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Abstract Solar wind Fe and Mg fluences (atoms/cm²) were measured from Genesis collectors. Fe and Mg have similar first ionization potentials and solar wind Fe/Mg should equal the solar ratio. Solar wind Fe/Mg is a more valid measure of solar composition than CI chondrites and can be measured more accurately than spectroscopic photospheric abundances. Mg and Fe fluences analyzed in four laboratories give satisfactory agreement. Si and diamond‐like carbon collector fluences agree for both elements. The Mg and Fe fluences are 1.731 ± 0.073 × 10¹²and 1.366 ± 0.058 × 10¹²atoms/cm². All plausible sources of errors down to the 1% level are documented. Our value for the solar system Fe/Mg, 0.789 ± 0.048 agrees within 1 sigma errors with CI chondrites, spectroscopic photospheric abundances, and with the solar wind data from the ACE spacecraft. CI samples from asteroid Ryugu give Fe/Mg in agreement with Genesis and meteoritic CI samples despite very small sample sizes. The higher accuracy of the Genesis solar Fe/Mg permits a comparison with chondritic Fe/Mg at the 10% level. Intermeteorite Fe/Mg averages differ among the main C chondrite groups but are within, or very close to, the ±1 sigma Genesis solar Fe/Mg. 

Abstract This study conducts mineralogical and chemical investigations on the oldest achondrite, Erg Chech 002 (∼4565 million yr old). This meteorite exhibits a disequilibrium igneous texture characterized by high-Mg-number (atomic Mg/(Mg + Fe²⁺)) orthopyroxene xenocrysts (Mg number = 60–80) embedded in an andesitic groundmass. Our research reveals that these xenocrysts were early formed crystals, loosely accumulated or scattered in the short-period magma ocean on the parent body. Subsequently, these crystals underwent agitation due to the influx of external materials. The assimilation of these materials enriched the¹⁶O component of the magma ocean and induced a relatively reduced state. Furthermore, this process significantly cooled the magma ocean and inhibited the evaporation of alkali elements, leading to elevated concentrations of Na and K within the meteorite. Our findings suggest that the introduced materials are probably sourced from the reservoirs of CR clan meteorites, indicating extensive transport and mixing of materials within the early solar system. 

RationaleBack‐side thinning of wafers is used to eliminate issues with transient sputtering when analyzing near‐surface element distributions. Precise and accurate calibrated implants are created by including a standard reference material during the implantation. Combining these methods allows accurate analysis of low‐fluence, shallow features even if matrix effects are a concern. MethodsImplanted Na (<2.0 × 10¹¹ions/cm², peaking <50 nm) in diamond‐like carbon (DLC) film on silicon (solar wind returned by NASA's Genesis mission) was prepared for measurement as follows. Implanted surfaces of samples were epoxied to wafers and back‐side‐thinned using physical or chemical methods. Thinned samples were then implanted with reference ions for accurate quantification of the solar wind implant. Analyses used a CAMECA IMS 7f‐GEO SIMS in depth‐profiling mode. ResultsBack‐side‐implanted reference ions reduced the need to change sample mounts or stage position and could be spatially separated from the solar wind implant even when measuring monoisotopic ions. Matrix effects in DLC were mitigated and the need to find an identical piece of DLC for a reference implant was eliminated. Accuracy was only limited by the back‐side technique itself. ConclusionsCombining back‐side depth profiling with back‐side‐implanted internal standards aides quantification of shallow mono‐ and polyisotopic implants. This technique helps mitigate matrix effects and keeps measurement conditions consistent. Depth profile acquisition times are longer, but if sample matrices are homogeneous, procedural changes can decrease measurement times. 

We report on the design and performance of an improved duoplasmatron ion source for secondary ion mass spectrometers. The source is designed specifically to optimize extraction of negative oxygen ions while suppressing electron extraction using a built-in magnetic asymmetry in the anode electrode. Other changes from conventional designs are (a) drilling the ion extraction aperture directly into the magnetic steel anode rather than in a refractory (nonmagnetic) metal insert, thereby eliminating a magnetic “hole” that acts to counter the desired magnetic concentration of the discharge at the aperture and (b) forming the anode into a conical shape convex toward the intermediate electrode to increase the magnetic field concentration at the extraction aperture, hence the term “Canode.” The built-in magnetic asymmetry allows the width and shape of the intermediate electrode to be varied to further optimize magnetic concentration of the discharge. Tests were performed with both ims 6f and NanoSIMS 50L instruments manufactured by Cameca Instruments, Inc. (Fitchburg, WI, USA). In the ims 6f, the Canode design gave O− primary ion currents up to a factor of five greater than the factory ion source design. In the NanoSIMS 50L, the Canode source produced a focused O− ion beam at the sample with a diameter of 50 nm, identical to the performance of the radio-frequency Hyperion ion source developed by Oregon Physics (Beaverton, OR, USA) and offered as an option by Cameca. 

Abstract 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). 

The sulfur chemistry of (162173) Ryugu particles can be a powerful tracer of molecular cloud chemistry and small body processes, but it has not been well explored. We report identification of organosulfurs and a sulfate grain in two Ryugu particles, A0070 and A0093. The sulfate grain shows oxygen isotope ratios (δ¹⁷O = −11.0 ± 4.3 per mil, δ¹⁸O = −7.8 ± 2.3 per mil) that are akin to silicates in Ryugu but exhibit mass-independent sulfur isotopic fractionation (Δ³³S = +5 ± 2 per mil). A methionine-like coating on the sulfate grain is isotopically anomalous (δ¹⁵N = +62 ± 2 per mil). Both the sulfate and organosulfurs can simultaneously form and survive during aqueous alteration within Ryugu’s parent body, under reduced conditions, low temperature, and a pH >7 in the presence of N-rich organic molecules. This work extends the heliocentric zone where anomalous sulfur, formed by selective photodissociation of H₂S gas in the molecular cloud, is found. 

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.