Record of paleofluid circulation in faults revealed by hematite (U-Th)/He and apatite fission-track dating: An example from Gower Peninsula fault fissures, Wales
Record of paleofluid circulation in faults revealed by hematite (U-Th)/He and apatite fission-track dating: An example from Gower Peninsula fault fissures, Wales
复制标题
赤铁矿 (U-Th)/He 和磷灰石裂变径迹测年揭示的断层中古流体循环记录：威尔士高尔半岛断层裂缝的一个例子
作者：
A. Ault;M. Frenzel;P. Reiners;N. Woodcock;S. Thomson
断裂带岩石低温热时测定可以反映断裂带热液循环的时间、温度和意义。通过对威尔士高尔半岛断层相关裂隙的赤铁矿(U-Th)/He （He）测年、砂岩磷灰石裂变径迹（AFT）以及磷灰石和锆石(U-Th)/He （He）热时测定，我们证明了这一点。赤铁矿He年龄为141±5.1 Ma ~ 120±5.0 Ma，与砂岩充填131±20 Ma的AFT年龄重叠。个别锆石He年代为402 ~ 260 Ma，反映了物质的侵蚀作用，暗示了最大的晚二叠世充填沉积时代。埋藏历史重建显示，三叠纪-早白垩纪的现代暴露物没有充分埋藏，没有引起重新加热到重新设置AFT或赤铁矿He系统所需的温度，因此这些日期不能单独反映由于侵蚀引起的冷却。早白垩纪通过裂缝循环的热流体重置了AFT系统。赤铁矿要么被流体重置，要么从这些流体中析出。类似的赤铁矿He产于南格拉摩根（威尔士）和坎布里亚（英格兰）与断层有关的矿化，表明伴随有沿断层的区域性热地下水流动。在本例中，与北大西洋裂陷同时发生的热液流体循环在高渗透率裂缝和断脉形成后很长时间内就发生了，直接影响了局部和区域地温梯度。
Fault rock low-temperature thermochronometry can inform the timing, temperature, and significance of hydrothermal fluid circulation in fault systems. We demonstrate this with combined hematite (U-Th)/He (He) dating, and sandstone apatite fission-track (AFT) and apatite and zircon (U-Th)/He (He) thermochronometry from fault-related fissures on the Gower Peninsula, Wales. Hematite He dates from 141 ± 5.1 Ma to 120 ± 5.0 Ma overlap with a 131 ± 20 Ma sandstone infill AFT date. Individual zircon He dates are 402–260 Ma, reflecting source material erosion, and imply a maximum Late Permian infill depositional age. Burial history reconstruction reveals modern exposures were not buried sufficiently in the Triassic–Early Cretaceous to have caused reheating to temperatures necessary to reset the AFT or hematite He systems, and thus these dates cannot reflect cooling due to erosion alone. Hot fluids circulating through fissures in the Early Cretaceous reset the AFT system. Hematite was either also reset by fluids or precipitated from these fluids. Similar hematite He dates from fault-related mineralization in south Glamorgan (Wales) and Cumbria (England) imply concomitant regional hot groundwater flow along faults. In this example, hydrothermal fluid circulation, coeval with North Atlantic rifting, occurred in higher-permeability fissures and fault veins long after they initially formed, directly influencing local and regional geothermal gradients.