粒可以通过 SEMCL 下可见的结构特征来区分。 这为深入研究沉积颗粒创造了新的机会。 由于它可以检查小颗粒，例如石英粉砂颗粒，因此具有用于泥岩来源研究的潜力。 SEM-CL对晚泥盆世泥岩中石英粉砂的研究表明，与变质岩、深成岩和火山石英相关的结构仍然可识别，SEM-CL很可能成为泥岩研究的重要工具。本研究是系统研究烃源岩相关SEM-CL特征的第一步。 我们希望制定基于 SEM-CL 特征来区分变质、深成和火山石英颗粒的标准，然后检查这些特征在成土和沉积过程中保留的可靠性。 一旦该技术的应用奠定了坚实的基础，SEM-CL将有很大潜力成为研究各种含石英沉积岩的一个非常重要的工具。 由于沉积记录以泥岩为主，了解其石英成分的起源将极大地有助于对地质记录的合理解释。 我们对变质岩、深成岩和火山石英的 SEM-CL 特征目录也应该会刺激火成岩和变质岩岩石学家对这些特征背后的过程和原因的研究，并带来对火成岩和变质岩起源的新见解。 由于观察到的 SEM-CL 特征反映了火成岩和变质岩形成过程中发生的基本过程，因此这项研究的结果也适用于其他世界岩石的研究。 具体来说，它们可能提供解释石英颗粒的新方法，这些石英颗粒很可能在不久的将来从火星上回收。