碳酸盐岩紫外激光微区原位碳、氧同位素分析方法与地质应用

Microprobe analysis is one of major topics for development of isotopic measurements. The traditional method for carbon and oxygen isotope analysis of carbonate is phosphoric acid decomposition to carbonate powder in a vacum tube. This method is widely accepted for the reason that easy and stability. However, it needs more than 10mg samples and can not meets the requirement of today's high-resolution in situ analysis. In situ laser microprobe techniques for stable isotope analysis to carbonate developed in the 1980s, the carbonate minerals were decomposited into CaO and CO2 gas with the infrared laser. However, this method was hampered for the reason that the oxygen isotopic fractionation during laser ablation can not be overcomed. In this study, the UV laser (or Femtosecond laser), which has higher energy and lower thermal effect than infrared laser, will be choosed as the laser ablation sampler to carbonate minerals. Therefore, rare isotopic fractionation will be occurred while UV laser ablation sampling. We use this materials like quartz filters to collect the carbonate particles which carried out by the Helium gas while ablation, and transfer the micro-samples into the device for oxygen and carbon isotope measurement after decomposition with phosphoric acid. We aim to establish a new high-precision and high accuracy in situ carbon and oxygen isotope analysis method to replace the traditional method, while for the high-resolution analysis to carbonate samples. And we would like to reveal the environment change informantion recorded by these oyster shells in Bohai Bay area with the results of carbon and oxygen isotopes, which were accomplished with this UV laser in situ carbonate analysis techniques.

微区同位素组成变化研究已成为地球化学分析技术发展的重要方向之一。碳酸盐岩碳、氧同位素的常规分析方法是磷酸分解法，操作简单、数据稳定，但样品用量大、空间分辨率低，不能满足现今高分辨率的需求。红外激光探针碳酸盐微区原位碳、氧同位素分析方法存在无法克服且难以准确校正的同位素分馏，影响了其分析结果的精度和准确度，制约了其应用与发展。本申请利用紫外激光（或分馏更小的飞秒激光）剥蚀系统对碳酸盐岩进行微区原位剥蚀，同时以高纯氦气为载气将剥离出来的固体气溶胶颗粒携出后富集，采用经典的磷酸法，将收集的微量样品与100%磷酸反应产生CO2气体，通过进样与测样方式的改进，实现微量碳酸盐样品的高精度质谱测定。并利用新建立的方法对贝类碳酸盐壳体进行高分辨率的微区原位碳、氧同位素分析，揭示壳体记录的气候环境变化信息。

微区同位素组成变化研究已成为地球化学分析技术发展的重要方向之一。碳酸盐岩碳、氧同位素的常规分析方法是磷酸分解法，操作简单、数据稳定，但样品用量大、空间分辨率低，不能满足现今高分辨率的需求。红外激光探针碳酸盐微区原位碳、氧同位素分析方法存在无法克服且难以准确校正的同位素分馏，影响了其分析结果的精度和准确度，制约了其应用与发展。本项目采用紫外激光剥蚀系统对碳酸盐岩进行了微区原位剥蚀，将剥蚀后的气溶胶样品收集后采用连续流方法进行微量样品的高精度碳、氧同位素测定，碳、氧同位素的分析精度达0.20‰和0.29‰，接近微量样品的常规分析测试精度（0.20‰）。对微量碳酸盐样品的碳、氧同位素高精度质谱测定方法进行了研究，最小样品量仅需20微克，通过测试方法的改进，含硝酸盐的微量碳酸盐样品的测试精度与纯净样品的精度相当。