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

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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.