[MGI34-P04] Micro X-ray fluorescence mapping for the whole cross-section of ferromanganese nodules in the western North Pacific
Keywords:ferromanganese nodule, micro X-ray analysis, Minamitorishima EEZ
To further investigate the relationship between structure of oxide layers and its geochemical features, we conducted mapping analysis for polished slab of nodules including nuclei and whole layers of oxide by a microfocus X-ray fluorescence analytical microscope (XGT-7000; HORIBA) at Kyoto University. Analysis was conducted in vacuo, and the intensity of Si, Al, P, Ca, K, Mn, Fe, Ti, Ni, Cu, and Y were determined by an energy-dispersive spectrometer at an accelerating voltage of 50 kV, 100 µm beam, and intervals of approximately 160 µm.
We identified that L2 is further sub-divided into three layers, which correspond to layers obtained by X-ray CT . The most inner part of L2 (around nuclei) is characterized by high intensity of Ti and Fe. In contrast, outer part of L2 is characterized by higher intensity of Mn than that of the inner part. Many spots of high intensity of P, Ca, and Y, indicating particles of calcium phosphate including highly amount of Y (and probably rare-earth elements), are observed in the entire area of L2. We found that L1 is clearly characterized by low Si. Furthermore, we observed thin layers showing high intensity of Cu and Ni at the sediment-filled boundaries between L1 and L2, and L1 and L0. Existence of such thin layers suggests that nodules were fully covered by pelagic sediment at the intervals before formation of L1 and L0.
References:  Machida et al. (2016) Geochem. J.50, 539-555.  Shimomura et al. (2018) Goldschmidt Conference 2018.