H2O Content Measurement in Phengite by Secondary Ion Mass Spectrometry: A New Set of Reference Materials

Five new natural white mica reference materials (RMs) were developed for in situ H₂O content analyses by secondary ion mass spectrometry at the SwissSIMS laboratory of Lausanne University, Switzerland. The white mica reference materials cover a large part of the natural muscovite–phengite compositional range and are therefore suitable as reference materials for the analysis of natural rocks as well as individual minerals. The independent H₂O content of the reference materials UNIL_WM1 to UNIL_WM5 was obtained by thermal conversion elemental analyser and corresponds to 4.35 ± 0.02, 4.33 ± 0.03, 4.30 ± 0.07, 4.50 ± 0.02 and 4.42 ± 0.11 (% m/m, ± 1s), respectively. SIMS determinations of H₂O content revealed a matrix effect correlated to the FeO content of white mica. The compositional range in FeO of the reference materials that were calibrated for H₂O determination is from 1.13% to 3.67% m/m. No crystallographic orientation dependency was observed at the level of homogeneity of these reference materials. An analytical precision of 0.02% to 0.08% m/m (1SE) is expected for the final uncertainty on measurements of unknown white micas in natural samples.     

The compositional variation of synthetic sodic amphiboles at high and ultra-high pressures

Sodic amphiboles in high pressure and ultra-high pressure (UHP) metamorphic rocks are complex solid solutions in the system Na₂O–MgO–Al₂O₃–SiO₂–H₂O (NMASH) whose compositions vary with pressure and temperature. We conducted piston-cylinder experiments at 20–30?kbar and 700–800?°C to investigate the stability and compositional variations of sodic amphiboles, based on the reaction glaucophane=2jadeite+talc, by using the starting assemblage of natural glaucophane, talc and quartz, with synthetic jadeite. A close approach to equilibrium was achieved by performing compositional reversals, by evaluating compositional changes with time, and by suppressing the formation of Na-phyllosilicates. STEM observations show that the abundance of wide-chain structures in the synthetic amphiboles is low. An important feature of sodic amphibole in the NMASH system is that the assemblage jadeite–talc?±?quartz does not fix its composition at glaucophane. This is because other amphibole species such as cummingtonite (Cm), nyböite (Nyb), Al–Na-cummingtonite (Al–Na-Cm) and sodium anthophyllite (Na-Anth) are also buffered via the model reactions: 3cummingtonite?+?4quartz?+?4H₂O=7talc, nyböite?+?3quartz=3jadeite?+?talc, 3Al–Na-cummingtonite + 11quartz + 2H₂O=6jadeite + 5talc, and 3 sodium anthophyllite?+?13quartz?+?4H₂O=3 jadeite + 7talc. We observed that at all pressures and temperatures investigated, the compositions of newly grown amphiboles deviate significantly from stoichiometric glaucophane due to varying substitutions of Al^IV for Si, Mg on the M(4) site, and Na on the A-site. The deviation can be described chiefly by two compositional vectors: [Na^AAl^IV]<=>[□^ASi] (edenite) toward nyböite, and [Na^(M4)Al^VI]<=>[Mg^(M4)Mg^VI] toward cummingtonite. The extent of nyböite and cummingtonite substitution increases with temperature and decreases with pressure in the experiments. Similar compositional variations occur in sodic amphiboles from UHP rocks. The experimentally calibrated compositional changes therefore may prove useful for thermobarometric applications.     

Volatiles in amphiboles from xenoliths,Vulcan's Throne,Grand Canyon,Arizona, USA

Analyses of major element and volatile components of amphiboles from Vulcan's Throne, a Recent volcano on the north rim of the Grand Canyon, Arizona, USA, have been performed by using the electron microprobe and high temperature mass spectrometry. The amphiboles occur as megacrysts, as oikocrysts in peridotite and pyroxenite xenoliths, in amphibole-rich selvages on lherzolite xenoliths, and as grains in hornblendite xenoliths. Total volatiles range from 1.27 to 1.75 wt.%. In all samples, H₂O is the principal volatile species. Lesser amounts of structurally bound fluorine, chlorine, and oxygen were also released. The amphiboles studied are hydroxyl-deficient. The O(3) site is probably partially occupied by O^2?, which was detected as O₂ during degassing of the amphibole. Ti shows a strong positive correlation with the amount of hydroxyl deficiency in the amphiboles except for one oxidized sample. Thus, Ti probably is significant in charge balancing the substitution of O^2? for OH^? and the substitution probably occurred during crystallization rather than by dehydrogenation. Small amounts of both oxidized and reduced carbon and sulfur-bearing volatile species (e.g., CO₂, CO, CH₄, SO₂, H₂S) were detected in all samples. The observation of reduced carbon species supports the hypothesis that the oxygen fugacity of at least portions of the upper mantle is probably less than the quartz-fayalite-magnetite buffer.     

Inter‐laboratory Characterisation of Apatite Reference Materials for Chlorine Isotope Analysis

Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca₁₀(PO₄)₆(F,Cl,OH)₂ solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for ³⁷Cl/³⁵Cl homogeneity using SIMS followed by δ³⁷Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10‰ (1s) for the five samples with > 0.5 % m/m Cl and ± 0.19‰ (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38‰ between the mean ³⁷Cl/³⁵Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ³⁷Cl_SMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 10³δ³⁷Cl_SMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.     

Happy Jack Uraninite: A New Reference Material for High Spatial Resolution Analysis of U‐Rich Matrices

There is currently a lack of well‐characterised matrix‐matched reference materials (RMs) for forensic analysis of U‐rich materials at high spatial resolution. This study reports a detailed characterisation of uraninite (nominally UO_2+x) from the Happy Jack Mine (UT, USA). The Happy Jack uraninite can be used as a RM for the determination of rare earth element (REE) mass fractions in nuclear materials, which provide critical information for source attribution purposes. This investigation includes powder X‐ray diffraction (pXRD) data, as well as major, minor and trace element abundances determined using a variety of micro‐analytical techniques. The chemical signature of the uraninite was investigated at the macro (cm)‐scale with micro‐X‐ray fluorescence (µXRF) mapping and at high spatial resolution (tens of micrometre scale) using electron probe microanalysis (EPMA) and laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analyses. Based on EPMA results, the uraninite is characterised by homogeneous UO₂ and CaO contents of 91.57 ± 1.49% m/m (2s uncertainty) and 2.70 ± 0.38% m/m (2s), respectively. Therefore, CaO abundances were used as the internal standard when conducting LA‐ICP‐MS analyses. Overall, the major element and REE compositions are homogeneous at both the centimetre and micrometre scales, allowing this material to be used as a RM for high spatial resolution analysis of U‐rich samples.     

Characterisation of Three Sri Lankan Zircon Megacrysts as Potential Reference Materials for Microbeam U-Pb Geochronology and Hf-O-Zr Isotope Measurements

In situ U-Pb geochronology and hafnium, oxygen and zirconium isotope measurements in zircons using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and ion microprobe techniques can provide essential isotopic data to constrain geological evolutionary histories. Developing reliable zircon reference materials is the cornerstone for in situ zircon chronology and isotopic studies. In this study, the homogeneity of U-Pb ages and Hf-O-Zr isotope ratios in three Sri Lankan zircon megacrysts (SLZA, SLZB and SLZC) were investigated using multiple analytical methods. The obtained U, Th, Pb and Hf mass fractions of the SLZA zircon were 839 ± 56 μg g^-1 (1s), 151 ± 15 μg g^-1 (1s), 198 ± 28 μg g^-1 (1s) and 8635 ± 286 μg g^-1 (1s), respectively. The mass fractions of U, Th, Pb and Hf in the SLZB zircon were 1106 ± 106 μg g^-1 (1s), 331 ± 61 μg g^-1 (1s), 376 ± 57 μg g^-1 (1s) and 9673 ± 976 μg g^-1 (1s), respectively. The U, Th, Pb and Hf mass fractions determined in the SLZC zircon were 551 ± 35 μg g^-1 (1s), 111 ± 8 μg g^-1 (1s), 129 ± 18 μg g^-1 (1s) and 7881 ± 393 μg g^-1 (1s), respectively. The chemical abrasion isotope dilution thermal ionisation mass-spectrometry (CA-ID-TIMS) method yielded a Th-corrected weighted mean ²⁰⁶Pb/²³⁸U age of 556.94 ± 1.29 Ma (95% conf., n = 5) for the SLZA zircon, 552.90 ± 1.29 Ma (95% conf., n = 7) for the SLZB zircon and 560.83 ± 1.29 Ma (95% conf., n = 7) for the SLZC zircon. The obtained Hf isotopic compositions of the SLZA, SLZB and SLZC zircons determined with the solution MC-ICP-MS method were 0.281651 ± 0.000014 (2s, n = 10), 0.281704 ± 0.000008 (2s, n = 10) and 0.281676 ± 0.000006 (2s, n = 10), respectively. The obtained O isotopes of the SLZA and SLZB zircons measured with the laser fluorination method were 12.14 ± 0.56‰ (2s, n = 4) and 11.91 ± 0.30‰ (2s, n = 4), respectively. The Zr isotopes of the SLZA, SLZB and SLZC zircons determined with double spike TIMS analysis yielded mean δ⁹⁴/⁹⁰Zr_SRM3169 values of -0.03 ± 0.06‰ (2s, n = 10), -0.03 ± 0.04‰ (2s, n = 10) and 0.00 ± 0.07‰ (2s, n = 8), respectively. The SLZA zircon can be used as a primary reference or quality control material for microbeam U-Pb, Hf and Zr isotope measurements because of its slight heterogeneity. The U-Pb, Hf and Zr isotopic compositions of the SLZB and SLZC megacrysts were homogeneous. The O isotopic compositions in the SLZA and SLZB zircon were slightly dispersed, indicating that these two megacrysts can only serve as secondary reference materials for microbeam O isotope measurements.     

Diffusion-controlled growth of albite and pyroxene reaction rims

The growth rates of albite and pyroxene (enstatite + diopside + spinel) reaction rims were measured at 1000°C and ˜700 MPa and found to be parabolic indicating diffusion-controlled growth. The parabolic rate constants for the pyroxene (+ spinel) rims in samples with 0.5 wt% H₂O added or initially vacuum dried at 25°C and 250°C are 1.68 ± 0.09, 0.54 ± 0.05 and 0.25 ± 0.06 μm²/h, respectively. The values for albite rim growth in samples initially dried at 60°C and with 0.1 wt% H₂O added are 0.25 ± 0.04 and 0.33 ± 0.03 μm²/h, respectively. The latter values were used to derive the product of the grain boundary diffusion coefficient D′_A, where A = SiO₂, NaAlO₂, or NaAlSi₋₁, and the grain boundary thickness δ in albite. The calculated D′_SIO2δ in the albite aggregate for the situations of two different water contents are about 9.9 × 10⁻²³ and 1.4 × 10⁻²² m³ s⁻¹, respectively. Both the rate constants and the calculated D′_Aδ demonstrate that the effect of water content on the grain boundary diffusion rate in monomineralic albite and polymineralic pyroxene (+ spinel) aggregates is small, consistent with recent studies of monomineralic enstatite and forsterite rims. Received: 1 July 1995 / Accepted: 1 August 1996     

Molar volume and thermal expansion of glaucophane

The molar volume of glaucophane [Na₂Mg₃Al₂Si₈O₂₂(OH)₂] has been determined in this study by correcting synthetic glaucophane-rich amphiboles made in the system Na₂O–MgO–Al₂O₃–SiO₂–H₂O for very small deviations from ideal glaucophane composition using recent volume data on key amphibole components. The derived unit-cell volume for end-member glaucophane is 862.7±1.6 Å³, which gives a molar volume of 259.8±0.5 cm³/mol and a calculated density of 3.016±0.006 g/cm³. This value has been corroborated through an essentially independent method by correcting the volumes of natural sodic amphiboles reported in the literature for non-glaucophane components, particularly including calcium-rich components, to yield a value of 861.2±1.9 Å³. The unit-cell volume derived from the synthetic amphiboles, which is considered here to be more reliable, is somewhat smaller than that reported previously in the literature. A thermal expansion (α_V) at 298 K of 1.88±0.06×10^?5/K was derived from unit-cell volumes measured in the range of 25–500°C for a synthetic glaucophane sample, which is noticeably smaller than previously reported.     

Volatiles contents, degassing and crystallisation of intermediate magmas at Volcan de Colima, Mexico, inferred from melt inclusions

In volatile-saturated magmas, degassing and crystallisation are interrelated processes which influence the eruption style. Melt inclusions provide critical information on volatile and melt evolution, but this information can be compromised significantly by post-entrapment modification of the inclusions. We assess the reliability and significance of pyroxene-hosted melt inclusion analyses to document the volatile contents (particularly H₂O) and evolution of intermediate arc magmas at Volcán de Colima, Mexico. The melt inclusions have maximal H₂O contents (≤4 wt%) consistent with petrological estimates and the constraint that the magmas crystallised outside the amphibole stability field, demonstrating that pyroxene-hosted melt inclusions can preserve H₂O contents close to their entrapment values even in effusive eruptions with low effusion rates (0.6 m³ s^?1). The absence of noticeable H₂O loss in some of the inclusions requires post-entrapment diffusion coefficients (≤1 × 10^?13 m² s^?1) at least several order of magnitude smaller than experimentally determined H⁺ diffusion coefficient in pyroxenes. The H₂O content distribution is, however, not uniform, and several peaks in the data, interpreted to result from diffusive H₂O reequilibration, are observed around 1 and 0.2 wt%. H₂O diffusive loss is also consistent with the manifest lack of correlations between H₂O and CO₂ or S contents. The absence of textural evidence supporting post-entrapment H₂O loss suggests that diffusion most likely occurred via melt channels prior to sealing of the inclusions, rather than through the host crystals. Good correlation between the melt inclusion sealing and volcano-tectonic seismic swarm depths further indicate that, taken as a whole, the melt inclusion population accurately records the pre-eruptive conditions of the magmatic system. Our data demonstrate that H₂O diffusive loss is a second-order process and that pyroxene-hosted melt inclusions can effectively record the volatile contents and decompression-induced crystallisation paths of vapour-saturated magmas.     

Molybdenum Mass Fractions and Isotopic Compositions of International Geological Reference Materials

The double‐spike method with multi‐collector inductively coupled plasma‐mass spectrometry was used to measure the Mo mass fractions and isotopic compositions of a set of geological reference materials including the mineral molybdenite, seawater, coral, as well as igneous and sedimentary rocks. The long‐term reproducibility of the Mo isotopic measurements, based on two‐year analyses of NIST SRM 3134 reference solutions and seawater samples, was ≤ 0.07‰ (two standard deviations, 2s, n = 167) for δ^98/95Mo. Accuracy was evaluated by analyses of Atlantic seawater, which yielded a mean δ^98/95Mo of 2.03 ± 0.06‰ (2s, n = 30, relative to NIST SRM 3134 = 0‰) and mass fraction of 0.0104 ± 0.0006 μg g^?1 (2s, n = 30), which is indistinguishable from seawater samples taken world‐wide and measured in other laboratories. The comprehensive data set presented in this study serves as a reference for quality assurance and interlaboratory comparison of high‐precision Mo mass fractions and isotopic compositions.     

Density Calculation for NaCl-H2O Solutions in the Liquid-Solid Two-Phase Field in NaCl-H2O Three-Phase Inclusions

Three-phase NaCl-H₂O fluid inclusions featuring halite dissolution temperature（Tm）higher than vapor bubble disappearance temperature（T_h） are commonly observed in porphyry copper/molybdenum deposits,skarn-type deposits and other magmatic- hydrothermal ore deposits.Based on |ΔV₁|（the absolute value of volume variation of NaCl-H₂O solution in a heating or cooling process of inclusions）= |ΔV_s|（the absolute value of volume variation of the halite crystal in a heating or cooling process of inclusions） and on the principle of conservation of the mass of NaCl and H₂O,we systematically calculated the densities of NaCl-H₂O solutions in the solid-liquid two-phase field for temperatures（T_h） from 0.1℃ to 800℃ and salinities from 26.3 wt%to 99.2wt%.Consequently for the first time we obtained the upper limit of the density of NaCI-H₂O solutions in the solid-liquid twophase field for T_bm inclusions with variant salinities.The results indicate that for inclusions of the T_hm type with the same T_h,the higher the T_m or salinity is,the higher the density of the NaClsaturated solution will be.If a group of fluid inclusions were homogeneously trapped,they must have the same T_h value and the same T_m or salinity value.This may be used to distinguish homogeneous,inhomogeneous,and multiple entrapments of fluid inclusions.     

Tourmaline Reference Materials for the In Situ Analysis of Oxygen and Lithium Isotope Ratio Compositions

Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum (schorl 112566, dravite 108796 and elbaite 98144), which are already widely used for the calibration of in situ boron isotope measurements, are characterised here for their oxygen and lithium isotope compositions. Homogeneity tests by secondary ion mass spectrometry (SIMS) showed that at sub‐nanogram test portion masses, their ¹⁸O/¹⁶O and ⁷Li/⁶Li isotope ratios are constant within ± 0.27‰ and ± 2.2‰ (1s), respectively. The lithium mass fractions of the three materials vary over three orders of magnitude. SIMS homogeneity tests showed variations in ⁷Li/²⁸Si between 8% and 14% (1s), which provides a measure of the heterogeneity of the Li contents in these three materials. Here, we provide recommended values for δ¹⁸O, Δ’¹⁷O and δ⁷Li for the three Harvard tourmaline reference materials based on results from bulk mineral analyses from multiple, independent laboratories using laser‐ and stepwise fluorination gas mass spectrometry (for O), and solution multi‐collector inductively coupled plasma‐mass spectroscopy (for Li). These bulk data also allow us to assess the degree of inter‐laboratory bias that might be present in such data sets. This work also re‐evaluates the major element chemical composition of the materials by electron probe microanalysis and investigates these presence of a chemical matrix effect on SIMS instrumental mass fractionation with regard to δ¹⁸O determinations, which was found to be < 1.6‰ between these three materials. The final table presented here provides a summary of the isotope ratio values that we have determined for these three materials. Depending on their starting mass, either 128 or 512 splits have been produced of each material, assuring their availability for many years into the future.     

Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.     

Enhanced Oxygen Isotope Determination in Uranium Oxides Using BrF5 Fluorination

A new method for accurate determination of oxygen isotopes in uranium oxides encountered in the nuclear fuel cycle was developed using the conventional BrF₅ fluorination technique. Laser‐assisted fluorination was tested for comparison. We focused on fine powders of triuranium octoxide (U₃O₈), uranium dioxide (UO_2±x with 0 ≤ x ≤ 0.25), uranium trioxide (UO₃.nH₂O, with 0.8 ≤ n ≤ 2) and diuranates (M₂U₂O₇.nH₂O, with M = NH₄, Na or Mg_0.5 and 0 ≤ n ≤ 6). Fluorination at room temperature and heating under vacuum at 150 °C are shown to eliminate both adsorbed and structural water from the powder samples. Precision fit for purpose of δ¹⁸O values (± 0.3‰, 1s) and oxygen yields (close to 100%) were obtained for U₃O₈ and UO₂ where oxygen is only bound to uranium. A lower precision was observed for UO₃.nH₂O and M₂U₂O₇.nH₂O where oxygen is both present in the structural H₂O and bonded to uranium and where the extracted O_2(g) can be contaminated by NF₃ and NO_x compounds. Laser‐assisted fluorination gave shifted δ¹⁸O values between +0.8 and +1.4‰ for U₃O₈, around ?0.8‰ for UO₃.nH₂O and between ?3.9 and ?4.5‰ for M₂U₂O₇.nH₂O (± 0.3‰, 1s) compared with the conventional method.     

A New LA‐ICP‐MS Method for Ti in Quartz: Implications and Application to High Pressure Rutile‐Quartz Veins from the Czech Erzgebirge

Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti‐in‐quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining ⁴⁸Ti mass fractions in quartz by LA‐ICP‐MS at the 1 μg g^?1 level, relevant to quartz in HP‐LT terranes. We suggest that natural quartz such as the low‐CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g^?1 Ti, 2s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are insignificant, thus allowing for the use of ⁴⁸Ti as a normalising mass. Average titanium mass fraction from thirty‐three analyses of low temperature quartz from the Czech Erzgebirge is 0.9 ± 0.2 μg g^?1 (2s) using ⁴⁸Ti as a normalising mass and Bishop Tuff quartz rims as a reference material. The 2s average analytical uncertainty for individual analyses of ⁴⁸Ti is 8% for 50 μm spots and 7% for 100 μm spots, which offers much greater accuracy than the 21–41% uncertainty (2s) incurred from using ⁴⁹Ti as an analyte.     

Apatite Reference Materials for SIMS Microanalysis of Isotopes and Trace Elements

Twelve apatite samples have been tested as secondary ion mass spectrometry (SIMS) reference materials. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis shows that the SLAP, NUAN and GR40 apatite gems are internally homogeneous, with most trace element mass fractions having 2 standard deviations (2s) ≤ 2.0%. BR2, BR5, OL2, AFG2 and AFB1, which have U > 63 μg g^-1, ²⁰⁶Pb/²⁰⁴Pb > 283, and homogeneous SIMS U-Pb data, have respective isotope dilution thermal ionisation mass spectrometry (ID-TIMS) ages of 2053.83 ± 0.21 Ma, 2040.34 ± 0.09 Ma, 868.87 ± 0.25 Ma, 478.71 ± 0.22 Ma and 473.25 ± 0.09 Ma. Minor U-Pb heterogeneity exists and accurate SIMS results require correction with the 3D Concordia-constrained common Pb composition. Among the studied samples, AFG2 and BR5 are the most homogeneous U-Pb reference materials. The SIMS sulfur isotopic compositions of eight of the apatites shows they are homogeneous, with 2s for both 10³δ³⁴S and 10³δ³³S < 0.55‰. One apatite, BR96, has Δ³³S = -0.36 ± 0.2‰. The apatite samples have ID-TIMS ⁸⁷Sr/⁸⁶Sr between 0.704214 ± 0.000030 and 0.723134 ± 0.000035.     

Synthetic ANaB(Na x Li1 − x Mg1)CMg5Si8O22(OH)2 (with x = 0.6, 0.2 and 0) P21/m amphiboles at high pressure: a synchrotron infrared study

The high-pressure behavior of three synthetic amphiboles crystallized with space group P2₁/m at room conditions in the system Li₂O–Na₂O–MgO–SiO₂–H₂O has been studied by in situ synchrotron infrared absorption spectroscopy. The amphiboles have compositions ^ANa ^B(Na _x Li_1 − x Mg₁) ^CMg₅ Si₈ O₂₂(OH)₂ with x = 0.6, 0.2 and 0.0, respectively. The high-P experiments up to 32 GPa were carried out on the U2A beamline at Brookhaven National Laboratory (NY, USA) using a diamond anvil cell under non-hydrostatic or quasi-hydrostatic conditions. The two most intense absorption bands in the OH-stretching infrared spectra can be assigned to two non-equivalent O–H dipoles in the P2₁/m structure, bonded to the same local environment ^M1M3Mg₃–OH–^ANa, and pointing toward two differently kinked tetrahedral rings. In all samples these bands progressively merge to give a unique symmetrical absorption with increasing pressure, suggesting a change in symmetry from P2₁/m to C2/m. The pressure at which the transition occurs appears to be linearly correlated to the aggregate B-site dimension. The infrared spectra collected for amphibole ^B(Na_0.2Li_0.8Mg₁) in the frequency range 50 to 1,400 cm⁻¹ also show a series of changes with increasing pressure. The data reported here support the inference of Iezzi et al. (Am Miner 91:479–482, 2006a) regarding a new high-pressure amphibole polymorph.     

Mud Tank Zircon: Long‐Term Evaluation of a Reference Material for U‐Pb Dating,Hf‐Isotope Analysis and Trace Element Analysis

Zircon megacrysts from the Mud Tank carbonatite, Australia, are being used in many laboratories as a reference material for LA‐ICP‐MS U‐Pb dating and trace element measurement, and LA‐MC‐ICP‐MS determination of Hf isotopes. We summarise a database of > 10000 analyses of Mud Tank zircon (MTZ), collected from 2000 to 2018 during its use as a secondary reference material for simultaneous U‐Pb and trace element analysis, and for Hf‐isotope analysis. Trace element mass fractions are highest in dark red‐brown stones and lowest in colourless and gem‐quality ones. Individual unzoned grains can be chemically homogeneous, while significant variations in trace element mass fraction are associated with oscillatory zoning. Chondrite‐normalised trace element patterns are essentially parallel over large mass fraction ranges. A Concordia age of 731.0 ± 0.2 Ma (2s, n = 2272) is taken as the age of crystallisation. Some grains show lower concordant to mildly discordant ages, probably reflecting minor Pb loss associated with cooling and the Alice Springs Orogeny (450–300 Ma). Our weighted mean ¹⁷⁶Hf/¹⁷⁷Hf is 0.282523 ± 10 (2s, n = 9350); the uncertainties on this ratio reflect some heterogeneity, mainly between grains. A few analyses suggest that colourless grains have generally lower ¹⁷⁶Hf/¹⁷⁷Hf. MTZ is a useful secondary reference material for U‐Pb and Hf‐isotope analysis, but individual grains need to be carefully selected using CL imaging and tested for homogeneity, and ideally should be standardised by solution analysis.     

Calcic amphiboles in calc-alkaline and alkaline magmas: thermobarometric and chemometric empirical equations valid up to 1,130°C and 2.2 GPa

The following article presents constraints of the stability of Mg-rich (Mg/(Mg + Fe²⁺) > 0.5) calcic amphibole in both calc-alkaline and alkaline magmas, testing of previous thermobarometers, and formulation of new empirical equations that take into consideration a large amount of literature data (e.g. more than one thousand amphibole compositions among experimental and natural crystals). Particular care has been taken in choosing a large number of natural amphiboles and selecting quality experimental data from literature. The final database of experimental data, composed of 61 amphiboles synthesized in the ranges of 800–1,130°C and 130–2,200 MPa, indicates that amphibole crystallization occurs in a horn-like P–T stability field limited by two increasing curves (i.e. the thermal stability and an upper limit), which should start to bend back to higher pressures. Among calcic amphiboles, magnesiohornblendes and tschermakitic pargasites are only found in equilibrium with calc-alkaline melts and crystallize at relatively shallow conditions (P up to ~1 GPa). Kaersutite and pargasite are species almost exclusively found in alkaline igneous products, while magnesiohastingsite is equally distributed in calc-alkaline and alkaline rocks. The reliability of previous amphibole applications was checked using the selected experimental database. The results of this testing indicate that none of the previous thermobarometers can be successfully used to estimate the P, T and fO₂ in a wide range of amphibole crystallization conditions. Multivariate least-square analyses of experimental amphibole compositions and physico-chemical parameters allowed us to achieve a new thermobarometric model that gives reasonably low uncertainties (T ± 23.5°C, P ± 11.5%, H₂O_melt ± 0.78wt%) for calc-alkaline and alkaline magmas in a wide range of P–T conditions (up to 1,130°C and 2,200 MPa) and ∆NNO values (±0.37 log units) up to 500 MPa. The ^AK-^[4]Al relation in amphibole can be readily used to distinguish crystals of calc-alkaline liquids from those of alkaline magmas. In addition, several chemometric equations allowing to estimate the anhydrous composition of the melts in equilibrium with amphiboles of calc-alkaline magmas were derived.     

Electron Probe Microanalysis of Bromine in Minerals and Glasses with Correction for Spectral Interference from Aluminium,and Comparison with Microbeam Synchrotron X‐Ray Fluorescence Spectrometry

The strong spectral interference between Br‐ and Al‐induced X‐ray lines hampers the utilisation of electron probe microanalysis (EPMA) for measuring Br mass fractions in Al‐bearing minerals and glasses. Through measuring Br‐free Al‐bearing materials, we established an EPMA method to quantify the overlap from AlKα on BrLβ, which can be expressed as a linear function of the Al₂O₃ content. The count rate of the BrLβ peak signal was enhanced by high beam currents and long measurement times. Application of this EPMA method to Al‐ and Br‐bearing materials, such as sodalite and scapolite, and to five experimental glasses yielded Br mass fractions (in the range of 250–4000 μg g^?1) that are consistent with those measured by microbeam synchrotron X‐ray fluorescence (μ‐SXRF) spectrometry. The EPMA method has an estimated detection limit of ~ 100–300 μg g^?1. We propose that this method is useful for measuring Br mass fractions (hundreds to thousands of μg g^?1) in Al‐bearing minerals and glasses, including those produced in Br‐doped experiments. In addition, the natural marialitic scapolite (ON70) from Mpwapwa (Tanzania) containing homogeneously distributed high mass fractions of Br (2058 ± 56 μg g^?1) and Cl (1.98 ± 0.03% m/m) is an ideal reference material for future in situ analyses.