Elements In Olivine Research Articles

DiffSim: a user-friendly tool for precise magmatic timescale determination and error propagation via major element diffusion chronometry in magmatic phases

Diffusion chronometry is a technique gaining interest in the scientific community related to volcanology and petrology; however, modelling can be challenging for non-expert users. Here, we present DiffSim, a user-friendly standalone freeware that allows users to calculate magmatic timescales simulating 1D diffusion of major elements in olivine, orthopyroxene, titanomagnetite, and melt (inclusions). The freeware works solving the Fick’s second law equation (for both Cartesian and spherical polar coordinates, depending on the phase) using finite differences through the Crank-Nicolson method. Users must specify the initial composition vs. distance profile, the time resolution, and the intensive conditions (such as temperature, pressure, and oxygen fugacity). For orthorhombic phases, such as olivine and orthopyroxene, users must also specify the plunge and the trend of the (001)-axis and the angle traverse of the 2D section being studied. The best-fitting profile, comparing the natural (measured) and the modelled (calculated) profiles, is obtained using the least-squares fitting method in accordance with the total time specified by the user for performing the diffusion modelling. To determine the uncertainties of the timescale calculation, DiffSim propagates errors based on the uncertainties associated with each intensive condition and the experimental diffusivity measurements. DiffSim is available as executable freeware, allowing researchers and students to use diffusion chronometry to elucidate information about crustal processes with ease and precision.

Determination of ultra-trace rare earth elements in olivine by laser ablation-sector field-inductively coupled plasma-mass spectrometry

Ultra-trace rare earth elements (REEs) in olivine could be precisely measured by LA-SF-ICP-MS.

Trace elements in olivine: Analysis, geochemical behavior, and case studies

Trace elements in olivine: Analysis, geochemical behavior, and case studies

CO2‐Undersaturated Melt Inclusions From the South West Indian Ridge Record Surprisingly Uniform Redox Conditions

AbstractThe behavior of Fe3+ during mantle partial melting strongly influences the oxidation state of the resulting magmas, with implications for the evolution of the atmosphere's oxidation state. Here, we challenge a prevailing view that low‐degree partial melts are more oxidized due to the incompatible behavior of Fe3+. Our study is based on measurements of Fe3+/∑Fe along with major, minor, trace and volatile elements in olivine‐ and plagioclase‐hosted melt inclusions of CO2 undersaturated mantle melts in South West Indian Ridge lava. These inclusions record minimum entrapment pressures equivalent to depths up to 10 km below the seafloor, record magma ascent rates of 0.03–0.19 m/s, and display exceptionally high CO2/Ba, CO2/Rb, and CO2/Nb ratios, indicative of a CO2‐rich mantle source. Accounting for fractional crystallization, we find a uniform melt oxidation state (with an Fe3+/ΣFe at 0.140 ± 0.005 at MgO = 10 wt.%) that displays no systematic variation with major, minor, volatile or trace element contents, thus providing no evidence for a relationship between the degree of partial melting and Fe3+/ΣFe. This can be explained by efficient buffering of Fe3+/∑Fe and fO2 of mid‐ocean ridge basalt melts by their surrounding mantle and/or a decrease in the bulk peridotite‐melt Fe2O3 partition coefficient with increasing partial melting. We conclude that changes in the Earth's upper mantle temperature over geological time need not have affected the oxidation state of volcanic products or of the atmosphere.

Geochemistry of Trace Elements in Minerals of Porphyritic and Nonporphyritic Chondrules from Equilibrated Ordinary Chondrites

The paper presents the results of SIMS and EPMA studies of silicate minerals and bulk compositions (SEM-EDS) of porphyritic and nonporphyritic chondrules from equilibrated ordinary chondrites. The trace-element distribution in olivine, low-Ca pyroxene, and mesostasis of porphyritic and nonporphyritic chondrules in the equilibrated ordinary chondrites reflects heterogeneous conditions of chondrule-forming processes in the protoplanetary disk and provides insight in their evolution. The porphyritic chondrules are composed of olivine with the low content of Y and Yb relative to nonporphyritic chondrules. The enrichment of low-Ca pyroxene from porphyritic chondrules in trace elements correlates with the amount of pyroxene in the chondrule. Olivine composition in granular chondrules is close to that of porphyritic chondrules, but low-Ca pyroxene is distinguished by the high content of Y, Ti, Sr, Ba, V, and REE compared to all other chondrules. Barred chondrules are characterized by olivine enriched in trace elements (Zr, Y, Ti, Ba, Cr, and HREE) and low-Ca pyroxene highly depleted in trace elements (Zr, Y, Nb). The pyroxene of radial chondrules is enriched in Nb, Sr, and Ba. Trace elements in olivine and low-Ca pyroxene indicate the formation of the porphyritic and granular chondrules in a stable region of the protoplanetary disk, which is responsible for low-temperature heating and slow cooling of a chondrule. Trace element enrichment of olivine from the barred chondrules testifies strong heating of a precursor material and rapid cooling of the chondrule melt. Mineral composition of radial chondrules demonstrate rapid cooling of a low-temperature melt depleted in Mg and trace elements. High melt temperatures of barred chondrules and rapid cooling of nonporphyritic chondrules indicate their formation in an unstable region of the protoplanetary disk. Trace elements in silicate minerals of porphyritic and nonporphyritic chondrules reflect their formation as a result of melting of precursor minerals.

Secondary fluorescence effect quantification of EPMA analyses of olivine grains embedded in basaltic glass

Trace element analysis of olivine is challenging but vital, since trace elements in olivine can potentially record crystallization conditions and, correspondingly, conditions of magma generation, evolution, and transport dynamics. Electron microprobe analysis (EPMA) is one of the most widely used methods for trace element analysis in olivine for many reasons including but not limited to high-spatial resolution and high precision. EPMA protocols with high-beam currents and long-counting times provide accurate trace element concentrations with low-detection limits. However, these protocols neglect the effect of secondary fluorescence (SF) across phase boundaries, which may lead to fictitious analytical results when analyses are performed near other phases. In these cases, obtaining accurate EPMA data requires correction of SF effects from the adjacent or surrounding phase. In this study, the contents of olivine trace elements Ca, Ni, Mn, Ti, Cr, and Al have been measured in run products of experimental high-temperature studies on mafic magmatic systems consisting of olivine grains embedded in basaltic glass. Olivine grain fragments with known composition, were embedded in basaltic powder, and heated to 1250 °C in 1-atm vertical gas-mixing furnace for a few minutes and quenched. EPMA analyses of the olivine grains before and after the experiments were used to quantify the effect of SF, which was found to be most significant for Ca and Ti, and to a lesser extend for Al, and to depend on the distance from the interface, olivine grain geometry, accelerating voltage, and olivine and glass compositions. By combining our experimental results with systematic SF calculations performed with the Monte Carlo simulation program PENEPMA, analytical expressions that give the apparent Ca, Ti, and Al concentrations due to SF in equant olivine grains embedded in basaltic glass were derived. These equations, which allow for a rapid correction of SF effects, are used to assess the average overestimation due to SF of olivine analyses included in current experimental databases, which might be the source of major discrepancies observed in petrological tools utilizing trace element contents in olivine.

Trace Elements in Olivine of Volcanic Rocks: Application to the Study of Magmatic Systems

A quantitative local analytical method with the application of inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS) was tested at Vernadsky Institute for the determination of contents of trace elements (Cu, Zn, Co, Ni, Mn, Cr, Sc, V, Ca, Ti, Al, Y, and REE) in olivine. Olivine phenocrysts from volcanic rocks of various geological settings have been studied: island-arc basalts, mid-ocean ridge (MOR) basalts, and high-alkaline continental volcanic rocks. The contents of some elements (Ni, Co, Mn, Cr, Sc, and Zn) systematically vary during the evolution of the composition of olivine, and the concentration fields of these elements in olivine from different settings overlap one another. At the same time, the contents of some other elements (Ca, Al, Ti, V, and Cu) fundamentally differ in olivine from different geological settings. Copper content in olivine from oceanic tholeiites and highly alkaline continental volcanics is 1–3 ppm, which is systematically lower than copper content in olivine from island-arc basalts (3–9 ppm). The concentrations of vanadium in olivine in MOR basalts are higher than in island-arc and alkaline continental ones, which may be due to relatively more reduced crystallization conditions as more favorable for the incorporation of V3+ into the olivine structure. Variations in the distribution coefficients of trace elements between olivine and silicate melt (DOl/Melement) were determined for volcanic rocks from Kamchatka, the Bouvet Triple Junction, and Gaussberg volcano. It has been demonstrated that the unusually high values DOl/MNi of DOl/MNi = 50–150 previously identified for the lamproites of Gaussberg volcano indicate a mismatch between the composition of the quenched glass and the composition of the equilibrium melt for olivine phenocrysts. When using the bulk compositions of Gaussberg rocks, values of DOl/MNi = 11–21 were obtained, which correspond to experimental estimates for high-potassium rocks. The redox crystallization conditions of the studied rocks were estimated using several oxybarometers based on the distribution of vanadium between coexisting olivine and melt. These values were: ΔQFM= +0.6 to +1.5 for oceanic tholeiites of the Bouvet Triple Junction area, South Atlantic, and ΔQFM = +1.5 to +2.4 for Mutnovsky volcano, Kamchatka. Estimates of the redox crystallization conditions of the highly alkaline rocks of Gaussberg volcano significantly vary depending on which model is chosen: ΔQFM= +0.2 to +4.8, which may be due to the strong effect of K2O content in the melt involved in one of the models. The newly acquired analytical data confirmed the possibility of using contents of trace elements in olivine to characterize igneous systems from different geological settings and highlighted the need for additional experimental studies on the distribution of these elements between olivine and melt, especially in highly alkaline systems.

Trace Elements in Olivine of Volcanic Rocks: Application to the Study of Magmatic Systems

Trace Elements in Olivine of Volcanic Rocks: Application to the Study of Magmatic Systems

Accurate analyses of key petrogenetic minor and trace elements in olivine by electron microprobe

Abundances of minor and trace elements in olivine are increasingly used as petrogenetic indicators for mantle source lithologies, mantle metasomatism history, mantle potential temperatures, and magmatic differentiation. As it is common for olivine to be complexly zoned on a fine-scale, high precision analytical methods for EPMA (electron microprobe microanalyzer, or Electron Microprobe) trace element analysis under high spatial resolution have been developed. However, previous studies have focused more on analytical precision with fewer efforts in examining the accuracy of the data. In this study, we used the Cameca SXFive field emission (FE) EPMA to fully evaluate the effects of beam settings, background offsets and background regression models, and primary calibration standards on the data accuracy of 10 key petrogenetic elements (Na, Al, P, Ca, Ti, Cr, Mn, Co, Ni, and Zn) using MongOlSh11–2 olivine as a reference material. Our results indicate that high voltage, high beam current and long counting time not only improve data precision, but also improve data accuracy, especially on elements with low P/B (peak/background) ratios such as Zn and Cr. Importantly, careful background offsets and background regression models need to be obtained via high resolution WDS relative scans or step scans on each target element. Special care needs to be paid to Co element analysis to avoid or correct for peak interference of Fe Kβ. Among 10 minor and trace elements, exponential background regression models need to be applied to Al, Mn, and Ti elements, whereas other elements require linear background regression. Furthermore, to avoid Al and Zn surface contamination due to alumina polishing or brass presence, ultrasonic cleaning between each intermediate polishing steps and plasma cleaning immediately prior to EPMA experiments is highly recommended. Micro-inclusions such as chromite and spinel in olivine or adjacent Ca-rich phases need to be avoided to minimize primary or secondary fluorescence-related contamination on Al, Cr, or Ca. As a volatile element, Na element needs to be analyzed first with appropriate counting time to minimize the Na loss under high beam conditions. It needs mentioning that major elements (Mg, Fe, and Si) are best analyzed using MongOlSh11–2 or San Carlos olivine as primary standards for calibrations, which can yield more accurate data for both major elements and trace elements because of the improved matrix-corrections. Using our recommended analytical protocols, we have successfully discriminated “depleted” mantle olivine cores from an EMORB in northern East Pacific Rise (EPR) via Ca, Ti, Ni, Co, and Mn abundances. Our olivine data from Siqueiros Transform and the nearby 8°20′ N seamounts also help reveal a metasomatized peridotite mantle beneath the northern EPR. Overall, the protocols proposed in this study can serve as a guide for accurate EPMA olivine trace element analyses, which potentially contributes to the efforts of fostering a comparable olivine database worldwide.

Trace elements in olivine fingerprint the source of 2018 magmas and shed light on explosive-effusive eruption cycles at Kīlauea Volcano

Understanding magma genesis and the evolution of intensive parameters (temperature, pressure, composition, degree of melting) in the mantle source of highly active volcanic systems is crucial for interpreting magma supply changes over time and recognizing cyclic behavior to anticipate future volcanic behavior. Major and trace elements in olivine are commonly used to study variations in mantle lithologies and melting conditions (e.g., temperature, pressure, oxygen fugacity) affecting the mantle over time. Here, we track the temporal evolution of primary melts through the most recent cycle of explosive and effusive eruptions at Kīlauea (Hawai‘i), which spans the last ∼500 years. We report major and trace elements in olivine from the last explosive period (∼1500 – early 1820’s Keanakāko‘i Tephra) and the most recent decade of the current effusive period (2018 LERZ, 2015–2018 Pu‘u‘ō‘ō, 2008–2018 lava lake and 2020 eruption in Halema‘uma‘u). Scandium concentrations in olivine allow characterizing changes in mantle source between 1500 and 2018, and suggest that the recent (2015–2018) magma feeding the Pu‘u‘ō‘ō cone did not significantly interact with the magma that erupted in the LERZ in 2018. The evolution of olivine and melt compositions over the past 500 years is not easily reconcilable with variations in mantle potential temperature, pressure of mantle melt pooling and storage, or oxygen fugacity. Instead, Sc, Mn, and Co concentrations and Ni/Mg ratio in high forsterite (Fo >87) olivine advocate for an increase in the proportion of clinopyroxene in the mantle source associated with a slightly higher degree of partial melting from 1500 to 2018. Changes in primitive melt compositions and degrees of mantle melting may well modulate magma supply to the crust and formation-replenishment of steady or ephemeral summit reservoirs, and thereby control transitions between explosive and effusive periods at Kīlauea. Analyzing trace elements in olivine at Kīlauea and elsewhere could therefore provide important clues on subtle changes occurring at the mantle level that might herald changes in volcanic behavior.

Features of olivine crystallization in ordinary chondrites (Saratov meteorite): geochemistry of trace and rare earth elements

The paper discusses the geochemistry of major (EPMA) and trace (SIMS) elements in olivine of porphyritic, nonporphyritic chondrules, and the matrix of equilibrated ordinary chondrite Saratov (L4). Olivine corresponds to forsterite and is rather heterogeneous (Fo 73-77). No differences in the content of the major elements in the olivine of the chondrule and the matrix of the meteorite were found. However, the content of major and trace elements in olivine within chondrules varies considerably; high values found in olivine from barred chondrules. Olivine from porphyritic chondrules and the matrix of the Saratov meteorite have similar concentrations of trace elements. High concentrations of refractory (Zr, Y, Al) and moderately volatile (Sr and Ba) trace elements in barred olivine chondrule indicate the chondrule melt formation due to the melting of precursor minerals and its rapid cooling in the protoplanetary disk, which is consistent with the experimental data. The olivine of the chondrules center of the Saratov meteorite differs from the olivine of the chondrules rims and meteorite matrix by the increased values of the Yb/La ratio. No relict grains and magnesian cores of olivine were found in meteorite chondrules. Individual grains in the chondrules are distinguished by their enrichment in trace elements relative to the rest of the olivine grains in the chondrule.

EVALUATION OF THERMAL METAMORPHISM TEMPERATURE OF EQUILIBRATED ORDINARY CHONDRITES

The article provides an evaluation of thermal metamorphism temperatures on chondrite parent bodies using an olivine-Сr spinel geothermometer. To calculate temperatures, the results of EPMA analysis of the major and trace elements in olivine and Cr spinel of Kargapole, Orlovka, Saratov, Elenovka, Buschhof, Bjurböle and Knyahinya meteorites are used. The obtained temperatures are consistent with the onion-shell model of the planetesimal structure, in which the most metamorphosed chondrites are closer to the heating source (Buschhof, L6-734 °C), meteorites of the 5th petrologic type (p.t.) occupied an intermediate position (Orlovka, H5 – 687 °С; Elenovka, L5 – 691 °С; Knyaginya, LL5 – 700 °C), and the chondrites of the 4th p.t. were closer to the surface (Kargapole, H4 – 691 °C; Saratov, L4 – 670 °С; Bjurböle, LL4 – 682 °C). The Kargapole and Saratov meteorites are characterized by evaluation of Mg and Fe equilibrium temperatures that disagree with the onion-shell model, which can be explained by the individual history of the meteorite (for example, impact metamorphism, slow and prolonged heating).

Element Partitioning and Li‐O Isotope Fractionation Between Silicate Minerals and Crustal‐Derived Carbonatites and Their Implications

AbstractIn order to investigate element partitioning and Li‐O isotope fractionation between silicate minerals and carbonatite melts at variable levels from mantle to crust, we document elemental and Li‐O isotopic data for major minerals from crust‐derived carbonatites at Eppawala, Sri Lanka. Partition coefficients (D) of elements between olivine or clinopyroxene and carbonatite melts are consequently estimated. The estimated D values indicate that Li, Zn, Co, Cr, Mn, and Ni behave compatibly in olivine, while P and Sc are slightly compatible, and V and Al are mildly incompatible. Partition coefficients of elements between clinopyroxene and carbonatite melts are defined here, including highly compatible Li, Sc, Ti, V, Al, and Na, moderately compatible Zn, Co, Cr, and Ga, and incompatible Mn, Ni, P, and Cu. They are systematically higher than literature values obtained from mantle conditions, but their relative compatibilities at different systems are consistent. This indicates that element partitioning between silicates and carbonatite melts is highly temperature‐ and pressure‐dependent and can be used to evaluate geochemical proxies of carbonatite metasomatism, and evolution and mineralization of carbonatite melts. Profile analyses on olivine grains reveal that Fe‐loving elements in olivine could well preserve features of crystal growth and modal metasomatic interaction, while Li and O isotope fractionations are strongly controlled by element diffusion and Li isotopes are robust indicators of cryptic metasomatic interaction.

Coupled Li-P Zoning and Trace Elements of Olivine from Magmatic Ni-Cu Deposits: Implications for Postcumulus Re-Equilibration in Olivine

Abstract Olivine is an important mineral in mafic–ultramafic rocks and records various crustal and mantle processes in basaltic magma. Generally, phosphorus (P) is immobile in olivine and its zoning tends to record magmatic processes. In contrast, lithium (Li) is one of the most mobile elements in olivine and tends to be re-distributed by postcumulus to hydrothermal processes. This study reports coupled Li-P oscillatory and sector zoning in cumulus olivine (Fo > 80 mol%) from magmatic Ni-Cu deposits in northwest China. The close to 1:1 relationship between Li + Na cation and P cation in olivine suggests P substitutes for slowly diffusing Si at the tetrahedral site and Li (Na) substitutes for Mg at the octahedral metal site. The preservation of such coupled Li-P zoning suggests that the charge-balanced–controlled substitution of Li+P5+ for Mg2+Si4+, producing a member of the Li(Fe)PO4 structure, may cause sluggish Li diffusion in olivine. The Li-P zoning is uncorrelated to other elements (Fe, Mg, Cr, Al, Ca, Ti, V, Ni, Zn, Mn, Co, and Sc). The Ca abundances in cumulus olivine are significantly depleted relative to those in volcanic olivine and modeled for olivine using the rhyolite–MELTS program, whereas the Mg, Fe, Mn, Zn, Ni, and Co contents show no signs of depletion. The Cr and Al contents in high Fo olivine are lower than those in volcanic olivine with a similar Fo value. The depletions in Ca, Cr, and Al (both divalent and trivalent cations) have been attributed to post-crystallization re-equilibration processes. We suggest that the selective Ca-Cr depletion in olivine resulted from re-equilibration between olivine and clinopyroxene–orthopyroxene–spinel–melts at the postcumulus stage, whereas the Al content variation in olivine is likely controlled by olivine–spinel (pyroxene) re-equilibration. Olivine fractionation modeling results reveal that Co content in both olivine and sulfides changes slightly during evolution, whereas the olivine Ni/Co ratio decreases dramatically from 30 (at Fo90) to 4 (Fo80). These are consistent with the variation of Ni and Co contents in olivine from sulfide-barren rocks but cannot explain the strong positive Ni-Co correlation observed in olivine from the sulfide-bearing rocks. The considerable increase in the Ni/Co ratio in olivine coexisting with the high Ni tenor sulfide compared with the slight increase of the Ni/Co ratio in olivine coexisting with moderate-low Ni tenor sulfide strongly suggests that the Ni and Co contents and Ni/Co ratio in olivine from the mineralized rocks were the results of olivine–sulfide interaction. The olivine Fe/Zn and Mn/Zn ratios show little difference between sulfide-barren and sulfide-rich rocks, but these ratios decrease considerably with the decreasing Fo values. Overall, the study suggests that elements (Ca, Cr, Al, Mg, Fe, Ni, Co, Zn, etc.) diffuse faster than P have been re-distributed in cumulus olivine by re-equilibration processes, modifying the elemental content and inter-element ratios in olivine. The characteristics of the crystallization, particularly the source recorded in cumulus olivine, may be obscured and overprinted by postcumulus processes.

Сlassification and characteristic of inclusions in the Severny Kolchim meteorite (H3.4)

Research subject.Fragments of the Severny Kolchim meteorite.Materials and methods.The study was performed in the Geoanalyst Centre for Collective Use, Institute of Geology and Geochemistry, UB RAS. The clast and inclusions were studied using a scanning electron microscope JSM-6390LV from JEOL with an energy dispersing attachment INCA Energy 450 X-Max 80. The bulk chondrule compositions were obtained by EDS analysis of whole chondrule areas in thin sections. The composition of minerals was studied using an electron microprobe analyser Cameca SX100 equipped with five wavelength spectrometers. The concentrations of trace elements in olivine were measured using a mass spectrometer with inductively coupled plasma NexION 300S (PerkinElmer) with a laser ablation attachment NWR 213 (ESI) at a crater diameter of 25 microns.Results.According to the revealed set of petrographic and mineralogical features, the meteorite was clarified as H3.4. In addition, this meteorite can be further classified as genomict breccia. In the Severny Kolchim meteorite, a 6×6 mm clast fragment composed of chondrite H3.9 was studied. This inclusion has a slightly higher degree of S2 shock transformations compared to the host rock. Refractory forsterite-rich objects were found and studied. These inclusions are composed of low-ferroan forsterite (f = 0.004–0.2, f – ratio Fe/(Fe + Mg)mol).Conclusion.The porphyry olivine chondrules consisting of refractory forsterite and high-calcium glass in mesostasis are likely to be parental to the refractory forsterite-rich inclusions. Al-rich chondrules and pyroxene chondrule with tridymite identified in the matrix of the chondrite are likely to be xenogenic, originating from the formation area of enstatite chondrites.

Trace elements in olivine: Proxies for petrogenesis, mineralization and discrimination of mafic-ultramafic rocks

Olivine is a ubiquitous mineral in mafic-ultramafic rocks and has been widely used as a mineral marker in various geological processes. However, its development of trace elements is limited. Here we present newly-obtained trace element data 7Li, 27Al, 29Si, 31P, 43Ca, 45Sc, 49Ti, 51V, 53Cr, 55Mn, 59Co, 60Ni, and 66Zn of olivine in typical mantle xenoliths, mantle peridotites in ophiolites, and plutonic rocks from layered and Alaskan-type intrusions to develop trace element proxies for the petrogenesis, mineralization and discrimination of various mafic-ultramafic rocks. Residual olivine grains in mantle xenoliths and ophiolitic peridotites, which represent residues of mantle melting, have higher Ni/Co (>20) and Ni/Mn (>2) ratios than magmatic olivine (Ni/Co < 20, Ni/Mn < 2), which are consistent with the compatibilities of these elements during partial melting and magma differentiation. Lower Ni content, and lower Ni/Co and Ni/Mn ratios at a given Fo content can distinguish olivine in Alaskan-type intrusions from layered intrusions, reflecting the nature of their mantle sources. The V and Sc contents and V/Sc ratios in olivine can distinguish mantle xenoliths (V > 2 ppm, V/Sc > 0.5) from ophiolitic peridotites (V < 2 ppm, V/Sc < 0.5), indicating a more reduced state of continental lithospheric mantle compared to the oceanic lithospheric mantle. As a consequence, the four occurrences of mafic-ultramafic rocks can be distinguished by olivine with (Sc × 10)-(Ti × 2)-Zn and V/Sc-(Co/Ni × 2)-(Zn/Mn × 5) ternary diagrams. In addition, Li, Ti and P contents in olivine are good tracers of melt/fluid metasomatism, whereas Ni/Co, Ni/Mn and Mn/Zn ratios are indicators of chromite mineralization. Therefore, trace elements in olivine can be used as chemical proxies to distinguish the origin of various mafic-ultramafic rocks, as well as the processes by which they evolved.

Formation process of dunites and chromitites in Orhaneli and Harmancık ophiolites (NW Turkey): Evidence from in-situ Li isotopes and trace elements in olivine

Trace elements and Li isotopic compositions of olivine from the mantle-crust transition zone of the Bursa ophiolites (including Orhaneli ophiolite and Harmancık ophiolite) in NW Turkey were measured to constrain the genesis of these dunites and chromitites. A cumulate origin for dunite can be ruled out due to the depletion of incompatible trace elements (Zr, Ti, and heavy rare earth elements) in olivine, instead the chemical signatures point to a replacive origin via melt-rock interaction. The olivine grains in the dunites have lower MnO (0.06–0.15 wt%), Co (106–137 ppm), and higher NiO (0.23–0.44 wt%) concentrations than olivine phenocrysts in MORB, suggesting these transition-zone dunites have equilibrated with extremely depleted melts. Additionally, the relatively small δ7Li variations of olivine (average δ7Li +4.8 to +8.7‰) of the Orhaneli suite indicate the Li isotopic compositions of melts percolating through these dunites are relatively homogeneous. However, the large δ7Li variations of olivine (−2.5 to +20.3‰) in Harmancık dunites can be explained by incomplete diffusive equilibration with melts percolating through these dunites, suggesting infiltration happened not long before obduction of the ophiolite. Olivine in chromitites has higher Fo (92.6–94.7) than coexisting dunites, likely induced by subsolidus Mg-Fe exchange between olivine and chromite. The higher chromite contents of the chromitites can also explain the lower concentrations of Sc, V, Co and Zn in coexisting olivine grains. Mixing of depleted mantle-derived melts and boninitic magmas is suggested to induce a compositional shift from the olivine-chromite cotectic line to the liquidus field of chromite, causing the precipitation of chromite and formation of chromitite layers in the dunites. The heavy Li isotopic compositions (+6 to +11‰) of olivine in chromitites compared to MORB, together with the estimated compositions of parental magmas (Al2O3: 9.8–11.4 wt%; TiO2: 0.22–0.38 wt%) for the chromitites, indicate an arc-like geochemical affinity, hence a subduction-related setting in which these mantle-crust transition zones formed

Elucidating the processes affecting highly primitive lavas of the Borgarhraun flow (northern Iceland) using trace elements in olivine

Olivine is typically the first phase to crystallise from basaltic melts and its chemistry can therefore inform on the earliest stages of magmatic evolution, not recorded by later crystallising phases. Despite the potential of olivine for understanding primitive differentiation, limited analytical capabilities have previously restricted the range of elements that can be routinely measured. Consequently, important processes controlling early magma evolution may have been overlooked or misidentified. This study reports a wide range of minor and trace elements in forsteritic (up to Fo92.2) olivine macrocrysts from the primitive Borgarhraun lava flow in northern Iceland.We define two distinct populations of olivine based on their forsterite (Fo) content and then apply minor and trace element data to discern mixing and crystallisation of subtly different high-MgO parental melts. High-Fo (90.9–92.2 mol%) olivines show approximately linear trends between Cr and other incompatible trace elements (Li, Na, Ca, Ti, Al and Y), implying mixing and concurrent crystallisation of two highly primitive melts. Low-Fo (87.4–90.0 mol%) olivines show trends that indicate mixing and crystallisation of multiple, genetically distinct and less primitive melts. The outermost 50 μm of the olivine microcrysts record diffusive re-equilibration of the olivine macrocrysts to a single, significantly more evolved carrier liquid over an ascent timescale of 70–250 days. Compared to the rest of Iceland, the Borgarhraun olivine macrocrysts are distinguished by their Cr contents, which extend from 97 to 1150 ppm. The uniquely steep trend in Fo vs. Cr can be explained by early crystallisation of Cr-spinel and Cr-rich clinopyroxene, stabilised by high pressures of differentiation (>0.8 GPa). Chromium-forsterite systematics may therefore be a powerful tool for qualitatively assessing relative pressures of crystallisation for different magmatic systems. Collectively, our new dataset clearly demonstrates the importance of measuring trace elements in olivine for identifying the formative stages and conditions of basaltic magmatic systems.

Simultaneous Quantification of Forsterite Content and Minor–Trace Elements in Olivine by LA–ICP–MS and Geological Applications in Emeishan Large Igneous Province

Olivine forsterite contents [Fo = 100 × Mg/(Mg + Fe) in mol%] and minor–trace element concentrations can aid our understanding of the Earth’s mantle. Traditionally, these data are obtained by electron probe microanalysis for Fo contents and minor elements, and then by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) for trace elements. In this study, we demonstrate that LA–ICP–MS, with a simplified 100% quantification approach, allows the calculation of Fo contents simultaneously with minor–trace elements. The approach proceeds as follows: (1) calculation of Fo contents from measured Fe/Mg ratios; (2) according to the olivine stoichiometric formula [(Mg, Fe)2SiO4] and known Fo contents, contents of Mg, Fe and Si can be computed, which are used as internal standards for minor–trace element quantification. The Fo content of the MongOLSh 11-2 olivine reference material is 89.55 ± 0.15 (2 s; N = 120), which agrees with the recommended values of 89.53 ± 0.05 (2 s). For minor–trace elements, the results matched well with the recommended values, apart from P and Zn data. This technique was applied to olivine phenocrysts in the Lijiang picrites from the Emeishan large igneous province. The olivine compositions suggest that the Lijiang picrites have a peridotitic mantle source.

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.