Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain

No abstract available

Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain

No abstract available

Atom scale element and isotopic investigation of 25Mg-rich stardust from a H-burning supernova

We have discovered a presolar olivine from ALH 77307 with the highest 25Mg isotopic composition measured in a silicate to date (δ25Mg = 3025.1‰ ± 38.3‰). Its isotopic compositions challenge current stellar models, with modeling of magnesium, silicon, and oxygen showing a closest match to formation in a supernova (SN) where hydrogen ingestion occurred in the pre-SN phase. Presolar grains within primitive astromaterials retain records of processes and environmental changes throughout stellar evolution. However, accessing these records has proved challenging due to the average grain size (∼150 nm) of presolar silicates, their sensitivity to extraction agents, and instrumental restrictions, limiting the range of isotopic and chemical signatures which can be studied per grain volume. Here, we present the first known detailed geochemical study of a presolar silicate from a hydrogen-burning SN, studied in 3D without contributions to the analysis volume and at unprecedented spatial resolutions (<1 nm), essential for constraining physical and chemical processes occurring within this recently proposed stellar environment. From our results, we infer either (i) condensation within an environment depleted of heavy elements compatible with the olivine lattice under the pressure and temperature conditions during condensation, or (ii) during periods of limited mixing either near the end of the pre-SN phase or from a collapse so rapid localized pockets of different gas compositions formed

Ice Ice Baby: Improving Water Quantification of Hydrous Minerals by Cryofocussed Ion Beam and Cryo Vaccum Transfer to Atom Probe

No abstract available

Application of Atom Probe Microscopy to Nanoscale Os Isotopic Studies

No abstract available

Application of Atom Probe Microscopy to Nanoscale Os Isotopic Studies

No abstract available

Nanoscale Characterisation of Grains From the Itokawa Asteroid by FIB-ToF-SIMS, APM and TEM

No abstract available

Nanoscale Characterisation of Grains From the Itokawa Asteroid by FIB-ToF-SIMS, APM and TEM

No abstract available

Partial retention of radiogenic Pb in galena nanocrystals explains discordance in monazite from Napier Complex (Antarctica)

International audienceThe discordance of U-Th-Pb isotopic systems in geochronometers, and how such data are interpreted, are still major issues in the geosciences. To better understand the disturbance of isotopic systems, and how this impacts the derivation of geologically-meaningful ages, previously studied discordant monazite from the ultrahigh temperature paragneiss of the Archean Napier Complex (Antarctica) have been investigated. Monazite grains were characterized from the micro to the nanoscale using an analytical workflow comprising laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), secondary-ion mass spectrometry (SIMS), electron microprobe (EMP), transmission electron microscopy (TEM) and atom probe tomography (APT). Results reveal that the least discordant monazite, hosted in garnet and rutilated quartz, contain a large number of small Pb-bearing nanominerals (Ø ~ 50 nm) while the most discordant monazite, hosted in the quartzo-feldspathic matrix, contain a smaller number of Pb-bearing nanominerals bigger in size (Ø ~ 50 to 500 nm). The degree of the discordance, which was previously correlated with textural position is mechanistically related to the partial retention of radiogenic Pb (Pb *) in distinct Pb *-bearing nanominerals (e.g. PbS) within the monazite grains. In-situ dating (U-Pb systems with LA-ICP-MS and SIMS), and isotopic information obtained by using APT (207 Pb/ 206 Pb isotopic signature of galena and 208 Pb/ 232 Th ages of the monazite matrix) allow the timing of Pb-disturbance and mobility to be constrained. Results show that monazite grains crystallized at ca. 2.44 Ga and were affected by two episodes of Pb * mobility. The first episode (t1) at ca. 1.05 Ga, led to crystallization of a first generation of Pb *-bearing nanominerals and a complete resetting of the monazite matrix at the nanoscale. The second episode (t2) at ca. 0.55 Ga was associated with the crystallization of a second generation of Pb *-bearing nanominerals with a 207 Pb/ 206 Pb signature indicating a mixing of two Pb * components: a component from the monazite matrix and remobilized Pb * from the first generation of Pb *-bearing nanominerals. This second event is characterized by a more localized resetting of the monazite matrix at the nanoscale compared to the t1 event. These results indicate the potential of nanoscale studies of Pb-rich nanominerals within monazite to yield important details of the themal history of complex metamorphic terranes