Environmental controls on mid-ocean ridge hydrothermal fluxes
Environmental controls on mid-ocean ridge hydrothermal fluxes
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DOI：
10.1016/j.chemgeo.2019.119285
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发表时间：
2019-12-05
期刊：
影响因子：
3.9
通讯作者：
Pester, Nicholas J.
中科院分区：
文献类型：
--
作者：
Coogan, Laurence A.;Seyfried, William E.;Pester, Nicholas J.
大洋中脊的高温热液通量被认为是海洋生物地球化学循环的重要组成部分。然而，很少有人考虑到这些通量如何因地球历史上环境条件变化而变化。在这里，我们考虑海平面和海洋化学的变化如何影响显生宙条件下的轴上高温热液通量。海平面的变化导致热液系统底部附近的静水压力发生变化，其中峰值流体-岩石反应温度和相分离都发生。一般来说，全球海平面升高将导致流体-岩石反应的峰值温度升高。此外，较高压力下的相分离往往会导致形成更富含 Cl 的蒸气，从而构成系统的更大质量分数。这些综合因素可能会显着改变热液通量，甚至对于 100 m 规模的海平面变化也是如此。海洋化学的变化也会以多种方式影响轴向热液通量。海水硫酸盐含量控制硬石膏的形成量，硬石膏具有物理（孔隙填充）和化学作用。海洋化学在控制高温喷口流体成分方面最重要的方面可能是海洋盐度。如果蒸发岩的形成和溶解极大地改变了显生宙的海洋盐度，那么热液通量可能会发生很大的变化。海洋化学在控制热液羽流中的运行过程以及与热液系统相关的元素进出海洋的净通量方面也发挥着重要作用。我们的结论是，需要进一步开展大量工作来量化海平面和海洋化学对高温热液通量的影响，包括开发整合现场、实验室和理论观测的更稳健的模型。
High temperature hydrothermal fluxes at mid-ocean ridges are thought to be an important component of oceanic biogeochemical cycles. However, little consideration has been given to how these fluxes vary as a consequence of changing environmental conditions over Earth history. Here we consider how changes in sea level and ocean chemistry are likely to have impacted on-axis, high-temperature, hydrothermal fluxes focusing on Phanerozoic conditions. Changes in sea level lead to changes in hydrostatic pressure near the base of hydrothermal systems where both peak fluid-rock reaction temperatures and phase separation occur. In general, higher global sea level will lead to higher peak temperatures of fluid-rock reaction. Additionally, phase separation at higher pressure tends to lead to formation of a more Cl-rich vapor, that constitutes a larger mass fraction of the system. These combined factors may serve to significantly modify hydrothermal fluxes even for sea level changes on the scale of 100 m. Changes in ocean chemistry can also affect axial hydrothermal fluxes in several ways. Seawater sulfate contents control the amount of anhydrite that forms, which has both physical (porosity filling) and chemical effects. The most important aspect of ocean chemistry in controlling the composition of high-temperature vent fluids may be ocean salinity. If evaporite formation and dissolution has changed ocean salinity substantially over the Phanerozoic, hydrothermal fluxes could have been greatly modified. Ocean chemistry also plays a large role in controlling processes operating in hydrothermal plumes and hence the net flux of elements into and out of the ocean associated with hydrothermal systems. We conclude that there is a need for substantial further work to quantify the effects of sea level and ocean chemistry on high-temperature hydrothermal fluxes, including the development of more robust models that integrate field, laboratory and theoretical observations.