Redox conditions in magma oceans (MOs) have a key influence on the mass and composition of Earth's early atmosphere. If the shallow part of the MO is oxidized, it may be overlain by an H2O–CO2 ...atmosphere, but if the near-surface magma is close to equilibrium with Fe-rich alloy, then the atmosphere will consist chiefly of H2, H2O, and CO, and on cooling will be rich in CH4. Although MOs are intimately associated with core-forming metal, the redox conditions in their shallow parts are not necessarily reducing. The magmatic Fe3+/FeT ratio is set by equilibrium with metal at depth and homogenized through the magma column by convection. Indirect evidence suggests that the Fe3+/FeT ratio of magmas in equilibrium with alloy at high pressure is greater than at low pressure, such that the shallow part of the MO may be comparatively oxidized and coexist with an atmosphere consisting chiefly of H2O and CO2. The mass of the atmosphere is dictated by the concentrations of volatile-species dissolved in the magma, which in turn are determined by partitioning between magma and alloy. Very strong partitioning of C into alloy may capture most of the carbon delivered to the growing planet, leaving behind a C-poor bulk silicate Earth (BSE) and a C-poor atmosphere. However, modest solubility of CH4 in the magma may allow the BSE to retain significant C. Alternatively, if partitioning of C into alloy is extreme but the fraction of metal equilibrated with the MO is small, the alloy may become saturated with diamond. Floatation of diamond in the MO may retain a substantial inventory of C in the early mantle. BSE C may also have been replenished in a late veneer. Following segregation of metal to the core, crystallization of the MO may have prompted precipitation of C-rich phases (graphite, diamond, carbide), limiting the C in the early atmosphere and creating a substantial interior C inventory that may account for the large fraction of BSE carbon in the mantle today. Such precipitation could have occurred owing to a combination of the redox evolution of the crystallizing MO and cooling.
► Magma oceans (MOs) have vertical variations in oxidation state. ► Precipitation of diamond in MO may store C in the early mantle. ► Atmospheres are likely H2O+CO2, over deep MO and H2–CO–H2O over shallow ones.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We present new experimentally determined trace element partition coefficients for nine garnet/melt and two clinopyroxene/melt pairs at 2.9–3.1 GPa and 1325°–1390°C, applicable to anhydrous partial ...melting of MORB‐like eclogite in the upper mantle. Phase compositions are similar to those documented in partial melting experiments of eclogite at these conditions: garnets with 16–25% grossular component and 0.4–2.0 wt % TiO2 coexist with siliceous partial melts having 52.4–57.1 wt % SiO2 and 1.1–6.7 wt % TiO2. Observed garnet/melt partitioning depends on TiO2 concentrations in garnet. Among the high‐TiO2 garnets (1.4–2.0 wt % TiO2), partition coefficients (Dgt/melt) increase with increasing grossular content of garnet (16–24%), but for the low‐TiO2 garnets (0.4–0.6 wt % TiO2) there is no difference in partitioning behavior at 19–24% grossular. In general, partition coefficients for the low‐TiO2 garnets tend to be higher than for the high‐TiO2 garnets. DZr and DHf increase with higher grossular content, as does DZr/DHf, but DZr and DHf always remain smaller than unity, and TiO2 in garnet appears to have little effect on DZr/DHf. DTh and DU have average values of 0.0012 and 0.0111 for the high‐TiO2 garnets and 0.0074 and 0.0376 for the low‐TiO2 garnets (DU/DTh of 9.1 and 5.1, respectively), affirming that partial melting of eclogite in the upper mantle can produce liquids with significant (230Th)/(238U) excess. D values of highly charged cations (Nb, Ta, Th, U) are lower in high‐TiO2 garnets. This is likely because Ti4+ occupying the garnet Y site requires charge balance by 2+ cations in Y or 3+ cations in Z, thereby limiting the availability of these charge‐balancing substitutions to accommodate other highly charged cations. The overall range of our new garnet/melt partition coefficients, regardless of Ti and grossular content, is similar to literature garnet/melt partitioning data applicable to garnet peridotite melting, and therefore bulk partition coefficients for eclogite and peridotite depend largely on mineral modes and choice of partitioning data for clinopyroxene. Using our new data and previously published data from the literature, we calculate bulk partition coefficients appropriate for two MORB‐like eclogites (82% clinopyroxene + 18% garnet and 75% clinopyroxene + 25% garnet) and a garnet peridotite (60% olivine + 17% orthopyroxene + 13% clinopyroxene + 10% garnet). Bulk partition coefficients are generally much higher for MORB‐like eclogite when compared to garnet peridotite, with the exception of Th and U. However, the ratios of bulk partition coefficients of eclogite and garnet peridotite are similar for pairs such as DSm/DYb, DZr/DHf and DU/DTh, indicating that both lithologies can induce similar trace element fractionations during partial melting in the presence of garnet.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT
We present the addition of nebular emission from the narrow-line regions (NLR) surrounding active galactic nuclei (AGNs) to beagle (BayEsian Analysis of GaLaxy sEds). Using a set of ...idealized spectra, we fit to a set of observables (emission-line ratios and fluxes) and test the retrieval of different physical parameters. We find that fitting to standard diagnostic-line ratios plus O ii λ3726, λ3729/O iii λ5007, H β/H α, O i λ6300/O ii λ3726, λ3729, and H α flux, degeneracies remain between dust-to-metal mass ratio ($\xi _\rm {d}^{\small NLR}$) and ionization parameter ($U_\rm {s}^{\small NLR}$) in the NLR gas, and between slope of the ionizing radiation ($\alpha _{\small PL}$, characterizing the emission from the accretion disc around the central black hole) and total accretion-disc luminosity ($L_\rm {acc}$). Since these degeneracies bias the retrieval of other parameters even at maximal signal-to-noise ratio (S/N), without additional observables, we suggest fixing $\alpha _{\small PL}$ and dust-to-metal mass ratios in both NLR and H ii regions. We explore the S/N in H β required for un-biased estimates of physical parameters, finding that S/N(H β) ∼ 10 is sufficient to identify an NLR contribution, but that higher S/N is required for un-biased parameter retrieval (∼20 for NLR-dominated systems, ∼30 for objects with approximately equal H β contributions from NLR and H ii regions). We also compare the predictions of our models for different line ratios to previously published models and data. By adding He ii λ4686-line measurements to a set of published line fluxes for a sample of 463 AGN NLR, we show that our models with $-4\lt \hbox{$\log U_{\small S}^{\small NLR}$}\lt -1.5$ can account for the full range of observed AGN properties in the local Universe.
In this ab initio study, we expand previous investigations of charge-balanced hydrous Mg ((2H)MgX) and Si ((4H)SiX) defects in forsterite, the Mg end-member of olivine, to address the relative ...stability of these two defects. First, we systematically search for (2H)MgX configurations to find possible defect states; second, we include the contribution of vibrational energy and defect configurational entropy in the calculation of formation energies of both defects; third, we address the effect of pressure and temperature simultaneously on their relative stability. Based on these considerations, we demonstrate that hydrous Mg defects ((2H)MgX) can be stabilized with respect to hydrous Si defects ((4H)SiX) at relevant mantle conditions and that configurational entropy and vibrational free energy play key roles in this stabilization. Our results reveal that water speciation in olivine is influenced by temperature and pressure. As mantle physical and chemical properties may be affected by the speciation of water in olivine, application of experimental results to the mantle should account for the temperature- and pressure-dependent changes in water speciation.
We have measured hydrogen partition coefficients between nominally anhydrous minerals (olivine, pyroxenes) and basaltic melts in 13 hydrous melting experiments performed at upper mantle P‐T ...conditions (1–2 GPa and 1230–1380°C). Resulting liquids have 3.1–6.4 wt.% H2O and average mineral/melt partition coefficients as follows: DHol/melt = 0.0017 ± 0.0005 (n = 9), DHopx/melt = 0.019 ± 0.004 (n = 8), and DHcpx/melt = 0.023 ± 0.005 (n = 2). Mineral/mineral partition coefficients are DHol/opx = 0.11 ± 0.01 (n = 4), DHol/cpx = 0.08 ± 0.01 (n = 2) and DHcpx/opx = 1.4 ± 0.3 (n = 1). These measurements confirm that water behaves similarly to Ce during mantle melting (DHperidotite/melt is ∼0.009). For mantle water concentrations of 50–200 ppm, the onset of melting is 5–20 km deeper than the dry solidus, less than previous estimates.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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We derived stellar ages and metallicities Z/H for ∼70 passive early-type galaxies (ETGs) selected from VANDELS survey over the redshift range 1.0 < z < 1.4 and stellar mass range 10 < ...log(M*/M⊙) < 11.6. We find significant systematics in their estimates depending on models and wavelength ranges considered. Using the full-spectrum fitting technique, we find that both Z/H and age increase with mass as for local ETGs. Age and metallicity sensitive spectral indices independently confirm these trends. According to EMILES models, for 67 per cent of the galaxies we find Z/H > 0.0, a percentage which rises to ∼90 per cent for log(M*/M⊙) > 11 where the mean metallicity is Z/H = 0.17 ± 0.1. A comparison with homogeneous measurements at similar and lower redshift does not show any metallicity evolution over the redshift range 0.0 < z < 1.4. The derived star formation (SF) histories show that the stellar mass fraction formed at early epoch increases with the mass of the galaxy. Galaxies with log(M*/M⊙) > 11.0 host stellar populations with Z/H > 0.05, formed over short time-scales (Δt50 < 1 Gyr) at early epochs (tform < 2 Gyr), implying high star formation rates (SFR > 100 M⊙ yr−1) in high-mass density regions (log(Σ1kpc) > 10 M⊙/kpc2). This sharp picture tends to blur at lower masses: log(M*/M⊙) ∼ 10.6 galaxies can host either old stars with Z/H < 0.0 or younger stars with Z/H > 0.0, depending on the duration (Δt50) of the SF. The relations between galaxy mass, age, and metallicities are therefore largely set up ab initio as part of the galaxy formation process. Mass, SFR, and SF time-scale all contribute to shape up the stellar mass–metallicity relation with the mass that modulates metals retention.
To understand possible volcanogenic fluxes of CO₂ to the Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the Adirondack-class Humphrey basalt at ...1–2.5GPa and 1400–1625°C. Starting materials included both oxidized and reduced compositions, allowing a test of the effect of iron oxidation state on CO₂ solubility. CO₂ contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and Fe³⁺/Feᵀ was measured by Mössbauer spectroscopy. The CO₂ contents of glasses show no dependence on Fe³⁺/Feᵀ and range from 0.34 to 2.12wt.%. For Humphrey basalt, analysis of glasses with gravimetrically-determined CO₂ contents allowed calibration of an integrated molar absorptivity of 81,500±1500Lmol⁻¹cm⁻² for the integrated area under the carbonate doublet at 1430 and 1520cm⁻¹. The experimentally determined CO₂ solubilities allow calibration of the thermodynamic parameters governing dissolution of CO₂ vapor as carbonate in silicate melt, KII, (Stolper and Holloway, 1988) as follows: lnKII ⁰=-15.42±0.20, ΔV⁰=20.85±0.91cm³mol⁻¹, and ΔH⁰=−17.96±10.2kJmol⁻¹. This relation, combined with the known thermodynamics of graphite oxidation, facilitates calculation of the CO₂ dissolved in magmas derived from graphite-saturated Martian basalt source regions as a function of P, T, and Formula: see text . For the source region for Humphrey, constrained by phase equilibria to be near 1350°C and 1.2GPa, the resulting CO₂ contents are 51ppm at the iron–wüstite buffer (IW), and 510ppm at one order of magnitude above IW (IW+1). However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459). This, combined with hotter source temperatures (1540°C and 1.2GPa) could allow hot plume-like magmas similar to Y 980459 to dissolve 240ppm CO₂ at IW and 0.24wt.% of CO₂ at IW+1. For expected magmatic fluxes over the last 4.5Ga of Martian history, magmas similar to Humphrey would only produce 0.03 and 0.26bars from sources at IW and IW+1, respectively. On the other hand, more primitive magmas like Y 980459 could plausibly produce 0.12 and 1.2bars at IW and IW+1, respectively. Thus, if typical Martian volcanic activity was reduced and the melting conditions cool, then degassing of CO₂ to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water. However, if a significant fraction of Martian magmas derive from hot and primitive sources, as may have been true during the formation of Tharsis in the late Noachian, that are also slightly oxidized (IW+1.2), then significant contribution of volcanogenic CO₂ to an early Martian greenhouse is plausible.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We describe a newly calibrated model for the thermodynamic properties of magmatic silicate liquid. The new model, pMELTS, is based on MELTS Ghiorso and Sack, 1995 but has a number of improvements ...aimed at increasing the accuracy of calculations of partial melting of spinel peridotite. The pMELTS algorithm uses models of the thermodynamic properties of minerals and the phase equilibrium algorithms of MELTS, but the model for silicate liquid differs from MELTS in the following ways: (1) The new algorithm is calibrated from an expanded set of mineral‐liquid equilibrium constraints from 2439 experiments, 54% more than MELTS. (2) The new calibration includes mineral components not considered during calibration of MELTS and results in 11,394 individual mineral‐liquid calibration constraints (110% more than MELTS). Of these, 4924 statements of equilibrium are from experiments conducted at elevated pressure (200% more than MELTS). (3) The pMELTS model employs an improved liquid equation of state based on a third‐order Birch‐Murnaghan equation, calibrated from high‐pressure sink‐float and shockwave experiments to 10 GPa. (4) The new model employs a revised set of end‐member liquid components. The revised components were chosen to better span liquid composition‐space. Thermodynamic properties of these components are optimized as part of the mineral‐liquid calibration. Comparison of pMELTS to partial melting relations of spinel peridotite from experiments near 1 GPa indicates significant improvements relative to MELTS, but important outstanding problems remain. The pMELTS model accurately predicts oxide concentrations, including SiO2, for liquids from partial melting of MM3 peridotite at 1 GPa from near the solidus up to ∼25% melting. Compared to experiments, the greatest discrepancy is for MgO, for which the calculations are between 1 and 4% high. Temperatures required to achieve a given melt fraction match those of the experiments near the solidus but are ∼60°C high over much of the spinel lherzolite melting interval at this pressure. Much of this discrepancy can probably be attributed to overstabilization of clinopyroxene in pMELTS under these conditions. Comparison of pMELTS calculations to the crystallization and partial melting experiments of Falloon et al. 1999 shows excellent agreement but also suffers from exaggerated calculated stability of clinopyroxene. Finally, comparison of pMELTS calculations to the garnet peridotite experiments of Walter 1998 at 3–7 GPa reveals disparities between calculations and experiments that increase with pressure. The most prominent of these disparities is manifest as overprediction of the stability of garnet and underprediction of that of olivine. Part of this problem may be attributed to inadequacies in the Birch‐Murnaghan equation of state in reproducing the behavior of highly compressible liquids at high pressures and temperatures.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT
We study the impact of the local environment on the transformation of spiral galaxies in three nearby (z < 0.08) Abell clusters: A85/A496/A2670. These systems were observed in H i with the ...Very Large Array, covering a volume extending beyond the virial radius and detecting 10, 58, and 38 galaxies, respectively. High fractions (0.40–0.86) of bright spirals log(M*/M⊙) = 9−10 are not detected in H i. We provide further evidence of environmental effects consisting in significant fractions (0.10–0.33) of abnormal objects and a number of red (passive) spirals, suggesting an ongoing process of quenching. Ram-pressure profiles and the sample of the brightest spirals used as test particles for environmental effects indicate that ram-pressure plays an important role in stripping and transforming late-types. Phase-space diagrams and our search for substructures helped to trace the dynamical stage of the three systems. This was used to compare the global cluster effects versus pre-processing, finding that the former is the dominating mechanism in the studied clusters. By contrasting the global distribution of H i normal versus H i disturbed spirals in the combined three clusters, we confirm the expected correlation of disturbed objects located, on average, at shorter projected radii. However, individual clusters do not necessarily follow this trend, and we show that A496 and A2670 present atypical behaviour. In general, we provide conclusive evidence about the dependence of the transformation of infalling spirals on the ensemble of cluster properties like mass, ICM density, dynamical stage, and surrounding large-scale structure.
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