盆地流体年代学研究新技术:方解石激光原位U-Pb定年法

Abstract

Basin fluid is the most active geological agent in sedimentary basins, having a close relationship with the generation, migration and accumulation of hydrocarbon resources. Accurate determination of fluid flow history has been a challenging and frontier research topic. In general, the previous studies of basin fluids mainly rely on the analysis of fluid inclusions, which is difficult to successfully reconstruct the events of basin fluids. More seriously, this method is unable to determine the timing of fluid flow events. Authigenic calcite is the direct product of basin fluids. Thus, accurate dating of authigenic calcite provides a new approach to determine the history of fluid flow events. In the field of calcite geochronology, the most widely used dating method was the isotope dilution U-Pb dating approach. However, this approach is time-consuming, and has a low success rate. In recent years, laser ablation technology has greatly facilitated U-Pb dating of accessory minerals (including calcite) because of its high spatial resolution and rapid data acquisition. It has been confirmed that the newly-developed in-situ U-Pb dating method is able to accurately determine the age of calcite with U content less than 10×10 . This method has successfully reconstructed the history of fluid flow events in the sedimentary basins, suggesting that it has a good application prospect in the field of basin fluid geochronology. In the future, it can be expected that the application of in-situ U-Pb dating of calcite together with C-O isotope and rare earth element analysis will be a significant development direction in the field of basin fluid studies. It is worth noting that the determination of stage of authigenic calcite through systematic microscopic identification and diagenetic observation is the premise of application success.