Dolomitization of Cambro-Ordovician Platform Carbonates, Appalachians

该研究涉及地质、地球化学、 寒武纪地台橄榄岩的同位素研究 美国弗吉尼亚州及邻近地区的奥陶纪 states. 从3 ~ 4km厚的地层中选出两个层序 被动边缘演替，被认为是 层序中白云岩类型为早寒武世阴 白云岩（1500米厚）和早奥陶世诺克斯白云岩 (600 m厚）。 可能的白云石类型包括高盐型 潮坪和可能的浅海白云岩，浅 地下白云岩由地下卤水或混合流体形成 平坦地带、混合带、火山岩（可能与火山灰有关） 平坦或具有覆盖两个连续的不整合）， 与陡峭的寒武纪地台有关的海相碳酸盐岩 边缘和各种类型的埋藏白云岩，局部伴生 与MVT矿化有关。 这些研究将与区域地质研究相结合， 台地层序计算机模拟研究 （提供有关海平面变化、 潮滩旋回的形成、海侵速率和迁移 早期成岩带和平台出现的持续时间 在回归事件期间）。 对于每种白云石类型，数据将 获得主要和微量元素化学，稳定 同位素组成和放射成因锶组成的 花岗岩，以及流体包裹体数据。 的影响 重结晶或交代早期镁铁质岩 将确定随后的成岩环境。 的 可能涉及的水文和化学系统 岩化史将综合埋葬史 将提供流体迁移时间和可能的P- 成岩作用的T条件。

This research involves an integrated geologic, geochemical, and isotopic study of platform dolomites in the Cambro- Ordovician of the U.S. Applachians in Virginia and adjacent states. Two sequences selected from the 3 to 4 km thick passive margin succession and considered representative of the dolomite types in the sequence are the Early Cambrian Shady Dolomite (1500 m thick) and the Early Ordovician Knox Dolomite (600 m thick). Possible dolomite types include hypersaline tidal-flat and possible shallow marine dolomite, shallow subsurface dolomite forming from brines or mixed fluids beneath flats, mixing zone dolomites (possibly associated with prograded flats or with unconformities that cap the two successions), marine dolomites associated with the steep Cambrian platform margin and various types of burial dolomite, locally associated with MVT ore mineralization. The studies will be integrated with regional geologic studies involving computer modelling of platform sequences (which provides information on sea-level behavior, duration of cycle formation, progradation rates of tidal flats and migration of early diagenetic zones, and duration of emergence of flats during regressive events). For each dolomite type, data will be obtained on major and trace element chemistry, stable isotopic composition, and radiogenic Sr composition of the dolomites, as well as fluid inclusion data. The effects of recrystallization or replacement of early dolomites in subsequent diagenetic environments will be determined. The likely hydrologic and chemical systems involved in dolomitization history will be integrated will burial history plots that will provide timing of fluid migration and likely P- T conditions during diagenesis.