Low Temperature Serpentinite Replacement by Carbonates during Seawater Influx in the Newfoundland Margin

• Published in: Minerals
• Main Authors: Picazo, Suzanne, Malvoisin, Benjamin, Baumgartner, Lukas P., Bouvier, Anne-Sophie
• Other Authors: Université de Lausanne = University of Lausanne (UNIL), Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: carbonation; CO 2 sequestration; replacement process; low temperature carbonate precipitation; Secondary Ion Mass Spectrometer; seawater influx; hydrothermal circulation; ophicalcite; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy; Newfoundland
• Online Access: https://hal.science/hal-02504014; https://hal.science/hal-02504014/document; https://hal.science/hal-02504014/file/Picazo_et_al_2020_Minerals.pdf; https://doi.org/10.3390/min10020184

International audience Serpentinite replacement by carbonates in the seafloor is one of the main carbonation processes in nature providing insights into the mechanisms of CO2 sequestration; however, the onset of this process and the conditions for the reaction to occur are not yet fully understood. Preserved serpentine rim with pseudomorphs of carbonate after serpentine and lobate-shaped carbonate grains are key structural features for replacement of serpentinite by carbonates. Cathodoluminescence microscopy reveals that Ca-rich carbonate precipitation in serpentinite is associated with a sequential assimilation of Mn. Homogeneous δ18O values at the µm-scale within grains and host sample indicate low formation temperature (<20 °C) from carbonation initiation, with a high fluid to rock ratio. δ13C (1–3 ± 1‰) sit within the measured values for hydrothermal systems (−3–3‰), with no systematic correlation with the Mn content. δ13C values reflect the inorganic carbon dominance and the seawater source of CO2 for carbonate. Thermodynamic modeling of fluid/rock interaction during seawater transport in serpentine predicts Ca-rich carbonate production, at the expense of serpentine, only at temperatures below 50 °C during seawater influx. Mg-rich carbonates can also be produced when using a model of fluid discharge, but at significantly higher temperatures (150 °C). This has major implications for the setting of carbonation in present-day and in fossil margins.