碳酸盐Δ48-Δ47 团簇同位素体系的动力学分馏研究

作为新型的地质温度计，碳酸盐团簇同位素(Δ47)已被广泛应用于古温度重建研究。但是，这种温度计在使用时需确保同位素达到平衡状态。然而，自然界的碳酸盐在形成时普遍处于同位素不平衡状态，一定程度上影响到团簇同位素指示温度的准确性。由于不同团簇同位素的不平衡程度之间可能存在一定的相关性，利用Δ48-Δ47团簇同位素体系在理论上可校正Δ47的不平衡分馏，但由于缺乏Δ48动力学分馏的实验证据，该校正方法目前尚未能应用到实际研究中。因此，本项目拟首先通过优化质谱分析和改进样品前处理系统来建立碳酸盐Δ48-Δ47高精度分析方法，然后在不同温度下制备具有不同Δ48-Δ47平衡程度的碳酸盐溶液，通过碳酸钡沉淀来揭示碳酸盐Δ48-Δ47的动力学分馏特征，尝试建立有效的经验校正方程。本项研究将为深入认识碳酸盐Δ48-Δ47的分馏机理提供理论和实验依据，有助于利用Δ48-Δ47团簇同位素体系获得更准确的温度信息。

As a novel geothermometer, carbonate clumped isotope (Δ47) has been broadly applied to studies of reconstructing paleo-temperature. The prerequisite for the Δ47 thermometer is to ensure that isotopic equilibrium is achieved. However, most of natural carbonates are generally precipitated out of isotopic equilibrium, impacting the accuracy of the Δ47 thermometer to certain degree. As the magnitudes of disequilibrium in the different clumped isotopes (e.g. Δ48 and Δ47) are possibly correlated, the Δ48-Δ47 system can be used to correct the Δ47 disequilibrium theoretically. However, as the lack of the experimental evidences regarding the kinetic fractionation of Δ48, the correction cannot be applied to current researches. Consequently, we propose to firstly establish a high precision Δ48-Δ47 analysis of carbonates through optimizing the mass spectrometry and improving the pre-treatment system. Secondly, we will prepare carbonate solutions at different temperatures with different degrees of clumped isotopic disequilibrium. The kinetic fractionation signature of the Δ48-Δ47 will then be revealed based on barium carbonate precipitates. An effective empirical correction equation will be established tentatively. This work will provide theoretical and experimental basis for better understanding the fractionation mechanism of the Δ48-Δ47 in carbonates and will also allow the use of the Δ48-Δ47 for better indicating accurate temperature information.