Olivine Component Research Articles

T-matrix and Hapke Modeling of the Thermal Infrared Spectra of Trojan Asteroids and (944) Hidalgo: Implications for Their Regolith Particle Size and Porosity

Trojan asteroids (911) Agamemnon, (1172) Aneas, and (624) Hektor and primitive asteroid (944) Hidalgo share a common thermal infrared spectral feature: a prominent 10 μm plateau that is also present in cometary comae spectra. To fit these asteroid spectra, we modeled individual minerals using the light-scattering multiple sphere T-matrix (MSTM) and Hapke reflectance models. Modeled mineral spectra were then combined using a weighted least-squares (WLS) model that included a spectral library of varied particle sizes and porosities. We later refined our method by using the mineral abundances, particle sizes, and porosities computed by WLS as an input to rerun the MSTM and Hapke models. We were able to model the asteroid spectral features using a mixture of olivine components, fine particles, and lunar-like porosities. The Trojan asteroids and (944) Hidalgo are comparable in mineral composition and particle size to spectrally similar bodies such as comet Hale-Bopp and CO3 and CY chondrite meteorites. While the required porosities for modeling are like those present on the lunar surface, they are lower than those in the meteorites and higher than those in comets.

Mineralogical and Chemical Investigations of the Amguid Crater (Algeria): Is there Evidence on an Impact Origin?

Mineralogical and chemical investigations were carried out on intra-craterial bedrocks (Lower Devonian sandstone) and regolithic residual soil deposits present around the Amguid structure, to discuss the hypothesis of its formation through a relatively recent (about 0.1 Ma) impact event. Observations with an optical microscope on intra-craterial rocks do not unequivocally confirm the presence of impact correlated microscopic planar deformation features (PDFs) in quartz crystals. Field observations, and optical and instrumental analysis (Raman spectroscopy) on rocks and soils (including different granulometric fractions) do not provide any incontrovertible pieces of evidence of high energy impact effects or products of impact (e.g., high pressure—temperature phases, partially or totally melted materials, etc.) either in target rocks or in soils. A series of selected main and trace elements (Al, Fe, Mg, Ni, Co and Cu) were analysed on rocks and soils to evaluate the presence in these materials of extraterrestrial sources. Comparative chemical data on rocks and soils suggest that these last are significantly enriched in Fe-poor Mg-rich materials, and in Co, Ni and Cu, in the order. A large number of EDAX-SEM analyses on separated soil magnetic particles indicate an abnormally high presence of Al-free Mg-rich sub-spherical or drop-like silicate particles, showing very similar bulk chemistries compatible with forsterite olivine. Some particles were found associated with a Ni-rich iron metal phase, and this association suggests a specific extraterrestrial origin for them. Electron microscope analysis made on a large number of soil magnetic particles indicates that 98% of them are terrestrial phases (almandine garnet, tourmaline and Fe-oxides, in abundance order), whereas, only a few grains are of questionable origin. One of the Mg-rich silicate particles was found to be a forsterite (Mg = 0.86) Mn-rich (MnO: 0.23%) Cr-free olivine, almost surely of extraterrestrial sources. Electron microprobe analysis of three soil particles allowed identification of uncommon Cr-rich (Cr2O3 about 8%) spinels, poorly compatible with an origin from terrestrial sources, and in particular from local source rocks. We propose a specific extraterrestrial origin for sub-spherical olivine particles characterised by quite similar magnesian character. Excluding any derivation of these particles from interplanetary dust, two other possible extraterrestrial sources should be considered for them, i.e., either normal micrometeorite fluxes or strongly un-equilibrated, or the Vigarano type Carbonaceous (CV) chondrite meteorite material. In this case, further studies will confirm an impact origin for Amguid, as such magnesian olivine components found in soils might represent the only remnants of a vaporised projectile of ordinary non-equilibrated meteoritic composition.

Merging spatial and spectral datasets to place olivine in stratigraphic context at Arruntia crater, a rare window into Vesta's northern hemispheric crust

A major goal of the Dawn mission to Vesta was to test and refine current models of the asteroid's formation by characterizing the distribution of mineral components on its surface. Detection of the mineral olivine by the Visible and Infrared Mapping spectrometer (VIR) and the Framing Camera (FC) onboard Dawn was a key milestone in this effort, and was expected to help resolve a debate regarding the dominant mode of Vesta's petrologic evolution (i.e., magma ocean vs. serial magmatism). However, the subtleties of the olivine spectral signature combined with the small size of individual olivine-rich exposures (tens of meters) prohibits detailed mapping of this petrologically significant mineral component when the data from either instrument are evaluated independently. As a result, the particular role of these olivine exposures in Vesta's geologic history remains largely unresolved.Here, we fully characterize the type locality of Vesta's olivine-rich materials, the northern hemisphere craters Bellicia and Arruntia, using a novel data fusion approach for linking the VIR and FC datasets. Specifically, we have leveraged a spectral mixture analysis framework to create a new dataset that maps, or “extrapolates”, full resolution spectra, derived from VIR data, onto the higher spatial resolution of FC. When used as an exploratory tool in conjunction with the original FC and VIR data, the new “extrapolated” dataset reveals important new details about the distribution of olivine around Bellicia and Arruntia craters.There are clear compositional distinctions between the exposures at the two craters, with a much stronger olivine component in the walls of Bellicia than Arruntia. The proximal Arruntia ejecta appear more consistent with high proportions of an evolved high‑calcium pyroxene (as in eucrites) than with an enhanced olivine component. Examples of diogenite-rich howardite also occur in the region. Further, we leverage Arruntia's role as the freshest large crater in the northern hemisphere, and thus a rare window into the Vesta's northern hemispheric crust, to suggest an overall stratigraphy for the region: a thin veneer of howardite overlies a sequence of diogenite-rich (near surface), olivine-rich (intermediate), and eucrite-rich materials (at depth). The manner of exposure of these various components in a marked stratification point to a plutonic model for emplacing these mineralogically unique components in the near surface of Vesta.

SPINMELT-2.0: Simulation of Spinel–Melt Equilibrium in Basaltic Systems under Pressures up to 15 Kbar: III. The Effects of Major Components in the Melt on the Chrome-Spinel Stability and a Possible Solution of the Problem of Origin of Chromitites

The effect of variations in the fo, fa, en, fs, di, an and ab components in high-Mg basaltic melts on the topology of the spinel liquidus was quantified by conducting simulations with the new SPINMELT-2.0 model for the spinel–melt equilibrium. It has been established that enrichment of the melt in pyroxene components leads to an increase, and conversely, enrichment in plagioclase and olivine components, to a decrease in the solubility of chromite. This effect can be important at the gravitational compaction of cumulates accompanied by the extraction of intercumulus melt and its infiltration upward. In this case, it is reasonable to expect sequential reequilibration of the infiltrating melt with cumulate piles of different composition. This suggests that Cr-spinel can be transferred and concentrated again during the postcumulus solidification stage of layered intrusions. The concentrating process involves Cr-spinel extraction into the melt enriched in pyroxene components and the subsequent redeposition of the mineral during when this melt reacts with the feldspar-rich matrix of proto-anorthosite layers or horizons enriched in olivine. Some of these layers and horizons may be produced by additional injections of more primitive magma. The realism of the proposed mechanism is evident from the well-known spatial relations between the chromite layers with anorthosites and dunite–harzburgites of the Bushveld complex.

Microstructural evidence for crystallization regimes in mafic intrusions: a case study from the Little Minch Sill Complex, Scotland

The magma forming the 20 m thick crinanitic/picrodoleritic Dun Raisburgh sill, part of the Little Minch Sill Complex of NW Scotland, comprised a mafic carrier liquid with a crystal cargo of plagioclase and olivine (1 vol%). The olivine component of the cargo settled on the floor of the intrusion while the more buoyant plagioclase component remained suspended during solidification, resulting in a relatively high plagioclase content in the centre of the sill. The settled olivine grains form a lower fining-upwards sequence overlain by a poorly sorted accumulation formed of grains that grew within the convecting magma. The accumulation of olivine on the sill floor occurred over 5–10 weeks, synchronous with the upwards-propagation of a solidification front comprising a porous (~ 70 vol% interstitial liquid) plagioclase-rich crystal mush.

An 57Fe Mössbauer study of the ordinary chondrite meteorite Lynch 001

The Lynch 001 meteorite was found in the Nullarbor Plain region of Western Australia in 1977. This meteorite is classified as an ordinary chondrite of the petrologic group L5/6 that has undergone ‘minor to moderate’ terrestrial weathering. Here, we characterize the Fe-bearing phases in this chondrite using 57Fe Mossbauer spectroscopy carried out over the temperature range 13 K to room temperature (295 K). The paramagnetic doublets of olivine, pyroxene and a superparamagnetic ferric phase dominate the room temperature Mossbauer spectrum. On the basis of the room temperature quadrupole splitting of the olivine component, we estimate its composition to be Fa 30(5). Besides the paramagnetic ferric component, accounting for ∼15 % of the spectral area at room temperature, magnetically ordered ferric phases were also detected. The total relative proportion of the Fe 3+ components allows us to estimate the terrestrial age of Lynch 001 to be 6,500 ± 1,500 yr, consistent with the value of 6,700 ± 1,300 yr determined by 14C dating.

57Fe Mössbauer study of the chainpur meteorite

The Chainpur meteorite is one of 23 ordinary chondrites classified as LL3-type (low-Fe & low-metal). It was observed as a shower of stones falling on May 9, 1907 in Uttar Pradesh, India. We report here the characterization of the Fe-bearing phases in this chondrite using 57Fe Mossbauer spectroscopy carried out at 298 K, 120 K, 50 K and 13 K. The paramagnetic doublets of olivine and pyroxene dominate the room temperature spectrum, accounting for around 70 % of the spectral area. Moreover, a doublet present with a spectral area of 5 % and assigned to a superparamagnetic Fe 3+ phase is a consequence of terrestrial weathering. On the basis of the measured 57Fe electric quadrupole splitting of the olivine component at room temperature we estimate the mean Fe:Mg ratio in this meteoritic olivine to be around 35:65 % although there is clearly a wide range of composition. The effects of magnetic ordering of the major components olivine and pyroxene are observed at 13 K.

Depressed mantle discontinuities beneath Iceland: Evidence of a garnet controlled 660 km discontinuity?

The presence of a mantle plume beneath Iceland has long been hypothesised to explain its high volumes of crustal volcanism. Practical constraints in seismic tomography mean that thin, slow velocity anomalies representative of a mantle plume signature are difficult to image. However it is possible to infer the presence of temperature anomalies at depth from the effect they have on phase transitions in surrounding mantle material. Phase changes in the olivine component of mantle rocks are thought to be responsible for global mantle seismic discontinuities at 410 and 660 km depth, though exact depths are dependent on surrounding temperature conditions. This study uses P to S seismic wave conversions at mantle discontinuities to investigate variation in topography allowing inference of temperature anomalies within the transition zone. We employ a large data set from a wide range of seismic stations across the North Atlantic region and a dense network in Iceland, including over 100 stations run by the University of Cambridge. Data are used to create over 6000 receiver functions. These are converted from time to depth including 3D corrections for variations in crustal thickness and upper mantle velocity heterogeneities, and then stacked based on common conversion points. We find that both the 410 and 660 km discontinuities are depressed under Iceland compared to normal depths in the surrounding region. The depression of 30 km observed on the 410 km discontinuity could be artificially deepened by un-modelled slow anomalies in the correcting velocity model. Adding a slow velocity conduit of −1.44% reduces the depression to 18 km; in this scenario both the velocity reduction and discontinuity topography reflect a temperature anomaly of 210 K. We find that much larger velocity reductions would be required to remove all depression on the 660 km discontinuity, and therefore correlated discontinuity depressions appear to be a robust feature of the data. While it is not possible to definitively rule out the possibility of uncorrected velocity anomalies causing the observed correlated topography we show that this is unlikely. Instead our preferred interpretation is that the 660 km discontinuity is controlled by a garnet phase transition described by a positive Clapeyron slope, such that depression of the 660 is representative of a hot anomaly at depth.

Seismically deduced thermodynamics phase diagrams for the mantle transition zone

Seismic discontinuities at 410 and 660 km depth are usually attributed to solid phase changes within the olivine component of the mantle. The Clapeyron slopes γ410 and γ660, i.e. the thermal dependence of the depths of reactions, have been shown experimentally to be of opposite signs. Yet, their values are not well constrained by laboratory measurements. Seismological observations have not been more precise due to the difficulty to separate the competing effects of background wave-velocities and of temperature on the topography of discontinuities. In this study we use conversion imaging of interfaces under western US. We propose a new approach to derive a seismological estimate of the Clapeyron slopes with respect to γ410 for the major and minor phase changes of the transition zone. We obtain γ660≈−3 MPaK−1 for γ410≈+3 MPaK−1. We construct “seismic phase diagrams” of the transition zone that can be directly compared with experimental phase diagrams. We also apply a “Z–Γ” transform to better constrain the Clapeyron slopes γ of the minor phase changes. Although tenuous, signals in seismic phase diagrams suggest that minor phase transitions, both in the olivine and the non-olivine component of the mantle, have visible seismic expressions. They can tentatively be described as follows. The ‘410’ is overlaid at low temperature by an interface corresponding to a decrease of velocity with depth and γ≈+3 MPaK−1. The ‘660’ widens at high temperature and is preceded at low temperature by an interface, the ‘620’, with γ≈+7 MPaK−1. A ‘520’ is suggested with γ≈2–3 MPaK−1. These last two interfaces correspond to velocity increases with depth. At last, near 590 km depth, an interface may be associated with a velocity reduction showing a weak dependence on temperature (γ∼0 MPaK−1).

Experimental simulation of orthopyroxene enrichment and carbonation in the suprasubduction mantle under the influence of H2O, CO2, and SiO2

Thermal and chemical gradients at the boundary of a subducting plate and suprasubduction mantle lead to a variety of poorly understood geologic processes. This paper reports the results of experiments simulating interaction between olivine (Ol, mantle analog) and carbonated glaucophane schist (Gls, analog of the upper layer of the subducted crust) under the P-t conditions of a ‘hot’ subduction zone. The experiments were carried out at a pressure of P = 25 kbar under temperature gradient conditions (tminGls = 720°C and tmaxOl = 1000°C) and at a constant temperature of t = 800°C corresponding to the boundary between the materials in the gradient experiment. A comparison of experimental data obtained using two different methods showed that the temperature gradient experiment reproduced the character of schist-olivine interaction under isothermal conditions and provided additional information on the effect of temperature on mineral reactions. Orthopyroxene occurs in the experimental products in different textural positions, forming a layer (with or without magnesite) at the base of the olivine zone or separate grains and intergrowths with magnesite at the boundary of olivine grains. The development of orthopyroxene and carbonate redeposition are described by reactions between olivine and aqueous fluid components, SiO2 and CO2, at \(a_{SiO_2 } = 0.23\) and \(a_{CO_2 } = 0.07\). The calculated silica content in the fluid under such thermodynamic conditions is 0.39 mol/kg H2O. Given these parameters, the estimated SiO2 flux at a depth of ∼80 km from the downgoing slab of the Cascadia subduction zone in the northwester United States is 180 t/yr at a very moderate (for the considered depth level) aqueous fluid flux of one million moles per year per kilometer. Modern concepts on convective flows initiated by a subducting slab in the mantle wedge allow us to suggest that orthopyroxene-enriched ultramafic rocks must occur both above the areas of the release of volatile components and silica from the slab and at deeper levels of subduction zones.

Amphibole-bearing Multiphase Solid Inclusions in Olivine and Plagioclase from a Layered Gabbro: Origin of the Trapped Melts

This study presents new data regarding the petrographic and mineralogical characteristics of amphibole-bearing multiphase solid inclusions (MSI) enclosed in olivine and plagioclase from a well-characterized Japanese layered gabbro, the Murotomisaki Gabbroic Intrusion. Bulk compositions of the MSI were obtained using wavelength-dispersive (WDS) and energy-dispersive (EDS) techniques combined with modal analysis. Many MSI in olivines are spherical or polygonal in shape and are mainly composed of pargasitic amphibole, orthopyroxene, and mica (biotite and aspidolite). The MSI in olivine phenocrysts in the chilled margins of the intrusion are composed of plagioclase and hornblende rather than pargasite. Many of them are found to be enriched in olivine components in their bulk compositions, and therefore they cannot be regarded as simple trapped basaltic melts or their derivatives. The MSI in plagioclase are more irregular in shape and occur in the resorbed part of calcic plagioclase cores; they are mainly composed of pargasite and sodic plagioclase. Attempts were made to obtain the original composition of the MSI melts by applying a correction for Fe^Mg exchange reactions with the host olivine. It was found that after the correction, the MSI in the chilled margin were closest to the published initial basaltic melt composition, whereas the olivine-hosted MSI from the olivine gabbros were still fairly high in olivine components despite the correction. Such post-entrapment modification was probably minimal for the plagioclase-hosted MSI because plagioclase is essentially free of Mg and Fe, and therefore plagioclase-hosted MSI are believed to represent the compositions of the original trapped melts. These are characteristically enriched in plagioclase components. We believe that the anomalous compositions of the trapped melts (after the corrections) were generated by local dissolution of olivine and plagioclase caused by the introduction of water from lower horizons of the crystallization boundary layer in a magma chamber. The MSI are therefore considered to provide new evidence for the dissolution of silicates by hydrous fluxing in a lower crystallizing boundary layer of a magma reservoir during solidification of basaltic magma.

Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville and Vigarano (CV3) chondrites: A record of condensate evolution in the solar nebula

Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville, and Vigarano CV3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components. Our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution. Spinel-rich nodules and ribbons in AOAs often show Group II trace element patterns and formed either by fractional condensation or by condensation following partial vaporization. The dominant olivine component in AOAs can be explained as a condensate produced in the same way, but with fractionation occurring at a lower temperature. Other spinel-rich material in AOAs appears to be a vaporization residue. Ca-rich pyroxene+anorthite patches in AOAs show chemical signatures similar to those observed for spinel- or melilite-bearing regions but with lower refractory element and higher Mg and Si contents, supporting the idea that the patches formed by reaction between CAI-like material and Mg–Si-rich gas. Different trace element patterns (Group II and non-Group II refractory) are sometimes found for Al-rich regions (Ca-pyroxene+anorthite, or melilite-bearing) in a given AOA, suggesting that AOAs agglomerated from materials that formed under different conditions and that they did not subsequently homogenize. AOAs appear to have originated in a system with near-canonical solar composition and a low pressure gas (∼10−6–10−4bar) over a range of temperatures (mainly ∼1200–1384K) under somewhat non-equilibrium conditions. Relative to predicted equilibrium condensates, most AOAs show an apparent paucity of metal, possibly reflecting differential, density-dependent sorting between olivine and metal grains during aggregate formation. Trace element data are consistent with a simple model involving melting and igneous fractionation of AOA-like olivine to produce Type I chondrule olivine, but other data suggest that open-system melting of chondrules occurred in a different gaseous environment than that which produced AOAs.

Evidence for heterogeneous enriched shergottite mantle sources in Mars from olivine-hosted melt inclusions in Larkman Nunatak 06319

Larkman Nunatak (LAR) 06319 is an olivine-phyric shergottite whose olivine crystals contain abundant crystallized melt inclusions. In this study, three types of melt inclusion were distinguished, based on their occurrence and the composition of their olivine host: Type-I inclusions occur in phenocryst cores (Fo 77–73); Type-II inclusions occur in phenocryst mantles (Fo 71–66); Type-III inclusions occur in phenocryst rims (Fo 61–51) and within groundmass olivine. The sizes of the melt inclusions decrease significantly from Type-I (∼150–250 μm diameter) to Type-II (∼100 μm diameter) to Type-III (∼25–75 μm diameter). Present bulk compositions (PBC) of the crystallized melt inclusions were calculated for each of the three melt inclusion types based on average modal abundances and analyzed compositions of constituent phases. Primary trapped liquid compositions were then reconstructed by addition of olivine and adjustment of the Fe/Mg ratio to equilibrium with the host olivine (to account for crystallization of wall olivine and the effects of Fe/Mg re-equilibration). The present bulk composition of Type-I inclusions (PBC1) plots on a tie-line that passes through olivine and the LAR 06319 whole-rock composition. The parent magma composition can be reconstructed by addition of 29 mol% olivine to PBC1, and adjustment of Fe/Mg for equilibrium with olivine of Fo 77 composition. The resulting parent magma composition has a predicted crystallization sequence that is consistent with that determined from petrographic observations, and differs significantly from the whole-rock only in an accumulated olivine component (∼10 wt%). This is consistent with a calculation indicating that ∼10 wt% magnesian (Fo 77–73) olivine must be subtracted from the whole-rock to yield a melt in equilibrium with Fo 77. Thus, two independent estimates indicate that LAR 06319 contains ∼10 wt% cumulate olivine. The rare earth element (REE) patterns of Type-I melt inclusions are similar to that of the LAR 06319 whole-rock. The REE patterns of Type-II and Type-III melt inclusions are also broadly parallel to that of the whole-rock, but at higher absolute abundances. These results are consistent with an LAR 06319 parent magma that crystallized as a closed-system, with its incompatible-element enrichment being inherited from its mantle source region. However, fractional crystallization of the reconstructed LAR 06319 parent magma cannot reproduce the major and trace element characteristics of all enriched basaltic shergottites, indicating local-to-large scale major- and trace-element variations in the mantle source of enriched shergottites. Therefore, LAR 06319 cannot be parental to the enriched basaltic shergottites.

Reconciling Pacific 410 and 660 km discontinuity topography, transition zone shear velocity patterns, and mantle phase transitions

We observe that the depths of the 410 and 660 km seismic discontinuities are, on average, slightly positively correlated globally. This is due in large part to a modestly depressed 660 km discontinuity and a large depression of the 410 km discontinuity across the Pacific. The Clapeyron slope (dP/dT), the change in pressure (depth) of a phase transition with a change in temperature, can be used to predict the depth of a phase transformation assuming lateral temperature variations. The phase change of olivine to β-spinel is well understood experimentally, almost certainly produces the 410 km discontinuity, and has a positive Clapeyron slope. At the base of the transition zone, both the olivine component of the mantle ( γ-spinel) and the pyroxene component (garnet) transform to perovskite and periclase. Observations of 660 km discontinuity depths are often consistent with the negative Clapeyron slope of the γ-spinel to perovskite and periclase transition, with an apparent anti-correlation with the depth of the 410 km discontinuity. However, under the Pacific, the depression of the 410 km discontinuity and slow seismic velocities indicate that the mantle is warmer than average. Using a negative Clapeyron slope for the perovskite-forming reaction, the 660 km discontinuity is predicted to be shallow in this region. However, we observe that it is either depressed or has little deflection from its average depth. We find that if the Clapeyron slope associated with the 660 km discontinuity changes sign from negative to positive between 1920 and 2020 K, we can explain the correlation of discontinuity structure with seismic velocities in the transition zone. This shift in sign is in accord with the dominant 660 km transition-forming reaction shifting from γ-spinel to garnet near this temperature.

The generation of a diverse suite of Late Pleistocene and Holocene basalt through dacite lavas from the northern Cascade arc at Mount Baker, Washington

Mt. Baker is a dominantly andesitic stratovolcano in the northern Cascade arc. In this study, we show that the andesites are not all derived from similar sources, and that open-system processes were dominant during their petrogenesis. To this end, we discuss petrographic observations, mineral chemistry, and whole rock major and trace element chemistry for three of Mt. Baker’s late Pleistocene to Holocene lava flow units. These include the basalt and basaltic andesite of Sulphur Creek (SC) (51.4–55.8 wt% SiO2, Mg# 57–58), the Mg-rich andesite of Glacier Creek (GC) (58.3–58.7 wt% SiO2, Mg# 63–64), and the andesite and dacite of Boulder Glacier (BG) (60.2–64.2 wt% SiO2, Mg# 50–57). Phenocryst populations in all units display varying degrees of reaction and disequilibrium textures along with complicated zoning patterns indicative of open-system processes. All lavas are medium-K and calc-alkaline, but each unit displays distinctive trace element and REE characteristics that do not correlate with the average SiO2 content of the unit. The mafic lavas of SC have relatively elevated REE abundances with the lowest (La/Yb)N (~4.5). The intermediate GC andesites (Mg- and Ni-rich) have the lowest REE abundances and the highest (La/Yb)N (~6.7) with strongly depleted HREE. The more felsic BG lavas have intermediate REE abundances and (La/Yb)N (~6.4). The high-Mg character of the GC andesites can be explained by addition of 4% of a xenocrystic olivine component. However, their depleted REE patterns are similar to other high-Mg andesites reported from Mt. Baker and require a distinct mantle source. The two dominantly andesitic units (GC and BG) are different enough from each other that they could not have been derived from the same parent basalt. Nor could either of them have been derived from the SC basalt by crystal fractionation processes. Crystal fractionation also cannot explain the compositional diversity within each unit. Compositional diversity within the SC unit (basalt to basaltic andesite) can, however, be successfully modeled by mixing of basalt with compositions similar to the dacites in the BG unit. Given that the BG dacites erupted at ~80–90 ka, and a similar composition was mixed with the SC lavas at 9.8 ka, the process that produced this felsic end-member must have been repeatedly active for at least 70 ka.

Characteristics of xLiFePO4·y Li3V2(PO4)3 electrodes for lithium batteries

A series of mechanical mixture of lithium–iron–vanadium–phosphate compositions that can be represented in two-component notation, xLiFePO4·y Li3V2(PO4)3 (LFVP), has been evaluated as electrodes in lithium cells for x:y = 0:1, 1:1, 5:1, 10:1, and 1:0, in which an olivine component, LiFePO4 (LFP), and a monoclinic component, Li3V2(PO4)3 (LVP), coexisted. Powder X-ray diffraction (XRD) patterns show that the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the olivine LiFePO4(x = 1, y = 0) and for monoclinic Li3V2(PO4)3 (x = 0, y = 1). XRD data and the changes of cell parameters indicate that there existed some V- and Fe-doping in the composite xLiFePO4·y Li3V2(PO4)3, resulting with a good performance compared with single LiFePO4 and Li3V2(PO4)3. Electrochemical characteristics were evaluated by using cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the electron transfer activity and the lithium ion diffusion rate in LFVP are better than single LFP and LVP.

40Ar/ 39Ar analyses on Quaternary K–Ar standard BB-24: Evaluations

Quaternary K–Ar standard BB-24 is evaluated by 40Ar/ 39Ar analyses. Total-fusion results show that BB-24 is poorly reproducible either as 40Ar * (radiogenic 40Ar) or as 39Ar k, at a sample size of 15–40 mg. Much lower ages produced by the purified aliquots of BB-24 show the excess 40Ar * sited in the olivine component within the standard. The step-heating experiment produces a different total gas age of 440 ± 21.2 ka and a plateau age of 424.4 ± 15.0 ka, indicating different components degassing at different temperatures. The first and last steps have elevated ages and distort the age spectrum. This is vital when total-fusion experiments are performed. Age spectra of purified aliquots produce concordant age spectra, implying mineral impurities or excess 40Ar within the sample. As a conclusion, BB-24 is not a suitable neutron monitor in 40Ar/ 39Ar dating.

Optical characterization of laser ablated silicates

We perform an optical characterization of UV laser ablated silicates (olivine, pyroxene), starting from their reflectance spectra in the 0.3–2.5 μm spectral range. The goal is to provide useful tools to model space weathering effects on surfaces of asteroids and TNOs (trans-neptunian objects). We determine that the reddening and darkening spectral trend is compatible with the Hapke's space weathering model, using the optical constants of metallic iron in a silicate matrix. This result is supported by new magnetic susceptibility measurements on laser ablated orthopyroxene. We also investigate the potential contribution of formation of amorphous silicates in the process. Applying our results to silicate-rich surfaces in the Solar System, we investigate the possibility of a weathered olivine component on the surface of Centaur 5145 Pholus. Inclusion of this component slightly decreases the amount of complex organics and water ice from those previously estimated. Thus, the current Pholus spectrum is consistent with the presence of either unweathered or weathered olivine, or potentially both materials.

Melt inclusions in scoria and associated mantle xenoliths of Puy Beaunit Volcano, Chaîne des Puys, Massif Central, France

In order to characterize the composition of the parental melts of intracontinental alkali-basalts, we have undertaken a study of melt and fluid inclusions in olivine crystals in basaltic scoria and associated upper mantle nodules from Puy Beaunit, a volcano from the Chaine des Puys volcanic province of the French Massif Central (West-European Rift system). Certain melt inclusions were experimentally homogenised by heating-stage experiments and analysed to obtain major- and trace-element compositions. In basaltic scoria, olivine-hosted melt inclusions occur as primary isolated inclusions formed during growth of the host phase. Some melt inclusions contain both glass and daughter minerals that formed during closed-system crystallisation of the inclusion and consist mainly of clinopyroxene, plagioclase and rhonite crystals. Experimentally rehomogenised and naturally quenched, glassy inclusions have alkali-basalt compositions (with SiO2 content as low as 42 wt%, MgO>6 wt%, Na2O+K2O>5 wt%, Cl~1,000–3,000 ppm and S~400–2,000 ppm), which are consistent with those expected for the parental magmas of the Chaine des Puys magmatic suites. Their trace-element signature is characterized by high concentration(s) of LILE and high LREE/HREE ratios, implying an enriched source likely to have incorporated small amounts of recycled sediments. In olivine porphyroclasts of the spinel peridotite nodules, silicate melt inclusions are secondary in nature and form trails along fracture planes. They are generally associated with secondary CO2 fluid inclusions containing coexisting vapour and liquid phases in the same trail. This observation and the existence of multiphase inclusions consisting of silicate glass and CO2-rich fluid suggest the former existence of a CO2-rich silicate melt phase. Unheated glass inclusions have silicic major-element compositions, with normative nepheline and olivine components, ~58 wt% SiO2, ~9 wt% total alkali oxides, 3,000 ppm) but their sulphur concentrations are low (<200 ppm). Comparison with experimental isobaric trends for peridotite indicates that they represent high-pressure (~1.0 GPa) trapped aliquots of near-solidus partial melts of spinel peridotite. Following this hypothesis, their silica-rich compositions would reflect the effect of alkali oxides on the silica activity coefficient of the melt during the melting process. Indeed, the silica activity coefficient decreases with addition of alkalis around 1.0 GPa. For mantle melts coexisting with an olivine-orthopyroxene-bearing mineral assemblage buffering SiO2 activity, this decrease is therefore compensated by an increase in the SiO2 content of the melt. Because of their high viscosity and the low permeability of their matrix, these near-solidus peridotite melts show limited ability to segregate and migrate, which can explain the absence of a chemical relationship between the olivine-hosted melt inclusions in the nodules and in basaltic scoria.

Temperature dependence of elastic moduli of β‐(Mg, Fe)2SiO4

The elastic moduli of polycrystalline wadsleyite, β‐(Mg0.91Fe0.09)2SiO4, were measured up to 470 K by means of the resonant sphere technique. The adiabatic bulk (KS) and shear (μ) moduli were found to be 165.72(6) and 105.43(2) GPa at room temperature. The average slopes (dKS/dT and dμ/dT) in the range were determined to be −0.0175(3) and −0.0159(1) GPa/K. We estimated that the P‐, S‐wave velocity and density jumps for the α‐ to β‐phase transformation at the 410‐km depth condition were 9.5, 11.2 and 5.4%, respectively. These results suggest that the olivine component at the depth should be 52 and 42 volume % for P‐ and S‐waves.