Thermal effects on rare earth element and strontium isotope chemistry in single conodont elements

A low-blank, high sensitivity isotope dilution, ICP-MS analytical technique has been used to obtain REE abundance data from single conodont elements w eighing as little as 5 mug. Sr isotopes can also be measured from the colum n eluants enabling Sr isotope ratios and REE abundance to be determined fro m the same dissolution. Results are comparable to published analyses compri sing 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 basalti c dyke and from the internationally used colour alteration index (CAI) "sta ndard set." Our analyses span the range of CAI 1 to 8. Homogeneous REE patt erns, "bell-shaped" shale-normalised REE patterns are observed across the r ange 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 sea water chemistry. Above CAI 6 REE patterns become less predictable and pertu rbations 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 Sr-87/Sr-86 ratio of 0.708165, within the broad range of publis hed mid-Carboniferous seawater values. Our analysis indicates conodonts up to CAI 6 record primary geochemical signals that may be a proxy for ancient seawater. Copyright (C) 2001 Elsevier Science Ltd.