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Abstract-A low-blank, high sensitivity isotope dilution, ICP-MS analytical technique has been used to obtain REE abundance data from single conodont elements weighing as little as 5 g. Sr isotopes can also be measured from the column eluants enabling Sr isotope ratios and REE abundance to be determined from the same dissolution. Results are comparable to published analyses comprising tens to hundreds of elements.To study the effects of thermal metamorphism on REE and strontium mobility in conodonts, samples were selected from a single bed adjacent to a basaltic dyke and from the internationally used colour alteration index (CAI) "standard set." Our analyses span the range of CAI 1 to 8. Homogeneous REE patterns, "bell-shaped" shale-normalised REE patterns are observed across the range of CAI 1 to 6 in both sample sets. This pattern is interpreted as the result of adsorption during early diagenesis and could reflect original seawater chemistry. Above CAI 6 REE patterns become less predictable and perturbations from the typical REE pattern are likely to be due to the onset of apatite recrystallisation. Samples outside the contact aureole of the dyke have a mean 87 Sr/ 86 Sr ratio of 0.708165, within the broad range of published mid-Carboniferous seawater values. Our analysis indicates conodonts up to CAI 6 record primary geochemical signals that may be a proxy for ancient seawater.

New trace-element and Nd-isotope analyses were carried out on the Coppermine River basalts, a suite of 1.27 Ga old continental flood basalts in the Northwest Territories of Canada. Although all the samples are tholeiitic basalts, their chemical and isotopic compositions change upwards in the sequence. The lowermost unit has relatively high contents of SiO2 and incompatible trace elements, high ratios of elements with different compatibilities (e.g., Th/Nb, La/Sm), high Gd/Yb, negative Nb anomalies, and low εNd. Samples at the top of the sequence have less pronounced enrichment and fractionation of incompatible elements coupled with an absence of Nb anomalies and positive εNd values. These results are interpreted to indicate that the lavas lowest in the sequence were produced by melting in the garnet stability field, at depths greater than 90 km, and probably in a mantle plume beneath the continental lithosphere. These magmas passed through magma chambers in the lower and upper crust where they became contaminated with crustal rocks. During the course of the eruption of the entire volcanic sequence the extent of crustal contamination became minimal and the lavas lost the chemical signature of residual garnet. The youngest lavas formed by melting in the spinel field and were free of crustal contamination. The site of mantle melting apparently became shallower, perhaps because of lithosphere thinning.