Control mechanisms of Os isotope anomalies of Co-rich crusts from the Line and Marcus–Wake seamounts areas

Abstract

The evolution curve of the Os isotopic composition (187Os/188Os) of Co-rich ferromanganese crusts reflects the correlation between the supply of continental and mantle-derived materials to seawater in different growth periods of the crusts. In general, a certain ratio of the supply of these materials to the ocean is maintained based on the input–output law. This means that the evolution curves of the Os isotopic composition of crusts in different growth periods can be compared with that of seawater in the Central and Western Pacific Ocean. However, the Os isotopic composition of crusts from the Line and Marcus–Wake seamounts areas is anomalous before 40 Ma and after 7 Ma, respectively, with the ratio being higher than that of seawater, respectively. Throughout the long growth history of the crusts, continental denudation materials entering the marine system through monsoons and atmospheric circulation have been important sources of terrigenous materials in the metallogenetic process. Variations in the contents of indicator elements, such as Si and Al, reflect the input flux of terrigenous materials. During growth periods of the crusts, seamounts they located successively entered the influencing range of the southeast trade wind and westerlies owing to plate tectonics. Depending on the evolution of the atmospheric circulation system, the supply of terrigenous materials to the crusts changes in different seamount areas. The supply of aeolian dust from the Americas and Eurasia may be the dominant factor causing the Os isotope anomalies of the crusts. However, further paleoceanographic studies at the tectonic scale are required to understand the anomalies and enrichment of elements during the metallogenetic process of the crusts. Overall, increased supply of terrigenous materials, along with the evolution of the paleoceanographic environment, may promote the growth rate of the crusts.