Forearc Basin Provenance Analysis by SHRIMP Detrital Zircon Geochronology

项目名称：利用SHRIMP碎屑锆石年代学进行弧前盆地物源分析 砂岩中颗粒的成分可以诊断出这些颗粒的原始来源，就像火山弧侵蚀的火山颗粒一样。 传统上，这种分析是用标准的光学显微镜进行的，但所有火山弧的沙子的成分相似性很大，往往导致具体来源的模糊性。更大的解释杠杆将提供的能力，以确定个别颗粒的年龄，这种能力存在于敏感的高分辨率离子微探针（SHRIMP）。 SHRIMP技术在地质特征良好的弧相关沉积盆地（即，沉积物的来源是独立已知的）可以作为一个标准，对鲜为人知但类似的盆地进行研究。 加州大峡谷盆地的中生代地层提供了这样一个机会，因为沉积物的散装颗粒和微量元素成分已经确定，并且邻近的Sierran和克拉马斯弧的沉积物来源也是众所周知的。 因此，SHRIMP研究大峡谷锆石沙粒的年龄将形成一个模型的基础上的沉积物源关系在一个古老的弧相关的盆地，以及提供洞察火山弧的长期侵蚀率和沉积衍生物。 随后将大峡谷模型与华盛顿和不列颠哥伦比亚省中生代梅托盆地锆石颗粒的SHRIMP分析结果进行比较。 如果与大峡谷的研究一致，方法的结果可能会证明更广泛的实用性的分析方法，以及有助于解决该地区的地质演化的一些具体问题。

Project Title: Forearc Basin Provenance Analysis by SHRIMP Detrital Zircon GeochronologyPI: Stephan GrahamABSTRACT The composition of grains in sandstone can be diagnostic of the original source of those grains, as in the case of volcanic grains eroded from volcanic arcs. Conventionally, such analyses are conducted with a standard optical microscope, but the broad compositional similarity of sand from all volcanic arcs often results in ambiguity as to specific sources. Greater interpretational leverage would be provided by an ability to determine the ages of individual grains, and that capability exists in the Sensitive High Resolution Ion Microprobe (SHRIMP). The application of SHRIMP technology to a geologically well-characterized arc-related sedimentary basin (i.e., one for which the sources of sediment are independently known) could serve as a standard against which studies of poorly known but analogous basins might be gauged. The Mesozoic strata of the Great Valley basin of California present such an opportunity, because the bulk-grain and trace element compositions of sediment are already determined, and the sources of sediment in the adjacent Sierran and Klamath arcs are generally known. Thus, SHRIMP study of the ages of Great Valley zircon sand grains will form the basis of a model of sediment source relations in an ancient arc-related basin, as well as provide insights into long-term rates of erosion of volcanic arcs and sedimentation of derivative sediments. The Great Valley model subsequently will be compared with results of SHRIMP analysis of zircon grains from the Mesozoic Methow basin of Washington and British Columbia. If consistent with the Great Valley study, the Methow results may demonstrate the broader utility of the analytical method, as well as contribute to solving some specific problems of the geologic evolution of that region.