Olivine Samples Research Articles

THERMOBAROMETRY OF DEPLETED PERIDOTITES

An assessment was made of the possibility of using olivine thermobarometry for xenoliths of depleted peridotites from the Udachnaya pipe (Yakutia), represented by 76 megacrystalline dunites and 5 megacrystalline harzburgites. Specially developed and tested method of microprobe analysis was used to determine Al and Ca microimpurities in the olivine samples studied. PT-parameters of megacrystalline dunite xenoliths were calculated using the equations of olivine, garnet, and olivine-garnet thermobarometers. Enstatite geobarometers were additionally used for some megacrystalline harzburgites. Comparison of the obtained data showed that the geothermobarometric pair of FinnertyRigden barometer (Ca in olivine) for wide PT-range peridotites and thermometer [Bussweiler et al., 2017] (Al in olivine) for garnet peridotites is most suitable for assessing the PT-parameters of the megacrystalline dunite collection studied, though some of the high PT-parameters (>60 kbar and 1200 °C) are questionable. Garnet barometer [Grütter et al., 2006] (CaO – Cr2O3 ratio in pyrope) does not always agree with olivine geothermometers. This may be caused by the necessity to adjust the barometer equations for a wider range of compositions, as well as by the possible imbalance between garnet and olivine. We admit that more accurate results can be obtained by using this barometer in combination with garnet thermometers based on the determination of Ni in garnet. There is not enough data on harzburgites to draw certain conclusions. However, it should be recognized that the traditional pair of McGregor enstatite barometer and O’Neill-Wood garnet-olivine thermometer still remains the most acceptable for estimating the PT-parameters of megacrystalline harzburgites, though with some temperature underestimation.

Phosphorus availability from olivine for biospheres

Phosphorus plays a multifaceted role for all known life and hence understanding its sources on the early Earth provides constraints on how life developed to incorporate this element into its biochemistry. Currently, the major phosphorus mineral group on the surface of the Earth are the apatites, which are poorly soluble calcium phosphates and hence may not have been a good source of phosphorus on the early Earth. An alternative source of phosphorus may be the mineral olivine. Given that olivine makes up a large part of the upper mantle of Earth and presumably other rocky planets and moons, it stands to reason that olivine may be a potential phosphorus reservoir for prebiotic chemical environments. Here we examine the phosphorus content of 10 olivine samples from different terrestrial localities to determine their P content and P speciation. We find that extracts of the samples contain varying amounts of phosphate, and some contain pyrophosphate. Olivine may have served as a source of phosphate on the early Earth and possibly elsewhere in the solar system, and its dissolution could have supplied this nutrient to a nascent biosphere.

From electron tomography of dislocations to field dislocation mechanics: application to olivine

We propose a new procedure to extract information from electron tomography and use them as an input in a field dislocation mechanics. Dislocation electron tomography is an experimental technique that provides three-dimensional (3D) information on dislocation lines and Burgers vectors within a thin foil. The characterized 3D dislocation lines are used to construct the spatial distribution of the equivalent Nye dislocation density tensor. The model dislocation lattice incompatibility equation and stress balance equation are solved with a spectral code based on fast Fourier transform algorithms. As an output of the model, one obtains the 3D distribution of mechanical fields, such as strains, rotations, stresses, resolved shear stresses (RSSs) and energy, inside the material. To assess the potential of the method, we consider two regions from a previously compressed olivine sample. Our results reveal significant local variations in local stress fields and RSSs in various slip systems, which can impact the strong plastic anisotropy of olivine and the activation of different dislocation slip systems. It also evidences the built-up of kinematic hardening down to the nanometre scale.

Investigating the role of incident ion flux in solar wind space weathering of carbon-rich asteroidal regolith via H+ and He+ irradiation of the Murchison meteorite

We present results from a set of low and high flux 1 keV/amu H+ and He+ irradiation experiments performed on slabs of the Murchison CM2 carbonaceous chondrite. The low flux conditions for H+ and He+ irradiation were ~1–1.5 orders of magnitude lower than the high flux conditions, and each experiment was irradiated to a total fluence between ~3 × 1016 to ~6 × 1016 ions/cm2. Irradiation-induced changes in the surface chemistry and optical properties of the Murchison samples were evaluated using in situ X-ray photoelectron spectroscopy (XPS) and visible and near-infrared spectroscopy (VNIR). We characterized the microstructure and composition of ion damaged rims in focused ion beam (FIB) cross-sections extracted from olivine and matrix material in each irradiated Murchison slab using transmission electron microscopy (TEM). XPS results suggest that both low flux and high flux H+ and He+ irradiation cause minor sputtering of surface carbon as well as a reduction in the valence state of iron, from Fe3+ to Fe2+. Slope bluing is observed in VNIR spectra of the irradiated samples which may reflect carbonization and dehydrogenation of organic species and contrasts with reddening trends associated with npFe0 formation. Although we do not observe a strong flux-dependence on the crystallinity of ion-damaged olivine, TEM analyses reveal a variety of microstructures in all olivine FIB-sections, suggesting that crystallographic orientation may affect amorphization efficiency. Analyses of matrix FIB-sections indicate that phyllosilicate alteration is mainly driven by He+ irradiation, where the higher incident flux leads to greater amorphization and the formation of more distinct ion-damaged layers, similar to smooth layers in returned Ryugu particles. TEM results also provide some evidence that higher ion flux leads to greater vesiculation, with He+ irradiation being more efficient at vesiculation than H+ irradiation, and promotes the segregation of Mg and Si into laterally extensive lenses and layers in olivine samples. We discuss the implications of these findings for constraining the role that ion flux plays in the development of space weathering characteristics in silicate phases present in carbonaceous asteroidal regoliths. These results will be important for understanding the complexity of this process and how it operates on carbon-rich airless bodies like asteroids Bennu and Ryugu.

High precision measurement of trace F and Cl in olivine by electron probe microanalysis

Fluorine (F) and chlorine (Cl) are important volatiles in olivine and its high-pressure polymorphs, which would significantly affect olivine phase transition, melting temperature, and physical property of the mantle. F and Cl concentrations in olivine can be detected by electron probe microanalysis (EPMA). However, the analytical accuracy and precision can be impeded by severe peak overlaps, low peak intensities of traditional analytical crystals, and secondary fluorescence effects. In this study, we constructed an optimized analytical method with high accuracy and precision to analyze trace F and Cl in olivine. Key parameters of analytical crystals, beam conditions, peak overlaps, and secondary fluorescence effects were discussed. Variations in the levels of the analyzed trace elements fall within ± 10%. The detection limits (3σ) for F and Cl are lowered to 30 ppm and 5 ppm, respectively. This method can provide precise F and Cl analysis for natural olivine samples and help to provide significant information on its formation process.

Predicting olivine formation environments using machine learning and implications for magmatic sulfide prospecting

Abstract Global volcanic and plutonic olivines record the compositional characteristics and physicochemical conditions of the parental magmas. Thus, they have significant potential for use as petrogenetic discriminators of the olivine formation environment and prospecting indicators for potential host rocks of magmatic sulfide deposits. Several data visualization approaches have been proposed by researchers to determine olivine origins. However, they can only discriminate specific olivine populations and require the incorporation of trace elements for which data are lacking globally. In this study, a machine-learning method consisting of the random forest algorithm and the synthetic minority oversampling technique (SMOTE) is used to discriminate the crystallization environments of olivine and predict the sulfide potential of olivine-bearing mafic-ultramafic intrusions. We employ a global data set of 24 341 olivine samples from 12 environments to determine the contents of MgO, FeO, Ni, Ca, Mn, and Cr and the Fo number [100 × Mg/(Mg+Fe)]. The results indicate that the proposed method can classify olivine into genetically distinct populations and distinguish olivine derived from mineralized intrusions from that derived from sulfide-barren intrusions with high accuracies (higher than 99% on average). We develop a dimensionality reduction algorithm to visualize the olivine classifications using low-dimensional vectors and an olivine classifier (accessible at http://101.33.204.62:8080/olivine_web/main.html, China University of Geosciences, Beijing). The model is used successfully to identify the contributions of distinct sources to regional magmatism using olivines from the late Permian picrite and basalt along the western margin of the Yangtze block (SW China) and to predict the sulfide potential of the newly discovered Qixin mafic-ultramafic complex in the southern Central Asian Orogenic Belt (NW China). The findings suggest that the proposed approach enables the accurate identification of olivine origins in different formation environments and is a reliable indicator suitable for global Ni-Cu-platinum group element (PGE) exploration.

In-situ study of microstructures induced by the olivine to wadsleyite transformation at conditions of the 410 km depth discontinuity

Abstract The olivine-wadsleyite transformation is believed to occur at depths of about 410 km in the Earth, producing a major seismic discontinuity in this region of the Earth’s mantle. The mechanism of this phase transition controls the microstructures of the newly nucleated wadsleyite, the major phase of the upper part of the mantle transition zone, and thus impacts seismic observations in the region. Here, we study the microstructures produced by the olivine-wadsleyite transformation using in situ laboratory experiments at pressures and temperatures relevant for the mantle transition zone. We transform pure olivine samples in laser-heated diamond-anvil cells at pressures ranging from 12.3 to 20.2 GPa and temperatures of 1400–1730 K. At different steps of the transformation we measure the orientation and size distribution of individual sample grains using multigrain crystallography at synchrotron radiation sources. We find that the olivine to wadsleyite transformation is incoherent at the conditions of the mantle transition zone, and is probably dominated by nucleation of wadsleyite at grain boundaries of the parent olivine. Thus, we expect that seismic anisotropy near 410 km would drop significantly due to the randomized lattice preferred orientation of newly nucleated wadsleyite induced by the incoherent transformation.

High-Temperature Oxidation of Magnesium- and Iron-Rich Olivine under a CO2 Atmosphere: Implications for Venus

Understanding crust–atmosphere interactions on Venus is fundamentally important to interpretations of Venus’ surface spectroscopic data. Olivine, in basaltic crust, is oxidized under a heated CO2 atmosphere. However, the oxidation rates, product assemblages and spectral characteristics of olivine samples with different Fa# values remain largely unclear. Herein, we investigated the oxidation of olivine with different Fa# values (Fa09, Fa29 and Fa71) under CO2 atmosphere at 470 °C and 900 °C and characterized the oxidation products (both microscopically and macroscopically), conversion rates and VNIR spectra. The results showed that the oxidation of olivine produced magnesioferrite, magnetite, laihunite, hematite and maghemite at 470 °C and hematite, magnetite, magnesioferrite and amorphous SiO2 at 900 °C. Both high temperature and high Fa# values accelerated the oxidation rates. The production of oxide coatings on olivine grains (74 μm in size) was estimated to be completed within tens to hundreds of years at 470 °C in natural settings, with even shorter periods under higher temperatures. Thus, CO2 oxidation would quickly eliminate olivine spectral characteristics, and spectral parameters at 850 and 1020 nm, as well as other relevant spectral windows (considering shifts induced by the elevated temperature), could be used to trace olivine oxidation processes. This work presented a case study connecting microscopic features to spectral characteristics for Venus’ surface–atmosphere interactions. Further studies considering more realistic Venus’ surface–atmosphere conditions will be essential to better interpret the measured spectroscopic data and determine the origins of the high emissivity detected on elevated terrain on Venus.

Sound velocities and single-crystal elasticity of hydrous Fo90 olivine to 12 GPa

Nominally anhydrous minerals (NAMs) may contain significant amounts of water and constitute an important reservoir for mantle hydrogen. The colloquial term ‘water’ in NAMs is related to the presence of hydroxyl-bearing (OH−) point defects in their crystal structure, where hydrogen is bonded to lattice oxygen and is charge-balanced by cation vacancies. This hydrous component may therefore have substantial effects on the thermoelastic parameters of NAMs, comparable to other major crystal-chemical substitutions (e.g., Fe, Al). Assessment of water concentrations in natural minerals from mantle xenoliths indicates that olivine commonly stores ∼0–200 ppm of water. However, the lack of samples originating from depths exceeding ∼250 km coupled with the rapid diffusion of hydrogen in olivine at magmatic temperatures makes the determination of the olivine water content in the upper mantle challenging. On the other hand, numerous experimental data show that, at pressures and temperatures corresponding to deep upper mantle conditions, the water storage capacity of olivine increases to 0.2–0.5 wt%. Therefore, determining the elastic properties of olivine samples with more realistic water contents for deep upper mantle conditions may help in interpreting both seismic velocity anomalies in potentially hydrous regions of Earth's mantle as well as the observed seismic velocity and density contrasts across the 410-km discontinuity.Here, we report simultaneous single-crystal X-ray diffraction and Brillouin scattering experiments at room temperature up to 11.96(2) GPa on hydrous [0.20(3) wt% H2O] Fo90 olivine to assess its full elastic tensor, and complement these results with a careful re-analysis of all the available single-crystal elasticity data from the literature for anhydrous Fo90 olivine. While the bulk (K) and shear (G) moduli of hydrous Fo90 olivine are virtually identical to those of the corresponding anhydrous phase, their pressure derivatives K′ and G′ are slightly larger, although consistent within mutual uncertainties. We then defined linear relations between the water concentration in Fo90 olivine, the elastic moduli and their pressure derivatives, which were then used to compute the sound velocities of Fo90 olivine with higher degrees of hydration. Even for water concentrations as high as 0.5 wt%, the sound wave velocities of hydrous and anhydrous olivines were found to be identical within uncertainties at pressures corresponding to the base of the upper mantle. Contrary to previous claims, our data suggest that water in olivine is not seismically detectable, at least for contents consistent with deep upper mantle conditions. In addition to that, our data reveal that the hydration of olivine is unlikely to be a key factor in reconciling seismic velocity and density contrasts across the 410-km discontinuity with a pyrolitic mantle.

Noble gas isotopes reveal degassing-derived eruptions at Deception Island (Antarctica): implications for the current high levels of volcanic activity

Deception Island is one of the most active volcanoes in Antarctica with more than twenty explosive eruptions in the past two centuries. Any future volcanic eruption(s) is a serious concern for scientists and tourists, will be detrimental to marine ecosystems and could have an impact to global oceanographic processes. Currently, it is not possible to carry-out low and high frequency volcanic gas monitoring at Deception Island because of the arduous climatic conditions and its remote location. Helium, neon and argon isotopes measured in olivine samples of the main eruptive events (pre-, syn- and post caldera) offer insights into the processes governing its volcanic history. Our results show that: (i) ascending primitive magmas outgassed volatiles with a MORB-like helium isotopic signature (3He/4He ratio); and (ii) variations in the He isotope ratio, as well as intensive degassing evidenced by fractionated 4He/40Ar* values, occurred before the beginning of the main eruptive episodes. Our results show how the pre-eruptive noble gas signals of volcanic activity is an important step toward a better understanding of the magmatic dynamics and has the potential to improve eruption forecasting.

Comparison on Quantitative Analysis of Olivine Using MarSCoDe Laser-Induced Breakdown Spectroscopy in a Simulated Martian Atmosphere

A Mars Surface Composition Detector (MarSCoDe) instrument mounted on Zhurong rover of Tianwen-1, adopts Laser-Induced Breakdown Spectroscopy (LIBS), with no sample preparation or dust and coatings ablation required, to conduct rapid multi-elemental analysis and characterization of minerals, rocks and soils on the surface of Mars. To test the capability of MarSCoDe LIBS measurement and quantitative analysis, some methods of multivariate analysis on olivine samples with gradient concentrations were inspected based on the spectra acquired in a Mars-simulated environment before the rover launch in 2020. Firstly, LIBS spectra need preprocessing, including background subtraction, random signal denoising, continuum baseline removal, spectral drift correction and wavelength calibration, radiation calibration, and multi-channel spectra subset merging. Then, the quantitative analysis with univariate linear regression (ULR) and multivariate linear regression (MLR) are performed on the characteristic lines, while principal component regression (PCR), partial least square regression (PLSR), ridge, least-absolute-shrinkage-and-selection-operator (LASSO) and elastic net, and nonlinear analysis with back-propagation (BP) are conducted on the entire spectral information. Finally, the performance on the quantitative olivine analyzed by MarSCoDe LIBS is compared with the mean spectrum and all spectra for each sample and evaluated by some statistical indicators. The results show that: (1) the calibration curve of ULR constructed by the characteristic line of magnesium and iron indicates the linear relationship between the spectral signal and the element concentration, and the limits of detection of forsterite and fayalite is 0.9943 and 2.0536 (c%) analyzed by mean spectra, and 2.3354 and 3.8883 (c%) analyzed by all spectra; (2) the R2 value on the calibration and validation of all the methods is close to 1, and the predicted concentration estimated by these calibration models is close to the true concentration; (3) the shrinkage or regularization technique of ridge, LASSO and elastic net perform better than the ULR and MLR, except for ridge overfitting on the testing sample; the best results can be obtained by the dimension reduction technique of PCR and PLSR, especially with PLSR; and BP is more applicable for the sample measured with larger spectral dataset.

Experimental phase function and degree of linear polarization curve of olivine and spinel and the origin of the Barbarian polarization behaviour

ABSTRACT We explore experimentally possible explanations of the polarization curves of the sunlight reflected by the Barbarian asteroids. Their peculiar polarization curves are characterized by a large-inversion angle, around 30°, which could be related to the presence of FeO-bearing spinel embedded in Calcium–Aluminum inclusions. In order to test this hypothesis, we have measured the phase function and degree of linear polarization of six samples of Mg-rich olivine and spinel. For each material, we have analysed the light scattering properties of a millimeter-sized grain and of two powdered samples with size distributions in the micrometer size range. The three spinel samples show a well-defined negative polarization branch with an inversion phase angle located around 24°–30°. In contrast, in the case of the olivine samples, the inversion angle is highly dependent on particle size and tends to decrease for larger sizes. We identify the macroscopic geometries as a possible explanation for the evident differences in the polarization curves between olivine and spinel millimeter samples. Although the polarization behaviour in near backscattering of the Barbara asteroid is similar to that of our spinel mm-sized sample in random orientation, this similarity could result in part from crystal retro-reflection rather than composition. This is part of an ongoing experimental project devoted to test separately several components of CV3-like meteorites, representative of the Barbarians composition, to disentangle their contributions to the polarization behaviour of these objects.

A TEM Study on a Polycrystalline Olivine Sample Deformed in a D-DIA under Mantle Conditions

We carried out an electron microscopy study on a polycrystalline olivine sample that was deformed with multiple deformation cycles under controlled differential stresses and strain rates at high pressures and high temperatures. Low-angle backscattered electron images thereof showed randomly oriented grains. Most of the grains were about 10–20 μm wide. The grains were irregular with wavy grain boundaries, indicating high grain boundary mobility during deformation. Transmission electron microscopy (TEM) images showed complex dislocation microstructure characteristics of high temperature, high pressure, and high strain. Free dislocations were predominantly either short and straight screw dislocations or curved dislocations with mixed screw and edge characters. Many of them split into partial dislocations. The differential stress estimated with the free dislocations was ~780 MPa, which was close to the value of differential stress attained in the final deformation cycle. We also observed dense dislocation tangles, which formed dislocation cell substructures under high strain. The existence of dislocation loops and jogs indicated significant climbing activity, providing evidence for high-temperature creep as the dominant deformation mechanism. All of the dislocations observed in this study were exclusively with a [001] Burgers vector. Dislocations with a [100] Burgers vector were absent, suggesting that the activity of the a-slip (i.e., (010)[100] and (001)[100] slip systems) was completely suppressed. These observations support a conclusion that was reported based on an X-ray texture analysis, which considered that a high pressure promotes the activities of the c-slip (i.e., (010)[001] and (100)[001] slip systems). It appears that the transition from the a-slip to the c-slip was complete with multiple deformation cycles at a relatively lower pressure of 5.1 GPa than previously thought, corresponding to a depth of 165 km in the mantle.

Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading

AbstractSeismic anisotropy produced by aligned olivine in oceanic lithosphere offers a window into mid‐ocean ridge (MOR) dynamics. Yet, interpreting anisotropy in the context of grain‐scale deformation processes and strain observed in laboratory experiments and natural olivine samples has proven challenging due to incomplete seismological constraints and length scale differences spanning orders of magnitude. To bridge this observational gap, we estimate an in situ elastic tensor for oceanic lithosphere using co‐located compressional‐ and shear‐wavespeed anisotropy observations at the NoMelt experiment located on ∼70 Ma seafloor. The elastic model for the upper 7 km of the mantle, NoMelt_SPani7, is characterized by a fast azimuth parallel to the fossil‐spreading direction, consistent with corner‐flow deformation fabric. We compare this model with a database of 123 petrofabrics from the literature to infer olivine crystallographic orientations and shear strain accumulated within the lithosphere. Direct comparison to olivine deformation experiments indicates strain accumulation of 250%–400% in the shallow mantle. We find evidence for D‐type olivine lattice‐preferred orientation (LPO) with fast [100] parallel to the shear direction and girdled [010] and [001] crystallographic axes perpendicular to shear. D‐type LPO implies similar amounts of slip on the (010)[100] and (001)[100] easy slip systems during MOR spreading; we hypothesize that grain‐boundary sliding during dislocation creep relaxes strain compatibility, allowing D‐type LPO to develop in the shallow lithosphere. Deformation dominated by dislocation‐accommodated grain‐boundary sliding (disGBS) has implications for in situ stress and grain size during MOR spreading and implies grain‐size dependent deformation, in contrast to pure dislocation creep.

Third‐Order Padé Thermoelastic Constants of Solid Rocks

AbstractClassical third‐order thermoelastic constants are generally derived from the theory of small‐amplitude acoustic waves in isotropic materials during heat treatments. Investigating higher‐order thermoelastic constants for higher temperatures is challenging owing to the involvement of the number of unknown parameters. These Taylor‐type thermoelastic constants from the classical thermoelasticity theory are formulated based on the Taylor series of the Helmholtz free energy density for preheated crystals. However, these Taylor‐type thermoelastic models are limited even at low temperatures in characterizing the temperature‐dependent velocities of elastic waves in solid rocks as a polycrystal compound of different mineral lithologies. Thus, we propose using the Padé rational function to the total thermal strain energy function. The resulting Padé thermoelastic model gives a reasonable theoretical prediction for acoustic velocities of solid rocks at a higher temperature. We formulate the relationship between the third‐order Padé thermoelastic constants and the corresponding higher‐order Taylor thermoelastic constants with the same accuracy. Two additional Padé coefficients and can be calculated using the second‐, third‐, and fourth‐order Taylor thermoelastic constants associated with the Brugger's constants, which are consistent with those obtained by fitting the experimental data of polycrystalline material. The third‐order Padé thermoelastic model (with four constants) is validated by the fourth‐order Taylor thermoelastic prediction (with six constants) with ultrasonic measurements for polycrystals (olivine samples) and solid rocks (sandstone, granite, and shale). The results demonstrate that the third‐order Padé thermoelastic model can characterize thermally induced velocity changes more accurately than the conventional third‐order Taylor thermoelastic prediction (with four constants), especially for solid rocks at high temperatures. The Padé approximation could be considered a more accurate and universal model in describing thermally induced velocity changes for polycrystals and solid rocks.

Natural Forsterite Strongly Enriched in Boron: Crystal Structure and Spectroscopy

Boron is a typical crustal element and largely incompatible in olivine. Most natural olivine samples have very low concentrations of boron. Recently, forsterite with high boron content (up to 60.53 wt% MgO and 1795.91 ppm B) has been discovered in the Jian forsterite jade in the Jian area of northeast China. In this study, B-rich forsterite was examined by electron microprobes, Laser Ablation-Inductively Coupled Plasma Mass Spectrometry, Single crystal X-ray diffraction, Raman spectroscopy, and infrared spectroscopy. The B-rich forsterite is orthorhombic, existing in space group Pnma, and its unit-cell parameters are: a = 10.1918(7) Å, b = 5.9689(4) Å, c = 4.7484(3) Å, α = 90°, β = 90°, γ = 90°, and V = 288.86(3) Å3. The results of single crystal X-ray diffraction analysis indicate that the unit-cell parameters (a, b, and c) and unit-cell volume of forsterite in Jian forsterite jade are much smaller than those of known olivine. An equivalent set of Raman and infrared spectra were measured for the natural B-rich forsterite and compared to the results for mantle forsterite with a Fo value of ~91. The Raman spectrum of B-rich forsterite is similar to that of mantle olivine. We conclude that the systematic peak position shifts towards higher Raman shift with increasing Fo content. The infrared spectrum of B-rich forsterite crystals is characterized by strong absorption bands at 761, 1168, 1259, and 1303 cm−1, which are assigned to stretching vibrations of BO3 groups. Our data further confirm the existence of the B(F, OH)Si–1O–1 coupled substitution in natural B-rich forsterite.

Hadean isotopic fractionation of xenon retained in deep silicates.

Our understanding of atmosphere formation essentially relies on noble gases and their isotopes, with xenon (Xe) being a key tracer of the early planetary stages. A long-standing issue, however, is the origin of atmospheric depletion in Xe1 and its light isotopes for the Earth2 and Mars3. Here we report that feldspar and olivine samples confined at high pressures and high temperature with diluted Xe and krypton (Kr) in air or nitrogen are enriched in heavy Xe isotopes by +0.8 to +2.3‰ per AMU, and strongly enriched in Xe over Kr. The upper +2.3‰ per AMU value is a minimum because quantitative trapping of unreacted Xe, either in bubbles or adsorbed on the samples, is likely. In light of these results, we propose a scenario solving the missing Xe problem that involves multiple magma ocean stage events at the proto-planetary stage, combined with atmospheric loss. Each of these events results in trapping of Xe at depth and preferential retention of its heavy isotopes. In the case of the Earth, the heavy Xe fraction was later added to the secondary CI chondritic atmosphere through continental erosion and/or recycling of a Hadean felsic crust.

Unveiling redox mechanism at the iron centers in the mechanochemically activated conversion of CO2 in the presence of olivine

The transformation of olivine during the conversion of CO2 to light hydrocarbons activated by mechanochemical treatments at different impact frequencies was studied by a combination of several complementary characterization methods including X-ray diffraction, Raman and 57Fe Mössbauer spectroscopy. Several olivine samples were studied as a function of the milling time, indicating the gradual transformation of FeII-containing olivine into new FeIII-containing weathering products including iron oxides, magnesium iron carbonates and silicates. The results presented here complement those of a previous study on the weathering process of olivine promoted by mechanochemical activation, by demonstrating the role of the redox activity of the iron species during the activation process. These additional spectroscopic results allow us to thoroughly understand the complex weathering mechanism and to correlate it with the efficiency of the CO2 conversion and storage properties of mechanochemically activated olivine.

Diffusion rates of hydrogen defect species associated with site-specific infrared spectral bands in natural olivine

We investigated hydrogen transport in naturally occurring, iron-bearing samples of San Carlos olivine that were hydrogenated at confining pressures of 200 or 300 MPa and 1173 to 1303 K or dehydrogenated at room pressure and 1191 to 1358 K. Chemical diffusion coefficients were determined from diffusion profiles for individual O-H-stretching bands from series of infrared spectra in orthogonal directions across each sample. Within experimental uncertainty, the diffusivities associated with all the individual bands are in good agreement with one another in both the hydrogenation and the dehydrogenation experiments. Hydrogenation proceeds by two diffusion mechanisms, as reported previously. The faster process involves interstitial diffusion of protons coupled with a counter-flux of polarons, with proton diffusion rate-limiting hydrogenation. For this mechanism, diffusion is faster along the olivine [100] direction than along [010] and [001], consistent with the anisotropy reported for proton diffusion and conductivity in olivine. The slower process involves interstitial proton diffusion coupled with a parallel flux of metal vacancies, with vacancy diffusion rate-limiting hydrogenation. For this mechanism, diffusion is faster along [001] than along [100] and [010], consistent with the anisotropy previously reported for the diffusion of metal cations in olivine. Diffusivities from our new dehydrogenation experiments are identical in both magnitude and anisotropy to those determined in our earlier hydrogenation experiments. This agreement demonstrates the validity of studies that used the results of our hydrogenation experiments to analyze dehydrogenation profiles in olivine xenocrysts and olivine in mantle xenoliths to determine rates of magma ascent from the source regions in Earth's interior.

A Tem Study on a Polycrystalline Olivine Sample Deformed in the D-Dia Under Mantle Conditions

A Tem Study on a Polycrystalline Olivine Sample Deformed in the D-Dia Under Mantle Conditions