fmars-07-584571 November 21, 2020 Time: 13:21 # 1 BRIEF RESEARCH REPORT published: 26 November 2020 doi: 10.3389/fmars.2020.584571 Hydrothermal Activity at a Cretaceous Seamount, Canary Archipelago, Caused by Rejuvenated Volcanism Andreas Klügel1*, Heinrich Villinger1, Miriam Römer1,2, Norbert Kaul1, Sebastian Krastel3, Kai-Frederik Lenz3 and Paul Wintersteller1,2 1 Fachbereich Geowissenschaften, Universität Bremen, Bremen, Germany, 2 MARUM – Center for Marine Environmental Sciences, Bremen, Germany, 3 Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Kiel, Germany Our knowledge of venting at intraplate seamounts is limited. Almost nothing is known about past hydrothermal activity at seamounts, because indicators are soon blanketed by sediment. This study provides evidence for temporary hydrothermal circulation at Henry Seamount, a re-activated Cretaceous volcano near El Hierro island, close to the current locus of the Canary Island hotspot. In the summit area at around 3000–3200 m Edited by: water depth, we found areas with dense coverage by shell fragments from vesicomyid Daphne Cuvelier, Marine and Environmental Sciences clams, a few living chemosymbiotic bivalves, and evidence for sites of weak fluid venting. Center (MARE), Portugal Our observations suggest pulses of hydrothermal activity since some thousands or tens Reviewed by: of thousands years, which is now waning. We also recovered glassy heterolithologic Crispin Thomas Stephen Little, tephra and dispersed basaltic rock fragments from the summit area. Their freshness University of Leeds, United Kingdom Christopher German, suggests eruption during the Pleistocene to Holocene, implying minor rejuvenated Woods Hole Oceanographic volcanism at Henry Seamount probably related to the nearby Canary hotspot. Heat Institution, United States flow values determined on the surrounding seafloor (49 ± 7 mW/m2) are close to the *Correspondence: Andreas Klügel expected background for conductively cooled 155 Ma old crust; the proximity to the [email protected] hotspot did not result in elevated basal heat flow. A weak increase in heat flow toward the southwestern seamount flank likely reflects recent local fluid circulation. We propose Specialty section: This article was submitted to that hydrothermal circulation at Henry Seamount was, and still is, driven by heat pulses Deep-Sea Environments and Ecology, from weak rejuvenated volcanic activity. Our results suggest that even single eruptions at a section of the journal submarine intraplate volcanoes may give rise to ephemeral hydrothermal systems and Frontiers in Marine Science generate potentially habitable environments. Received: 17 July 2020 Accepted: 29 October 2020 Keywords: seamount, heatflow, hydrothermal activity, Atlantic, vesicomyid clams, Canary Islands Published: 26 November 2020 Citation: Klügel A, Villinger H, Römer M, INTRODUCTION Kaul N, Krastel S, Lenz K-F and Wintersteller P (2020) Hydrothermal The seafloor is scattered with hundreds of thousands of volcanic seamounts of >100 m elevation Activity at a Cretaceous Seamount, Canary Archipelago, Caused by that occur in all parts of the ocean plates (Wessel, 2001; Hillier and Watts, 2007). During their Rejuvenated Volcanism. different evolutionary stages, seamounts interact in various ways with the ocean (Staudigel and Front. Mar. Sci. 7:584571. Clague, 2010). One particular and globally relevant interaction is hydrothermal circulation through doi: 10.3389/fmars.2020.584571 seamounts, which extracts significant lithospheric heat and promotes chemical exchange between Frontiers in Marine Science| www.frontiersin.org 1 November 2020| Volume 7| Article 584571 fmars-07-584571 November 21, 2020 Time: 13:21 # 2 Klügel et al. Hydrothermalism at Cretaceous Seamount crust and ocean (Villinger et al., 2002, 2017; Harris et al., 2004; radiocarbon ages of 3.4 and 18.6 ka, respectively (Klügel et al., Fisher and Wheat, 2010). At volcanically inactive seamounts, 2011). Many trachyte fragments were barite-metasomatized. On low-temperature hydrothermal circulation can be driven by heat the basis of these observations, these authors could show that from the cooling lithosphere in conjunction with topographic Henry Seamount is an extinct early Cretaceous age volcano that gradients and basement outcrops (Fisher et al., 2003; Harris et al., is unrelated to the Canary hotspot (cf. Geldmacher et al., 2005) 2004; Fisher and Wheat, 2010). At volcanically active seamounts, but shows low-temperature hydrothermal activity of Holocene vigorous hydrothermal activity can be driven by magmatic heat age. They suggested that seawater infiltrated through basement sources at comparatively shallow levels, which is common at arc outcrops of El Hierro’s submarine flank, migrated and became settings (Butterfield, 2000; de Ronde and Stucker, 2015; Caratori heated within the oceanic crust to finally discharge at Henry Tontini et al., 2019) but also at some intraplate volcanoes. Seamount. To test this hypothesis, we explored the seamount and Examples are very rare, however, and are mostly confined to the surrounding area in 2018 during R/V METEOR cruise M146 active systems (Sakai et al., 1987; Staudigel et al., 2004; German by high-resolution reflection seismics, heat flow determinations et al., 2020) with few exceptions (Medialdea et al., 2017). using a 6 m long probe, high-resolution hydroacoustic mapping Little is known, however, about ephemeral hydrothermal with an autonomous underwater vehicle (AUV), TV-sled surveys, circulation at the many intraplate seamounts and small volcanic and sediment sampling with a gravity corer and a Van Veen grab. cones that erupt only rarely, or are monogenetic. At low magma supply rates these volcanoes should not have a shallow magma reservoir as a heat source for sustained hydrothermal activity METHODS (Clague and Dixon, 2000). A single submarine eruption can result in residual hydrothermal activity due to cooling and A description of the shipborne methods is given in Klügel and degassing (Santana-Casiano et al., 2016), but duration and Shipboard Scientific Party(2018), and is summarized in the implications of such activity remain to be explored. What is the Supplementary Material. thermal footprint of temporary fluid circulation on the seafloor? Compositions of glasses from tephra and lava fragments were Can fluid circulation persist long enough for chemoautotrophic determined using a Cameca SX-100 electron microprobe (EMP) communities to develop, and are these common occurrences? at the Department of Geosciences, University of Bremen. Glass These questions are difficult to address, largely because few was analyzed for major elements, S and Cl with an acceleration deep-sea volcanoes have been thoroughly explored. Moreover, voltage of 15 kV, beam current of 40 nA, and a defocussed beam traces of previous hydrothermal activity are quickly buried by of 15 mm diameter. Peak counting times were 60 s for sulfur sediment, and any precipitated sulfide minerals and structures and chlorine and 10 s for most other elements; background from hydrothermal flow will quickly oxidize and collapse. Any counting times were half as long. Minerals and glasses from such discovery is rare. In this study, we provide evidence the Smithsonian Institution (Jarosewich et al., 1980) were used for waning Holocene hydrothermal activity at a Cretaceous for calibration. Sulfur was calibrated using pyrite because peak seamount located near the Canary Islands that was likely caused analyses indicated similar maxima positions for sulfides, basaltic − by a small pulse of rejuvenated volcanism. glass standards and samples, hence a predominance of S2 speciation. Between two and seven EMP analyses were averaged for each glass sample. Analytical quality was monitored by GEOLOGICAL BACKGROUND repeated analyses of the glass standards VG-2 and VG-A99 (Smithsonian) and BHVO-2G and BCR-2G (USGS; Jochum et al., The Canary Islands are part of an intraplate hotspot chain 2005) along with the samples. Precision of sulfur analyses was offshore NW Africa, with decreasing ages of seamounts and 3.5% for a concentration around 1400 ppm (VG-2), and 18% for volcanic islands from east to west (Figure 1A). El Hierro, situated a concentration around 150 ppm (VG-A99). on ∼155 Ma old ocean crust, is the youngest island along the chain (1.1 Ma; Guillou et al., 1996) and is located near the present Canary hotspot (Geldmacher et al., 2005). The only historic RESULTS eruption of El Hierro was submarine and occurred between 2011 and 2012 a few kilometers off the island’s southern tip, with the Seafloor Observations shallowest peak shoaling to 89 m below sea level (Martí et al., A major discovery of cruise M146 was the widespread occurrence 2013; Rivera et al., 2013). The new volcanic cone shows evidence of dead vesicomyid clams in the summit area and the flanks for waning hydrothermal activity, given mostly by the expulsion of Henry Seamount. Locally, the seafloor is completely covered of fluids rich in magmatic CO2 (Santana-Casiano et al., 2016). with shells, such that their distribution is very recognizable Henry Seamount, located 40 km southeast of El Hierro, is a as prominent backscatter on high-resolution hydroacoustic volcanic edifice that rises ~700 m above ~3700 m deep ocean maps (Figures 1C,D). Most clam shells belong to the genus floor (Gee et al., 2001; Figure 1B). A reconnaissance dredging Abyssogena southwardae, resembling those previously dredged at campaign over the seamount in 2005 yielded trachytic rocks the seamount (Klügel