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五台地区古元古界滹沱群底部砾岩层中发育浅变质的玄武岩-玄武安山岩.详细的地质调查确认其与上下沉积岩层为整合关系.对该岩层中玄武安山岩的锆石进行了SHRIMPU-Pb年龄测定,主要年龄结果分为两组.较老的一组锆石207Pb/206Pb年龄范围为2433～2558Ma,与五台-阜平地区地壳形成时代一致,推测为岩浆穿过地壳时捕获或火山岩沉积时陆源碎屑岩带入的锆石;较年轻的一组锆石13个点的Pb/206Pb年龄非常集中,其加权平均值为(2140±14)207Ma.该组锆石U含量极低(多数<50×10-6),Th/U比值高(0.49～1.11),为基性岩浆成因锆石.因此,(2140±14)Ma就是玄武安山岩的岩浆锆石结晶年龄,代表滹沱群的底界时代.这一结果进一步证实滹沱群形成于早元古代中期,是不同于五台运动的另一次地质事件的记录,很可能与华北中部2.2～2.1Ga的裂谷活动有关.
The shallow metamorphic basalts and basalts andesite are developed in the bottom conglomerate of the Paleoproterozoic Hutuo Group in Wutai.The detailed geologic survey confirmed that they are integrated with the upper and lower sedimentary formations.The SHRIMPU-Pb Age determination and main age results are divided into two groups.The older 207Pb / 206Pb zircons range in age from 2433 to 2558 Ma, consistent with the age of crustal formation in the Wutai-Fuping area and are presumed to be trapped by volcanic rocks or volcanic rocks Zircons from terrigenous clastic rocks during sedimentation. The Pb / 206Pb ages of 13 younger zircons in a younger group are very concentrated with a mean weighted average of (2140 ± 14) 207 Ma. The zircon U content is very low (Mostly <50 × 10-6) and high Th / U ratios (0.49-1.11), which are the basic magmatic zircons. Therefore, (2140 ± 14) Ma is the magmatic zircon age of basalt andesite, This result further confirms that the formation of the Yutuo Formation in the Early Proterozoic is a record of another geological event different from that of the Wutai movement and is likely to be related to the rift activity of 2.2 ~ 2.1Ga in the central North China.