锂同位素地球化学及其在热液活动研究中的应用

Li isotopic geochemistry and its application in the study of hydrothermal activity

在前人研究资料及成果的基础上,探讨了海底热液活动区锂和锂同位素地球化学组成及应用前景。与海底热液活动相伴的锂元素是海洋锂库的重要来源。海底热液系统中各部分锂及其同位素组成具有显著差异,热液流体中锂含量为20~1 421μmol/kg,δ7Li值为+2.6‰^+11.6‰;孔隙水中锂含量为9.0~5 720μmol/kg,δ7Li值为+4.5‰^+43.7‰;热液活动区沉积物中锂含量为(4.8~76)×10-6,δ7Li值为-4.31‰^+9.36‰;风化玄武岩中锂含量为(6.97~75.5)×10-6,δ7Li值为+7.5‰^+13.7‰;高温变质玄武岩中锂含量为(0.60~4.61)×10-6,δ7Li值为-2.1‰^+4.8‰。因此,锂及其同位素组成能提供热液系统中有关水-岩反应、水-沉积物反应、物质来源及流体循环的信息,是洋壳岩石蚀变及海底热液循环非常有效的指示剂。热液系统锂及其同位素组成能预测海底水岩比率,是海底热液矿床规模预测的有效参数。

The circulation of Li is accomplied by hydrothermal activity, which is an important input of oceanic Li flux. It is distinct difference for Li and Li isotopic composition in different parts of hydrothermal system including hydrothermal fluid, pore fluid, hydrothermal sediment, weathered basalt and altered basalts. Li concentration range of those parts of hydrothermal system are 20 -1 421 μmol/kg, 9.0-5 720 μmol/kg, （4.8 - 76） ×10^-6, （6.97 -75.5） ×10^-6and（ 0. 60 - 4. 61）×10^-6, respectively. Furthermore, δ^7Li of those vary from ＋2.6‰ to ＋11.6‰, ＋4.5‰ to ＋43.7‰, -4.31‰ to ＋9.36‰, ＋7.5‰ to ＋13.7‰, -2.1‰ and ＋4.8‰. Thus, Li and Li isotopic composition of hydrothermal systems can offer the informations of water-basalt and water-sediment alteration, material source and fluid circulating, and they are effective indicator of alteration of oceanic crust and circulation of hydrothermal fluid. They can be used to calculating the water-rock ratios for basalt alteration, and this is an effective parameter for determinating the size of hydrothermal deposition. Based on previous researches, we discussed Li and Li isotopic geochemistry of hydrothermal system and the prospect of its application.