Radiogenic Isotopic Study of Diagenesis and Low-Grade Metamorphism of Pelites

这项研究旨在发展放射性同位素分析在泥质沉积物中的应用，这些泥质沉积物通过低级别变质作用受到广泛的流体介导性成岩作用的影响。尽管富含粘土的沉积物的数据表明，与其他盆地沉积物相比，由于渗透率有限，它们对流体-岩石相互作用有记忆，但许多同位素数据导致结果不明确，部分原因是所分析的样品是不均匀的，包含一代以上细粒粘土矿物的未知比例。这项提议是对我们目前支持的一种更新，其中高分辨率扫描电子显微镜(STEM)与等效泥质岩石的同位素分析相结合。这些研究的最终目的是确定水-泥浆相互作用的时间和程度，从而确定盆地-区域尺度的流体/岩石相互作用的时间和程度。在以前专注于Rb-Sr和Sm-NK方法的发展之后，我们现在建议开发泥质沉积物的40Ar/39Ar激光技术，使用表征良好的样品(薄片和分离)和其他同位素技术来提供支持数据。我们打算确定这些方法在空间分辨率和年龄方面的局限性。根据我们之前对各种产状的页岩和板岩的观察，我们选择了从膨润土(作为具有单一来源的粘土的标准)和德克萨斯州墨西哥湾沿岸和威尔士沉积盆地的页岩以及其他海侵层序中获得数据。后者代表了被动边缘盆地中的成岩作用，而前者代表了从成岩作用到绿片岩相条件下的构造诱导的溶解和结晶作用。每个地点的样品代表了从低级变质作用到成岩作用的完整范围。

This research is designed to develop applications of radiogenic isotope analysis to pelitic sediments that have been affected by a wide range of fluid-mediated diagenesis through low- grade metamorphism. Although data for clay-rich sediments imply that they have a memory for fluid-rock interactions owing to their limited permeability as compared with other basin sediments, much isotope data lead to ambiguous results in part because analyzed samples are heterogeneous and contain unknown proportions of more than one generation of fine-grained clay mineral. This proposal is a renewal of our current support, in which high resolution scanning electron microscopy (STEM) is combined with isotopic analysis of equivalent pelitic rocks. The ultimate aim of these studies is to determine the timing and extent of water-pelite interactions and thus of basin- to regional-scale fluid/rock interactions. Having previously focused on Rb-Sr and development of Sm-Nk methods, we now propose to develop the 40Ar/39Ar laser technique for pelitic sediments, using well characterized samples (thin sections and separates), and other isotopic techniques to provide supporting data. We intend to determine the limitations of the methods, both with respect to spatial resolution and age. Based on our previous observations of shales and slates from a wide variety of occurrences, we have chosen to obtain data from bentonites (as standards having clays of a single origin) and shales from the Texas Gulf Coast and Welsh Sedimentary Basin, as well as other prograde sequences. The latter is representative of diagenesis in a passive marginal basin, whereas the former represents tectonically-induced dissolution and crystallization over the range of diagenesis to greenschist facies conditions. The samples from each locality represent the complete range of diagenesis through low-grade metamorphism.