Au Capsules Research Articles

H2 mobility and redox control in open vs. closed hydrothermal oceanic systems – evidence from serpentinization experiments

Abstract. New hydrothermal experiments in rapid-quench pressure vessels have been performed to investigate the effect of redox state on the serpentinization reaction. The experimental hydrogen fugacity (fH2) was controlled by monitoring the mobility of H2 in the reacting system (internal vs. external fH2 control). This was achieved by using either Au (H2 impermeable) or AgPd (H2 permeable) capsules and Ar pressurizing gas to control fH2. The experiments were performed with either San Carlos olivine powders or Åheim dunite chips. Water / rock mass ratios of 1–2, a total pressure of 50 MPa, and temperatures of 300 and 350 °C were investigated. Experimental durations of 30, 45, or ≈80 d were imposed. Serpentine production is observed in almost all experiments but is favored at 300 °C under external fH2 control. The serpentine–magnetite assemblage is observed in Au capsules (high fH2) at 300 °C, while the serpentine–hematite(–magnetite) is observed in AgPd capsules (low fH2). At 350 °C, less H2 is produced than at 300 °C and the serpentine–hematite(–magnetite) assemblage is present in both Au and AgPd capsules. Brucite is absent and this is interpreted to reflect both the initially oxidizing conditions and relatively low serpentine production in our experiments. Differences in product phase assemblages found in this study imply that natural serpentinization reaction mechanisms vary with redox conditions, and consequences for H2 production fluxes and rates can be expected. The high-fH2 (reduced) internally controlled experiments simulate low-permeability “closed” oceanic hydrothermal systems. The low-fH2 (oxidized) externally controlled experiments are analogous to “open” oceanic hydrothermal systems where serpentinization is driven by tectonically aided infiltration of an external fluid.

The use of boron nitride to impose reduced redox conditions in experimental petrology

Abstract Boron nitride (BN) is a commonly used pressure-transmitting material in experimental petrology. It is often considered to be as inert as MgO or Al2O3, and its redox potential is seldomly discussed. It is generally implied that, when used as a capsule sleeve, BN may impose relatively reduced conditions, similar to the effect of the fayalite-magnetite-quartz (FMQ) buffer. However, sediment melting experiments performed at 1050 °C and 3 GPa with BN as the capsule sleeve, produced a hydrous rhyolitic melt with dissolved H2S and CH4 (Li et al. 2021). The resulting fO2 estimate is significantly more reduced than that for the magnetite-wüstite (MW)-buffered experiment where H2S and CH4 were undetected (Li et al. 2021), possibly to the extent of the quartz-iron-fayalite (QIF) buffered conditions produced when BN is used as a capsule or crucible (Wendlandt et al. 1982). To establish an explanation for such a discrepancy, we have conducted further investigation to better constrain the fO2 imposed by BN, when used as a capsule sleeve. Here we report results on analyses of Fe content in Au capsules, a comparative experiment using a QIF buffer and an experiment with an Fe-(Mg,Fe) O sensor for direct analysis of fO2. The calibration of the equilibrium between FeO in melt and Fe in the Au capsule, from Ratajeski and Sisson (1999) appears to be inadequate in constraining fO2 for our experiments. However, we were able to obtain Fe diffusion coefficients in Au from the Fe diffusion profiles observed in the capsule of the Fe-(Mg,Fe)O sensor experiment, and both the inner and outer capsules of the MW-buffered experiment, with resulting values of 1 × 10–13 m2/s, 3 × 10–14 m2/s, and 5 × 10–14 m2/s, respectively. The QIF-buffered and Fe-(Mg,Fe)O sensor experiments provide several lines of evidence supporting the observation that BN imposes QIF-like redox conditions. First, the Fe-(Mg,Fe)O sensor returned an fO2 value of QIF. Second, the “apparent” partition coefficients between FeO content in melt and Fe in the Au capsules are similar between the BN experiment and the QIF-buffered experiment. Third, we observe CH4 and H2O peaks with similar intensities in the Raman spectra of melts from these two experiments, suggesting similar H2 and thus O2 fugacity. As our experiments were performed on a cubic press with the experimental assembly encased in a pyrophyllite cube, we interpret that the significantly reduced conditions imposed by BN are likely due to high H2O activity maintained by dehydration of pyrophyllite, which can be explained using the reaction 2BN + 3H2O = B2O3 + N2 + 3H2. Lower H2O activity will reduce or inhibit the oxidation of BN and its fO2 buffering ability. If heat-treated, BN acts as a highly efficient H2 barrier, as shown by Truckenbrodt et al. (1997). Through our efforts to determine the fO2 imposed by using BN as a capsule sleeve in our experimental assembly, we are able to demonstrate the reducing ability of BN as an assembly component and, furthermore, shed light on the process by which BN imposes such reduced fO2. We hereby present what we have learned during the course of this investigation in the hope that the effect of BN on fO2 control is both recognized and further exploited in future experimental studies.

Carbon recycling efficiency in subduction zones constrained by the effects of H2O-CO2 fluids on partial melt compositions in the mantle wedge

The extent of CO2 transfer from subducting lithologies to the overlying mantle wedge in general and to the arc magma source regions in particular remains debated. The limit of CO2 transfer to the sub-arc mantle could be estimated if the effects of CO2 on the primary hydrous melt compositions of mantle wedge can be assessed in relation to the observed compositions of primitive arc magmas. Here we present new piston cylinder and multi-anvil experiments using Au75Pd25 and Au capsules on four depleted peridotite + H2O ± CO2 starting compositions with 3.5 wt.% H2O and XCO2 [=molar CO2/ (CO2+H2O)] of 0–0.17. Experiments were performed at 2–4 GPa and 1200°C to constrain how the presence of variable CO2 in slab-derived aqueous fluids affects the composition of peridotite partial melts. All experiments consisted of low degree melts (<10 wt.%) in equilibrium with olivine + orthopyroxene ± clinopyroxene. Melts at 2–4 GPa are basaltic for XCO2 of 0–0.10 and become SiO2-poor and CaO-rich at XCO2 > 0.10. Comparison between our experimental partial melt compositions with a global dataset of the most primitive arc magmas suggests that the upper limit of XCO2 in fluids inducing melting in mantle wedges is ∼0.10 at 2–4 GPa. We apply these new constrains to an H2O and CO2 mass balance model for subduction zones and estimate that at least 34–86% of CO2 entering subduction zones bypasses the sub-arc melt generation zone and is subducted to the convecting mantle, either carried by the slab or by the down-dragged limb of the mantle wedge directly above the slab.

Partial melting of a depleted peridotite metasomatized by a MORB-derived hydrous silicate melt – Implications for subduction zone magmatism

Recent geodynamic models and geothermometers suggest that slabs in intermediate to hot subduction zone cross the water-saturated basalt solidus, indicating that hydrous silicate melts are important agents of mass transfer from slab to mantle wedge beneath arcs. Yet the effects of basaltic crust-derived hydrous melt fluxing on mantle wedge melting are poorly known. Here we present the melting phase relations of a depleted peridotite + a MORB-derived hydrous silicate melt at a melt:rock mass ratio of 0.1 and 0.05 (3.5 and 1.7 wt.% H2O, respectively) to simulate fluid-present partial melting of a depleted peridotite, which has been metasomatized by a hydrous silicate melt derived from subducting basaltic crust. Experiments were performed at 2–3 GPa and 900–1250 °C in a piston cylinder, using Au and Au75Pd25 capsules. Amphibole (7–10 wt.%) is stable up to 1000 °C at 2 and 3 GPa coexisting with an assemblage dominated by olivine and opx and with minor fractions of cpx and garnet at 3 GPa. The apparent fluid-saturated solidus of our bulk composition is located at 1000–1050 °C, coinciding with the exhaustion of amphibole at 2 and 3 GPa. Amphibole is exhausted between 0 and 5 wt.% melting at 2 and 3 GPa and dominates the melting reactions in this melting interval along with opx, generating SiO2 and Al2O3-rich, and FeO*- and MgO-poor primitive andesites under fluid-saturated conditions. The melting reactions during low-degree, fluid-saturated melting are incongruent, consuming opx and producing olivine + SiO2-rich melts and is observed over a wide range of starting compositions and pressures from this study and others. As extent of melting increases and the free fluid phase is consumed, a spectrum of basaltic andesites to basanites are produced. Comparison of experimental partial melts from this and other hydrous peridotite melting studies with natural primitive arc magmas suggests that melting of peridotites with varying bulk compositions but with 2.5 – 4.2 wt.% H2O can reproduce the major oxide spread and trends of primitive arc magmas globally. From this comparison, it is clear that differences solely in the pressure of hydrous mantle melting, where the partial melts are fluid-under saturated, can account for the first order trends observed in experimental and natural data, with differences in temperature and composition contributing to the compositional spread within these trends. The ubiquity of andesite genesis over a wide range of pressures and bulk compositions during aqueous fluid-saturated melting suggests that the relative rarity of primitive andesitic melt flux through the crust could be related to the fact that such melts are only produced at the base of the mantle wedge where temperatures are relatively low. As fluid-saturated andesitic melts ascend into the hotter core of the mantle wedge, they are likely consumed by higher-degree, fluid-undersaturated melting generating more common hydrous basaltic melts.

Reaction between Cu-bearing minerals and hydrothermal fluids at 800 °C and 200 MPa: Constraints from synthetic fluid inclusions

Abstract Transport and deposition of copper in the Earth's crust are mainly controlled by the solubility of Cu-bearing phases and the speciation of Cu in magmatic-hydrothermal fluids. To improve our understanding of copper mobilization by hydrothermal fluids, we conducted an experimental study on the interaction between Cu-bearing phases (metallic copper, Cu2O, CuCl) and aqueous chloride solutions (H2O ± NaCl ± HCl; with Cl concentrations of 0 to 4.3 mol kg-1). The experiments were run in rapid heat/rapid quench cold-seal pressure vessels at 800 °C, 200 MPa, and logfO2 ~ NNO+2.3. Either Cu or Au capsules were used as containers. The reaction products were sampled in situ by the entrapment of synthetic fluid inclusions in quartz. Fluid composition was subsequently determined by analyzing individual fluid inclusions using a freezing cell and laser ablation inductively coupled plasma-mass spectrometry. Our results show that large isolated and isometric inclusions, free of late-stage modifications, can be preserved after the experiment even when using a high cooling rate of 25 K s-1. The obtained results demonstrate that: (1) reaction between native Cu, NaCl solution, and quartz (± silica gel) leads to the coexistence of fluid inclusions and Na-bearing silicate melt inclusions. Micrometer-to submicrometer-sized cuprite (Cu2O) crystals have been observed in both types of the inclusions, and they are formed most probably due to the dissociation of CuOH. (2) When Cu0 reacts with HCl and CuCl solutions, or Cu+ reacts with NaCl solution, nantokite (CuCl) formed due to oversaturation has been found in fluid inclusion. Copper concentration in the fluid shows a strong positive dependence on the initial chlorine content, with Cu/Cl molal ratios varying from 1:9 to 1:1 in case 1 and case 2, respectively. When Cl is fixed to 1.5 m, initial fluid acidity has a major control on the Cu content, i.e., 0.17 ± 0.09 and 1.29 ± 0.57 m Cu were measured in fluids of case 1 and case 2, respectively. Cu solubility in pure water and in 1.5 m NaCl solutions are 0.004 ± 0.002 and 0.16 ± 0.07 m, respectively. The main responsible Cu-bearing complexes are CuOH(H2O)x in water, NaCuCl2 in NaCl solutions and HCuCl2 in alkali-free solutions. These results provide quantitative constraints on the mobility of Cu in hydrothermal solutions and confirm that Cl is a very important ligand responsible for Cu transport. The first observation that silicate melt can be generated in the fluid-dominated and native-copper-bearing system implies that transitional thermosilicate liquids can coexist with metal-rich fluids and may enhance Cu mobility in magmatic-hydrothermal systems. This may have important implications for the formation of Cu deposits in the systems with low S activities.

Formation of Hydrocarbons in the Presence of Native Iron under Upper Mantle Conditions: Experimental Constraints

The formation of hydrocarbons (HCs) upon interaction of metal and metal–carbon phases (solid Fe, Fe3C, Fe7C3, Ni, and liquid Fe–Ni alloys) with or without additional sources of carbon (graphite, diamond, carbonate, and H2O–CO2 fluids) was investigated in quenching experiments at 6.3 GPa and 1000–1400 °C, wherein hydrogen fugacity (fH2) was controlled by the Fe–FeO + H2O or Mo–MoO2 + H2O equilibria. The aim of the study was to investigate abiotic generation of hydrocarbons and to characterize the diversity of HC species that form in the presence of Fe/Ni metal phases at P–T–fH2 conditions typical of the upper mantle. The carbon donors were not fully depleted at experimental conditions. The ratio of H2 ingress and consumption rates depended on hydrogen permeability of the capsule material: runs with low-permeable Au capsules and/or high hydrogenation rates (H2O–CO2 fluid) yielded fluids equilibrated with the final assemblage of solid phases at fH2sample ≤ fH2buffer. The synthesized quenched fluids contained diverse HC species, predominantly light alkanes. The relative percentages of light alkane species were greater in higher temperature runs. At 1200 °C, light alkanes (C1 ≈ C2 &gt; C3 &gt; C4) formed either by direct hydrogenation of Fe3C or Fe7C3, or by hydrogenation of graphite/diamond in the presence of Fe3C, Fe7C3, and a liquid Fe–Ni alloy. The CH4/C2H6 ratio in the fluids decreased from 5 to 0.5 with decreasing iron activity and the C fraction increased in the series: Fe–Fe3C → Fe3C–Fe7C3 → Fe7C3–graphite → graphite. Fe3C–magnesite and Fe3C–H2O–CO2 systems at 1200 °C yielded magnesiowüstite and wüstite, respectively, and both produced C-enriched carbide Fe7C3 and mainly light alkanes (C1 ≈ C2 &gt; C3 &gt; C4). Thus, reactions of metal phases that simulate the composition of native iron with various carbon donors (graphite, diamond, carbonate, or H2O–CO2 fluid) at the upper mantle P–T conditions and enhanced fH2 can provide abiotic generation of complex hydrocarbon systems that predominantly contain light alkanes. The conditions favorable for HC formation exist in mantle zones, where slab-derived H2O-, CO2- and carbonate-bearing fluids interact with metal-saturated mantle.

An essential role for sulfur in sulfide-silicate melt partitioning of gold and magmatic gold transport at subduction settings

Sulfide-silicate melt partitioning controls the behavior of gold in magmas, which is critical for understanding the Earth's deep gold cycle and formation of gold deposits. However, the mechanisms that control the sulfide-silicate melt partitioning of gold remain largely unknown. Here we present constraints from laboratory experiments on the partition coefficient of gold between monosulfide-solid-solution (MSS) and silicate melt (DAuMSS/SM) under conditions relevant for magmatism at subduction settings. Thirty-five experiments were performed in Au capsules to determine DAuMSS/SM at 950-1050°C, 0.5-3 GPa, oxygen fugacity (fO2) of ∼FMQ-1.7 to FMQ+2.7 (FMQ refers to the fayalite-magnetite-quartz buffer), and sulfur fugacity (fS2) of −2.2 to 2.1, using a piston cylinder apparatus. The silicate melt composition changes from dry to hydrous andesite to rhyolite. The results obtained from electron microprobe and laser-ablation ICP-MS analyses show that the gold solubility in silicate melts ranges from 0.01 to 55.3 ppm and is strongly correlated with the melt sulfur content [S]melt at fO2 of ∼FMQ-1.7 to FMQ+1.6, which can be explained by the formation of complex Au-S species in the silicate melts. The gold solubility in MSS ranges from 130 to 2800 ppm, which is mainly controlled by fS2. DAuMSS/SM ranges from 10 to 14000 at fO2 of ∼FMQ-1.7 to FMQ+1.6, the large variation of which can be fully explained by combined [S]melt and fS2. Therefore, all of the parameters that can directly affect [S]melt and fS2, such as alkali metals, water, FeO, and fO2, can indirectly affect DAuMSS/SM. The mechanisms that control the sulfide-silicate melt partitioning of gold and the other chalcophile elements, such as Ni, Re, and Mo, differ significantly. This is because gold is dissolved mainly as Au-S species in the silicate melts, while the other chalcophile elements are dissolved mainly as metal oxides in the silicate melts. Applying the correlation between DAuMSS/SM and [S]melt to slab melting and arc magmatic differentiation under different redox conditions, we find that ancient to modern slab melts carry negligible to less than 25% of the slab gold to the subarc mantle; however, gold-enrichment can occur in MSS-saturated arc magmas that have differentiated under moderately oxidized conditions with fO2 between FMQ and FMQ+1.6, in particular if the magmatic crystallization follows a fractional crystallization model. We conclude that moderately oxidized magmas with high contents of alkali metals, sulfur, and water, owing to their low DAuMSS/SM and efficient magma-to-fluid transfer of gold and sulfur, have a high potential to form gold deposits.

Hydrogenation of carbon at 5.5–7.8 GPa and 1100–1400 °C: Implications to formation of hydrocarbons in reduced mantles of terrestrial planets

Formation of hydrocarbons (HCs) by reactions of hydrogen-bearing fluids with carbon (13C soot-like carbon, graphite, or diamond) has been simulated in experiments at pressures of 5.5–7.8 GPa and temperatures of 1100–1400 °C. Hydrogen fugacity (fH2) in tightly sealed Pt and Au capsules was controlled using the double capsule technique at the Mo + MoO2 + H2O (MMO) or Fe + FeO + H2O (IW) equilibria. Synthesis of light alkanes (C2 > C1 > C3 > C4), with smaller amounts of unsaturated hydrocarbons and O-bearing species, occurred all over the experimental P-T-fH2 ranges. For the first time, formation of hydrocarbons from inorganic compounds was directly proved by the reaction of 13C carbon with hydrogen, which yielded isotopically pure 13C light alkanes. In 6.3 GPa runs, the fluid-graphite reaction rate progressively grew, and the process became avalanche-like as the run duration exceeded 1 h. The greatest amounts of HCs (CH4/C2H6 < 1, CH4/C3H8, and CH4/C4H10 ≤ 10) formed at 1400 °C in the 10-hr run. The amount of HC fluid synthesized at 1200 °C was twice smaller. An increase in the experiment duration to 40 h had no effect on amounts of HCs and the composition of species, which indicated that the system achieved equilibrium. The rate of HCs formation was slowest in runs with diamond. The fluid composition varied with pressure and temperature: it contained less methane and slightly more unsaturated hydrocarbons and O-bearing species as pressure and temperature were increased from 5.5 to 7.8 GPa and from 1150 to 1350 °C. An increase in the CO2 concentration in the fluid led to a drastic decrease in the yield of hydrocarbons. The absence of C17O2 in products of the reaction between graphite and fluid containing 17O-labeled water indicated that water was not directly involved in HCs synthesis.The experiments have provided the first unambiguous evidence that volatile-rich and reduced mantles of terrestrial planets (at fO2 near or below IW) provided favorable conditions for formation of a wide range of HCs, mainly light alkanes. Carbon for the HC synthesis may come from graphite, diamond, and soot-like carbon. It should be expected that the efficiency of HCs formation by carbon hydrogenation should be maximal for an increased heat flux (>40 mW/m2) at mantle depths corresponding to the graphite stability region.

ChemInform Abstract: LiNbO3‐Type Oxide (Tl1‐xScx)ScO3: High‐Pressure Synthesis, Crystal Structure, and Electronic Properties.

AbstractPolycrystalline (Tl1‐xScx)ScO3 (x ≈0.26) is obtained by hot press sintering of stoichiometric amounts of Sc2O3 and Tl2O3 (Au or Pt capsules in belt‐type high‐pressure apparatus, 7.7 GPa, 1673 K, 1—2 h).

Synthesis of Au and Pt Hollow Capsules with Single Holes via Pickering Emulsion Strategy

Au and Pt hollow capsules with single holes were synthesized via a Pickering emulsion strategy. Pickering emulsions provided particles with oil–water interfaces as asymmetric platform for anisotropic structure sculpture. Reactive Cu2O particles were utilized not only as emulsifier to prepare Pickering emulsions but also as sacrificed hard template for the consequent asymmetric galvanic reaction at the oil–water interfaces, resulting in the formation of open-mouthed Au and Pt hollow capsules. The opened hollow structure can facilitate the diffusion of reactants to inner side of the shell wall, thus effectively activating the catalytic activity of the inner shell wall of the hollow capsules. The obtained open-mouthed Au hollow capsules show much higher catalytic performance than that of intact Au hollow capsules.

A kinetic pressure effect on the experimental abiotic reduction of aqueous CO2 to methane from 1 to 3.5 kbar at 300 °C

Aqueous abiotic methane concentrations in a range of geologic settings are below levels expected for equilibrium with coexisting CO2 and H2, indicating that kinetics can control the speciation of reduced carbon-bearing fluids. Previous studies have suggested that mineral catalysts or gas-phase reactions may increase the rate of methanogenesis. Here, we report on experiments that indicate pressure can also accelerate aqueous reduction of CO2 to CH4. Four series of cold-seal hydrothermal experiments were performed from 1 to 3.5kbar at 300°C for two weeks and analyzed using gas chromatography/mass spectrometry. The starting fluids were 10–20-μL solutions of 70-mmolal 13C-labeled formic acid (H13COOH) contained in welded gold capsules. Increasing pressure (P) resulted in a systematic, reproducible log-linear increase in 13CH4 yields. The pressure effect could be quantified the log-linear slope, Δlog[13CH4]/ΔP (log mmolal per kbar). The mean slope was 0.66±0.05 (±1s.e.), indicating that 13CH4 yields increased by an average factor of 40–50 over a P range of 2.5kbar. Pressure-independent variations in [13CH4] were observed as scatter about the log-linear regressions and as variations in the y-intercepts of the regressions. These variations were attributed to trace amounts of catalytic Fe along the inner capsule wall that remained despite cleaning the Au capsules in nitric acid prior to each experimental series. The mechanism for the pressure-dependent effect was interpreted to result from one or more of the following three processes: reduction of a metastable reaction intermediate such as methanol, formation of Fe-carbonyl complexes in the fluid, and/or heterogeneous catalysis by Fe. The results suggest that pressure may influence aqueous abiotic CH4 yields in certain geological environments, particularly when the relative effects of other kinetic factors such as temperature are diminished, e.g., in cool forearcs or other settings with a steep geothermal gradient. Because the experiments were performed over a limited pressure range, even modest isothermal increases in pressure may substantially enhance CH4 yields. A kinetic pressure effect may be especially important on the deep ocean floors of planetary bodies where pressure may compensate for the otherwise sluggish reaction kinetics expected at low T.

ChemInform Abstract: Temperature‐Induced Intersite Charge Transfer Involving Cr Ions in A‐Site‐Ordered Perovskites ACu3Cr4O12 (A: La and Y).

AbstractLaCu3Cr4O12 (I) and YCu3Cr4O12 (II) are prepared by high pressure reactions of Ln2O3 (Ln: La, Y), CuO, Cr2O3, and CrO2 in the molar ratio 1:6:0.5:7 (Au capsules, 9 GPa, 900 °C, 30 min).

ChemInform Abstract: Perovskite‐Structure TlMnO3: A New Manganite with New Properties.

AbstractThe title compound is prepared from a stoichiometric mixture of Mn2O3 and Tl2O3 (Au capsules, 6 GPa, 1500 °C, 2 h) and characterized by powder and single crystal XRD, magnetic, specific heat, and electrical resistivity measurements, Moessbauer spectroscopy, and DFT calculations.

ChemInform Abstract: Bi3Cr2.91O11: A Ferromagnetic Insulator from Cr4+/Cr5+ Mixing.

AbstractThe title compound is prepared by high pressure/high temperature reaction of stoichiometric mixtures of Bi2O3, CrO2, and CrO3 (Au capsules, 6 GPa, 1570 K, 2 h).

ChemInform Abstract: High‐Pressure Synthesis of A‐Site Ordered Double Perovskite CaMnTi2O6 and Ferroelectricity Driven by Coupling of A‐Site Ordering and the Second‐Order Jahn—Teller Effect.

AbstractFerroelectric A‐site‐ordered double perovskite CaMnTi2O6 is prepared from equimolar mixtures of MnTiO3 and CaTiO3 in Au (for single crystals) and Pt capsules (for polycrystalline material) under high‐pressure (TRY cubic multianvil press, 1200‐1700 °C, 7 GPa, 0.5 h) followed by annealing (N2 atmosphere, 500 °C, 6 h).

ChemInform Abstract: High‐Concentration Na Doping of SrRuO3 and CaRuO3.

AbstractHighly Na‐doped perovskite‐type ruthenates Sr1‐xNaxRuO3 (x = 0, 0.12, 0.25, 0.50, 0.75) and Ca1‐yNayRuO3 (y = 0, 0.10, 0.20, 0.50) are prepared by solid state reaction of stoichiometric amounts of SrCO3 or CaCO3 and Ru metal (1273 K, 12 h in air), followed by high temperature/high pressure treatment of the obtained powders in the presence of Na2O2 (Au capsules, 6—9 GPa, 1173 K, 30 min).

An experimental study on the influence of fluorine and chlorine on phase relations in peralkaline phonolitic melts

Fluorine and chlorine affect phase stabilities in magmatic rocks. We present phase equilibrium experiments investigating a peralkaline and iron-rich phonolitic composition with variable F and Cl contents. The starting composition represents a dyke rock, which is a possible parental melt to the peralkaline Ilimaussaq plutonic complex (South Greenland). Experiments were performed at 100 MPa, 1,000–650 °C and low oxygen fugacity adjusted with graphite-lined gold capsules in an internally heated argon pressure vessel and rapid quench cold seal pressure vessels. To cover this large T interval, we applied a two-step fractional crystallization strategy where glasses representing residual melt compositions at 800 °C were synthesized as starting material for consecutive experiments at lower T. In these experiments, oxidized starting glasses allocate oxygen by reduction of ferric iron and up to 1.2 wt% dissolved OH form through reaction with hydrogen provided by the pressure medium (H2O) in initially dry experiments. For OH determination, hydrated super-liquidus experiments in Au capsules were performed to calibrate the extinction coefficient for the fundamental OH stretching vibration using infrared spectroscopy (e 3,415 = 48 ± 3 L mol−1 cm−1). Observed mineral phases in our experiments are titanomagnetite, fayalitic olivine, clinopyroxene, aenigmatite (Na2Fe5TiSi6O20), alkali feldspar and nepheline (±native iron) coexisting with residual melt. Above 1.5 wt% Fmelt concentrations, fluorite (CaF2) and hiortdahlite (Ca6Zr2Si4O16F4) are stable in favor of Ca-rich clinopyroxene. Sodalite (Na8Al6Si6O24Cl2) and eudialyte (Na15Ca6Fe3Zr3Si26O73(OH)3Cl2) form at Clmelt concentrations of 0.2–0.5 wt% (depending on T) and ZrO2 melt concentrations >0.7 wt% are additionally needed to stabilize eudialyte and hiortdahlite. Therefore, F and Cl may become compatible in such systems and have the potential to influence F/Cl melt ratios in evolving magmas.

ChemInform Abstract: High‐Pressure Synthesis, Crystal Structures, and Properties of ScRhO3 and InRhO3 Perovskites.

AbstractThe title compounds are prepared from stoichiometric mixtures of In2O3 or Sc2O3 and Rh2O3 (Au capsules, 6 GPa, 1500 K, 2 h).

ChemInform Abstract: Crystal Structure and Properties of High‐Pressure‐Synthesized BiRhO3, LuRhO3, and NdRhO3.

AbstractBiRhO3 (I), LuRhO3 (II), and NdRhO3 (III) are prepared by solid state reaction of stoichiometric mixtures of M2O3 (M: Bi, Lu, Nd) and Rh2O3 (Au capsules, 6 GPa, 1600 °C for (I), 1300 °C for (II) and (III), 2 h).

ChemInform Abstract: High‐Pressure Synthesis, Crystal Structure, and Properties of BiPd2O4 with Pd2+ and Pd4+ Ordering and PbPd2O4.

AbstractThe title compounds are prepared from stoichiometric mixtures of Bi2O3, PdO, and KClO4 (BiPd2O4), or PbO2 and PdO (PbPd2O4) in Au capsules at 6 GPa and 1500 K (2 h).