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

在年龄超过100万年的海底，由热驱动的海水环流通过洋中脊的两侧，冷却并改变了地壳，并主导了海洋和海底之间的热物质和化学物质的运输。尽管这些过程具有重要意义，但对脊翼环流的机制知之甚少，包括排放和补给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海洋地壳的深度范围。主要元素和微量元素通过山脊两侧的全球通量也不确定。我们建议研究胡安·德·富卡山脊东侧剧烈流体环流和相关通量的模式。最近在该地区钻探样带的结果为两个重要的和意想不到的脊侧热液过程提供了证据：(1)深部热液流体上涌，穿透一个区域也存在浅层环流；(2)浅层基底显著的轴向平行补给，使补给海水沿着走向流动数到数十公里。我们将研究流体、热量和溶质运移的范围和效率(a)穿过基底凸起的走向（即沿着垂直于扩张轴的地壳老化剖面），(b)沿着埋藏和部分埋藏的基底隆起的走向，包括沿着深轴平行的断层，以及(c)在锥形基底建筑物附近，可能是小型的、长期灭绝的火山，穿透山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，以测试关于脊翼环流几何形状的相互竞争的假设，约束脊翼通量估计，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.