Pore-water chemistry at DSDP Leg 70 Holes

Geological and geophysical data collected during Deep Sea Drilling Project (DSDP) Leg 70 indicate that hydrothermal solutions are upwelling through the sediments of the mounds hydrothermal field (Sites 506, 507, and 509) and downwelling in the low heat-flow zone to the south (Site 508). Pore-water data are compatible with these conclusions. Pore waters at mounds sites are enriched in Ca and depleted in Mg relative to both seawater and Site 508 pore waters. These anomalies are believed to reflect prior reaction of the interstitial waters with basement rocks. The mounds solutions are also enriched in iron, which is probably hydrothermal and en route to forming nontronite. Concentrations of Si and NH3 in mounds pore water increase upcore as a result of the addition of dissolving biogenic debris to ascending hydrothermal solutions. Some low heat-flow pore-water samples (Site 508) are enriched in Ca and depleted in Mg. These anomalies likely reflect the presence of pockets of hydrothermal solutions in areas otherwise dominated by downwelling bottom water.深海钻探计划（Deep Sea Drilling Project, DSDP）第70航次采集的地质与地球物理数据显示，热液流体（hydrothermal solutions）正通过热液丘场（站位506、507与509）的沉积物向上涌升，并在南侧的低热流区（站位508）向下沉降。孔隙水（pore-water）数据与上述结论一致：相较于海水及站位508的孔隙水，热液丘场站位的孔隙水呈现钙富集与镁亏损特征。此类异常被认为反映了间隙水（interstitial waters）此前与基底岩（basement rocks）发生的水岩相互作用。热液丘场的流体还富含铁，该物质大概率为热液成因，并正逐步形成绿脱石（nontronite）。随着溶解的生物碎屑加入上升的热液流体，热液丘场孔隙水中的硅（Si）与氨（NH3）浓度沿岩芯向上逐渐升高。部分低热流区孔隙水样品（站位508）同样表现为钙富集与镁亏损，这类异常可能反映了在原本以下沉底层水为主的区域中，存在热液流体团块。