Thermal effects on rare earth element and strontium isotope chemistry in single conodont elements.
Thermal effects on rare earth element and strontium isotope chemistry in single conodont elements.
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DOI：
10.1016/s0016-7037(00)00548-2
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发表时间：
2001-02
影响因子：
5
通讯作者：
H.A Armstrong;D.G Pearson;M. Griselin
中科院分区：
文献类型：
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作者：
H.A Armstrong;D.G Pearson;M. Griselin
采用低空白、高灵敏度同位素稀释的ICP-MS分析技术，获得了牙形石单个元素的稀土元素丰度数据。Sr同位素也可以从柱洗脱液中测量，使得Sr同位素比率和REE丰度可以从相同的溶解中确定。其结果与已发表的包含数十至数百种元素的分析结果相当。为了研究热变质作用对牙形石中稀土元素和锶迁移率的影响，样品选自与玄武岩岩墙相邻的单一岩层和国际上使用的颜色蚀变指数（CAI）“标准集”。我们的分析涵盖CAI 1至8的范围。在两个样品组中，在CAI 1至6的范围内观察到均匀的REE模式，“钟形”页岩归一化的REE模式。这种模式被解释为早期成岩作用期间吸附的结果，并可以反映原始海水化学。以上CAI 6稀土元素模式变得不那么可预测和扰动的典型稀土元素模式可能是由于磷灰石重结晶的发病。样品外的接触晕的堤坝有一个平均87 Sr/86 Sr的比值为0.708165，在广泛的范围内公布的中石炭纪海水值。我们的分析表明，牙形刺CAI 6记录的主要地球化学信号，可能是一个代理古代海水。
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 μg. 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 mean87Sr/86Sr 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.