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

在超过一百万年的海底，海水通过大洋中脊两侧的热驱动循环，冷却和改变地壳，并主导海洋和海底之间的热和化学物质传输。尽管这些过程意义重大，但人们对脊侧环流的机制知之甚少，包括排放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洋壳的渗透深度。通过脊侧的主要和微量元素的全球通量也是不确定的。我们建议研究胡安德·富卡海脊东侧活跃的流体环流和相关的通量模式。最近在该地区钻探横断面的结果为两个重要和意想不到的脊侧热液作用提供了证据：(1)深源热液上涌，穿透也有浅层环流的地区；(2)浅层基底显著的轴向平行补给，使补给的海水能够沿着走向流动几到几十公里。我们将调查流体、热量和溶质传输的范围和效率：(A)穿过基底浮雕的走向(即，沿着地壳老化剖面，垂直于扩展轴线)，(B)沿着被埋藏和部分被埋藏的基底隆起的走向，包括沿着深轴平行断层，以及(C)在圆锥形基底建筑物内，可能是小型、长期熄灭的火山，穿过脊侧几乎连续的沉积物。这项工作将记录和评估这些解释，测试关于脊侧环流几何形状的相互竞争的假设，约束脊侧流量估计，并帮助选择钻井船返回现场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.