Geochemistry of CI chondrites: Major and trace elements, and Cu and Zn Isotopes

Abstract

In order to check the heterogeneity of the CI chondrites and determine the average composition of this group of meteorites, we analyzed a series of 6 large chips (weighing between 0.6 and 1.2 g) of Orgueil prepared from 5 different stones. In addition, one sample from each of Ivuna and Alais were analyzed. Although the sizes of the chips used in this study were "large", our results show evidence for minor chemical heterogeneity in Orgueil, particularly for alkali elements and U. After removal of one outlier sample, the spread of the results is considerably reduced. For most of the 46 elements analyzed in this study, the average composition calculated for Orgueil is in very good agreement with previous CI estimates. This average, obtained with a "large" mass of samples, is analytically homogeneous and is suitable for normalization purposes.Finally, the Cu and Zn isotopic ratios are homogeneously distributed within the CI parent body with a spread of less than 100 ppm per atomic mass unit (amu).

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

“…Previous studies have demonstrated the utility of Zn isotopes for this purpose. Zn isotopic determinations in chondrites and iron meteorites show significantly more variation than is found in terrestrial materials (Luck et al, 2005;Moynier et al, 2007;Barrat et al, 2012), suggesting volatilization processes and core/mantle segregation in their formation. On the Earth and on the Moon, volatization from impact events is the primary cause of Zn isotopic fractionation (Moynier et al, 2006(Moynier et al, , 2010Albarède et al, 2007;Herzog et al, 2009).…”

The origin of aubrites: Evidence from lithophile trace element abundances and oxygen isotope compositions

“…Powders were prepared using a boron-carbide mortar and pestle. Elemental abundances for most of the samples were determined using a high-resolution ICP-MS spectrometer Thermo Element 2 at Institut Universitaire Européen de la Mer (IUEM), Plouzané, following well-established procedures (e.g., Barrat et al, 2012). Results for international standards (BIR1, JB2, WS-E, UB-N, PCC1, Allende powder USNM 3529) have been reported previously (Barrat et al, 2012.…”

“…Based on replicate standards and samples (Barrat et al, 2012, the precision for abundances in powdered samples and residues is much better than 5 %. The precision for trace element ratios (e.g., Eu/Eu*, Tb/Tb*, and Yb/Yb*, where Eu*, Tb* and Yb* are respectively the interpolated Eu, Tb and Yb concentrations for a smooth CI-normalized REE pattern, such that Eu* n =(Sm n x Gd n ) 1/2 , Tb* n =(Gd n x Dy n ) 1/2 and Yb* n =Er n 1/3 x Lu n 2/3 ) is better than 2.5 % (2 x relative standard deviation).…”

“…1. REE+Y patterns of main-group aubrites and their residues after leaching (silicate fractions), normalized to CI chondrite (Barrat et al, 2012). Fig.…”

Geochemistry of Fluvial Sediments from Geregu, Southwest Nigeria

“…In addition, Figure 6). In contrast to Ba and Hf, which are abundant in the stud- Figure 8 and Table 4 show much enrichment in LREE over the HREE in the analysed samples, [18]; PAAS: post-Archean Australian shale [16]; CI-chondrite, after Barat et al [25]; g-Eu: Eu anomaly; g-Eu = Eu/Eu*; Eu* = (Sm + Gd)/2; g-Eu computed after Tang et al [26]. Values in square brackets are the detection limits for individual oxides.…”