方解石811N:一种可能的微区碳氧锶同位素分析标准

The Calcite 811N, a potential isotope standard material for isotopic analyses of carbon, oxygen and strontium

关键词:  碳酸盐  标准物质  碳氧同位素  矿物组成  原位分析

Key words:  carbonate  isotope standard material  carbon and oxygen isotope  mineral composition  situ and micro analysis

摘要:

同位素标准物质是同位素分析的基准物质和数据比较的重要依据。方解石811作为碳酸盐碳氧同位素的实验室标准物质，具有良好的适用性，但由于制备时间久远，存量日益减少，且性状信息缺乏，影响了该标准在微区微量分析中的运用。本次研究选用未制备的811方解石(811N)作为研究对象，结合多种分析技术从不同尺度对其矿物组成、元素含量分布、碳氧同位素组成进行分析，揭示其相关信息及规律，并探讨了其Sr同位素组成，从而为下一步811N的制备和使用提供参考信息，有助于该样在不同碳酸盐分析和研究，特别是微区微量元素和同位素中的运用。实验结果表明，方解石811N较为纯净，主要为方解石，只含有微量的白云石、针铁矿、黏土矿物；除主要化学成分(CaCO₃)外，含有微量的Mg、Mn、Sr、Si、REE、U、Th等元素，Mg、Mn、Sr含量在整体分布上存在一定的变化，但在局部相对均匀。碳氧同位素组成整体差异程度相对较小，且其差异程度和元素均匀性呈对应关系，主要区域碳氧同位素组成均匀。Sr同位素组成在不同区域中无明显差异。本次研究认为811N是合适的碳酸盐碳氧同位素分析标准物质，该样制备后能够满足碳氧同位素分析和研究的需要，同时该样具备适用于微区微量C、O、Sr同位素分析和研究的潜力。

Abstract:

The isotope standard materials are important in analyzing isotopic compositions in a lab. The Calcite 811 has been a laboratory standard material for analyses of isotopic compositions of carbon and oxygen isotope of carbonate, but it was made a long time ago and its stock on hand is decreasing day by day, and its current quality situation is usually unclear. This study selects the un-used Calcite 811 as a research object, using a variety of analysis techniques such as the LA-(MC)-ICP-MS, laser Raman spectroscopy, XRD and EDX-SEM, to study its mineral, chemical, and isotopic compositions, in order to find a method for making a new isotope standard material, the Calcite 811N, to substitute the Calcite 811 in the future. The results show that the Calcite 811N is almost composed of calcite, containing few dolomite, needle-shaped iron ore, and clay minerals. Apart from its main chemical compositions of CaCO₃, the Calcite 811N has trace amounts of elements such as Mg, Mn, Sr, Si, REE, U, and Th. As a whole, the contents of Mg, Mn, Sr are somewhat changeable, but they are relatively uniform in a small scope. The carbon isotopic and oxygen isotopic results are little different, the difference of which is consistent with the uniformity of distrubution of Mg，Mn,Sr. Isotopic compositions of carbon and oxygen are homogeneous in the main region of the Calcite 811N. The isotopic compositions of Sr have no significant differences in different parts. The δ¹³C and δ¹⁸O of Calcite 811N are changeable on the whole, but their differences are very small. So concluded that the Calcite 811N is a suitable isotopic standard material for situ and micro isotopic analyses of carbon, oxygen, and strontium of carbonate.