Causes for recent fluid venting at the Cretaceous Henry Seamount, Canary Archipelago

海水通过老化的洋壳的水热循环对岩石圈的冷却、地壳与海洋之间的化学交换以及海洋生态系统具有全球重要意义。在被沉积物覆盖的旧地壳，有效的流体循环需要基底露头，如海山，形成穿过不透水的沉积物毯子的通道。到目前为止，只有少数与活火山活动无关的喷发海山被发现；这些海山位于温暖而相对年轻的太平洋地壳上。古老地壳上的热液活动海山的第一个例子可能是加那利群岛埃尔耶罗附近的亨利海山。在R/V流星巡航M66/1期间的一次侦察疏浚活动中发现了样本，表明该海山存在全新世流体渗漏，尽管该建筑物的历史可追溯到1.26亿年前。为了发现、记录和采样渗漏地点，亨利·海蒙德在2018年R/V流星巡航M146期间进行了详细调查。人们发现，海山的大片区域覆盖着来自囊泡菌的贝壳，这证明了相对较新的广泛渗漏。然而，伴随而来的热流测量没有显示出各自的异常。重力取样器和Grab在当地对海底进行采样，除其他外，发现了许多贝壳和出人意料的新鲜玄武岩火山灰和青金石，这明确表明亨利·西蒙最近的火山活动。在拟议的项目中，我们将用岩石学-地球化学方法调查玄武岩样品，确定火山岩和贝壳的年龄，并评估来自邮轮M146的水声和电视雪橇测量数据。其目的是了解亨利海山推断出的流体渗漏的原因、程度和后果，并总体上提高对很少喷发的海底板内火山的热液系统的了解。

Hydrothermal circulation of seawater through ageing oceanic crust is globally important for cooling of the lithosphere, chemical exchange between crust and ocean, and marine ecosystems. At sediment-covered old crust, efficient fluid circulation requires basement outcrops, such as seamounts, that form pathways through the impermeable sediment blanket. Only few venting seamounts that are not related to active volcanism have been found so far; these are located on warm and relatively young Pacific crust. The probably first example for an hydrothermally active seamount on old crust is Henry Seamount near El Hierro, Canary Islands. A reconnaissance dredging campaign during R/V METEOR cruise M66/1 yielded samples that indicate Holocene fluid seepage at this seamount, even though the edifice was age dated to 126 million years. In order to discover, document and sample the seepage sites, Henry Seamount was investigated in detail during R/V METEOR cruise M146 in 2018. It was found that large areas of the seamount are covered with shells from vesicomyid clams, which documents relatively recent widespread seepage. Accompanying heat flow measurements, however, showed no respective anomalies. Local sampling of the seafloor by gravity corer and grab yielded, among others, numerous shells and unexpectedly fresh basaltic ash and lapilli, which unequivocally indicates recent volcanic activity of Henry Seamount. In the proposed project we will investigate the basaltic samples with petrological-geochemical methods, determine the ages of the volcanic rocks as well as of the shells, and evaluate hydroacoustic and TV-sled survey data from cruise M146. The aim is to understand causes, extent, and consequences of the inferred fluid seepage at Henry Seamount, and generally an improved understanding of hydrothermal systems at submarine intraplate volcanoes that erupt only rarely.