Multiple parameters enable deconvolution of water-rock reaction paths in low-temperature vent fluids of the Kamaʻehuakanaloa (Lōʻihi) seamount

Details

• Journal Title:
  Geochimica et Cosmochimica Acta
• Personal Author:
  Milesi, Vincent ; Shock, Everett ; Seewald, Jeffrey ; Trembath-Reichert, Elizabeth ; Sylva, Sean P. ; Huber, Julie A. ; Lim, Darlene S.S. ; German, Christopher R.
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research)
• Description:
  The contribution of venting fluids at mid-ocean ridges to global ocean biogeochemical cycles is well recognized. Less is known about the role of magmatically-active intra-plate volcanoes. In this study, new compositional fluid data were acquired from 20 to 50 °C vent fluids at Kamaʻehuakanaloa (previously known as Lōʻihi) seamount (Hawai’ian archipelago) and used to model the wide diversity of reaction conditions capable of producing the Fe-, Si- and CO2-rich vent fluids observed. Our conceptual model includes a first step where seawater reacts with increasing proportions of basalt and gas as the temperature increases, and a second step where the resulting hydrothermal fluid mixes with unaltered seawater while continuing to react with basalt until the fluid mixture reaches 20 °C. A series of reaction paths were chosen to vary: the maximum temperature during Step 1 (50 to 400 °C) and the proportions of basalt and gas reacting; the degree, F, of low-temperature basalt alteration during Step 2, which corresponds to the extent to which the hot fluid generated during Step 1 continues to react with more basalt as it ascends to the seafloor. Our model shows that the 20–50 °C vent fluids are greatly dependent on the degree of low-temperature basalt alteration during fluid upwelling. Indeed, the compositions of Kamaʻehuakanaloa vent fluids cannot be reconciled with a general model of subsurface mechanical mixing of high-temperature end-member vent fluid and seawater alone. Instead, they require both subsurface equilibrium mixing between a ≥350 °C hydrothermal fluid end-member and seawater and further basalt alteration that must occur as the fluid mixture rises to the seafloor. Although it involves only ∼4% of the amount of basalt having reacted during Step 1, this low-temperature basalt alteration during Step 2 leads to the characteristic enrichments in Fe observed in the Kamaʻehuakanaloa vent fluids and a concomitant depletion in H2S. We hypothesize that low-temperature basalt alteration during an extended path of fluid upwelling through the subseafloor might arise as a direct consequence of the height and steep-sloped topography of Kamaʻehuakanaloa seamount. If correct, this suggests a more general case - that input from magmatically-active intraplate volcanoes, which have been relatively overlooked throughout the history of submarine vent investigations to date, could differ significantly from global mid-ocean ridge fluxes and contribute more substantially than previously recognized to the global ocean Fe cycle.
• Source:
  Geochimica et Cosmochimica Acta, 348, 54-67
• DOI:
  https://doi.org/10.1016/j.gca.2023.03.013
• ISSN:
  0016-7037
• Format:
  PDF
• Publisher:
  Elsevier BV
• Document Type:
  Journal Article
• Funding:
  Grant no. NA17OAR0110336
• License:
  https://creativecommons.org/licenses/by-nc-nd/4.0/
• Rights Information:
  CC BY-NC-ND
• Compliance:
  Library
• Main Document Checksum:
  urn:sha-512:bb9335505eb0b1c2cf7ef1a6c6bb1a25f583a5cefa7bfa496d1c35dd83b48e73e738a5c4c8f5c1062e6a0da2ce7a7ac496387b0465460af725fd34ae9acd4069
• Download URL:
  https://repository.library.noaa.gov/view/noaa/64658/noaa_64658_DS1.pdf
• File Type:
  [PDF - 4.94 MB ]