Data_Sheet_1_Hydrothermal Activity at a Cretaceous Seamount, Canary Archipelago, Caused by Rejuvenated Volcanism.pdf

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 water depth, we found areas with dense coverage by shell fragments from vesicomyid clams, a few living chemosymbiotic bivalves, and evidence for sites of weak fluid venting. Our observations suggest pulses of hydrothermal activity since some thousands or tens of thousands years, which is now waning. We also recovered glassy heterolithologic tephra and dispersed basaltic rock fragments from the summit area. Their freshness suggests eruption during the Pleistocene to Holocene, implying minor rejuvenated volcanism at Henry Seamount probably related to the nearby Canary hotspot. Heat flow values determined on the surrounding seafloor (49 ± 7 mW/m2) are close to the expected background for conductively cooled 155 Ma old crust; the proximity to the 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 that hydrothermal circulation at Henry Seamount was, and still is, driven by heat pulses from weak rejuvenated volcanic activity. Our results suggest that even single eruptions at submarine intraplate volcanoes may give rise to ephemeral hydrothermal systems and generate potentially habitable environments.

我们对板块内海山喷发作用的认知仍显有限。关于海山过去的热液活动的了解几乎为零，因为指示标志很快就会被沉积物所覆盖。本研究为亨利海山短暂的热液循环提供了证据，亨利海山是一座位于埃斯帕特里奥岛附近、重新激活的白垩纪火山，靠近当前加那利热点活动中心。在大约3000至3200米水深的主峰区域，我们发现了壳碎片密集覆盖的区域，这些碎片来自蛤蜊类双壳贝，还有少量活着的化学共生双壳贝，以及微弱流体喷发地点的证据。我们的观察表明，自数千或数万年前以来，一直存在热液活动的脉冲，但目前这种活动正在减弱。我们还从主峰区域回收了玻璃质异构火山灰和散布的玄武岩岩石碎片。它们的新鲜度表明，上新世至全新世期间发生过喷发，这暗示亨利海山可能存在微弱的年轻火山活动，可能与附近的加那利热点有关。在周围海底测定的热流值（49 ± 7 mW/m²）接近预期背景值，对于导热冷却的15.5亿年古老地壳；热点的邻近并未导致基底热流的升高。向西南海山斜坡方向热流的微弱增加可能反映了最近局部流体循环。我们提出，亨利海山的热液循环过去是，并且仍然是由于微弱年轻火山活动的热脉冲所驱动。我们的结果表明，即使是海底板块内火山的一次单独喷发也可能引发短暂的热液系统，并生成可能适宜生命居住的环境。