K/T界线铂族元素丰度异常与地外撞击事件

ABUNDANCE ANOMALIES AND DISTRIBUTION PATTERNS OF PLATINUM GROUP ELEMENTS AT THE K/T BOUNDARY AND EXTRATERRESTRIAL IMPACT ORIGIN

遍布全球的Ｋ／Ｔ界线粘土层不仅存在着铱的丰度异常，其它铂族元素的含量也异常高，并且基本上保持着类似与地外物质中的丰度分布模式。实验表明，在粘土层中铂族元素主要呈可交换离子相和难溶金属相的形式存在，而在硫化物和硅酸盐相中的含量却很低。这与铂族元素来源于地外物体撞击的成因解释是一致的。此外，在铂族元素异常层位上普遍有超高温矿物变种（富镁铁尖晶石）、冲击变质矿物和玻璃陨石与其伴生。这些现象为Ｋ／Ｔ界线地外撞击事件的确定提供了无可争议的地质证据。

In the K/T boundary layers at all parts of the world,not only was there tremendous iridium anomaly,but the contents of other platinum group elements were enriched multiply as well.Additionally,the distribution patterns of PGEs were essentially consistent with extraterrestrial matter.The available data show that the PGEs exist primarily in forms of exchangeable phases and hard soluble metals in K/T boundary clay,and extremely depleted in sulfides and silicates.These are quite different from any terrestrial samples,but similar with extraterrestrial materials.Coupled with the extensive existence of ultra high pressure minerals,shocked glass and microtektites,it is suggested that the extraterrestrial impact event at the end of Cretaceous is unquestionable.