Collaborative Research: Recharge, Discharge and Routes of Fluid Flow within Young Oceanic Crust at the Juan de Fuca

在一百万年以上的海底，海水通过大洋中脊侧翼的热驱动循环冷却和改变了地壳，并主导了海洋和海底之间的热和化学物质迁移。尽管这些过程意义重大，但人们对海脊侧翼环流的机制知之甚少，包括排泄和补给地点的物理和化学性质、流动的路径和横向长度尺度以及渗透到洋壳的深度。全球通过海脊侧翼的常量和微量元素通量也不确定。我们建议调查模式的强有力的流体循环和相关通量的胡安德富卡脊东侧。最近在该地区进行的一次钻探断面的结果为两个重要的和意想不到的脊翼热液过程提供了证据：（1）深层来源的热液流体的上涌，穿透了一个也存在浅循环的区域;（2）浅基底中的显著轴向平行补给，使补给海水能够沿着走向流动几公里至几十公里。我们将研究流体、热量和溶质运移的程度和效率（a）穿过基底起伏的走向（即，沿着垂直于扩张轴的地壳年龄剖面），（B）沿着埋藏和部分埋藏的基底洋脊走向，包括沿着深轴平行断层，以及（c）在圆锥形基底大厦附近，可能是小型的长期死火山，它们穿透了洋脊侧面几乎连续的沉积物。这项工作将记录和评估这些解释，以测试有关脊侧翼环流的几何形状的相互竞争的假设，以约束脊侧翼通量估计，并帮助选择钻探船返回的地点进行额外的采样和井下实验。

Thermally-driven circulation of seawater through flanks of mid-ocean ridges, in seafloor older than one million years, cools and alters the crust, and dominates thermal and chemical mass transport between the oceans and the seafloor. Despite the significance of these processes, little is known about the mechanics of ridge-flank circulation, including the physical and chemical nature of discharge and recharge sites, the pathways and lateral length scales of flow, and the depth extent of penetration into the oceanic crust. Global fluxes of major and trace elements through ridge flanks are also uncertain. We propose to investigate patterns of vigorous fluid circulation and associated fluxes on the eastern flank of Juan de Fuca Ridge. Results from a recent drilling transect in this area produced evidence for two important and unexpected ridge-flank hydrothermal processes: (1) upwelling of deeply-sourced hydrothermal fluids that penetrate an area also hosting shallow circulation, and (2) significant axis-parallel recharge in shallow basement, allowing recharging seawater to flow along strike over several to tens of kilometers. We will investigate the extent and efficiency of fluid, heat, and solute transport (a) across the strike of the basement relief (i.e., along a crustal aging profile, perpendicular to the spreading axis), (b) along the strike of the buried and partially buried basement ridges, including along deep axis-parallel faults, and (c) within the vicinity of conical basement edifices, probably small, long-extinct volcanoes, that penetrate through the nearly continuous sediment on the ridge flank. This work will document and evaluate these interpretations, to test competing hypotheses regarding the geometry of ridge-flank circulation, to constrain ridge-flank flux estimates, and to help select sites for a return of the drill ship for additional sampling and downhole experiments.