Nickel isotopes and rare earth elements systematics in marine hydrogenetic and hydrothermal ferromanganese deposits

Attention is now being given to Ni isotope systematics in hydrogenetic marine ferromanganese (Fe-Mn) crusts as paleoceanographic proxies. Previous work focused on identifying both mineralogy (post-depositional) and source effects (Gall et al. 2013; Gueguen 2016), particular regarding hydrothermal inputs the oceans response of biogeochemical cycling through time. The most important sink for Fe-Mn oxides sink, but estimation its composition only based crusts. In this study, we investigated a range deposits including variably affected by inputs, from Lau back-arc basin (South West Pacific) Lo'ihi seamount (Hawaii), crust nodules Bauer Basin (Pacific Ocean). Nickel ratios were measured multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) using double-spike (61Ni 62Ni) correction method. combination isotopes rare earth element (REE) geochemistry show that fractionation essentially controlled formation processes (such rate formation, initial Mn-phase sorption processes) which are also related depositional environment. Consistent with previous studies, pure characterized isotopically heavy signatures (δ60/58Ni values ‰ 0.9 2.5‰) well-developed positive Ce anomalies. contrast, mixed hydrothermal‑hydrogenetic (East display negative anomaly lighter δ60/58Ni (0.3‰ 0.4‰), interpreted result far-field precipitates East Pacific Rise. (0.5 1.1‰) (−0.8 −1.5‰) than Light due removal during adsorption seawater fluid (between 0 1.4‰) Fe-oxides followed between mineral phase. Results suggest Fe-rich strongly fractionated relative seawater/fluid partial Fe-phases. Hydrothermal Mn-oxides acquired their signature continuous exchange seawater. We propose systematic difference hydrogeneous mechanisms uptake into oxide minerals (e.g., birnessite vs. todorokite; Mn-oxides) depend Mn Fe (i.e., environment) rather sources.