Fe Partitioning Research Articles

Magmatic evolution of KREEP‐free lunar meteorite Asuka‐881757 inferred from sector‐zoned clinopyroxene, pyroxene symplectites, and thermodynamic modeling

AbstractLunar basaltic meteorite Asuka‐881757 (A‐881757), a member of the source crater paired YAMM meteorites (Yamato‐793169, A‐881757, Miller Range 05035 and Meteorite Hills 01210), provides information on potassium‐rare earth element‐phosphorous (KREEP)‐free magmatic sources within the Moon. Asuka‐881757 is an unbrecciated and Fe‐rich (Mg# 36) gabbro with coarse pyroxene (2–8 mm) and plagioclase (1–3 mm). The coarse pyroxene preserves mm‐scale, near‐complete hour‐glass sector zoning with strong Ca and Fe partitioning, similar to some Fe‐rich Apollo basalts. In contrast to the most Mg‐rich Apollo basalts, A‐881757 contains various types of symplectites (~8 vol%) formed by the breakdown of pyroxferroite due to slow cooling, resembling a few extreme Fe‐rich (Mg# 40) Apollo basalts. Petrographic observations and thermodynamic modeling suggest crystallizing in the order: Fe‐poor pyroxenes (Mg# 58–55) → co‐crystallized plagioclase and Fe‐rich pyroxenes (Mg# 49–20) → late‐stage assemblage including Fe‐augite, Fayalite, and Fe‐Ti oxides. Combining phase stability at variable P–T with petrographic observations, the minimum depth of formation of the A‐881757 parent magma can be constrained to between 60 and 100 km. KREEP‐free basalts (such as A‐881757 and the YAMM meteorites) originated from a relatively shallow mantle source and later underwent polybaric crystallization that occurred prior to eruption at the lunar surface. In contrast, the Apollo mare basalts mostly crystallized within lava flows from relatively deeper‐seated mantle sources. The crystallization of A‐881757 and other YAMM meteorites is unlike most Apollo basalts from the Procellarum KREEP terrane, and likely represent hidden cryptomare basalts close to lunar surface.

Spatiotemporal Variability in Soil Properties and Composition in Mangrove Forests in Baía de Todos os Santos (NE Brazil)

Soil properties and components in mangrove ecosystems influence their geochemical processes and services. Despite the extensive mangrove areas present in Brazil, few studies focusing on these themes are under development. In this sense, this work aimed to investigate the spatial variability in soil attributes and composition, the geochemistry of Fe, and the isotopic characteristics of organic matter in mangroves in Baía de Todos os Santos (Cacha Prego, Ponta Grossa, Ilha de Maré, Pitinga), which constitutes Brazil’s second largest bay. The soils investigated showed spatial and temporal changes affecting their properties (pH, Eh) and composition (TOC, Fe fractions), as well as clear spatial changes in the redox potential values (+30–+188 mV), with higher values in PT. Soil textures ranged from predominantly sandy (CP, PT, PG: sand, >70%) to a finer granulometry (IM: sand, 33–64%). These characteristics influenced Fe partitioning and organic matter content, with higher TOC and pyrite values observed in IM (FeS2: 2720–9233 mg kg−1; TOC: 4.4–6.6%) and lower sulfide values found in PT, mainly in the dry season (FeS2: 85–235 mg kg−1). The soil δ13C and N/C ratios seem to suggest a mixed origin of organic matter.

Partitioning of Fe2+ and Fe3+ between bridgmanite and silicate melt: Implications for redox evolution of the Earth's mantle

Crystallization of deep magma oceans would have created the chemical heterogeneity of the Earth's mantle. Previous geophysical studies have suggested a possible existence of the Fe3+-rich lower mantle relative to the upper mantle because the seismic profile of the Earth's lower mantle is well explained by the presence of Fe3+-rich bridgmanite. Such a contrasting distribution of Fe3+/ΣFe ratios between the upper mantle and the lower mantle could have triggered the gradual oxidation of the upper mantle by upwelling Fe3+-rich lower mantle in the early Archean around 3 billion years ago (Ga). However, whether Fe3+-rich lower mantle and Fe3+-poor upper mantle could have been formed or not in the early Earth is still poorly understood. Here we report experimental constraints on the partitioning of Fe2+ and Fe3+ between bridgmanite and silicate melt at 23–27 GPa to investigate the solid-liquid fractionation of Fe2+ and Fe3+ in the deep magma ocean. Our results show negligible fractionation of Fe2+ and Fe3+ between bridgmanite and silicate melt at the uppermost lower mantle conditions, suggesting that preferential incorporation of Fe3+ into bridgmanite during magma ocean crystallization is unlikely. If the lower mantle had become enriched in Fe3+ during the formation of the Earth, another mechanism, such as the redox disproportionation of Fe2+, may have played a more important role in controlling the Fe3+/ΣFe ratio of the mantle.

Masked diversity and contrasting soil processes in tropical seagrass meadows: the control of environmental settings

Abstract. Seagrass meadows are among the most valuable ecosystems on Earth. However, in tropical countries, there is a substantial knowledge gap in “seagrass science”. To address this gap, seagrass soils from three Brazilian coastal regions were investigated (the northeastern, southeastern, and southern coasts). Soil profiles from different geological and bioclimatic settings were sampled, described, and analyzed. Thus, detailed macromorphological descriptions, soil classification, physicochemical analysis (soil particle size, soil pH, pHoxidation, Eh, total organic carbon: TOC), Fe partitioning, and X-ray diffractometry were performed. Additionally, water samples were analyzed for pH, salinity, and ion concentrations. Different environmental settings in the coastal compartments produced contrasting geochemical conditions, which caused different intensities of pedogenetic processes. On the northeastern coast, the denser plant coverage favored higher TOC contents (2.5 ± 0.1 %) and an anaerobic environment (Eh = +134 ± 142 mV) prone to an intense sulfidization (i.e., pyrite formation: Py-Fe). Py-Fe contents in northeastern soils were 6- and 2-fold higher than in southeastern and southern coastal soils, respectively. Conversely, lower TOC contents (0.35 ± 0.15 %) and a suboxic environment (Eh + 203 ± 55 mV) in the southeastern soils, along with the Fe-rich geological surroundings, decreased the intensity of gleization. The contrasting intensities in the soil processes, related to the (seemingly subtle) differences in the geochemistry of each environment, ultimately caused relevant pedodiversity among the studied sites. Our findings contribute to a better understanding of the general functioning of tropical seagrass meadows but also have significant environmental implications for studies focused on carbon sequestration in these ecosystems.

Detection of ferric iron in an exsolved lunar pyroxene using electron energy loss spectroscopy (EELS): Implications for space weathering and redox conditions on the Moon

AbstractTo shed light on the mechanism of formation of nanophase iron particles (npFe) in space‐weathered materials from airless bodies, we analyzed exsolved and unexsolved space‐weathered lunar pyroxenes from Apollo 17 sample 71501. The exsolved pyroxene allowed for the observation of the effects of space weathering on similar mineral phases with variable composition. Using coordinated scanning transmission electron microscopy with energy‐dispersive X‐ray spectroscopy and electron energy loss spectroscopy (EELS), we determined that two coexisting pyroxenes in the exsolved grain showed systematic variations in response to space weathering, despite equivalent exposure conditions. The npFe in the space‐weathered rim of augite lamellae were smaller and fewer than the npFe in the rim of pigeonite lamellae. EELS spectrum imaging revealed the presence and heterogeneous distribution of Fe0, Fe2+, and Fe3+ in the exsolved pyroxene. Metallic iron occurred in the npFe, a mixture of Fe2+ and Fe3+ occurred in the pigeonite lamellae, and the augite lamellae contained virtually all Fe3+. Approximately 50% of the total Fe measured in the exsolved pyroxene grain was ferric. Partitioning of Fe2+ and Fe3+ among the lamellae is invoked to explain the difference in npFe development in pigeonite and augite. The results of this study, the first to identify Fe3+ in a crystalline lunar ferromagnesian silicate, have implications for our understanding of how space weathering might proceed in oxidized phases. Furthermore, the discovery of an Fe3+‐rich pyroxene also supports attribution of the 0.7 μm absorption feature observed in Galileo Solid State Imager data to oxidized Fe in clinopyroxenes.

Early pedogenesis of anthropogenic soils produced by the world’s largest mining disaster, the “Fundão” dam collapse, in southeast Brazil

The overwhelming production of waste represents a complex environmental challenge for mining companies worldwide. Efforts are currently being made to develop methods for storing or reusing such potentially hazardous waste. Among innovative environmentally-friendly solutions, constructing Technosols from mining waste may be a feasible solution for revalorizing this type of waste. However, there is a knowledge gap regarding the pedogenic processes that govern the functioning of these soils. The Fundão Dam collapse (2015) offers a unique opportunity to evaluate the early pedogenesis of a Technosol unintentionally formed from Fe-rich tailings deposited in the Doce River estuary. This study aimed to assess the pathways of Technosol pedogenesis, four years after the world’s largest mining disaster. Based on a multi-technique approach (including macro-and micromorphological analysis, mineralogical analysis, physicochemical parameters and geochemical analysis of Fe partitioning), bare tailings and different Technosol profiles were analyzed to unravel the action of early pedogenesis in a hydromorphic environment. Within four years, rapid colonization by plants favored fine particle accumulation and triggered a process of cumulization, as evidenced by a 6-fold increase in the clay content. The vegetation also promoted input of organic carbon (from 0.4 to 2.1 %), which altered the geochemical environment and Fe dynamics. These changes promoted melanization, incipient paludization and gleization. The Fe partitioning revealed that the bare tailings, primarily comprising crystalline Fe oxides, transitioned to soil matrices dominated by poorly crystalline Fe oxyhydroxides (41 ± 3 %). Examination of thin sections revealed rapid Fe translocation through Technosol profiles associated with the formation of Fe coatings and hypocoating pedofeatures. This study provides valuable insights into the action of both time and organisms as factors for Technosol formation and functioning.

Kinetically Induced Fine Secondary α-Ti Phase Formation in a Novel As-Cast Titanium Alloy

The formation of fine secondary hexagonal close packed (HCP) α-Ti precipitates provides major strengthening in a new Ti-6Al-5Fe-0.05B-0.05C (mass fractions in pct) cast alloy. The phase transformation mechanisms from the body-centered cubic (BCC) β-Ti matrix to fine α phase in this new α-β titanium alloy were investigated experimentally and computationally using CALculation of PHAse Diagram (CALPHAD)-based thermodynamic and kinetic models. The discrete distribution of α precipitates was observed in the as-cast alloy with evidence of strong Fe partitioning. Two main size groups of α precipitates and the Fe partitioning were characterized using scanning electron microscopy, scanning transmission electron microscopy, and synchrotron-based small-angle X-ray scattering techniques. A hypothesis of Fe-partitioning driven α precipitate nucleation and growth was validated by precipitation simulation using TC-PRISMA with customized thermodynamic and kinetic descriptions. These results suggested a new titanium alloy design route involving high-mobility elements (enhancing fine secondary α precipitates) and demonstrated the capability of CALPHAD-based modeling in titanium alloy design.

Serpentinite dehydration at low pressures

Petrographic observations combined with mineral compositional analyses constrain the phase relations of prograde metamorphosed serpentinites in the Bergell contact aureole (Italy). In a 1500 m profile perpendicular to the north-eastern edge of the Bergell intrusion, seven dehydration reactions ran to completion. Three previously undocumented reactions have been identified within 70 m of the intrusive contact: olivine + anthophyllite = orthopyroxene + H2O, tremolite + Cr–Al-spinel = olivine + Mg-hornblende + H2O and chlorite = olivine + orthopyroxene + Cr-Al-spinel + H2O. Petrological analysis indicates that these reactions occur over a narrow range of pressure and temperature, 300 ± 30 MPa and 720 ± 10 °C respectively. Computed phase diagram sections reproduce the observed mineral parageneses with one notable exception. Due to the underestimation of aluminium and sodium contents in Ca-amphibole models, plagioclase is predicted above 700 °C instead of Mg-hornblende. In comparison with natural grains, the aluminium content of computed chlorite compositions is overestimated for low grade parageneses while it is underestimated near the upper thermal stability limit of chlorite. In the computed sections, Fe partitioning relative to Mg between olivine and other silicates, suggests a clear preference for Fe in olivine, that therefore shows lower Mg#s. In contrast, microprobe analyses of natural mineral pairs indicate that orthopyroxene, Mg-hornblende and anthophyllite have lower Mg#s than equilibrium olivine. The inferred thermal profile of the metamorphic aureole is not consistent with simple heat conduction models and indicates a contact temperature of ~ 800 °C, which is 120–230 °C higher than previously estimated. Petrography also reveals extensive retrograde overprint of the prograde parageneses within 200 m of the contact. Retrogression is related to metamorphic fluids that were released by dehydration reactions during contact metamorphism and magmatic fluids expelled from the tonalite intrusion. The thermal gradient between the intrusion and the country rocks induced hydrothermal circulation of these fluids throughout the contact aureole, which beyond peak metamorphic conditions caused retrograde overprint of the prograde parageneses. The proposed phase relations for low and high pressures, and in particular, the transition from tremolite to Mg-hornblende, provides a complete representation of hydration and dehydration processes in serpentinites in subduction zones, along deep oceanic transform faults, and at passive continental margins. The latter has new implications, specifically for subduction initiation.

Root-to-shoot iron partitioning in Arabidopsis requires IRON-REGULATED TRANSPORTER1 (IRT1) protein but not its iron(II) transport function.

IRON-REGULATED TRANSPORTER1 (IRT1) is the root high-affinity ferrous iron (Fe) uptake system and indispensable for the completion of the life cycle of Arabidopsis thaliana without vigorous Fe supplementation. Here we provide evidence supporting a second role of IRT1 in root-to-shoot partitioning of Fe. We show that irt1 mutants overaccumulate Fe in roots, most prominently in the cortex of the differentiation zone in irt1-2, compared to the wild type. Shoots of irt1-2 are severely Fe-deficient according to Fe content and marker transcripts, as expected. We generated irt1-2 lines producing IRT1 mutant variants carrying single amino-acid substitutions of key residues in transmembrane helices IV and V, Ser206 and His232, which are required for transport activity in yeast. Root short-term 55 Fe uptake rates were uninformative concerning IRT1-mediated transport. Overall irt1-like concentrations of the secondary substrate Mn suggested that the transgenic Arabidopsis lines also remain incapable of IRT1-mediated root Fe uptake. Yet, IRT1S206A partially complements rosette dwarfing and leaf chlorosis of irt1-2, as well as root-to-shoot Fe partitioning and gene expression defects of irt1-2, all of which are fully complemented by wild-type IRT1. Taken together, these results suggest a regulatory function for IRT1 in root-to-shoot Fe partitioning that does not require Fe transport activity of IRT1. Among the genes of which transcript levels are partially dependent on IRT1, we identify MYB DOMAIN PROTEIN10, MYB DOMAIN PROTEIN72 and NICOTIANAMINE SYNTHASE4 as candidates for effecting IRT1-dependent Fe mobilization in roots. Understanding the biological functions of IRT1 will help to improve Fe nutrition and the nutritional quality of agricultural crops.

Experimental calibration of an Fe3+/Fe2+-in-amphibole oxybarometer and its application to shallow magmatic processes at Shiveluch Volcano, Kamchatka

AbstractOxygen fugacity is an important but difficult parameter to constrain for primitive arc magmas. In this study, the partitioning behavior of Fe3+/Fe2+ between amphibole and glass synthesized in piston-cylinder and cold-seal apparatus experiments is developed as an oxybarometer, applicable to magmas ranging from basaltic to dacitic composition. The partitioning of Fe2+ is strongly dependent on melt polymerization; the relative compatibility of Fe2+ in amphibole decreases with increasing polymerization. The Fe2+/Mg distribution coefficient between amphibole and melt is a relatively constant value across all compositions and is, on average, 0.27. The amphibole oxybarometer is applied to amphibole in mafic enclaves, cumulates, and basaltic tephra erupted from Shiveluch volcano in Kamchatka with measured Fe3+/FeTotal. An average Fe3+/Fe2+ amphibole-glass distribution coefficient for basalt is used to convert the Fe3+/FeTotal of amphibole in samples from Shiveluch to magmatic oxygen fugacity relative to NNO. The fO2 of primitive melts at the volcano is approximately NNO+2 and is faithfully recorded in amphibole from an amphibole-rich cumulate and the basaltic tephra. Apparently, higher fO2 recorded by amphibole in mafic enclaves likely results from partial dehydrogenation of amphibole during residence in a shallow andesite storage region. We identify three pulses of mafic magma recharge within two weeks of, a month before, and two to three months before the eruption and find that, at each of these times, the host andesite was recharged by at least two magmas at varying stages of differentiation. Application of the amphibole oxybarometer not only gives insight into magmatic fO2 but also potentially details of shallow magmatic processes.

Thermomechanically processed powder metallurgy Ti-5Fe alloy: Effect of microstructure, texture, Fe partitioning and residual porosity on tensile and fatigue behaviour

The combination of low-cost alloying elements like Fe and powder metallurgy, a route with potential to lower the cost of processing titanium alloys, is an interesting option to process cost-effective titanium alloys. Using thermomechanical processing can help improve their behaviour, but limited work has been devoted to it. Additionally, there is a lack of knowledge on their fatigue performance. In this work, different extrusion and heat treatment conditions were applied to develop different microstructures and textures, and their effect on the tensile and fatigue behaviour was thus studied. Small differences in the extrusion and annealing temperatures, when in the α+β phase, result in strong Fe partitioning between α and prior β grains, developing an ultrafine transformed β microstructure instead of lamellar colonies. This results in a remarkable strengthening of the alloy plus an increase in ductility. Despite reaching practically full density after extrusion, residual pores influence the fatigue behaviour (but not the tensile behaviour), and the extent of their influence depends on the intrinsic strength of the alloy. By carefully selecting the thermomechanical processing conditions, the cost-effective powder metallurgy Ti-5Fe alloy can match the fatigue performance of the workhorse Ti-6Al-4V alloy.

Involvement of Arabidopsis Multi-Copper Oxidase-Encoding LACCASE12 in Root-to-Shoot Iron Partitioning: A Novel Example of Copper-Iron Crosstalk.

Numerous central biological processes depend on the participation of the essential elements iron (Fe) or copper (Cu), including photosynthesis, respiration, cell wall remodeling and oxidative stress protection. Yet, both Fe and Cu metal cations can become toxic when accumulated in excess. Because of the potent ligand-binding and redox chemistries of these metals, there is a need for the tight and combined homeostatic control of their uptake and distribution. Several known examples pinpoint an inter-dependence of Fe and Cu homeostasis in eukaryotes, mostly in green algae, yeast and mammals, but this is less well understood in multicellular plants to date. In Arabidopsis, Cu deficiency causes secondary Fe deficiency, and this is associated with reduced in vitro ferroxidase activity and decreased root-to-shoot Fe translocation. Here we summarize the current knowledge of the cross-talk between Cu and Fe homeostasis and present a partial characterization of LACCASE12 (LAC12) that encodes a member of the multicopper oxidase (MCO) protein family in Arabidopsis. LAC12 transcript levels increase under Fe deficiency. The phenotypic characterization of two mutants carrying T-DNA insertions suggests a role of LAC12 in root-to-shoot Fe partitioning and in maintaining growth on Fe-deficient substrates. A molecular understanding of the complex interactions between Fe and Cu will be important for combating Fe deficiency in crops and for advancing biofortification approaches.

The effects of Fe content on the microstructural evolution and tensile properties in Ti–6Al–4V-(2, 4)Fe alloys fabricated by thermomechanical powder consolidation

Two Ti–6Al–4V-(2, 4)Fe (wt.%) alloys were fabricated by thermomechanical powder consolidation. With 2 wt%Fe, the microstructure consists of grain boundary α layers and interpenetrating networks of α plates filled by the α/β lamellar structure. In contrast, with 4 wt%Fe, the microstructure consists of grain boundary α layers and α plates dispersed within a matrix of ultrafine β transformed structure. Fe partition between β and α and the β stabilization effect of Fe restrict the growth of α and depress the β→α phase transformation to a lower temperature. Hence, the volume fraction of β increases with the increasing Fe content. Due to solution hardening of Fe and α/β interface strengthening, a 4 wt%Fe addition increases the yield strength to 1.342 GPa. However, the high flow stress sustained by 78 vol% ultrafine β transformed structure may cause a significant strain localization in the weak grain boundary α layers, leading to intergranular fracture at a fairly small strain of only 1.6%. In contrast, with the addition of an appropriate amount of Fe which is likely around 2 wt%, a good combination of strength and tensile ductility can be achieved.

Iron force constants of bridgmanite at high pressure: Implications for iron isotope fractionation in the deep mantle

The isotopic compositions of iron in major mantle minerals may record chemical exchange between deep-Earth reservoirs as a result of early differentiation and ongoing plate tectonics processes. Bridgmanite (Bdg), the most abundant mineral in the Earth’s lower mantle, can incorporate not only Al but also Fe with different oxidation states and spin states, which in turn can influence the distribution of Fe isotopes between Bdg and ferropericlase (Fp) and between the lower mantle and the core. In this study, we combined first-principles calculations with high-pressure nuclear resonant inelastic X-ray scattering measurements to evaluate the effects of Fe site occupancy, valence, and spin states at lower-mantle conditions on the reduced Fe partition function ratio (β-factor) of Bdg. Our results show that the spin transition of octahedral-site (B-site) Fe3+ in Bdg under mid-lower-mantle conditions generates a +0.09‰ increase in its β-factor, which is the most significant effect compared to Fe site occupancy and valence. Fe2+-bearing Bdg varieties have smaller β-factors relative to Fe3+-bearing varieties, especially those containing B-site Fe3+. Our models suggest that Fe isotopic fractionation between Bdg and Fp is only significant in the lowermost mantle due to the occurrence of low-spin Fe2+ in Fp. Assuming early segregation of an iron core from a deep magma ocean, we find that neither core formation nor magma ocean crystallization would have resulted in resolvable Fe isotope fractionation. In contrast, Fe isotopic fractionation between low-spin Fe3+-bearing Bdg/Fe2+-bearing Fp and metallic iron at the core-mantle boundary may have enriched the lowermost mantle in heavy Fe isotopes by up to +0.20‰.

Cyclic plasticity and fatigue damage of CrMnFeCoNi high entropy alloy fabricated by laser powder-bed fusion

Abstract In-depth understanding of cyclic plasticity and fatigue damage is crucial for structural application of CrMnFeCoNi which is found to be highly printable. This study provides insights into the link between print processes, solidification microstructure, cyclic plasticity and fatigue damage evolution in the alloy fabricated by laser powder bed fusion. Thermodynamics-based predictions and experimental validation showed that Cr, Co and Fe partition to the core of the solidification cells, whilst Mn and Ni to the cell boundaries in all considered print parameters. Both dislocation slip and deformation twinning were found to be responsible for plastic deformation under monotonic loading. However, the former was found to be the single dominant mechanism for cyclic plasticity. The surface finish helped to substantially delay the crack initiation and cause lack-of-fusion porosity to be the main source of crack initiation. Most significantly, the scan strategies significantly affect grain arrangements and grain dimensions, leading to noticeable effects on fatigue crack propagation; in particular, the highest resistance crack propagation was seen in the meander scan strategy with 0° rotation thanks to the most columnar grains and the smallest spacing of grain boundaries along the crack propagation path.

Hydrogen generation and iron partitioning during experimental serpentinization of an olivine–pyroxene mixture

A series of laboratory experiments was conducted to investigate serpentinization of olivine–pyroxene mixtures at 230 °C, with the objective of evaluating the effect of mixed compositions on Fe partitioning among product minerals, H2 generation, and reaction rates. An initial experiment reacted a mixture of 86 wt.% olivine and 14 wt.% orthopyroxene (Opx) with the same initial grain size for 387 days. The experiment resulted in extensive reaction (∼53% conversion), and solids recovered at termination of the experiment were dominated by Fe-bearing chrysotile and relict olivine along with minor brucite and magnetite. Only limited amounts of H2 were generated during the first ∼100 days of the experiment, but the rate of H2 generation then increased sharply coincident with an increase in pH from mildly alkaline to strongly alkaline conditions. Two shorter term experiments with the same reactants (26 and 113 days) produced a mixture of lizardite and talc that formed a thin coating on relict olivine and Opx grains, with virtually no generation of H2. Comparison of the results with reaction path models indicates that the Opx reacted about two times faster than olivine, which contrasts with some previous studies that suggested olivine should react more rapidly than Opx at the experimental conditions. The models also indicate that the long-term experiment transitioned from producing serpentine ± talc early in the early stages to precipitation of serpentine plus magnetite, with brucite beginning to precipitate only late in the experiment as Opx was depleted. The results indicate that overall reaction of olivine and Opx was initially relatively slow, but reaction rates accelerated substantially when the pH transitioned to strongly alkaline conditions. Serpentine and brucite precipitated from the olivine-Opx mixture had higher Fe contents than observed in olivine-only experiments at mildly alkaline pH, but had comparable Fe contents to reaction of olivine at strongly alkaline pH implying that higher pH may favor greater partitioning of Fe into serpentine and brucite and less into magnetite. Despite the presence of brucite, dissolved silica activities during the long-term olivine-Opx experiment maintained levels well above serpentine-brucite equilibrium. Instead, silica activities converged on levels close to metastable equilibrium between brucite and olivine. It is proposed that silica levels during the experiment may have been regulated by exchange of SiO2 between the fluid and a silica-depleted, brucite-like surface layer on dissolving olivine.

Titanium alloy design and casting process development using an Integrated Computational Materials Engineering (ICME) approach

The application of titanium components is generally limited by their high raw material and manufacturing costs. In this paper, a lower cost cast titanium alloy based on the Ti-Al-Fe system has been designed using an ICME approach. The new alloy Ti-6Al-5Fe-0.05B-0.05C (all wt.%) significantly reduces raw material cost and demonstrates improved castability compared with the baseline Ti-6Al-4V alloy. The fine primary and secondary α phase microstructure in the new alloy, due to Fe partitioning, provides exceptionally high strength (1023 MPa yield strength and 1136 MPa ultimate tensile strength) and reasonable ductility (3.7% elongation) for structural applications. On the manufacturing front, the high cost multi-step investment casting process currently used can now be replaced with a low-cost permanent mold casting process using steel molds and a novel ceramic coating. An experimental casting setup, including an induction skull melting (ISM) system, a gravity tilt-pour system and a ceramic-coated H13 steel mold, has been used to produce near-net-shape permanent metallic mold castings with the new titanium alloy developed. Using this setup, and aided by casting process simulation, a prototype automotive connecting rod was cast successfully. The ZrO2 ceramic coating applied to the H13 steel mold was proven effective in minimizing the metal-mold reactions.

Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition

The Earth’s mantle is characterized by a sharp seismic discontinuity at a depth of 660 km that can provide insights into deep mantle processes. The discontinuity occurs over only 2 km—or a pressure difference of 0.1 GPa—and is thought to result from the post-spinel transition, that is, the decomposition of the mineral ringwoodite to bridgmanite plus ferropericlase. Existing high-pressure, high-temperature experiments have lacked the pressure control required to test whether such sharpness is the result of isochemical phase relations or chemically distinct upper and lower mantle domains. Here, we obtain the isothermal pressure interval of the Mg–Fe binary post-spinel transition by applying advanced multi-anvil techniques with in situ X-ray diffraction with the help of Mg–Fe partition experiments. It is demonstrated that the interval at mantle compositions and temperatures is only 0.01 GPa, corresponding to 250 m. This interval is indistinguishable from zero at seismic frequencies. These results can explain the discontinuity sharpness and provide new support for whole-mantle convection in a chemically homogeneous mantle. The present work suggests that distribution of adiabatic vertical flows between the upper and lower mantles can be mapped on the basis of discontinuity sharpness. The post-spinel transition in mantle composition, which occurs at 660-km depth in Earth’s mantle, takes place over a pressure range equivalent to 250 m in depth, according to multi-anvil experiments for realistic mantle compositions and temperatures.

Iron Absorption and Partitioning During Pregnancy (OR35-03-19)

ObjectivesIron (Fe) homeostasis must be tightly regulated during pregnancy to supply sufficient Fe to both the mother and her developing fetus. Stable isotopes have been utilized to understand Fe absorption during pregnancy by measuring maternal red blood cell incorporation. This measure, however, underestimates the true amount of Fe absorbed, as dietary Fe is transferred to the fetus and may be retained by the placenta. The objective of this study was to obtain a more accurate estimation of Fe absorption during pregnancy and determine factors associated with Fe partitioning between the mom, baby and placenta. MethodsSixty-eight women (6 carrying multiple fetuses (age 27–33), 20 carrying singletons from Rochester NY (age 16–32), and 42 carrying singletons from Peru (age 18–30)) were dosed with an oral stable Fe isotope during late pregnancy. Iron absorption was calculated as the sum of tracer recovered in maternal and umbilical cord red blood cells (RBC) and for isotope retained in placental tissue. The net amount of Fe in each compartment was calculated based on Hb concentration, body (or placental) weight and estimated blood volume. Hemoglobin (Hb), serum ferritin (SF), soluble transferrin receptor (sTfR), folate and vitamin B-12 were assessed in maternal and cord blood. ResultsThe amount of maternally absorbed Fe was significantly greater when neonatal and placental uptake of tracer was accounted for (Table 1). While the majority (> 85%) of absorbed Fe tracer was utilized by the mother for RBC production, neglecting net Fe tracer transferred to the placenta and neonatal compartment underestimated true Fe absorption by 4%-20%. There was a significant positive association between the net amounts of Fe tracer recovered in the fetal compartment and the maternal compartment (R2 = 0.63, P < 0.001). Net Fe tracer retained in placental tissue was significantly positively associated with the net amount of Fe tracer present in the neonatal RBC pool at birth (P = 0.04). ConclusionsIron absorption was underestimated by up to 20% when absorbed Fe that was transferred to the fetus or retained by the placenta was not measured. More research on determinants of iron partitioning in pregnant women is needed to fully evaluate maternal Fe demands and absorption. Funding SourcesNational Institutes of Health, United States Department of Agriculture, Nestle Foundation. Supporting Tables, Images and/or Graphs▪▪

Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District

This paper evaluates controls on cassiterite crystallization under hydrothermal conditions based on the textural setting and geochemistry of cassiterite from six different mineralization environments from the world-class Gejiu tin district, southwest China. The cassiterite samples feature diverse internal textures, as revealed by cathodoluminescence (CL) imaging, and contain a range of trivalent (Ga, Sc, Fe, Sb), quadrivalent (W, U, Ti, Zr, Hf), and pentavalent (Nb, Ta, V) trace elements, with Fe, Ti, and W being the most abundant trace elements. Cassiterite Ti/Zr ratios tend to decrease with distance away from the causative granite intrusion, and so has potential to be used as a broad tool for vectoring toward a mineralized intrusive system. Elemental mapping of cassiterite grains reveals that trace-element concentration variations correspond closely to CL zoning patterns. The exceptions are distinct irregular domains that sharply cut across the primary oscillatory zoning, as defined by the concentrations of W, U, Sb, and Fe. These zones are interpreted to have formed after primary cassiterite growth via fluid-driven dissolution-reprecipitation processes. Zones with low W and U (and Sb) and high Fe are interpreted to have formed during interaction with relatively oxidized fluids in which W and U are stripped from cassiterite due to cation exchange with Fe3+. Systematics of W, U, Sb, and Fe partitioning into cassiterite can, therefore, be used as a monitor of the relative oxidation state of the hydrothermal fluid from which cassiterite precipitates. Cassiterite U-Pb geochronology results obtained by LA-ICP-MS return ages between 77 and 83 Ma, which is consistent with previous geochronology from the region. Ages determined on zones of dissolution-reprecipitation are similar to ages for primary cassiterite growth, indicating a short (<3 m.y.) timespan of hydrothermal activity. These results confirm the potential of U-Pb dating of cassiterite for directly constraining the timing of Sn deposition.