Carbonation 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 Atlantic, Indian, and Arctic Oceans, where they are an indispensable part of the oceanic crust section formed in the slow-spreading oceanic ridges (Mid-Atlantic Ridge, Southwest Indian Ridge, and Gakkel Ridge). The final stage in the evolution of abyssal peridotites in the oceanic crust is their carbonation, which they experience on the ocean floor surface or near it. The main goal of this study was to reconstruct the geochemical trends accompanying the carbonation of abyssal peridotites using MAR ultramafic rocks as an example and to identify the main factors that determine their geochemical and mineralogical differences. The composition variations of rock-forming minerals and their characteristic assemblages indicate that the initial stages of carbonation of abyssal peridotites occurred in crustal conditions simultaneously with the serpentinization of these rocks. The final stage in the crustal evolution of the abyssal peridotites is their exhumation on the ocean floor where they were brought up along the detachment faults. On the ocean floor, the abyssal peridotites in close association with gabbro form oceanic core complexes, and the degree of their carbonation sharply increases with time of their exposure on 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.