Olivine Samples Research Articles

Hydrothermally synthesized nanostructured LiMnxFe1\u2212xPO4 (x\u2009=\u20090\u20130.3) cathode materials with enhanced properties for lithium-ion\xa0batteries

Nanostructured cathode materials based on Mn-doped olivine LiMnxFe1−xPO4 (x = 0, 0.1, 0.2, and 0.3) were successfully synthesized via a hydrothermal route. The field-emission scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyzed results indicated that the synthesized LiMnxFe1−xPO4 (x = 0, 0.1, 0.2, and 0.3) samples possessed a sphere-like nanostructure and a relatively homogeneous size distribution in the range of 100–200 nm. Electrochemical experiments and analysis showed that the Mn doping increased the redox potential and boosted the capacity. While the undoped olivine (LiFePO4) had a capacity of 169 mAh g−1 with a slight reduction (10%) in the initial capacity after 50 cycles (150 mAh g−1), the Mn-doped olivine samples (LiMnxFe1−xPO4) demonstrated reliable cycling tests with negligible capacity loss, reaching 151, 147, and 157 mAh g−1 for x = 0.1, 0.2, and 0.3, respectively. The results from electrochemical impedance spectroscopy (EIS) accompanied by the galvanostatic intermittent titration technique (GITT) have resulted that the Mn substitution for Fe promoted the charge transfer process and hence the rapid Li transport. These findings indicate that the LiMnxFe1−xPO4 nanostructures are promising cathode materials for lithium ion battery applications.

Origin of low oxygen isotopic compositions in alkalic lavas from Erebus volcano, Antarctica

Mount Erebus on Ross Island, Antarctica is an active volcano that has hosted a persistent phonolite lava lake for over 50 years. Oxygen isotope analysis of minerals in alkaline basanite to phonolite lavas from Erebus and surrounding volcanic centers show an anomalous trend of decreasing δ18O with magmatic evolution. The cold frozen climate and lack of radiogenic isotope evidence for assimilation of crustal materials makes this a unique location to investigate factors contributing to changes in oxygen isotope compositions. Olivine, feldspar, glass and whole rock samples from 29 lavas, 7 modern bombs and 2 xenoliths were analyzed for their oxygen isotopic compositions. Forward models indicate there should be an enrichment in δ18O of 0.4‰ in lavas due to Raleigh fractionation, but this is not observed. Olivine δ18O decreases from a typical mantle value of +5.3‰ in the parental basanite source to 4.3‰ in recently erupted phonolite lava bombs. The trend correlates with a decreasing forsterite content in the olivine. Feldspar and glasses exhibit δ18O values well below predicted values and are in fractionation disequilibrium with olivine compositions at measured magmatic temperatures of 1000 °C within the phonolite lava lake. Isotopic depletion of the melt may be accounted for by incorporation of 8–11% hydrothermally altered volcanic edifice over time assuming water–rock interaction from strongly isotopically depleted Antarctic precipitation. Enhanced disequilibrium with olivine phenocrysts, are seen during the late stages of Erebus volcano construction. This calls for differential fractionation of olivine and feldspar from their respective melts, and slow O-diffusion of olivine while in the shallow lava lake prior to eruption.

Dislocation interactions in olivine control postseismic creep of the upper mantle

Changes in stress applied to mantle rocks, such as those imposed by earthquakes, commonly induce a period of transient creep, which is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the accumulation of stresses among dislocations is the dominant cause of strain hardening in olivine at temperatures ≤600 °C, raising the question of whether the same process contributes to transient creep at higher temperatures. Here, we demonstrate that olivine samples deformed at 25 °C or 1150–1250 °C both preserve stress heterogeneities of ~1 GPa that are imparted by dislocations and have correlation lengths of ~1 μm. The similar stress distributions formed at these different temperatures indicate that accumulation of stresses among dislocations also provides a contribution to transient creep at high temperatures. The results motivate a new generation of models that capture these intragranular processes and may refine predictions of evolving mantle viscosity over the earthquake cycle.

Raman semi-quantification on Mars: ExoMars RLS system as a tool to better comprehend the geological evolution of martian crust

This work presents the latest chemometric tools developed by the RLS science team to optimize the scientific outcome of the Raman system onboard the ExoMars 2022 rover. Feldspar, pyroxene and olivine samples were first analyzed through the RLS ExoMars Simulator to determine the spectroscopic indicators to be used for a proper discrimination of mineral phases on Mars. Being the main components of Martian basaltic rocks, lepidocrocite, augite and forsterite were then used as mineral proxies to prepare binary mixtures. By emulating the operational constraints of the RLS, Raman datasets gathered from laboratory mixtures were used to build external calibration curves. Providing excellent coefficients of determination (R2 0.9942÷0.9997), binary curves were finally used to semi-quantify ternary mixtures of feldspar, pyroxene and olivine minerals. As Raman results are in good agreement with real concentration values, this work suggests the RLS could be effectively used to perform semi-quantitative mineralogical studies of the basaltic geological units found at Oxia Planum. As such, crucial information about the geological evolution of Martian Crust could be extrapolated. In light of the outstanding scientific impact this analytical method could have for the ExoMars mission, further methodological improvements to be discussed in a dedicated work are finally proposed.

OLİVİNİN REFRAKTER HAMMADDESİ OLARAK KULLANIMI İÇİN DEMİR İÇERİĞİNİN MANYETİK AYIRMA İLE AZALTILMASI

Bu çalışmada, kromit zenginleştirilmesinde nihai artık olarak elde edilen bir olivin numunesindeki demir içeriğinin manyetik ayırma yöntemleri ile azaltılabilme potansiyeli incelenmiştir. Bu kapsamda, öncelikle numune +212, -212+150 ve -150 µm olarak üç fraksiyona ayrılmıştır. Sonrasında iri boyutlara kuru, ince boyuta ise yaş manyetik ayırma uygulanmıştır. Sonuçlar manyetik olmayan fraksiyonun ağırlık yüzdesi, Fe2O3 içeriği ve demir giderimi (%) gibi parametreler kullanılarak değerlendirilmiştir. Ayrıca manyetik olmayan fraksiyonlardaki mineralojik fazların miktarlarındaki değişimler XRD analizleri ile belirlenmiştir. +212 ve -212+150 µm için optimum değerlere sırasıyla 0,50-0,75 ve 1,0-2,0 A akım şiddeti aralıklarında ulaşılabileceği tespit edilmiştir. Her ne kadar karşılaştırılabilir olmasa da, -150 µm için efektif ayırmanın 2,0-3,0 A aralığında sağlandığı görülmüştür. Küçülen tane boyutu ile azalan demir içerikleri elde edilen bu sonuçları doğrular niteliktedir. XRD desenlerindeki demir içeriği yüksek fazların pik şiddetlerindeki azalışların da yine manyetik ayırma sonuçları ile uyumlu olduğu tespit edilmiştir. Genel sonuçlar, olivince zengin numunedeki demir içeriğinin manyetik ayırma ile refrakter hammaddesi için gerekli sınır değerlere çekilebileceğini göstermiştir.

Evolution of Microstructural Properties in Sheared Iron‐Rich Olivine

AbstractIron‐rich olivine is mechanically weaker than olivine of mantle composition, ca. Fo90, and thus is more amenable to study under a wide range of laboratory conditions. To investigate the effects of iron content on deformation‐produced crystallographic preferred orientation (CPO) and grain size, we analyzed the microstructures of olivine samples with compositions of Fo70, Fo50, and Fo0 that were deformed in torsion under either anhydrous or hydrous conditions at 300 MPa. Electron backscatter diffraction (EBSD) observations reveal a transition in CPO from D‐type fabric, induced by dislocation glide on both the (010)[100] and the (001)[100] slip systems, at low strains, to A‐type fabric, caused by dislocation glide on the (010)[100] slip system, at high strains for all of our samples, independent of iron content and hydrous/anhydrous conditions. A similar evolution of fabric with increasing strain is also reported to occur for Fo90. Radial seismic anisotropy increases with increasing strain, reaching a maximum value of ∼1.15 at a shear strain of ∼3.5 for each sample, demonstrating that the seismic anisotropy of naturally deformed olivine‐rich rocks can be well approximated by that of iron‐rich olivine. Based on EBSD observations, we derived a piezometer for which recrystallized grain size decreases inversely with stress to the ∼1.2 power. Also, recrystallized grain size increases with increasing iron content. Our experimental results contribute to understanding the microstructural evolution in the mantle of not only Earth but also Mars, where the iron content in olivine is higher.

Laser-induced spallation of minerals common on asteroids

The ability to deflect dangerous small bodies in the Solar System or redirect profitable ones is a necessary and worthwhile challenge. One well-studied method to accomplish this is laser ablation, where solid surface material sublimates, and the escaping gas creates a momentum exchange. Alternatively, laser-induced spallation and sputtering could be a more efficient means of deflection, yet little research has studied these processes in detail. We used a 15-kW Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine (minerals commonly found on asteroids) to induce spallation. We observed the process with a high-speed camera and illumination laser, and used X-ray micro-tomography to measure the size of the holes produced by the laser to determine material removal efficiency. We found that pyroxene will spallate at power densities between 1.5 and 6.0 kW cm−2, serpentine will also spallate at 13.7 kW cm−2, but olivine does not spallate at 1.5 kW cm−2 and higher power densities melt the sample. Laser-induced spallation of pyroxene and serpentine can be two- to three-times more energy efficient (volume removed per unit of absorbed energy) than laser-induced spattering, and over 40x more efficient than laser ablation.

Primordial neon in high-3He/4He Baffin Island olivines

Paleocene basaltic lavas exposed on Baffin Island have the highest 3He/4He found in any terrestrial igneous rocks and potentially contain the most pristine primordial mantle material exposed on Earth's surface. By vacuum-crushing large (1–3 g) olivine mineral separates, we extracted enough magmatic gas to obtain the first coupled helium, neon, and argon isotopic compositions of Baffin Island lavas. The five Baffin Island olivine samples have 3He/4He ranging from 36.2 ± 0.6 to 48.6 ± 1.3 (1σ) times the atmospheric ratio (Ra), overlapping with the highest known mantle values. Neon isotopic results fall on a mixing line between atmosphere and a high 20Ne/22Ne mantle endmember (with a maximum 20Ne/22Ne of 12.2). The slope of this mixing line is indistinguishable from that in subglacial Holocene glass from Iceland, but distinct from other hotspots and mid-ocean ridge basalt trends. This result supports the hypothesis that Baffin Island and Iceland lavas share a common high-3He/4He mantle component, despite the fact that recent paleogeographic reconstructions place the Iceland hotspot far from Baffin Island at the time of eruption (61 Ma). Our results also demonstrate that high-3He/4He mantle reservoirs have 3He/22Ne variability that either reflects ancient mantle heterogeneity or helium addition in the upper or lower mantle.

Experimental investigation of structural OH/H2O in different lunar minerals and glass via solar-wind proton implantation

The possibility of OH/H2O formation on the lunar surface has been proposed because of the interaction between protons from the solar wind and oxygen in the regolith. In this study, we examined olivine, pyroxene, plagioclase, and volcanic glass samples together irradiated with 7 keV H+ at a dose of 1017 ions/cm2 under the same experimental conditions to simulate the solar-wind proton implantation process on the Moon. By comparing the infrared spectral characteristics of these samples before and after H+ implantation through an infrared spectrometer, we confirm that OH forms in all minerals and glass after H+ implantation, with a remarkable amount of OH/H2O found in plagioclase. This indicates that plagioclase can capture more H+ than other silicate phases to form the OH/H2O. The absorption characteristics of OH/H2O formed by H+ implantation are distinct and associated with the mineral structure. The efficiency of OH/H2O formation by H+ implantation is affected by crystal structure. We conclude that OH/H2O formed by solar-wind implantation in the lunar soil is likely to be mainly preserved in plagioclase, and the estimated OH/H2O absorption strength from 0.7 to 3.6% at 3356 cm−1 and from 0.9 to 4.8% at 3622 cm−1 of plagioclase is consistent with those found by recent lunar spacecraft missions.

Luminescence Characteristics of Intraplate-Derived Olivines

Abstract Olivine has so far attracted limited attention as a potential luminescence dosimeter. In particular, there is a dearth of information concerning the luminescence properties of geochemically characterised, pure olivine samples. Six well-characterised olivine samples from four intraplate settings are investigated in this study, including emission wavelengths and intensities, growth of signal with absorbed dose, signal stability and recovery of a given dose with a single aliquot regeneration (SAR) protocol. All tested olivines share a low-temperature (90–100°C) UV/blue thermoluminescence (TL) peak, and five of six samples also produce a low-temperature red/yellow emission. Higher temperature TL peaks, which would be thermally stable over geological timescales and could be used for dating, are rarely observed at low doses (c. 46 Gy), but detectable though dim at significantly higher doses (c. 460 Gy). Photostimulated luminescence (PSL) emissions are very dim, but reliably detected emissions are stimulated by blue, yellow and infrared (IR) light. PSL yielded generally successful dose recovery results; however, all tested signals are prone to significant anomalous fading and complex thermal transfer between unbleachable and bleachable traps. These characteristics must be addressed if olivine is to be used as a natural dosimeter for luminescence dating. Given the variety of luminescence responses, it appears that olivine samples in future dating work may need to be individually characterised prior to measurement.

High-temperature and high-pressure Raman spectra of Fo89Fa11 and Fo58Fa42 olivines: Iron effect on thermodynamic properties

AbstractThe intrinsic anharmonicity plays an important role in the thermodynamic properties of minerals at the high-temperature conditions of the mantle. To investigate the effect of iron on the thermodynamic properties of olivine, the most abundant mineral in the upper mantle, we collected in situ high-temperature and high-pressure Raman spectra of natural Fo89Fa11 and synthetic Fo58Fa42 samples. Fo58Fa42 dissociates to enstatite + quartz + Fe2O3(+Fe) at 893 K. All the Raman-active modes systematically shift to lower frequencies at elevated temperatures, whereas to higher frequencies with increasing pressure. The Ag mode at ~960 cm–1 is more sensitive to the variations of temperature and pressure than other internal modes. The crystal-field splitting of the vibrational energy states becomes slightly weakened at high temperatures but strengthened at elevated pressures. We calculated the isobaric (γiP) and isothermal (γiT) mode Grüneisen parameters for these olivine samples. The intrinsic anharmonic parameters (ai) are negative for both the lattice and internal vibrations, and our calculations indicate that the intrinsic anharmonicity makes positive contributions to the thermodynamic properties of olivine at high temperatures, such as the internal energy (U), heat capacities (CV and CP), and entropy (S). Iron incorporation further increases the magnitudes of these anharmonic contributions. In addition, the Fe effect on the intrinsic anharmonicity may also apply to other thermodynamic properties in olivine, such as equations of state and equilibrium isotopic fractionations, which are important in constraining physical and chemical properties of the upper mantle.

A Subgrain‐Size Piezometer Calibrated for EBSD

AbstractWe calibrate a subgrain‐size piezometer using electron backscatter diffraction (EBSD) data collected from experimentally deformed samples of olivine and quartz. Systematic analyses of angular and spatial resolution test the suitability of each data set for inclusion in calibration of the subgrain‐size piezometer. To identify subgrain boundaries, we consider a range of critical misorientation angles and conclude that a 1° threshold provides the optimal piezometric calibration. The mean line‐intercept length, equivalent to the subgrain‐size, is found to be inversely proportional to the von Mises equivalent stress for data sets both with and without the correction of Holyoke and Kronenberg (2010, https://doi.org/10.1016/j.tecto.2010.08.001). These new piezometers provide stress estimates from EBSD analyses of polymineralic rocks without the need to discriminate between relict and recrystallized grains and therefore greatly increase the range of rocks that may be used to constrain geodynamic models.

Laser processing of minerals common on asteroids

Asteroid mining and redirection are two trends that both can utilize lasers, one to drill and cut, the other to ablate and move. Yet little is known about what happens when a laser is used to process the types of materials we typically expect to find on most asteroids. To shed light on laser processing of asteroid material, we used a 300-W, pulsed Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine, and studied the process with a high-speed camera and illumination laser at 10 000 frames per second. We also measure the sizes of the resulting holes using X-ray micro-tomography to find the pulse parameters which remove the largest amount of material using the least amount of energy. We find that at these power densities, all three minerals will melt and chaotically throw off spatter. Short, low-power pulses can efficiently produce thin, deep holes, and long, high-power pulses are more energy efficient at removing the most amount of material.

Electrical Conductivity of Ti‐Bearing Hydrous Olivine Aggregates at High Temperature and High Pressure

AbstractWe investigated the electrical conductivity of Ti‐H‐doped synthetic olivine aggregates at 4 GPa, 873–1273 K, and controlled oxygen fugacities. Under a given pressure and temperature, electrical conductivity depends on both hydrogen and Ti content, but these samples show different conductivity behavior from that observed in Ti‐poor sample such as San Carlos olivine. We found that when Ti content is comparable to or larger than hydrogen content, Ti has notable effects on electrical conductivity, but the effects of Ti is different between the H‐rich and the H‐poor regimes. In the H‐rich regime, electrical conductivity of olivine is weakly dependent on Ti content but has different sensitivity to water content than a Ti‐poor olivine. In contrast, in the H‐poor regime, electrical conductivity of Ti‐rich olivine is substantially higher than the conductivity of Ti‐poor olivine. As a consequence, the effect of hydrogen for the Ti‐rich synthetic olivine on electrical conductivity is smaller than for the Ti‐poor (natural) olivine for the modest H content expected in the asthenosphere, whereas in the H‐poor lithosphere Ti will enhance the electrical conductivity substantially. Possible models to explain these observations are proposed including the interaction of Ti‐related defects and H‐related defects as well as the charge transfer caused by the hopping conduction due to Ti3+ ⇔ Ti4+ under the H‐poor conditions. We conclude that the addition of Ti to olivine affects the behavior of H‐related defects, and therefore the applications of results from Ti‐rich olivine samples to the Ti‐poor real Earth need to be made with great care.

Sintering properties of olivine and its utilization potential as a refractory raw material: Mineralogical and microstructural investigations

In this study, an olivine sample obtained as final tailing from a chromite enrichment plant was examined for its sintering properties and utilization potential as a refractory raw material. For this purpose, cylindrical specimens were first prepared and then sintered at the temperatures of 1300, 1400, 1450 and 1500 °C for 2 h in a laboratory furnace. Quality of the products was evaluated in terms of some physical and mechanical refractory specifications such as bulk density, water absorption, porosity, shrinkage and cold crushing strength. Furthermore, phase developments and microstructural changes due to the sintering were determined in detail with X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, respectively. According to the experimental results, with increasing temperature, the bulk density and shrinkage values increased while the porosity and water absorption values decreased. Specifically, the bulk density and shrinkage values varied in the ranges of 2.33–2.60 g/cm3 and 1–5%, respectively. The porosity values of 24.10 and 15.68% were obtained after sintering at 1300 and 1500 °C, respectively. The cold crushing strengths slowly increased from 46.90 to 55.86 MPa after sintering between 1300 and 1450 °C. A sudden rise to 93.44 MPa was then observed at 1500 °C. Accordingly, the thermo-optical analysis indicates that the olivine exhibited a sintering point of 1478 °C and no softening up to 1500 °C. However, the formation of undesirable low-melting enstatite was detected by the XRD and SEM analysis which also specified the increasing amorphous phase and crystallizations of forsterite and spinels with rising temperature. Overall results have shown that the olivine sample used has a promising potential as a refractory raw material mainly due to its high MgO content, low loss on ignition (LOI) value and appropriate particle size.

Surface characterization of ash-layered olivine from fluidized bed biomass gasification

The present study aims to present a comprehensive characterization of the surface of ash-layered olivine bed particles from dual fluidized bed gasification. It is well known from operation experience at industrial gasification plants that the bed material is activated during operation concerning its positive influence on gasification reactions. This is due to the built up of ash layers on the bed material particles; however, the chemical mechanisms are not well understood yet. Olivine samples from long-term operation in an industrial-scale gasification plant were investigated in comparison to fresh unused olivine. Changes of the surface morphology due to Ca-enrichment showed a significant increase of their surface area. Furthermore, the Ca-enrichment on the ash layer surface was distinctively associated to CaO being present. The presence of CaO on the surface was proven by adsorption tests of carbon monoxide as model compound. The detailed characterization contributes to a deeper understanding of the surface properties of ash layers and forms the basis for further investigations into their influence on gasification reactions.

Dislocation interactions during low-temperature plasticity of olivine and their impact on the evolution of lithospheric strength

The strength of the lithosphere is typically modelled based on constitutive equations for steady-state flow. However, strain hardening may cause significant evolution of strength in the colder load-bearing portion of the lithosphere. Recent rheological data from low-temperature deformation experiments on olivine suggest that strain hardening occurs due to the presence of temperature-independent back stresses generated by long-range elastic interactions among dislocations. These interpretations provided the basis for a flow law that incorporates hardening by the development of back stress. Here, we test this dislocation-interaction hypothesis by examining the microstructures of olivine samples deformed plastically at room temperature either in a deformation-DIA apparatus at differential stresses of ≤4.3GPa or in a nanoindenter at applied contact stresses of ≥10.2GPa. High-angular resolution electron backscatter diffraction maps reveal the presence of geometrically necessary dislocations with densities commonly above 1014m−2 and intragranular heterogeneities in residual stress on the order of 1 GPa in both sets of samples. Scanning transmission electron micrographs reveal straight dislocations aligned in slip bands and interacting with dislocations of other types that act as obstacles. The resulting accumulations of dislocations in their slip planes, and associated stress heterogeneities, are consistent with strain hardening resulting from long-range back-stresses acting among dislocations and thereby support the form of the flow law for low-temperature plasticity. Based on these observations, we predict that back stresses among dislocations will impart significant mechanical anisotropy to deformed lithosphere by enhancing or reducing the effective stress. Therefore, strain history, with associated microstructural and micromechanical evolution, is an important consideration for models of lithospheric strength. The microstructural observations also provide new criteria for identifying the operation of back-stress induced strain hardening in natural samples and therefore provide a means to test the applicability of the flow law for low-temperature plasticity.

Effect of Water on the Thermal Properties of Olivine With Implications for Lunar Internal Temperature

AbstractHow water could affect thermal transport properties is a key question that needs to be quantified experimentally when it is incorporated as structurally bound hydroxyl groups in the lattice of mantle minerals. In this study, thermal diffusivity (D) and thermal conductivity (κ) of San Carlos olivine aggregates with various water contents (up to 0.2 wt.% H2O) were measured simultaneously using transient plane‐source method up to 873 K and 3 GPa. Experimental results demonstrate that water content can significantly reduce the thermal diffusivity (D) and thermal conductivity (κ) of olivine aggregate. With the increase of H2O content from 0.08 to 0.2 wt.%, the absolute values of D and κ for olivine samples decrease by 5–13% and 17–33% and by 3–8% and 14–21%, respectively. D and κ of olivine aggregate decrease with temperature but increase with pressure. Heat capacity is influenced by pressure negatively. Combining the present data with surface heat flow of the Moon as well as heat production, the calculated temperature profiles provide new constraints on the lunar geotherm and possible H2O content in the lunar interior.

Geological Mapping and Characterization of Possible Primary Input Materials for the Mineral Sequestration of Carbon Dioxide in Europe

This work investigates the possible mineral input materials for the process of mineral sequestration through the carbonation of magnesium or calcium silicates under high pressure and high temperatures in an autoclave. The choice of input materials that are covered by this study represents more than 50% of the global peridotite production. Reaction products are amorphous silica and magnesite or calcite, respectively. Potential sources of magnesium silicate containing materials in Europe have been investigated in regards to their availability and capability for the process and their harmlessness concerning asbestos content. Therefore, characterization by X-ray fluorescence (XRF), X-ray diffraction (XRD), and QEMSCAN® was performed to gather information before the selection of specific material for the mineral sequestration. The objective of the following carbonation is the storage of a maximum amount of CO2 and the utilization of products as pozzolanic material or as fillers for the cement industry, which substantially contributes to anthropogenic CO2 emissions. The characterization of the potential mineral resources for mineral sequestration in Europe with a focus on the forsterite content led to a selection of specific input materials for the carbonation tests. The mineralogical analysis of an Italian olivine sample before and after the carbonation process states the reasons for the performed evaluation. The given data serves as an example of the input material suitability of all the collected mineral samples. Additionally, the possible conversion of natural asbestos occurring in minerals as a side effect of the carbonation process is taken into consideration.

Trace element analysis of high-Mg olivine by LA-ICP-MS – Characterization of natural olivine standards for matrix-matched calibration and application to mantle peridotites

The trace element composition of olivine is becoming increasingly important in petrological studies due to the ubiquity of olivine in the Earth's upper mantle and in primitive magmatic rocks. The LA-ICP-MS method allows for the routine analysis of trace elements in olivine to sub-ppm levels, but a major drawback of this method is the lack of knowledge about possible downhole fractionation effects when non matrix-matched calibration is used. In this contribution, we show that matrix-matched (i.e., olivine-based) calibration is preferable for small laser spot sizes (<100 μm) due to significant laser-induced inter-element fractionation between olivine and commonly used silicate glass calibration materials, e.g., NIST SRM 612, GSD-1G and BHVO-2G. As a result, we present two Mg-rich natural olivine standards (355OL and SC-GB) that have been characterized by independent methods (EPMA, solution ICP-MS), and by LA-ICP-MS in four different laboratories. These natural olivines have been used 1) as primary standards for the matrix-matched calibration of olivine samples for most elements of interest (e.g., Li, Na, Al, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn), and 2) as secondary standards to assess the accuracy of results. Comparison of olivine- and silicate glass-calibrated results for natural peridotitic olivine reveals that matrix-matched calibration is essential when using small laser spot sizes (<100 μm) in order to mitigate downhole fractionation effects for certain elements, especially Na, P, Mn, Co, Ni and Zn. If matrix-matched calibration is not feasible, we recommend that spot sizes of ≥100 μm, laser fluence of ≤4.0 J/cm2, and total laser shot counts of ≤250 (e.g., 5 Hz repetition rate for 50 s) are used in order to minimize fractionation effects between olivine and silicate glass calibration materials. We demonstrate the applicability of matrix-matched calibration on olivine from a suite of different mantle peridotite xenoliths sampled by kimberlites and alkali basalts from on-craton and off-craton localities.