Publication Date:
2015-06-10
Description:
Properly combining highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundance data, obtained by isotope dilution, with corresponding 187 Os/ 188 Os and 186 Os/ 188 Os measurements of rocks requires efficient digestion of finely-ground powders and complete spike-sample equilibration. Yet, because of the nature of commonly used methods for separating Os from a rock matrix, hydrofluoric acid (HF) is typically not used in such digestions. Consequently, some silicates are not completely dissolved, and HSE residing within these silicates may not be fully accessed. Consistent with this, some recent studies of basaltic reference materials (RMs) have concluded that an HF-desilicification procedure is required to fully access the HSE (Ishikawa et al . (2014) Chemical Geology , 384, 27–46; Li et al . (2015) Geostandards and Geoanalytical Research , 39, 17–30). Highly siderophile element abundance and Os isotope studies of intraplate basalts typically target samples with a range of MgO contents (〈 8 to 〉 18% m/m , or as mass fractions, 〈 8 to 〉 18 g/100 g), in contrast to the lower MgO mass fractions (〈 10 g/100 g) of basalt and diabase RMs (i.e., BIR-1, BHVO-2, TDB-1). To investigate the effect of HF-desilicification on intraplate basalts, experiments were performed on finely ground Azores basalts (8.1–17 g/100 g MgO) using a ‘standard acid digestion’ (2:1 mixture of concentrated HNO 3 and HCl), and a standard acid digestion, followed by HF-desilicification. No systematic trends in HSE abundances were observed between data obtained by standard acid digestion and HF-desilicification. Desilicification procedures using HF do not improve liberation of the HSE from Azores basalts, or some RMs (e.g., WPR-1). We conclude that HF-desilicification procedures are useful for obtaining total HSE contents of some young lavas, but this type of procedure is not recommended for studies where Re-Pt-Os chronological information is desired. This article is protected by copyright. All rights reserved.
Print ISSN:
1639-4488
Electronic ISSN:
1751-908X
Topics:
Geosciences
Permalink
