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Fe(III) hydroxides stabilize organic carbon (OC) and P in soils. Observations of rising stream Fe concentrations are controversially posited to result from a flushing of iron‐rich deeper soil layers or a decrease of competing electron acceptors inhibiting Fe reduction (NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ and SO42− $\mathrm{S}{{\mathrm{O}}_{4}}^{2-}$). Here, we argue that catchment topography constrains the release of Fe, OC, and P to streams. We therefore incubated organic topsoil and mineral subsoil and modified the availability of NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$. We found that Fe leaching was highest in topsoil. Fe, OC, and P released at quantities proportional to their ratios in the source soil. Supply of NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ reduced Fe leaching to 18% and increased pore water OC:Fe and P:Fe ratios. Subsoil, however, was an insignificant Fe source (, Plain Language Summary: Iron is the second most abundant metal in the crust; its cycle is tightly connected to those of carbon, oxygen, and sulfur. The oxidized form (FeIII) is almost insoluble, but Fe can be mobilized by complexation or microbial Fe reduction. Both processes depend on availability of organic C. We found that Fe concentrations in streams were constrained by the topography of catchments and NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ abundance. Shallower catchments are characterized by higher groundwater tables connecting the organic topsoils efficiently to streams. NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ suppresses Fe reduction as a competing electron acceptor to Fe. We conclude that trends in soil wetness or atmospheric N deposition can change the stability of Fe and thus the release of PO43− $\mathrm{P}{{\mathrm{O}}_{4}}^{3-}$ and harmful metals to surface waters., Key Points: Organic topsoils leach substantial amounts of Fe when incubated in the absence of NO3, a competing electron acceptor that inhibits Fe reduction. Shallow catchments with fluvially coupled topsoils and low NO3 availability release 200 fold more Fe than steep ones with high NO3 abundance. Catchment topography and NO3 availability explain 62%–64% of the variability of Fe concentration and OC:Fe and P:Fe ratios across 88 streams., EFRE‐Europe, https://doi.org/10.4211/hs.43601618877945c5a46b715aa98db729

An electrum–quartz pebble with a weight of 10.4 g was discovered in a cliff of Saalian glaciogenic sediments on the west coast of the German North Sea island of Sylt in 2012. It has a roundish water-worn appearance and consists of intergrown electrum and milky quartz. It is the largest known electrum find in Germany, and regarding its weight it also ranks amongst the largest gold finds discovered in Germany. We document and characterize this unusual discovery. Furthermore, an attempt is made to investigate its provenance. Therefore, reference samples of southern Scandinavian gold and electrum deposits and occurrences have been studied and compared to the Sylt find. The Au–Ag content determined by electron microprobe (EMP), trace element signature measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and Pb isotope compositions by multi-collector ICP MS (MC-ICP-MS) suggest a southern Norwegian origin. The most probable source might be the Kongsberg ore district or an adjacent, yet undiscovered, mineralization in the Oslo region. In general, Saalian glaciogenic sediments in Schleswig-Holstein (northern Germany) are dominated by rocks of Swedish provenance. Due to the intake of older Elsterian sediments by younger Saalian glaciers, southern Norwegian rocks are also not uncommon in Saalian sediments. A Saalian ice advance or a combination of Elsterian and Saalian ice advances might have provided a transport mechanism for an electrum sample from a south Norwegian mineralization to the island of Sylt.

The economically important platinum-group elements (PGE) are known to be mobile in the surface weathering environment, but their mobility in the presence of soil organic matter under surficial conditions has been poorly constrained so far. In this paper, the behavior of synthetic platinum-group minerals (PGM) placed in solutions containing humic acids is described. In order to approximate the natural weathering environment in the area of the Bushveld Igneous Complex, South Africa, humic acid solutions were prepared at concentrations of 0.1, 1, and 10 mg/l, and allowed to react with synthetic palladium monotelluride (PdTe), palladium ditelluride (PdTe2), palladium sulfide (PdS) and platinum disulfide (PtS2). The solutions remained stationary for a period of up to 306–308 days, with aliquots being taken at various intervals. The solutions were then analyzed by inductively coupled plasma mass spectrometry (ICP-MS). With both telluride minerals, Pd was not mobilized above concentrations of about 4 μg/l, but tellurium proved to be more mobile, reaching concentrations of several thousand μg/l. In these experiments, tellurium oxide crystals formed on the substrate of the humic-acid leached palladium tellurides. The palladium content of the initial palladium tellurides increased relative to tellurium, possibly approximating the structure of extant naturally forming palladium telluride minerals. The PdS and PtS2 solutions appear to have undergone hydrolysis of sulfur, producing sulfurous/sulfuric acid, which lowered the pH of these solutions from 7 to 8 to about 3. Due to this lowering of the pH, Pt was observed to precipitate out of solution between days 50–150. Meanwhile, Pd steadily increased in the 10 mg/l humic acid solution, reaching a final value of 162 μg/l. The increase in Pd in this solution matches a linear equation of y = 0.5× + 4.9, where x = time in days and y = concentration of Pd in μg/l, corresponding to a rate of mobilization for Pd of 0.5 μg/l per day.

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials that provide crucial information about the isotopic reservoirs present in the early Solar System. For a variety of elements, CAIs have isotope compositions that are uniform yet distinct from later formed solid material. However, despite being the most abundant metal in the Solar System, the isotopic composition of Fe in CAIs is not well constrained. In an attempt to determine the Fe isotopic compositions of CAIs, we combine extensive work from a previously studied CAI sample set with new isotopic work characterizing mass-dependent and mass-independent (nucleosynthetic) signatures in Mg, Ca, and Fe. This investigation includes work on three mineral separates of the Allende CAI Egg 2. For all isotope systems investigated, we find that in general, fine-grained CAIs exhibit light mass-dependent isotopic signatures relative to terrestrial standards, whereas igneous CAIs have heavier isotopic compositions relative to the fine-grained CAIs. Importantly, the mass-dependent Fe isotope signatures of bulk CAIs show a range of both light (fine-grained CAIs) and heavy (igneous CAIs) isotopic signatures relative to bulk chondrites, suggesting that Fe isotope signatures in CAIs largely derive from mass fractionation events such as condensation and evaporation occurring in the nebula. Such signatures show that a significant portion of the secondary alteration experienced by CAIs, particularly prevalent in fine-grained inclusions, occurred in the nebula prior to accretion into their respective parent bodies. Regarding nucleosynthetic Fe isotope signatures, we do not observe any variation outside of analytical uncertainty in bulk CAIs compared to terrestrial standards. In contrast, all three Egg 2 mineral separates display resolved mass-independent excesses in (56)Fe compared to terrestrial standards. Furthermore, we find that the combined mass-dependent and nucleosynthetic Fe isotopic compositions of the Egg 2 mineral separates are well correlated, likely indicating that Fe indigenous to the CAI is mixed with less anomalous Fe, presumably from the solar nebula. Thus, these reported nucleosynthetic anomalies may point in the direction of the original Fe isotope composition of the CAI-forming region, but they likely only provide a minimum isotopic difference between the original mass-independent Fe isotopic composition of CAIs and that of later formed solids.

The invention of photosynthesis was a key interval in Earth’s history, initiating major changes in the evolution of the oceans and atmosphere. Many studies suggest that oxygen levels were already enhanced before the Paleoproterozoic Great Oxidation Event (GOE, 2.45 to 2.32 Ga). However, the timing of the onset of photosynthetic oxygenation, as well as spatio-temporal fluctuations of atmospheric and oceanic oxygen levels are highly debated. Here, we present a new and substantial uranium (U) isotope dataset comprising marine sediments, e.g. black shales, carbonates and iron-rich sedimentary rocks, from the Hamersley Basin (Western Australia), Kaapvaal and Zimbabwe Cratons (both southern Africa) with depositional ages ranging from 3.4 to 2.2 Ga. Sub-recent U mobilization was monitored by analyzing 234U along with δ238U, and detrital U contribution was monitored with [Al]/[U] or [Th]/[U] ratios. Samples with significant authigenic U enrichment (EFU > 2), relative to post-Archean Australian Shale (PAAS), exhibit authigenic δ238U ranging from –0.96 to –0.02 ‰ (± 0.05 ‰, 2 s.d. long-term reproducibility), which deviates markedly from typical δ238U of the continental crust (-0.40 to –0.20 ‰). Remarkably, we find increased δ238U variability in the upper Ghaap Group (2.50 – 2.47 Ga, carbonates and black shales) and the lower Pretoria Group (2.42 – 2.32 Ga, Duitschland Formation, shales) of the Kaapvaal Craton. The predominantly light U isotope composition of those samples is likely explained by U isotope fractionation related to the onset of partial U mobilization during slow oxidative weathering of uraninite shortly before and during the GOE. The lack of low δ238U values in the Timeball Hill Formation (overlying the Duitschland Formation) indicate the onset of quantitative U mobilization during (modern-style) oxidative weathering of uraninite and other U-bearing minerals with limited U isotope fractionation. These limited U isotope variations measured in the Paleoproterozoic Timeball Hill Formation further suggest that, in contrast to modern oceans, in the period following the GOE, U was largely quantitatively reduced and removed from the water column of the Transvaal basin which remained mainly anoxic at depth.

The Kane Megamullion oceanic core complex located along the Mid-Atlantic Ridge (23°30′N, 45°20′W) exposes lower crust and upper mantle directly on the ocean floor. We studied chalcophile elements and sulfides in the ultramafic and mafic rocks of the crust-mantle transition and the mantle underneath. We determined mineralogical and elemental composition and the Cu isotope composition of the respective sulfides along with the mineralogical and elemental composition of the respective serpentines. The rocks of the crust-mantle transition zone (i.e., plagioclase harzburgite, peridotite-gabbro contacts, and dunite) overlaid by troctolites are by one order of magnitude enriched in several chalcophile elements with respect to the spinel harzburgites of the mantle beneath. Whereas the range of Cu concentrations in spinel harzburgites is 7–69 ppm, the Cu concentrations are highly elevated in plagioclase harzburgites with a range of 90–209 ppm. The zones of the peridotite-gabbro contacts are even more enriched, exhibiting up to 305 ppm Cu and highly elevated concentrations of As, Zn, Ga, Sb and Tl. High Cu concentrations show pronounced correlation with bulk S concentrations at the crust-mantle transition zone implying an enrichment process in this horizon of the oceanic lithosphere. We interpret this enrichment as related to melt-mantle reaction, which is extensive in crust-mantle transition zones. In spite of the ubiquitous serpentinization of primary rocks, we found magmatic chalcopyrites [CuFeS2] as inclusions in plagioclase as well as associated with pentlandite [(Fe,Ni)9S8] and pyrrhotite [Fe1−xS] in polysulfide grains. These chalcopyrites show a primary magmatic δ65Cu signature ranging from −0.04 to +0.29 ‰. Other chalcopyrites have been dissolved during serpentinization. Due to the low temperature (

The strong dependence of vanadium partitioning between olivine and silicate melt (DVOl-M) on redox conditions (fO2) can be used as sensitive oxybarometer in magmatic systems. Here we extend the experimental database on DVOl-M, obtained so far at high temperatures (mainly above 1250 °C), to lower temperatures that are typical for island-arc basalts. Crystallization experiments were performed using a composition from Mutnovsky volcano (Kamchatka), and the investigated temperature, pressure, and oxygen fugacity ranges were 1025–1150 °C, 0.1 and 0.3 GPa, and ΔQFM of –0.5 to +3.2, respectively. The water content in melts ranged from 0.6 to ∼6.5 wt% H2O. The data demonstrate a strong negative correlation between DVOl-M and oxygen fugacity, similar to the behavior observed previously at higher temperatures and in MgO-rich compositions. The correlation between DVOl-M and ΔQFM in the range from –0.5 to +3.2 is described for melts with MgO < 12 wt% and Na2O < 4 wt% at temperatures ≤1250 °C by the empirical equation: ΔQFM = −3.07−0.29+0.26 logDVOl-M – 3.34−0.49+0.40 with the standard error (SE) as a function of logDVOl-M: 2SE(ΔQFM) = –0.275logDVOl-M + 0.4. We suggest that this equation can be used as an oxybarometer, which is particularly well applicable to the hydrous island-arc magmas at relatively low temperature. Application of the equation to the composition of melt inclusions and their host olivine phenocrysts from basalts of Mutnovsky volcano, containing vanadium concentrations in the range of 250–370 and 4–6 ppm, respectively, reveals an oxygen fugacity in the range ΔQFM +1.9 to +2.3. The estimates are in a good agreement with olivine-spinel oxybarometry for Mutnovsky basalts and may be typical for moderately evolved island-arc magmas.

Many floodplain soils worldwide are contaminated by present and past industrial and mining activities. During flooding redox potential decreases, triggering the release of dissolved and colloidal metals. We used an anaerobic microcosm incubation to simulate flooding of a carbonate-rich floodplain soil for 40 days. Soil solution samples were extracted to determine the release of dissolved (< 0.02 μm) and colloidal fractions (0.02–10 μm). We analyzed stable isotope ratios of colloidal and dissolved Fe and Cu representing two groups of metals with different release behavior; release of Fe was steadily increasing, while that of Cu peaked sharply after flooding and decreased afterwards. The temporal trend of δ56Fe values of total Fe in solution indicated dissimilatory iron reduction. The apparent isotopic fractionation between dissolved and colloidal Fe (Δ56Fedissolved-colloidal = δ56Fedissolved − δ56Fecolloidal) varied from 0.31 ± 0.04‰ to − 1.86 ± 0.26‰. Low δ56Fecolloidal (− 1.16 ± 0.04‰) values on day 4 of the experiment suggested colloid formation by precipitation of dissolved Fe, while the strong temporal variation in Δ56Fedissolved-colloidal indicated subsequent changes in colloid mineralogy, sorption to soil components and/or electron transfer-atom exchange. The variations in δ65Cu values (Δ65Cudissolved-colloidal from 0.81 ± 0.03‰ to 1.58 ± 0.09‰) are probably linked to the changing oxidation state of colloidal Cu. While at the beginning of the experiment colloidal Cu and solid soil Cu exchange, these systems decouple after the onset of sulfate reduction in the second half of the experiment. The experimental results fit well to findings from redoximorphic soils described in the literature and highlight the importance of colloids for metal release and the isotopic pattern in carbonatic soils.

Vanadium is a redox-sensitive trace metal that occurs in nature as V II , V III , V IV , and V V , e.g. in a variety of ore-forming minerals like vanadates (hosting V V ), sulfides (e.g., patronite: V IV? S 4 ), silicates (e.g., roscoelite, hosting V III ; cavansite, hosting V IV ), and phosphates (e.g., sincosite, hosting V IV ). Similar to other redox-sensitive metals (e.g., Fe, Cu, U), the V isotope compositions of V minerals may provide valuable information for source fingerprinting and redox-controlled processes during ore formation. The first in situ V isotope analyses of several natural V minerals (cavansite, descloizite, patronite, sincosite, vanadinite) were performed in this study employing femtosecond-laser ablation-high resolution-MC-ICP-MS. The δ 51 V values are determined relative to a V metal (Alfa Aesar, 99.5% V) via standard-sample-standard bracketing, and are recast to the Oxford Alfa Aesar solution value. Mass bias was monitored by addition of an Fe standard to the sample aerosol during analyses. For comparison, aliquots of all mineral specimens were analyzed after chromatographic separation by solution-nebulization MC-ICP-MS. Our laser ablation and solution typically data agree well with each other (within 0.1‰ units), and indicate a significant variation of δ 51 V values between the analyzed minerals, ranging from − 0.5 to + 1.3‰ (2 s.e. per analysis typically between 0.04 and 0.06‰). This spread is significantly larger than reported for various reference rocks, and also exceeds the difference for δ 51 V between the bulk silicate Earth and the chondrite average. The extended range of δ 51 V values demonstrates that stable V isotope analyses may provide a new proxy for redox-processes in high- and low-temperature studies, including the fingerprinting of redox-induced V mobilization and enrichment processes during the formation of V-rich ores.

Investigation of redox variations in recent and paleo-oceans has been of particular scientific interest to elucidate the rise and variations of the atmospheric oxygen level by analyses of isotopic signatures of redox-sensitive elements like Fe, Mo, and U. Vanadium is another redox-sensitive metal that has become the target of stable isotope research during the last decade. Research of the oceanic V cycle revealed a rather complex interplay of riverine V as a major V source to the oceans on one side with V deposition in sediments and at hydrothermal vents as major sinks on the other. The balance between these major V pools is sensitive to the ocean water oxygen level and chemistry. The current data set of stable V isotope signatures of seawater is still very small, but indicates already subtle variation of the V isotope signatures in the marine environment. However, the V isotopes of marine sediments and particularly the riverine V isotope composition of dissolved and particulate V, i.e. the major source of V in modern marine environments, has not been constrained at all so far. In this study, we present a new method for efficient V separation from seawater that allows multiple analyses of the V isotope composition of a single sample. To separate V from large amounts (volume ≥2 L) of seawater samples, we employ the Bio-Rad® Chelex-100 resin and conventional cation and anion resins to yield a high V recovery of ≥90% from an UV-irradiated sample. Non-irradiated samples were marked by lower V recovery rates of ca. 75%, which was also observed in earlier studies. Further tests however revealed that even such reduced V yields do not incur significant V isotope fractionation within analytical uncertainty. Our δ51VAA value of +0.27‰ ±0.14 (2s.d., n = 3) for the NASS-6 seawater reference solution perfectly matched earlier results. In addition, seawater collected in the Wadden Sea at the German North Sea coast is marked by a δ51VAA signature of around +0.02‰ ±0.19 (2s.d., n = 17), which is slightly lower than those of the great oceans, and may be related to an influx of river water, bioactivity, or a tide-induced V mobilization. To characterize the V isotope composition of the major V source to the oceans, we determined for the first time V isotope signatures of 13 selected rivers (dissolved and particulate fractions of source water, tributary rivers, and the Yangtze River) in the Yangtze River Basin, China. A large variation of dissolved V (ca. 0.07 to 6.0 μg/L) and particulate-bound V (ca. 0.03 to 17 μg/L) was found for the sample suite. The obtained δ51VAA values of the dissolved V pool span a range of −0.76‰ (±0.18; 2s.d.) to −0.10‰ (±0.22, 2s.d.), whereas particulate-bound V extends to lower δ51V signatures between −2.13‰ (±0.30, 2s.d.) and −0.11‰ (±0.11, 2s.d.). Notably, dissolved V from the river sources and small tributaries scatters between ca. −0.4‰ to −0.7‰, and agrees well with the predicted average δ51VAA value of −0.6‰ ±0.3 for continental run-off. For the lower Yangtze River, however, the dissolved δ51VAA signatures increase from the Three-Gorges Dam towards the estuary from −0.76‰ to −0.10‰, suggesting V isotope fractionation due to adsorption to abundant particulate Fe oxides, but may also reflect an input of anthropogenic V. The low δ51VAA of particulate V largely follow this trend, and thus indicate ongoing V isotope fractionation during riverine V transport to the ocean. Our first results of stable V isotope investigation of river waters show that V isotope signatures can indeed carry their host rock signature, but are also sensitive to adsorption-driven fractionation in oxidized environments. The latter strongly depends, as predicted from earlier theoretical calculations, on the presence of particulate Fe-(oxyhydr)oxides and highlights gradual V isotope fractionation during riverine V transport to the ocean.

Dark brown sediment layers are a potential stratigraphic tool in Quaternary Arctic Ocean sediments. They are rich in Mn, Fe, and trace metals scavenged from the water column and were most likely deposited during interglacial intervals. In this study, we combine sediment and pore water data from sediment cores taken in different parts of the Arctic Ocean to investigate the influence of early diagenetic processes on sediment geochemistry. In most studied cores, Mn, Co, and Mo are released into the pore waters from Mn oxide dissolution in deeper (>1.5 m) sediment layers. The relationship between sedimentary Mn, Co, and Mo contents in excess of the lithogenic background (elementxs) shows thatCoxs/Moxs values are a diagnostic tool to distinguish between layers with diagenetic metal addition from the pore waters (Coxs/Moxs 10), and unaffected layers (Coxs/Moxs from 1 to 10). Steady-state calculations based on current pore water profiles reveal that in the studied cores, the diagenetic addition of these metals from the pore water pool alone is not sufficient to produce the sedimentary metal enrichments. However, it seems evident that dissolution of Mn oxides in the Mn reduction zone can permanently alter the primary geochemical signature of the dark brown layers. Therefore, pore water data and Coxs/Moxs values should be considered before core correlation when this correlation is solely based on Mn contents and dark sediment color. In contrast to the mostly nonlithogenic origin of Mn in the dark brown layers, sedimentary Fe consists of a large lithogenic (80%) and a small non-lithogenic fraction (20%). Our pore water data show that diagenetic Fe remobilization is not currently occurring in the sediment. The dominant Fe sources are coastal erosion and river input. Budget calculations show that Fe seems to be trapped in the modern Arctic Ocean and accumulates in shelf and basin sediments. The Fe isotopic signal δ56Fe of the solid phase is positive (~0.2 to 0.3‰) in samples defined as the lithogenic background without significant Fe enrichments. With increasing non-lithogenic Fe contents in the sediment, δ56Fe becomes more negative, which indicates a shelf-to-basin export of an isotopically lighter Fe fraction. We assume that the same transport process is true for Mn.

In this study, we applied high-precision in situ Fe and Mg isotope analyses by femtosecond laser ablation (fs-LA) MC-ICP-MS on chemically zoned olivine xeno- and phenocrysts from intra-plate volcanic regions in order to investigate the magnitude of Fe and Mg isotope fractionation and its suitability to gain information on magma evolution. Our results show that chemical zoning (i.e., Mg#) in magmatic olivines is commonly associated with significant zoning in δ56Fe and δ26Mg (up to 1.7‰ and 0.7‰, respectively). We explored different cases of kinetic fractionation of Fe and Mg isotopes by modeling diffusion in the melt or olivine and simultaneous growth or dissolution. Combining the information of chemical and isotopic zoning in olivine allows to distinguish between various processes that may occur during magma evolution, namely diffusive Fe–Mg exchange between olivine and melt, rapid crystal growth, and Fe–Mg inter-diffusion simultaneous to crystal dissolution or growth. Chemical diffusion in olivine appears to be the dominant process that drives isotope fractionation in magmatic olivine. Simplified modeling of Fe and Mg diffusion is suitable to reproduce both the chemical and the isotopic zoning in most of the investigated olivines and, additionally, provides time information about magmatic processes. For the Massif Central (France), modeling of diffusive re-equilibration of mantle olivines in basanites revealed a short time span (

Redox conditions control the release of iron (Fe) into soil pore waters. A fluctuating groundwater table in soils results in significant changes in redox conditions with both time and depth. The effects of short-term differences in redox conditions on the stable isotope inventory of dissolved Fe in such soils have not yet been studied. Bulk Fe isotope compositions of a Gleysol yielded δ57Fe values from + 0.3‰ (humic topsoil, Ah horizon) to − 0.2‰ (Fe-enriched subsoil, CrBg horizon). In microcosm experiments, soil suspensions of the Ah and CrBg horizons were subjected to controlled redox conditions ranging from high redox potential (EH) (> 430 mV, pH 5.1 to 5.6), moderate EH (~ 330 mV, pH 4.9 to 5.9), to low EH (≤ 170 mV, pH 5.2 to 6.7). Membrane-filtered (0.45 μm) solutions taken from the suspensions were analysed for their Fe concentrations (Fe2 +, and total Fe: Fetot) and isotopic compositions. The microcosm experiments demonstrated that the ferrihydrite- and organic-rich Ah horizon is a highly dynamic and rapidly responding reservoir with respect to Fe mobilization and isotopic fractionation at low EH. Iron concentrations and isotope ratios of the solutions from the Ah horizon varied depending on EH with negative δ57Fe values (− 0.4‰) and Fetot (~ 1.6 mg L− 1) at moderate EH, and even lower δ57Fe values (− 1.1‰) but high Fetot (~ 7.8 mg L− 1) at low EH. At high EH, δ57Fe values slowly increased from + 0.3‰ to + 1.0‰ and Fetot decreased to ~ 0.2 mg L− 1 within six weeks. The goethite-rich CrBg horizon constitutes a stable redox-insensitive pool with very low amounts of mobilized Fe and a small degree of isotopic fractionation, even after exposure to low EH over several weeks. In a natural open system, removal of Fe from the dynamic Ah horizon will result in progressively higher soil δ57Fe values due to preferential release of 54Fe. Vertical movement of a low-δ57Fe solution from the topsoil may result with time in the formation of a subsoil with δ57Fe values that are lower than the topsoil after repeated low and high EH cycles. At high EH, Fe mobility in the Ah horizon is much lowered, but release of Fe with high δ57Fe values is in agreement with earlier studies for the formation of Fe pools (Fe oxides, colloids, organic complexes) with high δ57Fe signatures.

In this study, a technique for high precision in situ Fe and Mg isotope determinations by femtosecond-laser ablation-multi collector-ICP-MS (fs-LA-MC-ICP-MS) was developed. This technique was employed to determine reference values for a series of common reference glasses that may be used for external standardisation of in situ Fe and Mg isotope determinations in silicates. The analysed glasses are part of the MPI-DING and United States Geological Survey (USGS) reference glass series, consisting of basaltic (BIR-1G, BCR-2G, BHVO-2G, KL2-G, ML3B-G) and komatiitic (GOR128-G and GOR132-G) compositions. Their Fe and Mg isotope compositions were determined by in situ fs-LA-MC-ICP-MS and by conventional solution nebulisation multi-collector ICP-MS. We determined δ56Fe values for these glasses ranging between -0.04‰ and 0.10‰ (relative to IRMM-014) and δ26Mg values ranging between -0.40‰ and -0.15‰ (relative to DSM-3). Our fs-LA-MC-ICP-MS results for both Fe and Mg isotope compositions agreed with solution nebulisation analyses within analytical uncertainties. Furthermore, the results of three USGS reference glasses (BIR-1G, BHVO-2G and BCR-2G) agreed with previous results for powdered and dissolved aliquots of the same reference materials. Measurement reproducibilities of the in situ determinations of δ56Fe and δ26Mg values were usually better than 0.12‰ and 0.13‰ (2s), respectively. We further demonstrate that our technique is a suitable tool to resolve isotopic zoning in chemically-zoned olivine crystals. It may be used for a variety of different applications on isotopically-zoned minerals, e.g., in magmatic or metamorphic rocks or meteorites, to unravel their formation or cooling rates. Dans cette etude, une technique pour la determination in situ avec une haute precision des isotopes du Fe et du Mg par ablation laser femtoseconde multi-collecteur-ICP-MS (fs-LA-MC-ICP-MS) a ete developpee. Cette technique a ete employee pour determiner les valeurs de reference pour une serie de verres communs de reference qui peuvent etre utilises comme materiaux de reference pour la determination in situ des isotopes du Fe et du Mg dans les silicates. Les verres analyses font partie des series de verres de reference MPI-DING et USGS et ils correspondent a des compositions basaltiques (BIR-1G, BCR-2G, BHVO-2G, KL2-G, ML3B-G) et komatiitiques (GOR128-G et GOR132- G). Leurs compositions isotopiques du Fe et du Mg ont ete determinees par la methode in situ fs-LA-MC-ICP-MS et par celle classique de nebulisation de solution multi-collecteur ICP-MS. Nous avons determine les valeurs δ56Fe pour ces verres qui sont comprises entre −0.04‰ et 0.10‰ (par rapport a IRMM-014) et les valeurs de δ26Mg qui varient entre −0.40‰ et −0.15‰ (par rapport au DSM-3). Nos resultats fs-LA-MC-ICP-MS pour les compositions isotopiques du Fe et du Mg sont en accord avec les analyses par nebulisation de solutions dans les limites des incertitudes analytiques. En outre, les resultats pour trois verres de reference USGS (BIR-1G, BHVO-2G et BCR-2G) sont en accord avec les resultats anterieurs obtenus a partir d'aliquotes des memes materiaux de reference reduits en poudre et dissous. Les reproductibilites des mesures in situ des valeurs de δ56Fe et δ26Mg etaient en general et respectivement meilleures que 0.12‰ et 0.13‰ (2s). Nous demontrons egalement que notre technique est un outil approprie pour etudier le zonage isotopique dans les cristaux d'olivine chimiquement zones. Il peut etre utilise pour une variete d'applications differentes sur les mineraux isotopiquement zones, par exemple, dans les roches magmatiques ou metamorphiques ou dans les meteorites, afin de mieux comprendre leur formation ou d'apprehender les taux de refroidissement qu'elles ont subies.

To understand the impact of dissolved water on structure and properties, four boron-rich glasses of molar compositions 15-x Na2O x CaO 15 SiO2 70 B2O3 (with x = 0, 7.5, 10) and 10 Na2O 15 SiO2 75 B2O3 were prepared and subsequently hydrated (up to 8 wt% H2O). Density measurements show a non-linear trend upon hydration implying large structural changes in particular at water contents 2 wt%. 11B MAS NMR spectra show that the abundance of BO4 species is mainly controlled by ratio of (Na2O + CaO)/B2O3 while incorporation of water plays a minor role. Compared to borate glasses, the efficiency of formation of BO4 tetrahedra is favored by crosslinking of the network by SiO4-units. The glass transition temperatures, determined by differential thermal analysis, decreases continuously with water content due to breakage of B-O-B bonds by hydrolysis. However, compared to silicates and aluminosilicates, the effect of dissolved water is less pronounced which can be explained by weaker B-O-B bonds in comparison to Si-O-Si bonds.

The central region of the Neoarchaean Belomorian Mobile Belt (BMB) is, except for the Solovetsky Archipelago, largely covered by the White Sea. A newly discovered granitic gneiss outcrop on Solovetsky Island, Russia, enables a first age determination of the archipelago and evaluation of the hitherto poorly constrained central BMB. Zircons separated from the orthogneiss were analysed with SIMS-SHRIMP and LA-ICP-MS techniques. Both techniques yield a concordant U-Pb age of ca. 2.430 Ga, coinciding with ages of granitic intrusions in the BMB ca. 50 km west of the Solovetsky Islands.

Potassium-enriched mafic lavas, and in particular basalts of the high-K series, are important end-members of subduction zone volcanism. Two petrogenetic models can explain the generation of mafic K-rich lavas, involving either melting of ancient, enriched lithospheric mantle sources (single-stage model) or melting triggered by recent refertilization by subduction-related components derived from subducted sediments or oceanic crust (multi-stage model). These two models are tested for post-collisional high-K rocks of Eocene-Oligocene age from the Rhodopes, SE Bulgaria, based on new major element, trace element and Sr-Nd-Hf-Pb isotope data. The single-stage model is evaluated by Sr-Nd isotope modelling assuming the presence of ancient enriched lithospheric domains whereas the multi-stage model is assessed by comparing the compositions of the Bulgarian lavas with those of lavas from Santorini. Santorini lavas are considered to sample the current trace element and isotope inventory of the long-lived Aegean subduction zone system. This northward facing system has been active most probably since late Jurassic or early Cretaceous times and was potentially involved in refertilizing the mantle sources of the Bulgarian lavas. In addition to the data for Bulgarian lavas, we present new major element, trace element and Sr-Nd-Hf-Pb isotope data for Santorini. These are evaluated together with previously published data to infer the mode of source enrichment in the Aegean realm. The Bulgarian lavas exhibit a broad range of compositions from medium-K to high-K and shoshonitic with radiogenic Sr-87/Sr-86 (0.706-0.709), and unradiogenic epsilon Nd (-5.7 to -1.9) and epsilon Hf (-3 to +3) isotope signatures. The trace element budget was apparently well buffered against shallow-level crustal assimilation as documented by the trace element and Sr-Nd isotope systematics. Modelling of the Sr-Nd isotope compositions of the Bulgarian lavas argues for recent (Mesozoic to Cenozoic) source enrichment. Therefore single-stage models involving melting of ancient (>1 Ga) lithospheric mantle can be confidently ruled out, in agreement with tectonic models for the region. The enriched isotope signatures, together with a pronounced enrichment of incompatible elements, rather indicate mantle refertilization by a subduction component similar to continent-derived sediments subducted at the Hellenic Trench at present. The Bulgarian lavas record a predominant influx of subduction fluid components in comparison with the Santorini lavas. Collectively, the data presented for the Bulgarian lavas are clearly in favour of a multi-stage model.

This study presents high-precision Pb isotope data obtained by MC-ICP-MS for lavas from the Solomon island arc that covers ca. 1000 km of the SW Pacific plate boundary. Following a reversal of subduction polarity, the presence of the old subducted Pacific oceanic crust, and the presently subducting Indian–Australian plate beneath the entire island arc is confirmed by geophysical and geochemical evidence. New high-precision Pb isotope data now permit to distinguish more clearly between Indian and Pacific-type subduction components in this complex plate tectonic constellation. The values range from 206Pb/204Pb = 18.345 to 18.845, 207Pb/204Pb = 15.498 to 15.545, and 208Pb/204Pb = 38.120 to 38.372, indicating the absence of pelagic sediments in the sub-arc mantle. These data reveal a predominance of subduction components derived from ancient subduction of the Pacific plate. In contrast, lavas with Indian-type Pb isotope signatures are confined to the central New Georgia Group of the Solomon Islands, where the young Woodlark Ridge spreading centre is currently subducting. All other Solomon arc segments with a lower geothermal gradient have apparently not yet been overprinted by younger subduction components over the past 6 Myrs. Moreover, trace element and Pb isotope data for Woodlark Ridge basalts show that subduction components from the fossil Pacific slab have locally modified the source of Woodlark Basin lavas. Altogether, our study highlights the potential of high-resolution Pb isotope measurements to distinguish between Indian and Pacific-type subduction components along the SW Pacific plate boundary.

Purpose Properties of Fe oxides are poorly understood in soils with fluctuating water tables and variable redox conditions. The objective of this research was to (a) characterize the mineralogical composition of Fe oxides and (b) determine the relationship to the stable Fe isotope ratio in a soil with temporally and spatially sharp redox gradients.

A flue dust originaly enriched in metal sulfides evolved as a by-product of Cu smelting. The dust was deposited as slurry in unsealed heaps. It is characterized by very high contents of toxic metals such as Pb and Zn. The slurry is a source of soil, sediment, and water contamination. We studied a Technosol profile developed from deposited flue-dust slurry by means of chemical and mineralogical characterization (SEM-EDX, XRD, FTIR, DTA-MS, XRF, Pb isotopes), by open-flow and closed-flow column experiments on contaminant release under water-saturated conditions, and by geochemical modeling to evaluate release processes and to quantify aqueous contaminant concentrations. Besides ash particles and quartz, the flue-dust slurry contains Fe oxides, silicates, sulfates, and sulfides (in varying states of weathering). In both column approaches, metal concentrations exceed inspection values. The concentration patterns in both experimental column approaches indicate near-equilibrium mineral dissolution. Geochemical modeling reveals partial dissolution of sulfates and precipitation of secondary carbonates. Their precipitation prevents complete sulfate dissolution, which would have led to even higher aqueous metal concentrations and contaminant export. The combination of detailed material characterization, column experiments, and modeling allows for quantitative and qualitative estimation of contaminant release into the soil solution.

Niobium–tantalum systematics of slab-derived melts are powerful tracers that discriminate residual high-pressure rutile-bearing eclogite from low-pressure garnet-bearing amphibolite in subducting plates. Previously reported low Nb–Ta ratios in modern slab melts suggested a predominance of shallow melting in the presence of residual amphibole and that deep melting of rutile-bearing eclogitic slabs, devoid of residual amphibole, is volumetrically insignificant. This study evaluates Nb/Ta in combination with other trace element systematics of modern intra-oceanic and slab melt-related arc lavas from the south-western volcanic chain of the Solomon Islands that cover over 1000 km of the SW Pacific plate border. After a change of subduction polarity, an old subducted Pacific slab and a recently subducting Indian–Australian slab are both present beneath the arc. Solomon arc lavas show sub- to superchondritic Nb–Ta ratios (ca. 10 to 27) which is the largest range ever reported in modern island arc lavas. The large range of Nb/Ta likely results from enrichment of the depleted sub-arc mantle by two distinct slab-derived melts in addition to fluids. One minor slab melt component is derived from the shallow and recent subducting Indian–Australian plate where amphibole is still a significant residual phase. The second slab melt component is predominant in Solomon arc lavas and can be attributed to deep rutile–eclogite-controlled melting of old subducted Jurassic Pacific oceanic crust where residual amphibole is entirely absent or insignificant. The deep Pacific slab melt component is the most likely origin of the extremely high and superchondritic Nb/Ta signatures that produce the upper half of the observed range of Nb/Ta in Solomon arc lavas. The slab melt component that enriched the sub-arc mantle with an unusually high Nb/Ta signature is derived from an initially intact Pacific plate that was probably subject to a slab break-off event and subsequent melting at depths exceeding 100 km. The geochemical evidence presented here shows that old and cold subducted oceanic crust, which is initially not torn, may resist shallow melting but can melt at greater depths instead. The resulting slab melts are generated in the presence of residual rutile-bearing eclogite and significantly fractionate Nb–Ta ratios which may be of relevance at a global scale.

Volcanism along Mid-Ocean Ridges is known to exhibit significant isotopic and elemental variations, traditionally regarded as reflecting global scale variations in mantle depletion history and refertilization processes. The ∼ 400 km long Mid-Atlantic Ridge (MAR) between the Ascension and Bode Verde Fracture Zones (7°30′S to 11°30′S) has been sampled at high spatial resolution (c. 10 km along-axis scale) and large elemental and isotopic variations have been identified covering almost the entire compositional spectrum of MAR basalts. In this paper we employ a multi-isotope (Sr–Nd–Hf–Pb) and trace element approach in order to explore the geodynamic implications of along-ridge compositional variations and their relationship to off-axis volcanism on nearby Ascension Island, commonly regarded as plume-related. The studied portion of the MAR consists of four major segments. Isotopic data from the deeply incised northern and southern segments A1 and A4 define a trend involving a high-eHf depleted mantle endmember. This isotopic signature is inferred to result from an ancient melting event in the garnet stability field, causing high time-integrated Lu/Hf and elevated 176Hf/177Hf. In contrast, a low-eHf depleted mantle endmember is indicated by the compositional trend for samples from the topographically elevated central portion (segments A2 and A3). Both trends converge at a common enriched endmember with least diluted compositions represented by samples from the subaerial eruptive stage of nearby Ascension Island. Because linear co-variations between isotope compositions and the respective parent–daughter ratios cannot be explained as representing “mantle isochrons” we infer that our data reflect arrays related to physical mixing of depleted and enriched mantle domains. This implies that distinctive mantle domains at kilometer scale may survive convection processes over time spans in the order of 1–2 Ga. This finding corroborates the results of recent Os-isotope studies of abyssal peridotite which returned similar conclusions. The systematics of along-axis isotopic variations show that mantle upwelling is highly variable. A systematic decrease of the enriched isotopic signature from the central segment A3 toward the northern termination of the segment A2 suggests a northward flow of enriched mantle material. In marked contrast, the compositional variations along the marginal segments A1 and A4 are random indicating heterogeneous mixing of mantle domains at a spatial resolution of With regard to Ascension Island we show that the submarine volcanic stage, sampled by a 3216 m long drill hole, was fed by a distinctive enriched mantle source currently inaccessible to partial melting. We interpret this observation within the framework of recent local-scale geophysical investigations and infer an on-axis origin of the bulk of the Ascension volcanic edifice at around 5 to 6 Ma, synchronous with the surrounding oceanic crust. Off-axis partial melting of the current common enriched mantle endmember accounts for rejuvenation of volcanism on Ascension generating the volumetrically subordinate subaerial portion of the island.

Boninites are subduction-related rocks originating from re-melting of highly depleted mantle sources left after extraction of tholeiitic melts. Due to their depleted nature, the incompatible trace element inventory of boninites is virtually entirely inherited from slab components without a significant contribution from the refractory mantle wedge. Thus, boninites constitute an excellent window into processes controlling trace element mobilization at the slab–mantle wedge interface. In order to constrain the behaviour of trace elements in subduction zones with a special emphasis on high field strength elements, we analyzed low-Ca boninites and associated tholeiitic basalts from Cape Vogel, Papua New Guinea (PNG) and compare them with compositions of high-Ca boninites and associated tholeiitic basalts from Cyprus. High-precision HFSE (Nb, Ta, Zr, Hf, W) concentration data of the boninites and associated tholeiitic basalts were obtained by isotope dilution. Major, trace element, and Sr–Nd–Hf–Pb isotope compositions clearly document a significant contribution of slab-derived melts involved in the petrogenesis of the PNG boninites, whereas only fluid-like subduction components were involved in the petrogenesis of the PNG basalts and the Cyprus suite. Low-Ca boninites from PNG are derived from a more refractory mantle source (∼21% depletion) than the high-Ca boninites from Cyprus (∼11% depletion) and their respective tholeiitic precursors ( W–Mo > Nb–Ta > Zr–Hf. Furthermore, Mo–W systematics may provide a potential novel tracer for the amount, composition and redox state of subducted pelagic sediments that contribute to the geochemical budget of intra-oceanic arc systems.

The Solomon island arc, SW Pacific, is of particular interest for understanding subduction zone volcanism, as magmatism in the active part of the arc is dominated by mafic melts, thus permitting direct insights into mantle processes. Along the Solomon island arc, the Indian^Australian plate is subducting at present beneath the Pacific plate. However, until at least c. 12 Myr ago, the Pacific plate was subducting beneath the Indian^Australian plate until the Cretaceous Ontong Java Plateau collided with the northern Solomon island arc.To evaluate the effects of the changes in tectonic regime on lava compositions, we present a comprehensive Sr^Nd^ Hf^Pb isotope, major element and trace element dataset, covering lavas erupted along the entire island arc (c. 1000 km). Basalts and andesites represent the most abundant rock types. Picrites and ankaramites occur in the New Georgia Group of the Solomon Islands, where they erupted above the subductingWoodlark spreading center, and also in the Santa Cruz archipelago, north of Vanuatu, where the Rennell Fracture Zone is subducting. Recent work has also identified the presence of adakites (Sr/Yup to c. 200), and high-Mg andesites (MgO45 wt %, Sr/Y c. 11^46). Most of the high-Mg andesites are genetically linked to the adakites, but some of the high-Mg andesites show affinities to boninitic compositions. Large ion lithophile element abundances in most Solomon island arc magmas indicate a strong source overprint by subduction components. Sr/Sr and eNd values along the arc range from 0 7029 to 0 7052 and from þ5 8 to þ8 3, respectively.The Sr^Nd values partially overlap the compositions of oceanic basalts from the Indian^Australian plate. Measured eHf values range from þ10 5 to þ14 6. If corrected for contributions from subduction components, combined eHf^eNd systematics also indicate that most of the studied Solomon arc lavas were generated within the Indian-type mantle domain. However, a few samples display eHf^eNd compositions resembling those of the Pacific-type mantle domain. These samples either originate from older Pacific basement (basalts) or represent melts derived from subducted Pacific crust (adakites). Lead isotope compositions, controlled by subduction components, can be used to identify the presence of two distinct types of subduction components that originate (1) from the Pacific plate including Ontong Java Plateau material (46 Myr old) and (2) from the more recently subducted Indian^ Australian plate. Combined Hf^Nd^Pb isotope data also reveal that lower parts of the Ontong Java Plateau entered the mantle wedge, as previously postulated by geophysical models.

Tungsten is highly incompatible and belongs to the high field strength element group (HFSE) that is traditionally regarded as immobile in subduction zone fluids. Due to the low concentrations of W in silicate rocks, a closer assessment of the geochemical behaviour of W in subduction systems was long hampered by analytical limitations. Here we present high-precision concentration measurements of W and other HFSE (Nb, Ta, Zr, Hf) by isotope dilution in combination with incompatible trace element (including Mo and Sb) and Sr-Nd-Hf-Pb isotope measurements. Two well-characterized representatives of subduction-related rock suites from the Solomon Islands and Cyprus were examined. The sources of the Cyprus lavas were mostly enriched by fluids originating from subducted pelagic sediment, whereas Solomon arc lavas originate from mantle sources that have only been overprinted by fluids and melts derived from subducted oceanic crust. Measured Ta/W in both suites (0.3 to 2.9) are always lower than values for MORB (ca. 5), indicating that W is more mobile in subduction components than other HFSE. Ratios of W-Th (up to 1) also extend towards higher values in both suites than MORB values (ca. 0.19). The Cyprus rocks display the highest W/Th, possibly reflecting an initially higher W/Th in subducted sediments. However, the elevated W/Th in Solomon Islands lavas argue for selective W mobilization by slat) fluids. Correlations between Ce/Pb, Sb/Ce and W/Th support this model. In the Cyprus lavas, the W enrichment is coupled to Sb, but decoupled from Mo, possibly reflecting different redox conditions. Collectively, our data therefore suggest a selective enrichment of W relative to Th, U, and Ta in the sub-arc mantle via fluids derived from subducted oceanic crust. As subduction zone volcanism significantly contributes to the growth of continental crust, continued recycling of continental material into the sources of subduction zone magmas may have amplified the extent of W enrichment, possibly leading to a higher W/Th and W/U in the Earth's crust compared to the Earth's mantle. (C) 2008 Elsevier B.V. All rights reserved.

The geologic evolution of the New Zealand microcontinent was characterised by intermittent Cretaceous to Quaternary episodes of intraplate volcanism. To evaluate the corresponding mantle evolution beneath New Zealand with a specific focus on the tectonic evolution, we performed a combined major and trace element and Hf, Nd, Pb, Sr isotope investigation on a suite of representative intraplate volcanic rocks from both main islands and the Chatham Islands. Isotopically, the data set covers a range between “HIMU-like” end member compositions (206Pb/204Pb: 20.57, 207Pb/204Pb: 15.77, 87Sr/86Sr: 0.7030, eHf: + 3.8, eNd: + 4.2), compositions tending towards MORB (206Pb/204Pb: 19.01, 207Pb/204Pb: 15.62, 87Sr/86Sr: 0.7028, eHf: + 9.9, eNd: + 7.0) and compositions reflecting the influence of subducted sediments (206Pb/204Pb: 18.99, 207Pb/204Pb: 15.67, 87Sr/86Sr: 0.7037, eHf: + 4.4, eNd: + 3.9). Whereas volcanism on the Chatham Islands constitutes the HIMU end member of our data set, intraplate volcanic rocks from the North Island are dominated by MORB-like compositions with relatively radiogenic 206Pb/204Pb signatures. Volcanic rocks from the South Island form a trend between the three end members. Assuming a polybaric melting column model, the primary melt compositions reflect variations in the degree of melting, coupled to variable average melting depths. As the three isotope and trace element end members occur throughout the volcanic episodes, the “HIMU-like” and the sediment influenced signatures most likely originate from a heterogeneous subcontinental lithospheric mantle, whereas an asthenospheric origin is inferred for the MORB-like component. For the South Island, affinities to HIMU wane with decreasing average melting depths whereas MORB and sediment-like signatures become more distinct. We therefore propose a polybaric melting model involving upper asthenospheric mantle and a lithospheric mantle source that has been modified by subduction components and veins of fossil “HIMU-like” asthenospheric melts. The proportion of asthenospheric versus lithospheric source components is controlled by variations in lithospheric thickness and heat flow, reflecting the different tectonic settings and rates of extension. Generally, low degree melts preferentially tap enriched vein material with HIMU signatures. The widespread occurrence of old Gondwana-derived lithospheric mantle beneath intraplate volcanic fields in East Gondwana is suggested by overall similarities between New Zealand intraplate volcanic rocks and volcanic rocks in East Australia and Antarctica. The petrogenetic model proposed here may therefore serve as a general model for the petrogenesis of Cretaceous to Recent intraplate volcanic rocks in former East Gondwana.

The petrogenesis of high-Mg andesites (HMA) in subduction zones involves shallow melting of refractory mantle sources or, alternatively, the interaction of ascending slab-derived melts with mantle peridotite. To unravel the petrogenesis of HMA, we report major, trace element and Sr–Nd–Hf–Pb isotope data for a newly found occurrence of HMA in the New Georgia group, Solomon Islands, SW-Pacific. Volcanism in the Solomon Islands was initiated by subduction of the Pacific plate beneath the Indian–Australian plate until a reversal of subduction polarity occurred ca. 10 Ma ago. Currently, the Indian–Australian plate is subducted northeastwards along the San Cristobal trench, forming the younger and still active southwestern Solomon island arc. However, a fossil slab of Pacific crust is still present beneath the arc. The edifice of the active volcano Simbo is located directly in the San Cristobal trench on top of the subducting Indian–Australian plate. Simbo Island lies on top of a strike-slip fault of the adjacent Woodlark spreading centre that is subducted beneath the Pacific plate. Geochemical and petrological compositions of volcanic rocks from Simbo are in marked contrast to those of volcanic rocks from islands north of the trench (mostly arc basalts). Simbo-type rocks are opx-bearing HMA, displaying 60–62 wt% SiO2 but rather primitive Mg–Ni–Cr characteristics with 4–6 wt% MgO, up to 65 ppm Ni, up to 264 ppm Cr and Mg# from 67 to 75. The compositions of the Simbo andesites are explained by a binary mixture of silicic and basaltic melts. Relict olivine phenocrysts with Fo88–90 and reaction-rims of opx also support a mixing model. The basaltic endmember is similar to back-arc basalts from the Woodlark Ridge. A slab melt affinity of the silicic mixing component is indicated by Gd(N)/Yb(N) of up to 2.2 that is higher if compared to MORB and other arc basalts from the Solomon Islands. 87Sr/86Sr, ɛNd and ɛHf values in the analysed rocks range from 0.7035 to 0.7040, +6.4 to +7.9 and +12 to +14.4, respectively. These values reveal the presence of the Indian–Australian mantle domain beneath Simbo (i.e. the Indian–Australian plate) and also beneath all other volcanic islands of the New Georgia group, which are located north of the San Cristobal trench. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values (18.43–18.52, 15.49–15.55 and 18.13–18.34, respectively) confirm the presence of slab melts from the subducted Pacific plate beneath southern Simbo where the highest Gd(N)/Yb(N) ratios are reported. A spatial shift towards an Indian–Australian slab signature is observed when approaching the active San Cristobal trench on northern Simbo, reflecting the decreasing influence of slab melts from the old subducted Pacific plate.

Subduction related picrites from the New Georgia archipelago (Solomon Islands) range in bulk MgO from 13 to 30 wt%. Two generations of olivine are identified based on CaO contents: High-CaO olivine phenocrysts from the picritic parental melt and low-CaO olivine xenocrysts incorporated from either lithospheric or asthenospheric upper mantle. There is also evidence that some of the low-CaO olivines are boninitic in origin. The bulk MgO range in the picrites is largely controlled by assimilation of low-CaO olivine xenocrysts. Oxidation states of the melt (ΔFMQ+2.2), calculated from magnetite activities in liquidus chromites, constrain the MgO content of the parental melt to 13 wt%, assuming Fe–Mg exchange equilibrium between melt and liquidus olivine composition. The dry liquidus temperature of the parent melt based on this MgO content is 1340°C, about 80°C above the temperature obtained with the olivine–clinopyroxene Ca-exchange thermobarometer. The residence time of the low-CaO olivine xenocrysts in the magma, estimated from Ca- and Fe–Mg interdiffusion profiles, did not exceed 1 year.

Island arc picrites are restricted to a few localities including the Lesser Antilles, Japan, Vanuatu and the Solomon Islands. The picrite occurrences appear to be linked to the subduction of young, hot oceanic crust and anomalous geotherms. At the Solomon arc, the Australian plate is presently subducted beneath the Pacific plate. A particular feature of the Solomon arc is the subduction of a spreading center (Woodlark Ridge). In the Solomon Islands, picrites only occur in the New Georgia archipelago, located above or close to the subducting Woodlark Ridge. These picrites contain between 12 and 30 wt% MgO, the associated primitive basalts show MgO contents from 11.5 to 13.6 wt%. Linear trends defined by Cr, Ni and other trace elements vs. MgO indicate that the picritic bulk compositions originate from mixing between a basaltic-picritic melt and a Mg- and Cr-rich endmember, rather than from fractional crystallization of extremely Mg-rich magmas. Major and trace element modeling identify mantle wedge peridotite as the most likely mixing endmember. Trace element abundances in the Solomon arc picrites indicate a mantle source enrichment by subduction components and a large depletion of Nb and Ta that is typical for island arc volcanic rocks. Most incompatible trace element patterns of the New Georgia picrites and basalts are parallel, supporting a cogenetic evolution of these rocks by mixing processes. 87Sr/86Sr and ɛNd values in the basalts and picrites range from 0.7033 to 0.7043 and +5.8 to +8.0, respectively. These values partially overlap with compositions of the Indian MORB field. Alternatively, subducted sediment and fluids from altered MORB may have displaced the Sr isotope composition to more radiogenic 87Sr/86Sr. ɛHf values range from +12.2 to +14.6 and show in combination with ɛNd that the picrites were most likely generated within the Indian mantle domain.

We have developed a new analytical setup for the determination of trace element concentrations in fluid inclusions by UV-fs-LA-ICP-MS. Laser ablation was performed at a low temperature of -40 degrees C by using a modified heating-freezing stage as the ablation cell. With this method it was possible to successfully analyse 53 of 55 frozen synthetic NaCl-H2O fluid inclusions in quartz, covering a size range between 8 mu m and 25 mu m down to a depth of 50 mu m. The high success rate could be achieved as the 194 nm UV-fs-laser allows excellent control over the opening procedure of frozen fluid inclusions. Trace element analyses were performed with a fast scanning magnetic sector field ICP-MS. The lower limits of detection for fluid inclusion analysis vary from 0.1 mu g g(-1) (for Bi-209) to 10 mu g g(-1) (for K-39). The typical analytical uncertainty, depending on the element and respective concentration level, ranges between 10% and 30% (1RSD), based on the reproducibility of experimentally synthesized fluid inclusions. All elements from a stock solution, which behaved inert during the HP/HT experiments (B, K, Cd, Te, Tl, Pb and Bi), could be recovered in the synthetic inclusions at concentrations that correspond within their specific analytical uncertainties to their original concentration of 53 mu g g(-1). The method represents a highly efficient tool for the determination of accurate trace element data on low concentration levels in small fluid inclusions with a high success rate of >90%. The latter is particularly advantageous considering the commonly time consuming characterization of fluid inclusions. NTH Graduate School GeoFluxes

Low iron and high phytic acid content make fonio based meals a poor source of bioavailable iron. Phytic acid degradation in fonio porridge using whole grain cereals as phytase source and effect on iron bioavailability when added to iron fortified fonio meals were investigated. Grains, nuts and seeds collected in Mali markets were screened for phytic acid and phytase activity. We performed an iron absorption study in Beninese women (n = 16), using non-dephytinised fonio porridge (FFP) and dephytinised fonio porridge (FWFP; 75% fonio-25% wheat), each fortified with 57Fe or 58Fe labeled FeSO4. Iron absorption was quantified by measuring the erythrocyte incorporation of stable iron isotopes. Phytic acid varied from 0.39 (bambara nut) to 4.26 g/100 g DM (pumpkin seed), with oilseeds values higher than grains and nuts. Phytase activity ranged from 0.17±1.61 (fonio) to 2.9±1.3 phytase unit (PU) per g (whole wheat). Phytic acid was almost completely degraded in FWFP after 60 min of incubation (pH≈5.0, 50°C). Phytate∶iron molar ratios decreased from 23.7∶1 in FFP to 2.7∶1 in FWFP. Iron fortification further reduced phytate∶iron molar ratio to 1.9∶1 in FFP and 0.3∶1 in FWFP, respectively. Geometric mean (95% CI) iron absorption significantly increased from 2.6% (0.8–7.8) in FFP to 8.3% (3.8–17.9) in FWFP (P, PLoS ONE, 8 (10), ISSN:1932-6203

Environmental context Iron (Fe) isotope analysis is a powerful tool to understand the transport of Fe within and from soils to rivers. We determined Fe isotopes and Fe concentrations of soil solutions at different depths and found that the Fe isotope compositions are modified owing to adsorption onto Fe oxides, especially in the subsoil. Hence Fe-rich capillary rising groundwater or seeping Fe-rich surface water are depleted in Fe and potentially other metals in Fe oxide-rich soil horizons. Abstract The mobility of iron (Fe) in soils is strongly affected by redox conditions, which also affect Fe input into groundwater and rivers. Stable Fe isotope analyses allow further investigation of Fe translocation processes within, into and out of soils. Soil solutions taken from a Gleysol in a lowland area (NW Germany) at different depths revealed that Fe concentration and isotope ratios strongly varied with abundance of solid Fe oxides. Low δ56Fe values of –1.7 ‰ and minimum Fe concentrations of ~0.2mgL–1 were recorded in soil solutions of Fe-rich horizons. Soil solutions of a Fe-poor horizon, however, yielded higher δ56Fe values (–0.39 ‰) and Fe concentrations of up to 68mgL–1. The water of an adjacent drainage ditch featured δ56Fe values of –1.1 ‰, in strong contrast to +0.60 ‰ of short-range ordered Fe oxide deposits in the ditch bed. We attribute the coupled low δ56Fe values and Fe concentrations to combined adsorption and atom exchange between dissolved Fe and Fe oxides. Consequently Fe oxide-poor horizons had higher δ56Fe values and dissolved Fe concentrations. Outflow of Fe-rich groundwater and surface water during rainfall into rivers is responsible for high δ56Fe for Fe-oxide precipitates and low riverine δ56Fe values.

Limited data exist on iron absorption from NaFeEDTA and FeSO(4) in legume-based flours. The current study compared iron absorption from NaFeEDTA and FeSO(4) as fortificants within and between red and white varieties of cowpea with different concentrations of polyphenols (PP) but similar phytic acid (PA)-to-iron molar ratios. We performed a paired crossover study in young women (n = 16). Red-cowpea (high-PP) and white-cowpea (low-PP) test meals (Tubani) were each fortified with ((57)Fe)-labeled NaFeEDTA or ((58)Fe)-labeled FeSO(4) and were randomly administered. Iron absorption was measured as erythrocyte incorporation of stable iron isotopes. Per serving, the mean (±SD) PP concentrations of the white- and red-cowpea-based meals were 74 ± 3.6 and 158 ± 1.8 mg, respectively, and the molar ratio of PA to iron was 3.0 and 3.3. Iron bioavailabilities from red and white cowpeas were 1.4 and 1.7%, respectively, in NaFeEDTA-fortified meals and 0.89 and 1.2%, respectively, in FeSO(4)-fortified meals. Compared with FeSO(4), fortification with NaFeEDTA increased the amount of iron absorbed from either of the cowpea meals by 0.05 to 0.08 mg (P