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NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material.SWanalyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due toSWformation. Mg isotopes are “ground truth” for these models since, except forCAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation ofSWMg is primarily that ofSWformation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulkSWdiamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in theDLC. The resultingSWMg fractionation relative to theDSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơSEof the data combined with a 2.5‰ (total) error in theIMFdetermination. Two of theSWfractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on theCAInebular composition of McKeegan et al. (2011).

 

Abstract Trace element analyses of silicate materials by secondary ion mass spectrometry (SIMS) typically normalize the secondary ion count rate for the isotopes of interest to the count rate for one of the silicon isotopes. While the great majority of SIMS analyses use the signal from Si+, some laboratories have used a multiply charged ion (Si2+ or Si3+). We collected data and constructed calibration curves for lithium, beryllium, and boron using these different normalizing species on synthetic basaltic glass and soda-lime silicate glass standards. The calibrations showed little effect of changing matrix when Si+ was used, but larger effects (up to a factor of ~2) when using Si2+ or Si3+ are a warning that care must be taken to avoid inaccurate analyses. The smallest matrix effects were observed at maximum transmission compared to detecting ions with a few tens of eV of initial kinetic energy (“conventional energy filtering”). Normalizing the light element ion intensities to Al3+ showed a smaller matrix effect than multiply-charged Si ions. When normalized to 16O+ (which includes oxygen from the sample and from the primary beam), the two matrices showed distinct calibration curves, suggesting that changing sputter yields (atoms ejected per primary atom impact) may play a role in the probability of producing multiply charged silicon ions. 

Ol Doinyo Lengai (ODL, Tanzania, East African Rift) is the only known volcano currently erupting carbonatite on Earth with 30 yr. cycles alternating between quiescent carbonatite effusion and explosive, compositionally-zoned silicate eruptions. We performed isothermal crystallization and thermal gradient experiments involving ODL nephelinite, Na 2 CO 3 and H 2 O to understand magmatic differentiation in this system using SEM-EDS x-ray analysis, x-ray tomography, SIMS and LA-ICPMS to characterize samples. Isothermal crystallization experiments document that hydrous liquids coexist with nepheline+feldspar; as peralkalinity increases, temperatures decrease. Presence of Na 2 CO 3 increases the solubility of water in the liquid. Experiments placing nephelinite with H 2 O+ Na 2 CO 3 in a 1,000–350°C thermal gradient show that rapid reaction occurs, resulting in virtually melt-free mineral aggregates having mineral layering reflecting systematic differentiation throughout the capsule. Both types of experiments argue that a continuous interconnected melt exists over a large temperature range in alkalic magmatic systems allowing for differentiation in a reactive mush zone process. Liquid compositions change from carbonate-water bearing nephelinites at high temperature down to hydrous carbonate silicate liquids at <400°C. We propose a model for ODL eruption behavior: 1) nephelinite magmas pond and build a sill complex downward with time; 2) hydrous carbonate melts form in the mush and buoyantly rise, ultimately erupting as natrocarbonatites observed; 3) H 2 O contents build up in melt at the bottom of the sill complex, eventually leading to water vapor saturation and explosive silicate eruptions. The model accounts for eruption cycling and the unusual compositional zoning of ODL silicate tephras. 

Secondary ion mass spectrometry techniques are used to study trace elements in organic samples where matrix compositions vary spatially. This study was conducted to develop calibrations for lithium content and lithium isotope measurements in kerogen. Known concentrations of Li ions (6Li and 7Li) were implanted into organic polymers, with a range of H/C and O/C ratios similar to kerogen, along with glassy carbon (SPI Glas‐22) and silicate glass (NIST SRM 612). Results show that Li content calibration factors (K*) are similar for carbonaceous samples when analysed using a 5kV secondary ion accelerating voltage. Using a 9 kV secondary ion accelerating voltage, K* factors are negatively correlated with the sample O content, changing ~ 30% between 0 and 15 oxygen atomic %. Thus, to avoid the matrix effect related to O content, using a 5 kV secondary ion accelerating voltage is best for quantification of Li contents based on 7Li+/12C+ ratios. Under these analytical conditions, Li ppm (atomic) = (132 (  8) × 7Li+/12C+) × 12C atom fraction of the sample measured. Lithium isotope ratio measurements of SPI Glas‐22 and NIST SRM 612 are within uncertainty; however, the organic polymer samples as a group show a 10‰ higher δ7Li than NIST SRM 612. 

Lithium isotopes (δ7Li) in coals have been shown to increase with thermal maturity, suggesting preferential release of 6Li from kerogen to porefluids. This has important implications for paleoclimate studies based on δ7Li of buried marine carbonates, which may incorporate Li from porefluids during recrystallization. Here, the Li content and isotopic composition of macerals from two coal seams intruded by dikes, were studied as a function of temperature across a thermal gradient into the unmetamorphosed coal. Samples were collected in Colorado (USA) from a Vermejo Fm. coal seam intruded by a mafic-lamprophyre dike and compared to a Dutch Creek No.2 coal seam intruded by felsic-porphyry dike; a potential source of Li-rich fluids. The Li-content and Li-isotope compositions of coal macerals were measured in situ by Secondary Ion Mass Spectrometry (SIMS). The macerals of the Vermejo coal samples, buried to VRo 0.68% (Tmax = 104 ◦C), contained <1.5 μg/g Li with an average vitrinite δ7Li of −28.4 ± 1.6‰, while liptinite and inertinite were heavier, averaging −15.4 ± 3.6‰ and − 10.5 ± 3.7‰, respectively. The contact metamorphosed vitrinite/coke showed the greatest change with temperature with δ7Li 18 to 37‰ heavier than the unmetamorphosed vitrinite. The Dutch Creek coal, buried to VRo 1.15% (Tmax = 147 ◦C), prior to dike emplacement, may have released Li during burial, as less isotopic change was observed between contact metamorphosed and unmetamorphosed macerals. Overall, Li contents were < 1 μg/g, and the vitrinite in metamorphosed coal had δ7Li values 8 to 21‰ heavier than the unmetamorphosed coal. SIMS measurements on macerals near the dike did not show an increase in Li-content indicative of Li derived from dike fluids, however previous bulk measurements that included silicates showed slightly higher (2-3 μg/g) Li-contents near the dike, suggesting possible Li incorporation from dike fluid into metamorphic silicates. A negative correlation was observed between Li-content and 12C+/30Si+ count ratios, indicating that at metamorphic temperatures Li becomes concentrated in silicates. 

Secondary ion mass spectrometry techniques are used to study trace elements in organic samples where matrix compositions vary spatially. This study was conducted to develop calibrations for lithium content and lithium isotope measurements in kerogen. Known concentrations of Li ions (⁶Li and⁷Li) were implanted into organic polymers, with a range of H/C and O/C ratios similar to kerogen, along with glassy carbon (SPI Glas‐22) and silicate glass (NIST SRM 612). Results show that Li content calibration factors (K*) are similar for carbonaceous samples when analysed using a 5 kV secondary ion accelerating voltage. Using a 9 kV secondary ion accelerating voltage,K* factors are negatively correlated with the sample O content, changing ~ 30% between 0 and 15 oxygen atomic %. Thus, to avoid the matrix effect related to O content, using a 5 kV secondary ion accelerating voltage is best for quantification of Li contents based on⁷Li⁺/¹²C⁺ratios. Under these analytical conditions, Li ppm (atomic) = (132 (± 8) × ⁷Li⁺/¹²C⁺) × ¹²C atom fraction of the sample measured. Lithium isotope ratio measurements of SPI Glas‐22 and NIST SRM 612 are within uncertainty; however, the organic polymer samples as a group show a 10‰ higher δ⁷Li than NIST SRM 612.