Systematic correlation of the Ce anomaly with the Co/(Ni+Cu) ratio and Y fractionation from Ho in distinct types of Pacific deep-sea nodules.

Abstract

Chemical characteristics of "diagenetic" and "hydrogenous" type deep-sea nodules from the central and northeastern Pacific were studied regarding their Ce anomalies and Y fractionation from heavy REE. Pacific nodules of both types show low Y/Ho ratios less than average shales or chondrites, contrasting to the other marine samples (seawaters, limestones, and phosphorites) having higher Y/Ho ratios than aver age shales or chondrites. The "hydrogenous" type nodules show large positive Ce anomalies up to log(Ce/ Ce*) = +0.6, whereas the "diagenetic" type nodules display only small positive Ce anomalies or even small negative ones. Two nodule subsamples, which are characterized by 10 A manganate but are chemi cally the intermediate between the two types, show Ce anomalies of log(Ce/Ce*) = +0.3 in the middle of the two end members. Interestingly, the Ce anomalies of the nodules vary coherently with their logarith mic Co/(Ni+Cu) ratios. This positive correlation is valid even after combing many literature data of Pa cific nodules with our data. In the plot of Ce anomaly vs. log[Co/(Ni+Cu)], the three distinct types of Pacific nodules are systematically distinguished: "sub oxic-diagenetis" <_ "diagenetic" <_ "hydrogenous". The systematics strongly suggest that: (i) the Ce anomaly and log[Co/(Ni+Cu)] are similar geochemical indexes showing how effectively oxidative uptake of Ce and Co occurred in each nodule relative to non oxidative uptake of nutrient-type metals in the respective metal groups, and (ii) there exists an initial source supplying metals common to all the types of Pacific nodules. We inferred from various reasons that the common initial source is biogenic particulates delivered from overlying surface water. Oxidative up take of Ce and Co by fast sinking large biogenic particulates is less effective, but such particulates can more effectively convey nutrient-type metals involved with them to the sea floor because of their shorter residence time in oxic water. However, the relationship between metal transports of scavenged and nutri ent-type elements is reversed in the case of slowly sinking biogenic particulates. High surface productiv ity inevitably provides high flux of fast sinking large organic particulates, whereas low productivity gives rise to organic particulate flux dominated by slowly sinking small ones. These mechanisms explain the observed systematics of Ce anomaly vs. log[Co/(Ni+Cu)] plots for Pacific nodules.

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

“…Although the experimental data to allow extraction of this information doesn't yet exist it is possible to comment that whilst Ce 4+ is generally extremely low in natural melt compositions it is enhanced at high fO 2 , in alkaline melts, at low temperatures and possibly with increasing pressures (Burnham and Berry, Thomson et al revision 1 submitted 19/08/2015 16 2014). Therefore it is possible that near solidus MORB melts, which are alkaline carbonatites generated at relatively low temperatures (Thomson et al, 2016) (Ohta et al, 1999). These anomalies are associated with the complexation of yttrium in hydrous fluids/melts (Bau, 1999;1996).…”

Rare earth element partitioning between Fe oxyhydroxide precipitates and aqueous NaCl solutions doped with NaHCO3: Determinations of rare earth element complexation constants with carbonate ions.

“…Rare earth elements (REEs) are highly enriched in marine ferromanganese nodules (Piper, 1974;Elderfield et al, 1981;Ohta et al, 1999) and ferromanganese crusts (De Carlo and McMurtry, 1992;Bau et al, 1996). The removal of REE by Fe-Mn oxyhydroxides from seawater into marine suspending particles and sediments is an important geochemical process.…”

Geochemical fractionation of rare earth elements in lacustrine deposits from Qaidam Basin

“…It was found that Fe-Mn oxides, such as deep-sea iron-manganese nodules, could lead to the enrichment of REE [22,23] . A comparison of the ΣREE concentration of AS to corresponding Rb/Sr values and contents of Mn and CaCO 3 showed a strong correlation between each other but with varying coefficients (Figure 7).…”