Evaluation and application of the ion microprobe in the strontium isotope geochemistry of carbonates
Evaluation and application of the ion microprobe in the strontium isotope geochemistry of carbonates
复制标题
离子探针在碳酸盐锶同位素地球化学中的评价及应用
DOI：
10.1016/0012-821x(83)90168-1
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发表时间：
1983
影响因子：
5.3
通讯作者：
R. Exley
中科院分区：
文献类型：
--
作者：
R. Exley
用改进的AEI-IM 20离子探针测定了碳酸盐岩中的~（87）Sr/~（86）Sr比值。在低和高（M/ΔM ≥ 3000）质量分辨率下研究了一组具有不同主量元素（Ca，Mg，Fe，Mn）的碳酸盐，以确定与Sr峰同量异位的分子种类和强度;在低质量分辨率下收集的Sr数据必须对Ca 2和CaMgO种类进行校正。Rb/Sr比值极低，不需要对~（87）Rb进行校正（~（87）Sr < 0.1‰），Sr ≥ 400 ppm时，可从方解石中获得有用的Sr同位素数据，当Sr > 5000 ppm时，在最佳条件下，~（87）Sr/~（86）Sr（2σ平均值）的精度可达± 0.0007。在方解石中，Ca 2+和CaMgO的校正值小于批内精度，而在白云石中，CaMgO的校正值为± 1.5%。~（87）Sr/~（86）Sr的质量分馏校正值（以~（86）Sr/~（88）Sr = 0.1194为基准）一般为+8 ~+10‰。对于已知Sr同位素组成的方解石，离子探针和固体源质谱仪结果之间存在良好的一致性：ST 4a（~ 400 ppm Sr），平均离子探针~（87）Sr/~（86）Sr = 0.7267 ± 0.0015，固体源~（87）Sr/~（86）Sr = 0.72680 ± 0.00008 [14];公司简介（~ 6000 ppm Sr），平均离子探针~（87）Sr/~（86）Sr = 0.7056 ± 0.0009，固体源~（87）Sr/~（86）Sr = 0.70588 ± 0.00009 [16]; JCG 44（~ 6000 ppm Sr），平均离子探针87 Sr/86 Sr = 0.7057 ± 0.0006，固体源87 Sr/86 Sr = 0.70540 ± 0.00008 [16]。利用离子探针测量方解石中10 μm点~（87）Sr/~（86）Sr的能力：（1）测量了苏格兰西北部斯凯岛（Isle of Skye）热液蚀变玄武岩中~（87）Sr/~（86）Sr的厘米级变化;（2）测定了南非Bultfontein脉状地幔二辉橄榄岩中小于35 μm方解石的Sr同位素组成。由于方解石在许多共生体中的普遍存在，该技术可能为测量87 Sr/86 Sr的精细尺度不均匀性提供许多机会。
A modified AEI-IM20 ion microprobe has been used to measure87Sr/86Sr ratios in carbonates. A suite of carbonates with varying major elements (Ca, Mg, Fe, Mn) was studied at low and high (M/ΔM ⋍ 3000) mass resolution to determine the types and intensities of molecular species isobaric with Sr peaks; Sr data collected at low mass resolution must be corrected for Ca2and CaMgO species. Rb/Sr ratios are extremely low, and correction for87Rb is not required (< 0.1‰ of87Sr).Usable Sr isotopic data may be obtained from calcite givenSr≥ 400ppm, and for Sr > 5000 ppm a precision of ∼ ± 1‰ (± 0.0007) in87Sr/86Sr (2σ mean) can be achieved under optimum conditions. The corrections for Ca2and CaMgO are smaller than the within-run precision in calcite, but in dolomite the correction for CaMgO is + 1.5%. Mass fractionation corrections to87Sr/86Sr (based on86Sr/88Sr= 0.1194) are typically +8 to +10‰. Good agreement between ion probe and solid source mass spectrometer results was found for calcites of known Sr isotopic composition: ST4a (∼ 400ppm Sr), average ion probe87Sr/86Sr= 0.7267 ± 0.0015, solid source87Sr/86Sr= 0.72680 ± 0.00008 [14]; JCG36 (∼ 6000ppm Sr), average ion probe87Sr/86Sr= 0.7056 ± 0.0009, solid source87Sr/86Sr= 0.70588 ± 0.00009 [16]; JCG44 (∼ 6000ppm Sr), average ion probe87Sr/86Sr= 0.7057 ± 0.0006, solid source87Sr/86Sr= 0.70540 ± 0.00008 [16]. The ability of the ion microprobe to measure87Sr/86Sr for 10-μm spots in calcite was used: (1) to measure variation in87Sr/86Sr of ∼ 0.01 on a centimetre scale in a hydrothermally altered basalt from the Isle of Skye, northwestern Scotland; and (2) to determine the Sr isotopic composition of tiny (< 35 μm) calcite grains in a veined mantle lherzolite from Bultfontein, South Africa. Because of calcite's ubiquitous occurrence in many parageneses this technique may offer many opportunities for the measurement of fine scale heterogeneities in87Sr/86Sr.