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<jats:title>Abstract</jats:title> <jats:p>Magmatic gas exsolving during late-stage cooling of shallow magmas has been considered an important facilitator of low-pressure alteration and metal transport. However, the chemical properties of such gas, particularly its metal transport mechanisms and capacity, remain elusive. Trace elements in minerals produced by gas-mediated surface reaction or precipitation from gas capture details of gas composition and reaction pathways. However, interpretation of mineral trace element contents is dependent on understanding crystallographic controls on gas/mineral partitioning. This work investigates the structural accommodation of As, Mn, Ga, Ge, Fe, and Ti in vapor-deposited topaz of vesicular topaz rhyolite from the Thomas Range, Utah, through single-crystal synchrotron microbeam X-ray techniques on picogram quantities of those trace elements. X-ray absorption near edge structure (XANES) data indicates that these elements are incorporated into topaz as As5+, Fe3+, Mn3+, Ti4+, Ga3+, and Ge4+. Extended X-ray absorption fine structure (EXAFS) analysis for these trace elements, compared to EXAFS of structural Al and Si, reveals that As5+ and Ge4+ are incorporated directly into the tetrahedral site of the topaz structure, with the octahedral site accommodating Mn3+, Fe3+, Ga3+, and Ti4+. For As5+ and Fe3+, the structural impact of substitution extends to at least second neighbors (other elements were only resolvable to first neighbors). Further interpretation of the EXAFS results suggests that the substitution of Ti4+ results in increased distortion of the octahedral site, while the other trace elements induce more uniform expansion correlating in magnitude to their ionic radius. Comparison of quantified X-ray fluorescence (XRF) data for two topaz crystals from this rhyolite reveals variable trace element concentrations for As5+, Fe3+, Ga3+, and Ti4+, reflective of a source gas undersaturated in these trace elements changing in concentration over the period of topaz deposition. The identical Ge4+ content of the two topaz crystals suggests that Ge4+ in the gas was buffered by the growth of another Ge4+-bearing phase, such as quartz. The very low Mn3+ content in the topaz crystals does not reflect the abundance of Mn3+ in the gas (saturation of Mn is evidenced by coexisting bixbyite). Instead, it suggests a strong Jahn-Teller inhibitory effect to the substitution of Mn3+ for Al3+ in the distorted octahedral site of topaz. It is proposed that exsolution of an HF-enriched gas from cooling rhyolitic magma led to local scouring of Al, Si, and trace metals from the magma. Once topaz crystals nucleated, self-catalyzed reactions that recycle HF led to continued growth of topaz.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Microbial Fe(II) oxidation has been proposed as a major source of Fe minerals during deposition of banded iron formations (BIFs) in the Archean and Proterozoic Eons. The conspicuous absence of organic matter or graphitic carbon from BIFs, however, has given rise to divergent views on the importance of such a biologically mediated iron cycle. Here, we present mineral associations, major element concentrations, total carbon contents and carbon isotope compositions for a set of lower amphibolite-facies BIF samples from the Neoarchean Zhalanzhangzi BIF in the Qinglonghe supracrustal sequence, Eastern Hebei, China. Graphite grains with crystallization temperatures (~470 °C) that are comparable to that predicted for the regional metamorphic grade are widely distributed, despite highly variable iron (12.9 to 54.0 wt%) and total organic carbon (0.19 to 1.10 wt%) contents. The crystalline graphite is interpreted to represent the metamorphosed product of syngenetic bio-mass, based on its co-occurrence with apatite rosettes and negative bulk rock δ13Corganic values (–23.8 to –15.4‰). Moreover, the crystalline graphite is unevenly distributed between iron- and silica-rich bands. In the iron-rich bands, abundant graphite relicts are closely associated with magnetite and/or are preserved within carbonate minerals (i.e., siderite, ankerite, and calcite) with highly negative bulk rock δ13Ccarb values (–16.73 to –6.33‰), indicating incomplete reduction of primary ferric (oxyhydr) oxides by organic matter. By comparison, only minor graphite grains are observed in the silica-rich bands. Normally, these grains are preserved within quartz or silicate minerals and thus did not undergo oxidation by Fe(III). In addition, the close association of graphite with iron-bearing phases indicates that ferric (oxyhydr)oxides may have exerted a first order control on the abundance of organic matter. Combined, the biological oxidation of Fe(II) in the oceanic photic zone and subsequent burial of ferric (oxyhydr)oxides and biomass in sediments to form BIFs, suggests that a BIF-dependent carbon cycle was important in the Archean Eon. Although significant re-adsorption of phosphorus to ferric (oxyhydr)oxides and the formation of authigenic phosphate minerals at the sediment-water interface would be expected, oxidation of biomass in BIFs may have recycled at least a portion of the P (and other nutrients) released from reactions between organic matter and ferric (oxyhydr)oxides to the overlying water column, potentially promoting further primary productivity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A centimeter-sized fragment of dunite, the first recognized fragment of Moon mantle material, has been discovered in the lunar highlands breccia meteorite Northwest Africa (NWA) 11421. The dunite consists of 95% olivine (Fo83), with low-Ca and high-Ca pyroxenes, plagioclase, and chrome spinel. Mineral compositions vary little across the clast and are consistent with chemical equilibration. Mineral thermobarometry implies that the dunite equilibrated at 980 ± 20 °C and 0.4 ± 0.1 gigapascal (GPa) pressure. The pressure at the base of the Moon’s crust (density 2550 kg/m3) is 0.14–0.18 GPa, so the dunite equilibrated well into the Moon’s upper mantle. Assuming a mantle density of 3400 kg/m3, the dunite equilibrated at a depth of 88 ± 22 km. Its temperature and depth of equilibration are consistent with the calculated present-day selenotherm (i.e., lunar geotherm).</jats:p> <jats:p>The dunite’s composition, calculated from mineral analyses and proportions, contains less Al, Ti, etc., than chondritic material, implying that it is of a differentiated mantle (including cumulates from a lunar magma ocean). The absence of phases containing P, Zr, etc., suggests minimal involvement of a KREEP component, and the low proportion of Ti suggests minimal interaction with late melt fractionates from a lunar magma ocean. The Mg/Fe ratio of the dunite (Fo83) is significantly lower than models of an overturned unmixed mantle would suggest, but is consistent with estimates of the bulk composition of the Moon’s mantle.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We focus on the ferric end-member of phase H: ε-FeOOH using density functional theory at the PBEsol+U level. At 300 K, we find that ε-FeOOH undergoes a hydrogen bond symmetrization at 37 GPa and a sharp high-spin to low-spin transition at 45 GPa. We find excellent agreement with experimental measurements of the equation of state, lattice parameters, atomic positions, vibrational frequencies, and optical properties as related to the band gap, which we find to be finite and small, decreasing with pressure. The hydrogen bond symmetrization transition is neither first-nor second-order, with no discontinuity in volume or any of the elastic moduli. Computed IR and Raman frequencies and intensities show that vibrational spectroscopy may provide the best opportunity for locating the hydrogen bond symmetrization transition experimentally. We find that ε-FeOOH is highly anisotropic in both longitudinal- and shear-wave velocities at all pressures, with the shear wave velocity varying with propagation and polarization direction by as much as 24% at zero pressure and 43% at 46 GPa. The shear and bulk elastic moduli increase by 18% across the high-spin to low-spin transition.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Identification of radioactive materials is a critical goal of resource exploration, basic actinide science, and nuclear forensics, and we provide here new insights toward rapid, nondestructive analysis of uranium-containing minerals and technogenic phases. Raman and infrared spectroscopic data are powerful indicators of solid-phase U(VI) coordination chemistry. In addition, U(VI) minerals exhibit high chemical and structural diversity as artifacts of geochemical processes leading to ore formation. Spectral signals of axial UO22+ (U-Oyl) bond lengths and the influences of additional oxyanions on these values are well documented for uranium oxide and oxysalt minerals and technogenic phases. Additional insight regarding the underlying crystallographic structure and chemical composition of uranium materials can be extracted through a survey of all available Raman spectroscopic data for these phases. To this end, we have developed the Compendium of Uranium Raman and Infrared Experimental Spectra (CURIES). CURIES was compiled via a thorough review of literature and databases, and for mineral species that lack measured and recorded spectra, data were obtained either from museum and academic collections or by direct syntheses. Characteristic Raman spectroscopic features for subgroups of uranyl minerals within CURIES were elucidated using multivariate statistical analyses. In addition, average spectra for groups of uranyl minerals were determined, providing insight into common spectroscopic characteristics that are indicative of the structural origins from which they arise. As of publication, 275 mineral species and technogenic phases have been entered in CURIES, and of these, 83 phases have published spectra that have been included in the CURIES database. Data collection is ongoing, and we have triaged missing data sets to assess CURIES for completion and to identify mineral groups that lack representation and should therefore be prioritized for data acquisition and inclusion in the database.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The current debate on volcanic-plutonic connection is centered on whether efficient liquid-crystal segregation dominates the evolution of a mushy reservoir to produce evolved, crystal-poor rhyolite and cumulate leftover. However, magma recharge may remarkably influence the evolution of a mushy reservoir and obscure the evidence of liquid-crystal segregation. This complexity poses a challenge to exploring the connection of volcanic-plutonic rocks. This study investigates the Qinzhou Bay granitic complex (~250–248 Ma) from South China, which contains crystal-poor (&amp;lt;19 vol%) peraluminous rhyolites and subsequent crystal-rich (28–54 vol%) porphyries. Although the rhyolite and porphyry units have a close spatio-temporal link, they do not share a fractionation trend and similar whole-rock Sr-Nd-O isotopic compositions; thus, a direct connection is not evidenced. We further present textural analyses, mineral and melt inclusion compositions, thermobarometry (the combination of Ti-in-zircon thermometer and Ti-in-quartz thermobarometer), and thermodynamic modeling to examine the alternative interpretations, i.e., the two units may have intrinsically independent origins or the connection of the two units has been obscured. For the rhyolite unit, thermobarometric results reveal a polybaric storage system consisting of middle (&amp;gt;600 ± 80 MPa) and upper (~150 ± 40 and ~60 ± 20 MPa) crustal reservoirs. Variations in quartz Fe content and chlorine-rich, metaluminous melt inclusions suggest that magma hybridization with less-evolved metaluminous magmas occurred at both crustal levels. In particular, the elevated Fe contents in the quartz population that crystallized at the shallowest level (~60 ± 20 MPa) suggest that recharge magmas were directly injected into the shallowest reservoir. Deviation of the whole-rock composition from the liquid evolution trend recorded in melt inclusions suggests a combined effect of magma mixing and crystal-melt segregation processes in upper crustal reservoirs. Thermodynamic modeling and mass balance calculations suggest that the whole-rock composition of the rhyolite could be reproduced by mixing between regionally exposed dacites and segregated melts at crystallinities of 50–60% (using parental magma represented by the least-evolved melt inclusion). For the porphyry unit, thermobarometric results reveal magma storage at middle (more than 450 ± 40 to 550 ± 40 MPa) and upper (110 ± 20 to 140 ± 20 MPa) crustal levels. The small-scale oscillatory zonation of plagioclase, the pervasive resorption of quartz and alkali feldspar, and the presence of peraluminous microgranular enclaves in the porphyries suggest a recharge event of metasediment-sourced magmas, triggering reactivation and convection of the reservoir. Autoclastic and overgrowth textures of quartz, plagioclase, and alkali feldspar phenocrysts and development of columnar jointing suggest that the reactivated porphyritic magmas ascended and emplaced at ultrashallow levels (~30 ± 10 MPa).</jats:p> <jats:p>Because of the similar storage pressures, the porphyries may represent remobilized cumulates of rhyolitic magmas, whereas the texture and geochemistry of the cumulate-liquid pair were modified, a key factor rendering a cryptic connection between the rhyolite and porphyry. Alternatively, the plumbing systems feeding the rhyolite and porphyry units are horizontally independent or vertically discrete, but this circumstance is inconsistent with the same evolution trend of quartz Fe and Al contents of the rhyolite and porphyry. Our study highlights that whole-rock composition may record blended information of complex processes, and caution should be taken when whole-rock composition is used to extract information of a single process. Multi-method constraints are required to evaluate the influence of recharge processes on the modification of liquid-cumulate records, and big data analysis on the basis of geochemistry should be conducted with caution to avoid biased understanding.</jats:p>