Carbonation of Serpentinites of the Mid-Atlantic Ridge: 2. Evolution of Chemical and Isotopic (δ18O, δ13С, Rb, Sr, Sm, Nd) Compositions during Exhumation of Abyssal Peridotites

Abstract

Carbonate minerals in oceanic crust are formed through CO₂ interaction with silicate minerals of ultramafic and mafic rocks. Carbonation leads to the generation of numerous carbonate veins, filling interstices in the rock matrix and producing partially and/or completely carbonated rocks that compose the protolith of slow-spreading mid-ocean ridges and are present in ophiolite complexes. Silantyev et al. (2023) proposed a conceptual model of the main stages in the formation of carbonated serpentinites in different segments of the Mid-Atlantic Ridge. In this study, we examined isotope variations (δ¹⁸O, δ¹³С, Rb, Sr, Sm, Nd) in the previously studied carbonated ultramafic rocks from oceanic core complexes of the slow-spreading mid-oceanic ridge. The carbon and oxygen isotope compositions obtained in our study are well consistent with results of our previous studies and make it possible to quantify the duration and spatial position of sea fluid interaction with serpentinites of different segments of the Mid-Atlatnic Ridge in the oceanic crust sequence. Peridotite groups previously distinguished based on the mineral and petrographic features are well consistent with relations of obtained parameters or with water/rock ratio calculated using Sr-Nd isotope systematics, and reflect the sequence of carbonation stages in the ultramafic protolith of oceanic crust and duration of its residence on the seafloor. Our results indicate that the oceanic core complexes containing the studied rocks were exhumed to the seafloor surface during different time periods.