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Abstract: This paper describes the development of a technique using NanoSIMS to make precise and accurate determination of the hydrogen isotopic composition and the hydroxyl content of apatite grains. An experiment was also performed to determine the effects, if any, of using secondary electron microscopy (SEM) and electron probe micro-analysis (EPMA) on the mobility of volatile elements (H) in apatite grains, prior to analysis by secondary ion mass spectrometry (SIMS). The results of the experiment show that using a relatively low beam current, for a short exposure time, did not have adverse effects on the mobility of H with no apparent change in the measured D/H ratio from or within a grain. Thus, based on our study, we suggest that routine SEM analysis can indeed be used to locate suitable apatite grains for SIMS analyses without jeopardising the hydrogen isotopic measurements. As such, apatite grains were located in the studied sections using SEM and the hydrogen isotopic compositions of the lunar apatite grains from two Apollo mare basalts were determined using NanoSIMS. The δD values for the samples analysed ranges from ~600 to 1000‰ and OH content from 1200 to 4400ppm. The measurements of δD and OH contents in apatites, performed in this study, are consistent with previous results for 10044 but the new dataset for 12064 consists of a larger range in δD values and OH contents than previously documented. We used a raster size of 10×10μm (with data collected from a 5×5μm area) for each analysis and obtained typically ±40 to 80‰ precision at the 2σ level. This demonstrates the capability of using the NanoSIMS 50L to accurately measure D/H ratios and OH contents in apatites containing more than 300–400ppm OH. The coupled hydroxyl abundance and hydrogen isotopic composition data permitted an assessment of the potential D/H fractionation which may have occurred during magmatic degassing, which may ultimately be responsible for the relatively high δD signatures of apatites from mare basalts. [Copyright &y& Elsevier]

• The angrite parent body (APB) was one of the most hydrated differentiated bodies in the early inner solar system. • No evidence of impacts adding to the H 2 O contents of planetismals in the early inner solar system. • The average δ D value for the angrites closely overlaps with acapulcoite-lodranites and eucrites. • A pervasive single source of water existed in the early inner solar system. The quenched (rapidly-cooled) angrite meteorites, which formed in the inner Solar System, record large-scale planetary mixing in the first few Ma of Solar System history, and therefore, provide a unique opportunity to investigate the role of impacts in terms of water addition to the growing planetesimals. Here we investigate the H isotopic composition and H 2 O abundance of relict olivine grains that survived impact melting within Asuka (A) 12,209 and compare them with impact melt-produced groundmass fractions using in-situ nanoscale secondary ion mass spectrometry (NanoSIMS). These analyses test if the angrite parent body (APB) acquired a CC-like H isotopic composition before early large-scale impact mixing and/or acquired volatiles by subsequent impact(s). Furthermore, we analyse the H isotopic composition and H 2 O abundance of later-forming plutonic (NWA 4801), intermediate (NWA 10,463) and dunitic (NWA 8535) angrite meteorites to assess the role of impacts, in terms of volatile delivery, during the first 50 Ma of the inner Solar System history. The H isotopic composition of most quenched angrites appears to be affected by degassing. Consequently, we opt to use the weighted average δ D of pyroxenes and olivines in the plutonic angrite, NWA 4801, to estimate the original composition of the APB (-235 ± 113 ‰ 1σ, n = 18), in agreement with recent studies on the hydrogen isotopic signatures of mineral-hosted melt inclusions in D'Orbigny and Sahara 99,555. Additionally, we use the H 2 O abundances of NWA 4801 pyroxene (7.9 ± 1 µg/g 2σ) and olivine (6.1 ± 0.6 µg/g 2σ) to estimate the lower (85 to 110 µg/g) and upper (519 to 1089 µg/g) limits of the primitive APB mantle H 2 O content, implying that the APB was one of the most hydrated bodies in the early inner Solar System. The similarity of δ D /H 2 O systematics in the relict olivine grains and groundmass olivine within A 12,209 argues against water delivery through impacts in the early inner Solar System. Overall, the non-carbonaceous reservoir in the inner Solar System appears to retain a single source of water, which isotopically resembles either water ice in carbonaceous chondrite parent bodies or fractionated nebula water. [ABSTRACT FROM AUTHOR]

The abundance and isotopic composition of volatile elements in meteorites is critical for understanding planetary evolution, given their importance in a variety of geochemical processes. There has been significant interest in the mineral apatite, which occurs as a minor phase in most meteorites and is known to contain appreciable amounts of volatiles (up to wt. % F, Cl, and OH). Impact-driven shock metamorphism, pervasive within many meteorites, can potentially modify the original signatures of volatiles through processes such as devolatilization and diffusion. In this study, we investigate the microstructures of apatite grains from six eucrites across a broad range of shock stages (S1–S5) using electron backscatter diffraction (EBSD) to explore shock-induced crystallographic features in apatite. New Cl and H abundance and isotopic composition data were collected on moderate to highly shocked samples (S3-S5) by Nano Secondary Ion Mass Spectrometry (NanoSIMS). Previously reported volatile data for S1 and S2 eucrites were integrated with EBSD findings in this study. Our findings indicate that apatite microstructures become increasingly more complex at higher shock stages. At low shock stages (S1–S2) samples display brecciation and fracturing of apatite. Samples in S3 and S4 display increasing crystal plastic deformation indicated by increasing spread in pole figures. At the higher shock stages (S4/S5) there is potential recrystallisation demonstrated by an increased density of subgrain boundaries. The Cl content and δ37Cl values of highly-shocked apatite grains range from ∼940 to 1410 ppm and −3.38 to +7.70‰, respectively, within the range observed in less-shocked eucrites. In contrast, H 2 O abundances are more variable (from 186 to ∼4010 ppm), however, the measured water content still falls within the range previously reported for low-shock eucrites. The measured δD values range from −157 to +163‰, also within the range of values from known low-shock basaltic eucrites. Weighted averages for both isotopic systems (δD −122 ± 20‰, δ37Cl + 1.76 ± 0.66‰) are consistent with the range displayed in other inner Solar System bodies. NanoSIMS isotope images of apatite grains display heterogeneity in their Cl abundance at the nanoscale which increases in complexity with shock stage. This increasing complexity, however, does not correlate with deformation microstructures observed in EBSD or with the Cl isotopic composition at either an inter-grain or intra-grain scale. These findings are similar to analyses of variably shocked lunar apatite and, therefore, apatite appears to be a robust recorder of Cl and H (at least at spatial resolution and precision currently achievable by NanoSIMS) on airless bodies, despite intensive shock. [ABSTRACT FROM AUTHOR]

Recent investigations of meteorites thought to originate from the asteroid 4 Vesta have suggested an early accretion of water on rocky bodies in the inner Solar System from a carbonaceous chondrite-like source. However, these studies have been based on the hydrogen isotope compositions (δD) of late-crystallizing apatite grains in eucrites that likely do not record the primary magmatic composition. We have determined the δD and H 2 O concentrations in some of the earliest-formed silicates (clinopyroxenes) from several eucrites with the goal of constraining the hydrogen isotope composition of their source reservoir on their parent body. The H 2 O concentrations in clinopyroxenes from eucrites Juvinas, Stannern and Tirhert range from 5 to 18 μg/g, with a weighted average δD of –263 ± 70‰. Their apatites and whitlockites exhibit a higher weighted average δD of –165 ± 73‰, possibly as a result of H 2 degassing during or after phosphate crystallization. Thermal metamorphism of these eucrites has most probably resulted in the loss of H, and an increase in their original δD values. While the weighted average δD value for the eucrite clinopyroxenes reported here is inferred to reflect an upper limit for the isotopic composition of the silicate mantle reservoir on their parent asteroid 4 Vesta, the average δD value of Stannern clinopyroxenes is considered to be closest to the initial δD of the source mantle (i.e., –373 ± 127‰), which is lighter than that of Earth's depleted upper mantle and most carbonaceous chondrites. We suggest that at least some of the water in 4 Vesta (and possibly other rocky bodies in the inner Solar System) was derived from a relatively deuterium-poor reservoir in the protosolar nebula, which was incorporated into planetesimals formed early in Solar System history. [ABSTRACT FROM AUTHOR]

• Chlorapatites and merrillites in NWA 5298 have a wide-range of shock nanostructures. • Shock features in apatite are linked to elemental and chlorine isotope heterogeneity. • Atom probe tomography can yield accurate chlorine isotope data at ‰ precision. • Nanoscale boundaries contain isotopically light chlorine mobilized during shock. • The primary chlorine isotopic composition of NWA 5298 is −0.3 ± 0.6 ‰ (2σ) The elemental and chlorine isotope compositions of calcium-phosphate minerals are key recorders of the volatile inventory of Mars, as well as the planet's endogenous magmatic and hydrothermal history. Most martian meteorites have clear evidence for exogenous impact-generated deformation and metamorphism, yet the effects of these shock metamorphic processes on chlorine isotopic records contained within calcium phosphates have not been evaluated. Here we test the effects of a single shock metamorphic cycle on chlorine isotope systematics in apatite from the highly shocked, enriched shergottite Northwest Africa (NWA) 5298. Detailed nanostructural (EBSD, Raman and TEM) data reveals a wide range of distributed shock features. These are principally the result of intensive plastic deformation, recrystallization and/or impact melting. These shock features are directly linked with chemical heterogeneities, including crosscutting microscale chlorine-enriched features that are associated with shock melt and iron-rich veins. NanoSIMS chlorine isotope measurements of NWA 5298 apatite reveal a range of δ37Cl values (−3 to 1‰; 2σ uncertainties <0.9‰) that is almost as large as all previous measurements of basaltic shergottites, and the measured δ37Cl values can be readily linked with different nanostructural states of targeted apatite. High spatial resolution atom probe tomography (APT) data reveal that chlorine-enriched and defect-rich nanoscale boundaries have highly negative δ37Cl values (mean of −15 ± 8‰). Our results show that shock metamorphism can have significant effects on chemical and chlorine isotopic records in calcium phosphates, principally as a result of chlorine mobilization during shock melting and recrystallization. Despite this, low-strain apatite domains have been identified by EBSD, and yield a mean δ37Cl value of −0.3 ± 0.6‰ that is taken as the best estimate of the primary chlorine isotopic composition of NWA 5298. The combined nanostructural, microscale-chemical and nanoscale APT isotopic approach gives the ability to better isolate and identify endogenous volatile-element records of magmatic and near-surface processes as well as exogenous, shock-related effects. [ABSTRACT FROM AUTHOR]

Generally, terrestrial rocks, martian and chondritic meteorites exhibit a relatively narrow range in bulk and apatite Cl isotope compositions, with δ37Cl (per mil deviation from standard mean ocean chloride) values between −5.6 and +3.8‰. Lunar rocks, however, have more variable bulk and apatite δ37Cl values, ranging from ∼−4 to +40‰. As the Howardite-Eucrite-Diogenite (HED) meteorites represent the largest suite of crustal and sub-crustal rocks available from a differentiated basaltic asteroid (4 Vesta), studying them for their volatiles may provide insights into planetary differentiation processes during the earliest Solar System history. Here the abundance and isotopic composition of Cl in apatite were determined for seven eucrites representing a broad range of textural and petrological characteristics. Apatite Cl abundances range from ∼25 to 4900 ppm and the δ37Cl values range from −3.98 to +39.2‰. Samples with lower apatite H 2 O contents were typically also enriched in 37Cl but no systematic correlation between δ37Cl and δD values was observed across samples. Modelled Rayleigh fractionation and a strong positive correlation between bulk δ66Zn and apatite δ37Cl support the hypothesis that Cl degassed as metal chlorides from eucritic magmas, in a hydrogen-poor environment. In the case of lunar samples, it has been noted that δ37Cl values of apatite positively correlate with bulk La/Yb ratio. Interestingly, most eucrites show a negative correlation with bulk La/Yb ratio. Recently, isotopically light Cl values have been suggested to record the primary solar nebular signature. If this is the case then 4 Vesta, which accreted rapidly and early in Solar System history, could also record this primary nebular signature corresponding to the lightest Cl values measured here. The significant variation in Cl isotope composition observed within the eucrites are likely related to degassing of metal chlorides. [ABSTRACT FROM AUTHOR]

Abstract: Terminal grains from C2063,1,154,1,0 (Track 154) and C2061,1,113,5 (Track 113) from the Stardust collection of Comet Wild2''s coma have been studied by TEM and NanoSIMS. Terminal grain 2 of C2063,1,154,1,0 consists of an Al-rich diopside (En 97–99%, Al2O3 9–11wt%), pigeonite (En 85% Wo 15% with TiO2 and Al2O3 contents of 0.5 and 5.2wt%) and minor forsterite and enstatite. The mineral assemblage and Al-rich, Ti-poor composition of the grain are consistent with being a fragment of an Al-rich chondrule, similar to those present in carbonaceous chondrites. The oxygen isotopic composition of the C2063,1,154,1,0 grain was determined by NanoSIMS analyses and found to be δ17O −10.6±5.7‰, δ18O −7.5±2.5‰ and δ17O +1.4±4.3‰, δ18O −6.5±1.6‰ (1σ errors) for the two sections. These figures are distinct from CAIs and consistent with an origin as Al-rich chondrule fragments. Terminal grain 5 of C2061,1,113,5 consists of low Ca pyroxene En 86–87% Fs 10–11% Wo 3–4% and ≤2wt% Al2O3 and in one section 5–10% of a Na-rich silicate phase. This assemblage may be a fragment of a low-Ca pyroxene-bearing chondrule and mesostasis. The original chondrule diameter for the C2063,1,154,1,0 and C2061,1,113,5 samples, by analogy with carbonaceous chondrite chondrules, might have been in the range 0.2–1.0mm. If they were of that size, then the presence of large grains of high temperature material (e.g. ≥1500K for such refractory assemblages) could be explained through commonly invoked models of radial drift from inner to outer Solar System, but only if the chondrules were first fragmented to dust within the inner Solar System. An alternative scenario is that some chondrule formation was associated with high temperature processing and planetesimals in the outer Solar System. [Copyright &y& Elsevier]