921 / 2024-09-19 20:16:53

Geochemical characteristics of sediments in the southern Mid-Atlantic Ridge indicate hydrothermal activity: Evidence from rare earth elements

Southern Mid-Atlantic Ridge,Sediments,Hydrothermal activity,rare earth elements (REE)

Geochemical analysis was carried out on ten sediment samples collected from the Southern Mid-Atlantic Ridge at 12°-15°S between 2010 and 2012 using inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometer (ICP-OES). The content of representative metals such as Fe, Mn, Co, and Zn was found to be higher in samples near hydrothermal vents than in pelagic sediments (e.g., 22Ⅴ-TVG14). The ratios of Co/Zn and Zn/Fe in stations near hydrothermal vents were 0.21-0.51 and 2.20×10^-3-3.00×10^-3, respectively, indicating a hydrothermal source. The ratio of light rare earth elements (LREE) to heavy rare earth elements (HREE) was between 3.71 and 6.03, indicating enrichment of LREE and depletion of HREE. The REE chondrite-normalized patterns of the samples (except for sample 22Ⅴ-TVG13) showed a negative Ce anomaly (δCe = 0.40-0.64) and slightly negative Eu anomaly (δEu = 0.68-0.89), suggesting that the REEs may have originated from a mixture of low-temperature dispersed hydrothermal fluids and seawater. The total REE content was higher in samples near hydrothermal vents (42.19-48.28 μg·g^-1) than in samples far from hydrothermal vents (17.33 μg·g^-1), indicating that hydrothermal activity affected the distribution of REE in the sediments. The Y/Ho ratios (except for 22Ⅴ-TVG14) were between 27.87 and 45.97, which also indicated that REE may be derived from hydrothermal fluids. Similar geochemical behavior of sample 22Ⅴ-TVG13 and samples near hydrothermal vents suggest the presence of an undiscovered hydrothermal field near the sampling station.