锡石是各种不同类型锡矿床中最重要的矿石矿物,其U-Pb/Pb-Pb同位素年代学研究对于精确厘定锡矿床的成矿时代以及进一步揭示其矿床成因等具有重要意义.本文通过计算锡石中Pb的扩散参数,从扩散动力学角度对U-Pb同位素体系的封闭性进行了研究,探讨了不同温度条件下锡石对其所含U-Pb同位素信息的保存能力.研究结果表明,锡石对U-Pb的封闭温度比较高,故在大多数地质环境条件下锡石中的U-Pb同位素体系容易保持封闭状态;与常用的其它同位素定年体系相比,锡石中的U-Pb同位素体系不易因扩散迁移导致同位素信息丢失.本研究为锡石U-Pb同位素定年方法的可靠性提供了理论依据,这对促进我国成矿年代学的发展具有十分重要的意义.%As the most important ore mineral in various tin deposits, cassiterite plays an important role in direct dating of tin mineralization and revealing ore genesis through the study of its U-Pb/Pb-Pb geochronology. In this paper, the diffusion parameters of Pb in cassiterite were calculated, and the closure of U-Pb isotopic system in the term of diffusion dynamics was discussed. In addition, the retention of Pb isotope information in cassiterite under different temperatures was also discussed. The results reveal that the closure temperatures of U-Pb in this mineral are relatively high, and its U-Pb isotope system could be easily kept closed under most geological conditions in various tin deposits. Compared with other isotope systems commonly used as geochronometers, original U-Pb isotope information in cassiterite should not be easily lost by diffusion. This conclusion obtained in this paper provides an important theoretical basis for the reliability of cassiterite U-Pb dating, and will further promote the development of geochronology on hydrothermal deposits in China.
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