Accretion and Preservation of D-rich Organic Particles in Carbonaceous Chondrites: Evidence for Important Transport in the Early Solar System Nebula

We have acquired NanoSIMS images of the matrices of CI, CM, and CR carbonaceous chondrites to study, in situ, the organic matter trapped during the formation of their parent bodies. D/H ratio images reveal the occurrence of D-rich hot spots, constituting isolated organic particles. Not all the organic particles are D-rich hot spots, indicating that at least two kinds of organic particles have been accreted in the parent bodies. Ratio profiles through D-rich hot spots indicate that no significant self-diffusion of deuterium occurs between the D-rich organic matter and the depleted hydrous minerals that are surrounding them. This is not the result of a physical shielding by any constituent of the chondrites. Ab initio calculations indicate that it cannot be explained by isotopic equilibrium. Then it appears that the organic matter that is extremely enriched in D does not exchange with the hydrous minerals, or this exchange is so slow that it is not significant over the 4.5 billion year history on the parent body. If we consider that the D-rich hot spots are the result of an exposure to intense irradiation, then it appears that carbonaceous chondrites accreted organic particles that have been brought to different regions of the solar nebula. This is likely the result of important radial and vertical transport in the early solar system

Neutron-rich Chromium Isotope Anomalies in Supernova Nanoparticles

Neutron-rich isotopes with masses near that of iron are produced in Type Ia and II supernovae (SNeIa and SNeII). Traces of such nucleosynthesis are found in primitive meteorites in the form of variations in the isotopic abundance of ^(54)Cr, the most neutron-rich stable isotope of chromium. The hosts of these isotopic anomalies must be presolar grains that condensed in the outflows of SNe, offering the opportunity to study the nucleosynthesis of iron-peak nuclei in ways that complement spectroscopic observations and can inform models of stellar evolution. However, despite almost two decades of extensive search, the carrier of ^(54)Cr anomalies is still unknown, presumably because it is fine grained and is chemically labile. Here, we identify in the primitive meteorite Orgueil the carrier of ^(54)Cr anomalies as nanoparticles (3.6 × solar). Such large enrichments in ^(54)Cr can only be produced in SNe. The mineralogy of the grains supports condensation in the O/Ne-O/C zones of an SNII, although a Type Ia origin cannot be excluded. We suggest that planetary materials incorporated different amounts of these nanoparticles, possibly due to late injection by a nearby SN that also delivered ^(26)Al and ^(60)Fe to the solar system. This idea explains why the relative abundance of ^(54)Cr and other neutron-rich isotopes vary between planets and meteorites. We anticipate that future isotopic studies of the grains identified here will shed new light on the birth of the solar system and the conditions in SNe

H2O and Cl in deep crustal melts: the message of melt inclusions in metamorphic rocks

The use of NanoSIMS on primary melt inclusions in partially melted rocks is a powerful approach to clarify the budget of volatiles at depth during crust formation and its reworking. Anatectic melt inclusions are indeed gateways to quantify H2O, halogens and other species (e.g. CO2, N) partitioned into the deep partial melts generated during metamorphism of the continental crust. Here we present new datasets of NanoSIMS measurements of H2O and Cl in preserved melt inclusions from metamorphic rocks with different protoliths – magmatic or sedimentary – which underwent partial melting at different pressure–temperature–fluid conditions. These new datasets are then compared with similar data on natural anatectic melts available in the literature to date. Our study provides novel, precise constraints for the H2O content in natural melts formed at high pressure, a field previously investigated mostly via experiments. We also show that H2O heterogeneities in partial melts at the microscale are common, regardless of the rock protolith. Correlations between H2O contents and P–T values can be identified merging new and old data on anatectic inclusions via NanoSIMS. Overall, the data acquired so far indicate that silicate melt generation in nature always requires H2O, even for the hottest melts found so far (&gt;1000 ∘C). Moreover, in agreement with previous work, preserved glassy inclusions always appear to be poorer in H2O than crystallized ones, regardless of their chemical system and/or P–T conditions of formation. Finally, this study reports the very first NanoSIMS data on Cl (often in amounts &gt;1000 ppm) acquired in situ on natural anatectic melts, showing how anatectic melt inclusions – additionally to magmatic ones – may become a powerful tool to clarify the role of halogens in many geological processes, not only in crustal evolution but also in ore deposit formation.</p

Solar Wind Abundances of C and O

Quantitative understanding of solar wind (SW) elemental fractionation is required to improve knowledge of the solar nebula abundances from Genesis samples, in particular abundances of volatile elements, depleted in CI chondrites. Ratios of elements with low and high first ionization potential (FIP) in the solar wind, e.g., Fe/He, are higher than photospheric abundances. C, O, and N have intermediate FIP and are thus critical as to whether this fractionation is stepwise or gradual as a function of FIP

Subducted organic matter buffered by marine carbonate rules the carbon isotopic signature of arc emissions

Ocean sediments consist mainly of calcium carbonate and organic matter (phytoplankton debris). Once subducted, some carbon is removed from the slab and returns to the atmo- sphere as CO2 in arc magmas. Its isotopic signature is thought to reflect the bulk fraction of inorganic (carbonate) and organic (graphitic) carbon in the sedimentary source. Here we challenge this assumption by experimentally investigating model sediments composed of 13C-CaCO3 + 12C-graphite interacting with water at pressure, temperature and redox con- ditions of an average slab–mantle interface beneath arcs. We show that oxidative dissolution of graphite is the main process controlling the production of CO2, and its isotopic compo- sition reflects the CO2/CaCO3 rather than the bulk graphite/CaCO3 (i.e., organic/inorganic carbon) fraction. We provide a mathematical model to relate the arc CO2 isotopic signature with the fluid–rock ratios and the redox state in force in its subarc source

The amino acid and hydrocarbon contents of the Paris meteorite: Insights into the most primitive CM chondrite

International audienc

Ultracarbonaceous Antarctic micrometeorites recovered from snow at the Dome C - CONCORDIA station.

第6回極域科学シンポジウム[OA] 南極隕石11月17日（火）　国立国語研究所 2階 講

Deep CO₂ in the end-Triassic Central Atlantic Magmatic Province

Large Igneous Province eruptions coincide with many major Phanerozoic mass extinctions, suggesting a cause-effect relationship where volcanic degassing triggers global climatic changes. In order to fully understand this relationship, it is necessary to constrain the quantity and type of degassed magmatic volatiles, and to determine the depth of their source and the timing of eruption. Here we present direct evidence of abundant CO2 in basaltic rocks from the end-Triassic Central Atlantic Magmatic Province (CAMP), through investigation of gas exsolution bubbles preserved by melt inclusions. Our results indicate abundance of CO2 and a mantle and/or lower-middle crustal origin for at least part of the degassed carbon. The presence of deep carbon is a key control on the emplacement mode of CAMP magmas, favouring rapid eruption pulses (a few centuries each). Our estimates suggest that the amount of CO2 that each CAMP magmatic pulse injected into the end-Triassic atmosphere is comparable to the amount of anthropogenic emissions projected for the 21st century. Such large volumes of volcanic CO2 likely contributed to end-Triassic global warming and ocean acidification

Early precipitated micropyrite in microbialites: A time capsule of microbial sulfur cycling

Microbialites are organosedimentary rocks that have occurred throughout the Earth’s history. The relationships between diverse microbial metabolic activities and isotopic signatures in biominerals forming within these microbialites are key to understanding modern biogeochemical cycles, but also for accurate interpretation of the geologic record. Here, we performed detailed mineralogical investigations coupled with NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) analyses of pyrite S isotopes in mineralising microbial mats from two different environments, a hypersaline lagoon (Cayo Coco, Cuba) and a volcanic alkaline crater lake (Atexcac, Mexico). Both microbialite samples contain two distinct pyrite morphologies: framboids and euhedral micropyrites, which display distinct ranges of δ34S values1. Considering the sulfate-sulfur isotopic compositions associated with both environments, micropyrites display a remarkably narrow range of Δpyr (i.e. Δpyr ≡ δ34SSO4 − δ34Spyr) between 56 and 62‰. These measured Δpyr values agree with sulfate-sulfide equilibrium fractionation, as observed in natural settings characterised by low microbial sulfate reduction respiration rates. Moreover, the distribution of S isotope compositions recorded in the studied micropyrites suggests that sulfide oxidation also occurred at the microbialite scale. These results highlight the potential of micropyrites to capture signatures of microbial sulfur cycling and show that S isotope composition in pyrites record primarily the local micro-environments induced by the microbialite

Detection of 15NH2D in dense cores: A new tool for measuring the 14N/15N ratio in the cold ISM

Ammonia is one of the best tracers of cold dense cores. It is also a minor constituent of interstellar ices and, as such, one of the important nitrogen reservoirs in the protosolar nebula, together with the gas phase nitrogen, in the form of N2 and N. An important diagnostic of the various nitrogen sources and reservoirs of nitrogen in the Solar System is the 14N/15N isotopic ratio. While good data exist for the Solar System, corresponding measurements in the interstellar medium are scarce and of low quality. Following the successful detection of the singly, doubly, and triply deuterated isotopologues of ammonia, we have searched for 15NH2D in dense cores, as a new tool for investigating the 14N/15N ratio in dense molecular gas. With the IRAM-30m telescope, we have obtained deep integrations of the ortho 15NH2D (1(1,1)-1(0,1)) line at 86.4 GHz, simultaneously with the corresponding ortho NH2D line at 85.9 GHz. o-15NH2D is detected in Barnard-1b, NGC1333-DCO+, and L1689N, while we obtained upper limits towards LDN1544 and NGC1333-IRAS4A, and a tentative detection towards L134N(S). The 14N/15N abundance ratio in NH2D ranges between 350 and 850, similar to the protosolar value of ~ 424, and likely higher than the terrestrial ratio of 270