Samples were crushed and powdered at Southampton Oceanography Centre (with the exception of BAS-206, which was ground in tungsten carbide on the JOIDES Resolution) and splits were sent to the GeoAnalytical Lab at Washington State University for analysis. Details of the digestion technique and analytical protocols are presented elsewhere (Knaack et al., 1994; see also http://www.wsu.edu/~geolab/note/icpms.html). Briefly, the method is as follows.
A rock powder sample (100 mg) is dissolved on a hot plate at 110°C, using a mix of HF, HNO3, and HClO4 in an open Teflon vial. The sample is evaporated to dryness, followed by an additional evaporation with 2 mL of HClO4 at 165°C to convert insoluble fluorides to soluble perchlorates. The sample is then dissolved in HNO3 plus trace H2O2 and HF, and an internal standard of In, Re, and Ru is added to the sample, which is then is diluted to 60 mL final volume. The samples are run on a Sciex Elan model 250 inductively coupled plasma–mass spectrometer equipped with a Babington nebulizer. In-house rock standards and an acid blank are run with each group of unknown samples. Data reduction is performed offline, and raw intensities are corrected for drift using the In, Re, and Ru internal standards. Calibration curves for each element are constructed from the rock standards and single acid blank. Concentrations for the unknown samples are then computed from this curve.
The following elements were analyzed: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ba, Th, Nb, Y, Hf, Ta, U, Pb, Rb, Cs, Sr, Sc, and Zr. Precision (assessed with reference to 50–60 analyses of two different rock standards over a 2-yr period) is 2%–5% for the rare earth elements (REE) and 5%–10% for other trace elements.