Collaborative Research: Long Term Continuous Monitoring of Pressure, Fluid Chemistry, and Hydrology in Instrumented Boreholes at the Costa Rica Subduction Zone

该项目将利用ODP第203航次期间安装的长期观测站（CORK和ACORK），持续监测哥斯达黎加俯冲带两个仪表化钻孔的压力、流体化学和水文。 现场项目将：1）在3个软木钻孔中部署压力计和数据记录仪、渗透取样器和渗透流量计，这些钻孔沿着一条横穿俯冲带变形前缘的横断面; 2）使用潜水器Alvin取回渗透取样器、数据记录仪中存储的数据，并部署新的渗透取样器和压力计。 在三个不同的水文地质系统中，储存在渗透取样器中的流体将以每周分辨率提供在原位条件下收集的连续1.3年的流体状况记录。第一个流动系统是传入的科科斯板块的上洋壳，第二个是深源流体的返回沿着滑脱和第三个是在俯冲沉积段压实脱水驱动。 通过记录这些水文地质系统的性质，将有可能更好地了解会聚边缘的流体流动对下沉板块的浅层热结构和流体含量、俯冲带界面的物理性质、变形方式和元素向海洋的迁移的影响。

This project will continuously monitor the pressure, fluid chemistry, and hydrology in two instrumented boreholes at the Costa Rica subduction zone, using long-term observatories (CORK and ACORK) installed during ODP Leg 203. The field program will 1) deploy pressure gauges and data loggers, OsmoSamplers, and osmotic flow meters in 3 CORKed boreholes along a transect across the deformation front of the subduction zone and 2) retrieve the OsmoSamplers, data stored in the data loggers and deploying new OsmoSamplers and pressure gauges, with the submersible Alvin. The fluid stored in the OsmoSamplers will provide a continuous 1.3 year record of fluid conditions collected at in situ conditions at weekly resolution, in three distinct hydrogeologic systems. The first flow system is the upper oceanic crust of the incoming Cocos Plate, the second is the return of a deeply sourced fluid along the decollement and the third is in the underthrust sediment section driven by compaction dewatering. By documenting the nature of these hydrogeologic systems it will be possible to better understand the effects of fluid flow at convergent margins on the shallow thermal structure and fluid content of the downgoing plate, the physical properties of the subduction zone interface, deformation style and transport of elements to the oceans.