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

该项目将在哥斯达黎加俯冲带的两个仪器井眼中持续监测压力、流体化学和水文，使用ODP Leg 203期间安装的长期观测站（CORK和ACORK）。现场项目将：1)沿着俯冲带变形前沿的样带在3个软木塞井眼中部署压力表和数据记录仪、OsmoSamplers和渗透流量计；2)回收OsmoSamplers，数据记录仪中存储的数据，并使用潜水器Alvin部署新的OsmoSamplers和压力表。存储在osmosampler中的流体将提供连续1.3年的流体条件记录，这些记录是在三种不同的水文地质系统中以周分辨率在原位条件下收集的。第一个流动体系是科科斯板块进入的上洋壳，第二个是沿滑脱的深源流体回流，第三个是压实脱水驱动的逆冲下沉积剖面。通过记录这些水文地质系统的性质，将有可能更好地了解汇聚边缘流体流动对下沉板块浅层热结构和流体含量的影响，俯冲带界面的物理性质，变形风格和元素向海洋的输送。

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.