In-situ LA-ICPMS analysis of rare earth elements of ferromanganese crusts from west Pacific Ocean seamounts

Rare earth elements (REEs) and trace elements compositions of ferromanganese crusts collected from North-West Pacific seamounts were analyzed by using an in-situ laser ablation inductively coupled plasma mass spectrometry (LA-ICAPMS). The results show that records of elements composition of ferromanganese crusts differ significantly between localities even though they have similar oceanographic settings and three-layered structures. Most of these samples show high total REE concentrations(Sigma REE), high LREE/HREE. marked positive Ce anomaly (delta Ce) and non-or weakly positive Ell anomaly (delta Eu), suggesting that most of them were of hydrogenetic origin. The REE compositions are quite different among various layers in the crusts, which probably results from their different growth environments and different mineral assemblages. In sample 0327, the Sigma REE vary widely over three layers and increasing from inner to outer layers. The values of delta Ce and Y/Ho in inner layer of sample 0327 are quite high and varies dramatically, with maximums of 38.61 and 105.3 respectively. This shows that growth environment of inner layer of sample 0327 was much more turbulent and oxidized than the ones of other two layers. Oil the contrary, the Sigma REE, in sample 0346 are quite high in all three layers and decline slightly from the inner to outer layers. The relatively oxidized environment of the seawater during growth of the inner layers might favor formation of ferromanganese oxyhydroxides and absorption of Ce4+, resulting in a higher Cc content and Sigma REE in the innerlayers. On the other hand, phosphatization events caused strong depletion of REE in the crusts. In the growth profile of the crusts, delta Ce increasing and varying more greatly from outer to inner layers, suggesting that the growth environments of these crusts varied from relatively turbulent and oxidized to peaceful and reduced during growth.