Carbonatization of Serpentinites of the Mid-Atlantic Ridge: 1. Geochemical Trends and Mineral Assemblages

Abyssal peridotite outcrops compose vast areas of the ocean floor in the Abyssal peridotite outcrops compose vast areas of the ocean floor in the Atlantic, Indian, and Arctic Oceans, where they are an indispensable part of the structure of the oceanic crust section formed in low-velocity oceanic spreading centers. The final stage in the evolution of abyssal peridotites in the oceanic crust is their carbonatization, which they undergo on the surface of the ocean floor or near it. The main goal of this study was reconstruction of the geochemical trends accompanying the carbonatization of abyssal peridotites using the example of MAR ultramafic rocks and to identify the main factors that determine their geochemical and mineralogical differences. It is shown that variations in the composition of rock-forming minerals and their characteristic assemblages indicate that the initial stages of carbonatization of abyssal peridotites occur in intra-crustal conditions simultaneously with the serpentinization of these rocks. The final stage in the crustal evolution of abyssal peridotites is their exposure to the surface of the ocean floor, to which they are transported along the detachment faults. Here, abyssal peridotites in close association with gabbro form oceanic core complexes, and the degree of their carbonatization sharply increases with the duration of their exposure on the surface of the ocean floor. The presented data made it possible to qualitatively reconstruct the sequence of events that determined the mineralogical and geochemical features of carbonatized abyssal peridotites of the MAR.