Collaborative Research: Chemical, pressure, temperature, and flow constraints on hydrologic horizons in the Costa Rica Subduction zone, ODP Sites 1253 and 1255

在大洋钻探方案第205阶段期间，在尼科亚半岛以西哥斯达黎加边缘活跃的水文地层中钻了两个钻孔。一个钻孔穿过上覆板块，进入了ODP1255号场地的塌陷。另一个钻孔穿过俯冲沉积段和板块，进入ODP1253站点的渗透性火成岩基底。这两个井眼被密封，并使用井眼观测站(CORK)进行仪器测量，以便在地层中测量压力、温度、流体流动速度和流体化学成分。迄今收集的1.5年的压力和两年的温度、流体速度和流体化学成分记录已经提供了关于地层性质的基本知识，尽管井中的流体尚未与周围的地层达到稳定状态。这些数据还提供了证据，表明与俯冲有关的构造强迫导致了消融带内可测量的压力、温度、流体速度和流体成分的瞬变。虽然初始数据为探讨几个重要的科学和技术问题提供了基线，但它们也提出了新的关键问题，这些问题将通过更多的连续钻孔数据加以解决。调查人员将进行为期6天的潜水作业，以找回仪器和存储的数据，这些数据将提供从2004年到2009年的最后一次访问期间另外五年的地层温度、压力、流体流量和化学成分的连续记录。该项目将对该俯冲带的水文、地球化学和地球动力学活动进行极为宝贵的长期同步记录，并为今后在广泛的构造和水文活动环境中进行钻孔研究奠定技术和科学基础。

During Leg 205 of the Ocean Drilling Program (ODP) two boreholes were drilled into active hydrologic formations on the Costa Rica margin west of the Nicoya Peninsula. One borehole penetrated through the overriding plate into the décollement at ODP Site 1255. The other borehole penetrated through the subducting sediment section and plate into permeable igneous basement at ODP Site 1253. These two boreholes were sealed and instrumented with a borehole observatory (CORK), allowing pressure, temperature, fluid flow velocity, and fluid chemical composition to be measured within the formation. The 1.5-yr pressure and two-year temperature, fluid velocity, and fluid chemical composition records collected to date have provided a basic knowledge of formation properties, although fluids within the boreholes had yet to reach steady state with the surrounding formations. The data also provide evidence that tectonic forcing related to subduction results in measurable transients in pressure, temperature, fluid velocity, and fluid composition within the décollement. While the initial data provide a baseline for approaching several important scientific and technical questions, they have raised new key questions that will be addressed from additional continuous borehole data. The investigators will a 6-day submersible operation to retrieve instruments and stored data that will provide a continuous record of formation temperature, pressure, fluid flow rate, and chemical composition for an additional five years, from the time of the last visit in 2004 to 2009. This project will result in an extremely valuable long-term synchronous record of hydrologic, geochemical, and geodynamic activity at this subduction zone, and establish a technical and scientific foundation for future borehole studies in a broad range of tectonically and hydrologically active settings.