Hydrothermal cooling of the ocean crust: Insights from ODP Hole 1256D
Hydrothermal cooling of the ocean crust: Insights from ODP Hole 1256D
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DOI：
10.1016/j.epsl.2017.01.010
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发表时间：
2017-03-15
影响因子：
5.3
通讯作者：
Teagle, Damon A. H.
中科院分区：
文献类型：
--
作者：
Harris, Michelle;Coggon, Rosalind M.;Teagle, Damon A. H.
大洋中脊处新洋壳的形成是板块构造循环的一个基本组成部分，涉及地幔大量的热量和物质转移。大洋中脊的热液循环对于将下地壳的潜热和显热平流输送至关重要，从而使靠近洋脊轴的洋壳得以凝固。席状岩墙杂岩（SDC）是喷发的熔岩和辉长岩之间的关键区域，海水衍生的补给流体必须通过该区域与形成下洋壳的岩浆房进行热交换。赤道东太平洋的大洋钻探计划（ODP）1256D井提供了唯一连续的原位完整的快速扩张速率下形成的上洋壳样本，从SDC一直到岩墙 - 辉长岩过渡带。在此，我们利用1256D井锶同位素组成的高样本密度剖面来量化通过SDC的时间积分热液补给流体通量。假设流体 - 岩石间锶交换受动力学限制，要产生所观测到的锶同位素变化，需要1.5 - 3.2×10⁶千克/平方米的流体通量。尽管1256D井与在其他海洋环境（ODP 504B井、赫斯海渊和皮托海渊）中采样的SDC在热液蚀变的分布和强度以及流体/岩石锶同位素交换方面存在显著差异，但所有地点估计的补给流体通量相似，这表明在中等到快速扩张速率下，上地壳轴向热液系统提取的热通量相对均匀。通过SDC的流体流动所带走的热液热通量仅足以带走下地壳中约20% - 60%的可用潜热和显热。因此，在地壳更深处必然存在额外的热和化学的流体 - 岩石交换，其规模至少与上地壳热液系统相当。针对这个更深的热液系统的潜在几何形态，提出了两种设想。第一种设想是，由于传导边界层向下迁移，上地壳热液系统向下扩展800米进入下地壳。第二种设想是下地壳存在一个独立的热液系统，其流体补给绕过与席状岩墙的反应，可能是通过沿断层向下流动。（C）2017作者。由爱思唯尔B.V.出版。这是一篇在知识共享署名许可下的开放获取文章。
The formation of new ocean crust at mid-ocean ridges is a fundamental component of the plate tectonic cycle and involves substantial transfer of heat and mass from the mantle. Hydrothermal circulation at mid-ocean ridges is critical for the advection of latent and sensible heat from the lower crust to enable the solidification of ocean crust near to the ridge axis. The sheeted dike complex (SDC) is the critical region between the eruptive lavas and the gabbros through which seawater-derived recharge fluids must transit to exchange heat with the magma chambers that form the lower ocean crust.ODP Hole 1256D in the eastern equatorial Pacific Ocean provides the only continuous sampling of in-situ intact upper ocean crust formed at a fast spreading rate, through the SDC into the dikegabbro transition zone. Here we exploit a high sample density profile of the Sr-isotopic composition of Hole 1256D to quantify the time-integrated hydrothermal recharge fluid flux through the SDC. Assuming kinetically limited fluid-rock Sr exchange, a fluid flux of 1.5-3.2 x 10(6) kgm(-2) is required to produce the observed Sr-isotopic shifts. Despite significant differences in the distribution and intensity of hydrothermal alteration and fluid/rock Sr-isotopic exchange between Hole 1256D and SDC sampled in other oceanic environments (ODP Hole 504B, Hess Deep and Pito Deep), the estimated recharge fluid fluxes at all sites are similar, suggesting that the heat flux extracted by the upper crustal axial hydrothermal system is relatively uniform at intermediate to fast spreading rates.The hydrothermal heat flux removed by fluid flow through the SDCs, is sufficient to remove only similar to 20 to 60% of the available latent and sensible heat from the lower crust. Consequently, there must be additional thermal and chemical fluid-rock exchange deeper in the crust, at least of comparable size to the upper crustal hydrothermal system. Two scenarios are proposed for the potential geometry of this deeper hydrothermal system. The first requires the downward expansion of the upper crustal hydrothermal system 800 m into the lower crust in response to a downward migrating conductive boundary layer. The second scenario invokes a separate hydrothermal system in the lower crust for which fluid recharge bypasses reaction with the sheeted dikes, perhaps via flow down faults. (C) 2017 The Author(s). Published'by Elsevier B.V. This is an open access article under the CC BY license.