The role of sedimentation history and lithology on fluid flow and reactions in off-axis hydrothermal systems: A perspective from the Troodos ophiolite
The role of sedimentation history and lithology on fluid flow and reactions in off-axis hydrothermal systems: A perspective from the Troodos ophiolite
复制标题
沉积历史和岩性对离轴热液系统中流体流动和反应的作用：来自特罗多斯蛇绿岩的视角
DOI：
10.1016/j.chemgeo.2015.09.006
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发表时间：
2015
期刊：
影响因子：
3.9
通讯作者：
C. Brant
中科院分区：
文献类型：
--
作者：
K. Gillis;L. A. Coogan;C. Brant
离轴热液系统被认为携带着全球重要的化学通量，但不同的海洋地壳剖面显示出很大程度的变化，使得这些通量的量化变得复杂。为了更好地了解这种蚀变程度多样性的成因，我们对特罗多斯蛇绿岩中两个具有不同沉积历史和火山构造的熔岩堆进行了研究。赤木剖面以枕状熔岩为主，上覆地壳的最古老沉积物比蛇绿岩年轻约20 Myr。岩浆顶部有一个300 m厚的带，富含co2和碱元素，具有高87sr /86Sr和δ7Li。这些特征表明与海水有广泛的化学交换。与Akaki地区相比，蛇绿岩剖面以片状流为主，最古老的沉积物与蛇绿岩年龄相同。这里CO2和碱元素富集带较薄（< 100 m），这些元素的富集较少（例如CO2的3倍），并且具有较低的87sr /86Sr和δ7Li。这些富CO2和富碱带方解石的o同位素组成由底水温（~ 10℃）的流体析出。赤木地区地壳在300米深处保持如此低的温度表明这是一个补给区。在这些富含二氧化碳和碱的区域下面，温度随深度增加而增加，因此在任何给定深度，Onophrious区域的方解石降水温度比Akaki区域高~ 10°C。降水温度随深度的增加表明地壳含水层内部热混合不佳，可能是由于横向连续的薄片流动限制了渗透率。化学和热约束表明，沉积开始的时间和火山构造在控制流体和化学通量方面起着重要作用。在现代海洋盆地的岩心数据中也可以看到同样的信号，较高的沉积速率导致地壳含水层的流体通量降低和温度升高。
Off-axis hydrothermal systems are thought to carry globally significant chemical fluxes but different ocean crust sections show widely differing extents of alteration making the quantification of these fluxes complex. With the aim of better understanding the origin of this diversity in alteration extent we have studied two sections of the lava pile in the Troodos ophiolite with distinct sedimentation history and volcanic architecture. The Akaki section is dominated by pillow lavas and the oldest sediments overlying the crust are ~ 20 Myr younger than the ophiolite. Here there is a 300 m thick zone at the top of the lavas that is enriched in CO2and alkali elements, and has high87Sr/86Sr and δ7Li. These features indicate extensive chemical exchange with seawater. In contrast to the Akaki area, the Onophrious section is dominated by sheet flows and the oldest sediments are of the same age as the ophiolite. Here the CO2and alkali element enriched zone is much thinner (< 100 m), is less enriched in these elements (e.g. by a factor of three for CO2), and has lower87Sr/86Sr and δ7Li. The O-isotopic compositions of calcites from these CO2- and alkali-enriched zones were precipitated from fluids with bottom water temperatures (~ 10 °C). Maintaining such low temperatures to 300 m depth in the crust in the Akaki area suggests that this was a region of recharge. Below these CO2- and alkali-enriched zones temperatures increase with depth such that calcite precipitation in the Onophrious area occurred at ~ 10 °C higher temperature, at any given depth, than in the Akaki area. The increase in precipitation temperature with depth indicates poor thermal mixing within the crustal aquifer, likely due to laterally continuous sheet flows restricting the permeability. The chemical and thermal constraints suggest that both timing of the onset of sedimentation and volcanic architecture play important roles in controlling fluid and chemical fluxes. The same signal can be seen in drill core data from the modern ocean basins, with higher sedimentation rates leading to lower fluid fluxes and higher temperatures in the crustal aquifer.
影响因子：
3.9
作者：
M. Regelous;K. Haase;S. Freund;M. Keith;C. Weinzierl;C. Beier;P. Brandl;T. Endres;H. Schmidt
通讯作者：
M. Regelous;K. Haase;S. Freund;M. Keith;C. Weinzierl;C. Beier;P. Brandl;T. Endres;H. Schmidt