TY - JOUR
T1 - Multiple parameters enable deconvolution of water-rock reaction paths in low-temperature vent fluids of the Kamaʻehuakanaloa (Lōʻihi) seamount
AU - Milesi, Vincent
AU - Shock, Everett
AU - Seewald, Jeffrey
AU - Trembath-Reichert, Elizabeth
AU - Sylva, Sean P.
AU - Huber, Julie A.
AU - Lim, Darlene S.S.
AU - German, Christopher R.
N1 - Publisher Copyright:
© 2023 Elsevier Ltd
PY - 2023/5/1
Y1 - 2023/5/1
N2 - 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.
AB - 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.
KW - Active intraplate volcano
KW - Fluid geochemistry
KW - Geochemical modeling
KW - Hydrothermal vents
KW - Low-temperature vent fluids
KW - Ocean Fe budget
KW - Water-rock reactions
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U2 - 10.1016/j.gca.2023.03.013
DO - 10.1016/j.gca.2023.03.013
M3 - Article
AN - SCOPUS:85150031243
SN - 0016-7037
VL - 348
SP - 54
EP - 67
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -