Genetic analysis and comparison of global ferromanganese crusts constrained by multiple geochemical indicators

Ferromanganese crusts are marine Fe-Mn oxide deposits widely distributed on hard substrates such as seamounts and oceanic ridges throughout the global oceans. They represent both important potential resources of critical metals and valuable archives of pale-oceanographic reconstruction. However, global-wise comparative studies across different ocean basins remain limited, and relationships between multi-geochemical proxies and environmental factors are poorly understood. Therefore, we compiled and studied global geochemical datasets containing more than 3 000 ferromanganese crust samples from various oceanic regions. Based on multiple geochemical proxies, including rare earth elements, major elements, and trace elements, together with genetic discrimination diagrams and principal component analysis (PCA), we systematically investigated the genetic classification, inter-oceanic variations, and environmental controls of global ferromanganese crusts. Results indicate that the distribution of global ferromanganese crusts is governed by multi-scale tectonic-environmental coupling processes, with preferential accumulation in long-lived stable tectonic uplift regions, mainly at water depths of 800-3 500 m. Multi-geochemical proxy analyses showed that ferromanganese crusts from the Arctic, Atlantic, Pacific, and Indian Oceans are predominantly hydrogenetic in origin, with localized influences from diagenetic alteration and hydrothermal contributions. PCA results further revealed significant differences in environmental controls on crust growth among ocean basins. The Arctic ferromanganese crusts are mainly hydrogenetic characterized by growth under strongly oxic conditions with substantial terrigenous detrital inputs and unique weak diagenetic modification associated with terrestrial material input compared with other oceans. The Atlantic crusts are dominated by hydrogenetic processes with additional influence from phosphatization. The Pacific crusts are primarily hydrogenetic with simultaneously recorded signals from terrigenous input, surface productivity, and hydrothermal activity; and extensive phosphatization is widespread in seamount regions of the western Pacific. The Indian Ocean crusts are also predominantly hydrogenetic but have experienced additional phosphatization diagenesis and dilution effects caused by terrigenous detrital inputs from northwestern Australia. This study provided a comprehensive dataset support and theoretical framework for worldwide genetic classification of ferromanganese crusts, and shall improve our understanding of the spatial differentiation of crust formation processes and the environmental mechanisms controlling their evolution across different ocean basins.