Dolomitization of Cambro-Ordovician Platform Carbonates, Appalachians

阿巴拉契亚寒武纪-奥陶系台地碳酸盐岩的白云石化作用

• 批准号: 8707737
• 负责人: James Read
• 金额: $ 11.55万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-08-01 至 1990-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8707737&HistoricalAwards=false
• 关键词: Dolomitization; Cambro; Ordovician; Platform; Carbonates

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.

这项研究涉及弗吉尼亚州及邻近各州美国阿帕契亚山脉寒武纪-奥陶系台地白云岩的地质、地球化学和同位素研究。从3~4公里厚的被动边缘序列中选择了两个被认为是层序中具有代表性的白云岩类型的层序，它们是早寒武世阴影白云岩(厚1500m)和早奥陶世诺克斯白云岩(厚600m)。可能的白云岩类型包括高盐度潮坪白云岩和可能的浅海白云岩，由平面以下的卤水或混合流体形成的浅层地下白云岩，混合带白云岩(可能与进积平面或覆盖两个层序的不整合有关)，与陡峭的寒武纪台地边缘有关的海相白云岩，以及与MVT成矿有关的各种埋藏白云岩。这些研究将与涉及地台序列计算机模拟的区域地质学研究结合起来(它提供关于海平面行为、旋回形成的持续时间、潮滩的进积速率和早期成岩带的迁移、以及在海退事件期间平地出现的持续时间的信息)。对于每种白云石类型，将获得白云岩的主量元素和微量元素化学、稳定同位素组成、放射性成因锶成分以及流体包裹体数据。将确定早期白云岩在后续成岩环境中重结晶或交代的影响。白云石化历史中可能涉及的水文和化学系统将被整合起来，并将埋藏历史地块，这些地块将提供流体迁移的时间和成岩过程中可能的P-T条件。