1983年我们从美国地质调查所C.W.Naeser处得到两个锆石年龄标准样(122号和123号),测定结果见表。标准样取自美国科罗拉多西南的鱼谷凝灰岩,对锆石及共生矿物已分送世界各国的有关实验室作了测定。其中共生的透长石、黑云母、角闪石和斜长石用钾-氩法测得的年龄值分布在27.1～28.5百万年之间。平均年龄为27.8百万年。用裂变径迹法测得 In 1983, two zircon age standards (Nos. 122 and 123) were obtained from the C.W. Naeser at the US Geological Survey. The results are shown in the table. The samples were taken from fish tuff in the southwest of Colorado, USA, and the zircon and symbiotic minerals were distributed to relevant laboratories in various countries in the world. Among them, the symbiotic age of feldspar, biotite, amphibole and plagioclase determined by potassium-argon method was between 27.1 and 28.5 million years. The average age is 27.8 million years. Measured by fission track method