Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge
Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge
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DOI：
10.1029/2006gc001509
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发表时间：
2007-11-13
影响因子：
3.5
通讯作者：
Weber, S.
中科院分区：
文献类型：
--
作者：
Haase, K. M.;Petersen, S.;Weber, S.
火山活动对海底热液系统的影响已经在快速和中等扩张中心得到了很好的记录，而在缓慢扩张的脊上则没有。事实上，火山爆发预计在缓慢蔓延的轴线上是罕见的。在这里，我们报告了在缓慢扩张的大西洋中脊南部靠近5°s附近的一个凸起的、明显岩浆活跃的部分中心，存在与极其新鲜的熔岩流相关的热液喷口。到目前为止，在不到2公里的走向长度上发现了三个高温喷口场，其中两个喷口是相分离的蒸汽型流体。其中一个油田的出口温度高达407摄氏度，在海水临界点的条件下，这是海底有记录以来的最高温度。流体和喷口场特征显示出喷口场之间有很大的变化，这种变化在如此有限的区域内是不可预料的。从热液沉淀物的矿物学研究中，我们得出结论，喷口流体成分最近从相对氧化条件向更多还原条件演变，这一转变也可能与该地区重新开始的岩浆活动有关。目前两个火山口流体中较高的出口温度、还原条件、低硅含量和高氢含量与浅岩浆源一致，可能与附近年轻的火山喷发事件有关，其中玄武岩岩浆正在活跃结晶。这是首次报道在缓慢扩张的洋中脊上直接存在岩浆-热液相互作用的证据。
[1] The effect of volcanic activity on submarine hydrothermal systems has been well documented along fast- and intermediate-spreading centers but not from slow-spreading ridges. Indeed, volcanic eruptions are expected to be rare on slow-spreading axes. Here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated, apparently magmatically robust segment center on the slow-spreading southern Mid-Atlantic Ridge near 5 degrees S. Three high-temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase-separated, vapor-type fluids. Exit temperatures at one of the fields reach up to 407 degrees C, at conditions of the critical point of seawater, the highest temperatures ever recorded from the seafloor. Fluid and vent field characteristics show a large variability between the vent fields, a variation that is not expected within such a limited area. We conclude from mineralogical investigations of hydrothermal precipitates that vent-fluid compositions have evolved recently from relatively oxidizing to more reducing conditions, a shift that could also be related to renewed magmatic activity in the area. Current high exit temperatures, reducing conditions, low silica contents, and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source, probably related to a young volcanic eruption event nearby, in which basaltic magma is actively crystallizing. This is the first reported evidence for direct magmatic-hydrothermal interaction on a slow-spreading mid-ocean ridge.