Variations in content of Si, Al, and Ca during the growth of ferromanganese crusts on the 13°20′N seamount of Kyushu-Palau Ridge and indication to the supply of detrital materials

The detrital materials in diverse types are important components of deep-sea ferromanganese crusts. Detrital materials not only enrich the critical metals such as Co, Ni, Cu, Mn, REE and Y, but also record the oceanographic conditions and significant geological events during the growth of the crusts. Ferromanganese crust samples from the 13°20′N seamount of Kyushu-Palau Ridge were studied in detail using scanning electron microscopy and laser ablation-inductively coupled plasma-mass spectrometry based on previous research works. Results reveal that the large grain detrital materials in the samples are composed of mainly the aggregates of quartz and feldspar, and the foraminiferal fossils are mainly distributed in the outer part of the samples. The fine grain detrital materials include clay minerals, various forms of the fossil organisms and their fragments. The quartz and feldspar within the crusts are mainly derived from the Asian continental eolian dust, while the clay minerals are supplied by the eolian dust from the Asian continent and the weathering material from the surrounding island arc. The supply of detrital materials is at a high peak stage in the early stage of crust formation while it decreases to the lowest point in the later stage, which is consistent with the distribution characteristics of Si and Al contents in every part of the crusts, and a considerable amount of biogenic silica nanofossils may have incorporated into the ferromanganese oxide microlayers. The passively accreted Ca biogenic material within the crusts in the early stage suffers from fragmentation and dissolution in the middle and late stages, but the Ca in the inner part does not migrate out of the crusts completely. It is instead adsorbed by ferromanganese oxide microlayers in large quantities. The Ca contents in the bulk parts and the ferromanganese oxide microlayers are very similar to those in the three parts of the crust samples, which is due probably to that Ca in the crust is mainly distributed in fine grain detrital materials. The contents characteristics of Ca is completely different from Si and Al. The crust samples in the study area belong to normal open oceanic seamount-type crusts, but the enrichment of these critical metals is constrained by the supply of eolian dust from the Asian continent and the diatom from the surrounding seas.