{'fraction_non_alphanumeric': 0.027261462205700124, 'fraction_numerical': 0.01486988847583643, 'mean_word_length': 4.839059674502712, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Hydrogen content in chondrules of CM Chondrites: Influence of aqueous alteration or preaccretional heritage?

Introduction: Chondrites were formed during the early ages of the Solar System hence they witnessed this era. Hydrogen contents and isotopic compositions of these objects bring some constraints about the hydrogen accretion. Two main reservoirs of hydrogen, with distinct isotopic compositions, occurred in the early Solar System: the molecular gas of the protosolar nebula with a low D/H [1] and water ice. Water ice may have a presolar origin with a high D/H or solar origin, resulting from an exchange between presolar ice and molecular hydrogen (H2) . Water ice was likely accreted on the parent body of hydrated meteorites like carbonaceous chondrites, mostly in the matrices. When it melted, water then percolated into the matrices resulting in the aqueous alteration of its components. The aqueous alteration could have affected mineral components of both matrices and chondrules. The origin of the chondrules remains misunderstood. in part because they present a diversity of mineralogy and textures. Among this diversity, one typically distinguishes two main types of chondrules with different textures exist, type I (FeOpoor) and type II (FeO-rich), which were formed in a reducing and oxidizing environment, respectively, in the early Solar System when H2 was still abundant of the protoplanetary disk. Stephant et al. reported large hydrogen content in olivine in chondrules of carbonaceous chondrites. However, few studies have investigated hydrogen content in chondrules and this observation remains debatted. The aim of this study is to constrain the origin of hydrogen contained in chondrule olivines of CM chondrites and to assess the influence of aqueous alteration on hydrogen content and isotopic signature in these emblematic constituents of chondrites. Samples and Methods: Two carbonaceous chondrites showing different alteration degrees were investigated: Paris (CM2.7 to CM2.9) and Aguas Zarcas (CM2). Two polished sections were prepared in epoxy and were carbon coated. Olivines of chondrules of both type I (FeO-poor) and type II (Feo-rich) were analyzed. Hydrogen abundance and isotopic composition were measured with a CAMECA 1280 HR2 SIMS at the CRPG in Nancy, France. A liquid nitrogen cold trap was used to reduce the H2O background and maintain the vacuum below 2 × 10 mbar in the analytical chamber. We used a 10 keV O primary ion beam produced by a Hyperion radio-frequency plasma source. Prior to analysis, 180s of presputtering with a 15 nA current was applied over an area 10 μm × 10 μm to remove the carbon coating and reach the sputtering steady state. The samples were then analyzed with a 15 nA current rastered over the 10 μm × 10 μm area. A high magnification (M. Area = 60), a small field aperture (3000 μm) and 60% electronic gate were used to eliminate hydrogen contamination from the crater edges. Secondary ions of H, D, and Si were collected sequentially in monocollection mode, using an electron multiplier for H and D and a faraday cup equipped with a 10-ohm resistor for Si. The mass resolution (M/∆M) was set to 4,000 to avoid interferences of H on H and SiH on Si.