Multistage hydration during oceanic serpentinisation revealed by in situ oxygen isotope and trace element analyses

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Vesin, Coralie, Rubatto, Daniela, Pettke, Thomas, Deloule, Etienne
• Other Authors: Institute of Geological Sciences Bern, Universität Bern / University of Bern (UNIBE), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Oceanic serpentinisation; Serpentine textures; Oxygen isotopes; Fluid-mobile elements; Transition metals; [SDU]Sciences of the Universe [physics]; Newfoundland
• Online Access: https://insu.hal.science/insu-04149789; https://insu.hal.science/insu-04149789/document; https://insu.hal.science/insu-04149789/file/1-s2.0-S0016703723003058-main.pdf; https://doi.org/10.1016/j.gca.2023.06.032

International audience Serpentinisation of mantle peridotites below the seafloor is the most important hydration reaction in the Earth's deep water cycle. This critical step in water-rock interaction occurs over multiple serpentinisation stages and at variable temperatures and fluid compositions. We present the first study using spatially coupled in-situ analysis of oxygen isotopes (secondary ionization mass spectrometry) and trace elements (laser ablation inductively coupled plasma mass spectrometry) to unravel the multistage hydration history of oceanic serpentinites. We study samples from the Newfoundland-Iberia extended passive margins, which represents a magma-poor ocean-continent transition zone (Ocean Drilling Program cores, Leg 173 Site 1070 from Iberia, Leg 210 Site 1277 from Newfoundland). The concentrations of the fluid mobile elements chlorine and boron in serpentine are used as a proxy for the salinity of the serpentinising fluid. The correlation of Cl/B with δ18Oserpentine compositions provides new insights to disentangle temperature from fluid composition effects. The transition metal composition (V, Co, Sc, Mn, Zn, Ni, Cr) of dominantly lizardite in mesh after olivine and in bastite after orthopyroxene shows a chemical redistribution between textural sites in the Newfoundland samples, indicating the simultaneous serpentinisation of olivine and orthopyroxene. This feature is not observed in the Iberian samples, for which we propose sequential reactions. Lizardite in samples from both localities varies considerably in oxygen isotope composition at the scale of tens of micrometres depending on texture, with a range in δ18O of 3.3–13.5‰ for Iberia samples and a more restricted range of 5.7–9.3‰ for Newfoundland samples. Temperatures calculated from the δ18Oserpentine corresponding to the lowest Cl/B ratio (interpreted as closest to seawater composition) indicate sequential serpentinisation with decreasing temperature from ∼190 to ∼60°C in the Iberia setting. The Newfoundland samples were ...