Laboratoire de Minéralogie et de Cosmochimie du Muséum, Muséum National d’Histoire Naturelle, 57 rue Cuvier, Paris, 75005, France

The isotopic ratio of hydrogen was measured in an iron meteorite and terrestrial native iron using an IMS 3f ion microprobe. The extraterrestrial D/H ratio (93 ± 9 × 10^-6) was close to the terrestrial value (105 ± 6 × 10^-6), and both samples had low H concentrations (7 ± 4 and 33 ± 11 ng g^-1 for the iron meteorite and the terrestrial sample, respectively). Experiments on artificially D-enriched samples showed that the measured hydrogen signal is a combination of indigenous H and terrestrial atmospheric contamination. This contamination comes from the isotope exchange reaction between water adsorbed on the sample surface and atmospheric water, and would be continuously added to the indigenous H in the ion crater by the adsorbed water sinking into the crater during sputtering. Experiments showed that this contamination represents up to 20% of the signal but was within the uncertainty of the measured D/H ratio.

¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China

In this study, a high-precision method for the determination of Sm and Nd concentrations and Nd isotopic composition in highly depleted ultramafic rocks without a preconcentration step is presented. The samples were first digested using the conventional HF + HNO₃ + HClO₄ method, followed by the complete digestion of chromite in the samples using HClO₄ at 190–200 °C and then complete dissolution of fluoride formed during the HF decomposition step using H₃BO₃. These steps ensured the complete digestion of the ultramafic rocks. The rare earth elements (REEs) were separated from the sample matrix using conventional cation-exchange chromatography; subsequently, Sm and Nd were separated using the LN columns. Neodymium isotopes were determined as NdO⁺, whereas Sm isotopes were measured as Sm⁺, both with very high sensitivity using single W filaments with TaF₅ as an ion emitter. Several highly depleted ultramafic rock reference materials including USGS DTS-1, DTS-2, DTS-2b, PCC-1 and GSJ JP-1, which contain extremely low amounts of Sm and Nd (down to sub ng g^-1 level), were analysed, and high-precision Sm and Nd concentration and Nd isotope data were obtained. This is the first report of the Sm-Nd isotopic compositions of these ultramafic rock reference materials except for PCC-1.

Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, F-63000 Clermont-Ferrand, France CNRS, UMR 6524, LMV, F-63038 Clermont-Ferrand, France
IRD, R 163, LMV, F-63038 Clermont-Ferrand, France

We carried out stepwise dissolutions of four primitive enstatite chondrites (EC) belonging to the EH subgroup. Large Nd isotope anomalies are found in the most refractory phases, dissolved using strong acids. Residues are characterized by excesses in ¹⁴²Nd and deficits in ¹⁴⁵Nd, ¹⁴⁸Nd and ¹⁵⁰Nd isotopes. The Nd anomalies measured in the ALHA77295 residue are even greater than those measured in the Murchison carbonaceous chondrite (CC) using a similar analytical technique (Qin et al., 2011). Once corrected for a common Sm/Nd evolution, the ¹⁴²Nd excess in the ALHA77295 residue is equal to 700 ppm relative to the terrestrial standard value. The Nd isotope patterns measured in EC and CC residues can be adjusted to coincide by adding a small amount of an s-process-rich carrier phase such as SiC and 0.075% is required to fit the ALHA7795 residue. Small isotope differences still persist between these residues even if they can be considered similar within error. In enstatite chondrites, residues have a deficit in ¹⁵⁰Nd similar to or smaller than that measured in ¹⁴⁸Nd, whereas in SiC extracted from carbonaceous chondrites or in whole rock, the deficit in ¹⁵⁰Nd is always greater than that in ¹⁴⁸Nd. Moreover in a binary ¹⁴²Nd–¹⁴⁸Nd diagram, the best-fit lines obtained for leachates and residues from carbonaceous chondrites and enstatite chondrites have slightly different slopes. For the same ¹⁴⁸Nd/¹⁴⁴Nd ratio, the anomalous component in an enstatite chondrite has a higher ¹⁴²Nd/¹⁴⁴Nd ratio compared to carbonaceous chondrites, a feature already observed at the whole rock scale. Our results suggest that different chondrite groups sample different reservoirs of presolar grains formed in different environments. Assuming that the carrier of this anomalous component measured in residues of enstatite chondrites are SiC, our results may suggest that different meteorite parent bodies sample reservoirs of presolar SiC formed in different stellar environments. This could explain why ALHA77295, the sample which is the most enriched in presolar grains, has a bulk ¹⁴²Nd isotope composition similar to the terrestrial value. Further investigation of enstatite chondrites is needed to test whether the isotope composition of the most refractory phases is similar to that measured in carbonaceous chondrites and in particular the ¹⁴⁴Sm that is a p-process isotope only. Finally this study highlights the difficulty of interpreting the ¹⁴²Nd excess in terrestrial samples relative to chondrites since incomplete mixing of nucleosynthetic material in the solar nebula creates significant ¹⁴²Nd variation, as shown by ALHA77295.

¹Istituto di Astrofisica e Planetologia Spaziali, INAF, Rome, Italy
²Bear Fight Institute, 22 Fiddler’s Road, Box 667, Winthrop, Washington 98862, USA
³Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095–1567, USA
⁴NASA Lunar Science Institute, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA
⁵NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
⁶Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996–1410, USA
⁷Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA
⁸Jet Propulsion Laboratory, Pasadena, California 91109, USA
⁹University of Maryland, College Park, Maryland 20742–2421, USA

^aPlanetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
^b Max-Planck-Institute for Solar System Research, 37191 Katlenburg-Lindau, Germany
^c Institute of Geological Sciences, Freie Universitaet Berlin, 12249 Berlin, Germany
^d Astrogeology Science Center, USGS, Flagstaff, AZ 86001, USA
^e Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
^f Department of Geography, University of Winnipeg, Manitoba, Canada
^g Department of Space Studies, University of North Dakota, Room 518, Box 9008, Grand Forks, ND 58202, USA h Astromaterials Research Office, NASA Johnson Space Center, Houston, TX 77058, USA
ⁱ NASA Goddard Spaceflight Center, Greenbelt, MD 20771, USA
^j Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, CA 90095, USA
^k Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
^l Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Rome, Italy