Hydrogen Isotopic Composition of N-rich Clasts in the Cb/ch-like Chondrite Isheyevo

Metal-rich (CB, CH, Isheyevo) carbonaceous chondrites are characterized by the highest whole-rock enrichments in 15 N (δ 15 N up to +1500‰) and nearly complete absence of interchondrule fine-grained matrix [e.g., 1]. The fine-grained material occurs mainly as chondritic clasts, which experienced low-temperature aqueous alteration on their initial parent body(ies) and were subsequently accreted with the CH and CB high-temperature components [e.g.,1]. We have recently reported the discovery of a unique type of chondritic clasts in the CB/CH-like meteorite Ish-eyevo, which are characterized by the presence of numerous 15 N-hotspots (δ 15 N up to 4000‰) and by high bulk 15 N-enrichment (δ 15 N up to +1300‰). These clasts may represent surviving pieces of the body that brought the 15 N anomaly into metal-rich chondrites [2]. The identification of such isotopically anomalous material raises the questions of how, where and when the observed N-isotope fractionation occurred. FIB+STEM and NanoSIMS studies are under way to identify the 15 N carrier [3, 4], which is likely to be organic. Here we report H-isotope composition of the clasts to further characterize this unique material. The UH Cameca ims 1280 ion microprobe was used to collect isotope-ratio images (areas of 50×50 μm 2) of the Isheyevo 15 N-rich clasts. Ion images were acquired using a 15pA Cs + primary beam, focused to ~1.5 μm spot. The analyses were carried out in two steps: 1) images of H-, D-were acquired at low mass resolution with counting times of 3s and 60s respectively; 2) images of H