金沙江南流入红河的锆石U-Pb年龄谱物源示踪研究的质疑

Question of Using the Zircon U-Pb Age Technique for Sediment Tracing to Study Whether the Ancient Jinsha River Flew Southward to Joint Red River

Ping Kong等近期发表二篇文章,采用锆石U-Pb年龄谱物源示踪方法,研究得出古金沙江曾经石鼓南流入红河的结论,论文对此提出了质疑。测定U-Pb年龄谱的锆石粒度> 0. 25 mm,比重4. 5 g/cm^3左右,为推移质,该技术只适用于较短距离的无湖泊河流的物源示踪研究。将第四纪沉积物和现代河流泥沙的锆石U-Pb年龄谱与大区域岩层的进行对比,分析泥沙来源,研究金沙江河流演化的技术路线存在根本性的缺陷。

In this paper,a hypothesis was challenged,of which the ancient Jinsha River used to flow southward at Shigu,not eastward as present,to joint the Red River,which was asserted in Ping Kong’s two papers by using the zircon U-Pb age for sediment tracing. It is well known that the zircon mineral grains for U-Pb age analysis are narrowly applicable to bed-loading sediment. This is because the particle sizes for U-Pb age analysis are usually greater than 0. 25 mm and their density is about 4. 5 g/cm^3;therefore,the technique is only suitable for sediment tracing with a relative short transportation distance in rivers other than those in lakes. The technique has fundamental deficiencies for a study of the Jinsha river evolution by merely comparisons of the zircon U-Pb ages of the sands between quaternary or present river sediments and regional rocks in a large area.