Geochemical characteristics and genesis of ferromanganese nodules and crusts from the Central Rift Seamounts Group of the West Philippine Sea

Abstract

There is a lack of information on the geochemical characteristics and genesis of ferromanganese nodules and crusts from the Central Rift Seamounts Group of the West Philippine Sea (CRSGWPS). This study presents the major, trace, and rare earth contents and 10Be isotopic data for ferromanganese nodules and crusts from the CRSGWPS to determine their genetic origin, classification, and growth rate. The Mn/Fe ratio of the crust is 0.96–3.97, and the Co + Ni + Cu content is 4499–6324 ppm. The crust is rich in rare earth elements (REE), with significant positive Ce and negative Y anomalies. The Mn/Fe ratio of the nodule is 0.90–1.52, and the Co + Ni + Cu is 1617–9549 ppm. Samples near the core of the nodule have a relatively low REE content, with significant positive Ce and negative Y anomalies. 10Be specific activity and thickness of the nodules and crusts show that growth rates were 2.26 mm/Ma and 2.5 mm/Ma, respectively, indicating that proliferation of nodules and crusts in this area began in the mid-Miocene (9.32–12.03 Ma). A comprehensive study of the growth rate, mineralogy, structure, and chemical characteristics of nodules/crusts in the study area indicates that their formation was mainly hydrogenic, and the early growth of nodules is affected by hydrothermal action.