Effects of acid leaching on the Sr-Nd-Hf isotopic compositions of ocean island basalts

The ability to conduct multi-isotopic analyses (e. g., Sr-Nd-Hf-Pb) on the same sample is critical for studies that evaluate the mantle source components of oceanic basalts. The isotopic compositions of relatively immobile elements, such as Nd (and other REE) and Hf, are considered to be relatively resistant to alteration, however, accurate Sr and Pb isotopic analyses of oceanic basalts require thorough acid leaching prior to dissolution. A detailed study of the Sr, Nd and Hf isotopic systematics of acid-leached oceanic basalts from Hawaii and Kerguelen was undertaken to assess how acid leaching affects their isotopic compositions. Most of the Sr, Nd and Hf was removed in the first acid leaching steps. Hawaiian basalts lose up to 35% and 40% of their total Sr and Hf contents, respectively, whereas for Kerguelen basalts the corresponding losses are 63% and similar to 70%. Acid leaching leads to significant loss of the original Nd content (up to 90%), which cannot be solely explained by the elimination of alteration phases and is likely related to preferential removal of the REE in the constituent silicate minerals (e. g., plagioclase, clinopyroxene). The leached residues yield Sr isotopic ratios significantly less radiogenic than their respective unleached powders and Nd-Hf isotopic compositions that are within analytical uncertainty of the respective unleached powders. This study shows that multi-isotopic analyses on the same acid-leached sample aliquot can produce reliable results for use in the discrimination of mantle source components of oceanic basalts.