中文摘要:由于硅在自然界中没有化学价态变化，主要呈硅氧四面体形式存在，因此硅同位素的热力学分馏很小，由此产生的硅同位素变化不大。溶液中SiO2沉淀过程的同位素动力学分馏是引起自然界硅同位素明显变化的主要原因。本文实验测定了溶液中SiO2沉淀过程的硅同位素动力学分馏系数α，并结合所测定的硅同位素动力学分馏系数对现代海底黑烟囱、太古代条带状磁铁石英岩、风化成因粘土矿物的δ30Si值明显偏低，浅海碳酸盐台地中硅质岩的δ30Si值明显偏高的现象做了理论上的解释。
Abstract:Silicon has no valence change in nature and is present mainly as tentravalent cations in silicon-oxygen tetrahedral, showing very small silicon isotope equilibrium fractionation. Dynamic fractionation is the major cause for obvious change in silicon isotope composition. One of the most effective processes that cause silicon isotope dynamic fractionation is the precipitation of silica gel from the solution. In our experimental study, a silica acid solution (H4SiO4) was prepared at temperature(16～18℃)by reaction of 4 mol/1 HCl with sodium-silicate (Na2SiO3). The solution was unstable, and a polyreaction automatically proceeded, resulting in silica gel precipitation. Silicon isotope compositions of the precipitates and the solution were determined, and the precipitated/dissolved silicon isotope dynamic fractionation factors(α)were in the range of 0.9990～0.9996. The experiment shows that silicon isotope dynamic fractionation is controlled both by temperature and by precipitation speed. The faster the speed of silicon precipitation, the smaller the dynamic fractionation factor between the precipited and the dissolved phases. The experimental results have been used to account theoretically for silicon isotope variation of some natural occurrences, of which modern hot spring sinters, siliceous rocks from black smokers on seafloor, weathering clay minerals and Precambrian exhalative banded magnetite-quartzite show large negativeδ30Si values, whereas siliceous rocks from shallow-sea carbonate rock sequence, On the other hand, possess obvious highδ30Si values.
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李延河，丁悌平，万德芳.1994.硅同位素动力学分馏的实验研究及地质应用[J].矿床地质,13(3):282~288.1994.Experimental study of silicon isotope dynamic fractionation and its geological application[J].Mineral Deposits13(3):282~288
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