【摘要】 <正> 近几年来,为配合寻找富铁矿及其他科研任务,对冀东、辽东、豫西、川西等地的前寒武系,及庐枞、宁芜、繁昌和浙西等地的中生代火山岩地层进行了同位素年龄测定和研究。在所内外的大力支持协助下,进行了野外观察和采样,同时接受了所内外兄弟单位送来的样品及有关地层资料。我们对这些样品进行了同位素年龄测定。冀东、辽东、豫西和川西前寒武纪地层的样品,主要用Rb-Sr全岩等时线法,其中对川西的样品并用了少数K-Ar法。对庐枞、宁芜、繁昌和浙西的中生代地层样品,主要用K-Ar法。对浙西的个别样品并用了Rb-Sr全岩等时线法。对测定得到的部分年龄数据,以前曾以不同方式报道。本更多还原

【Abstract】 In the present work the Rb-Sr isochron method is mainly used for the age determination of Precambrian rocks.The Sanggan group and/or Qianxi group distributed in the eastern Hebei are the deeply metamorphosed formations of granulite and eclogite facies.All five ages obtained from this two groups are more than 2500 Ma,and in which an isochron age with better fit of 2743 Ma is found.So both of them belong to Archean,but the lower limit age still remains to be determined.The lower member of Dantazi group of amphibolite facies,which is stratigraphically higher than the above two groups in this area yields an isochron age of 2520±99 Ma.The upper member of Kuandian group consisting mainly of gneiss and granulite in eastern Liaoning yields an isochron age of 2206±229 Ma.And in western Henan,the amphibolite of the lower member of Denfeng group gives two isochron ages of 2124±44 Ma and 2143±85 Ma.Taking the boundary age between the Early and Middle Proterozoic as 1900 Ma,then the three groups mentioned above should belong to Early Proterozoic.The phyllite slate from Gaixian formation of the upper member of Liaohe group in eastern Liaoning yields an age of 1640±38 Ma,and the quastzose schist of Wuzhiling formation,the lower member of songshan group in Western Henan,yields an age of 1748±17 Ma,while the granite intruded the Songshan group and overlain unconfor-mably by the Wufushan group yields the K-Ar ages from 1500 to 1630 Ma.Therefore the upper limit age of Liaohe and Songshan groups should be about 1650 Ma,and belong to Middle Proterozoic.In western Sichuan,the Suxiong formation of the lower Sinian is chiefly composed of a variety of volcanic rocks and the dacite from the upper member of this formation gives an age of 822±9 Ma,so providing a direct evidence to determine the bottom limit age of the Sinian System.The ages of Mesozoie volcanic rocks distributed along the middle-lower Yangtze Valley are mostly determined by K-Ar method.The volcanic sequence of Lujiang-Tzungyang basin is divided downwards into Fushan,Shuangmiao and Zhunchao formations.14 samples,including whole rock,biotite and sanidine are measured and yield 16 age data ranging from 98 to 132 Ma.All the ages of volcanic rocks from Nanjing- Wuhu basin are less than 126.8 Ma.These data indicate that there were three extrusion episods during Cretaceous in this area,120.2-126.8 Ma,109.7-115.7 Ma and 89.7-105.7 Ma,and the first two belong to Early Cretaceous,while the last is assigned to Late Cretaceous.The volcanic sequence of Fanehang area descendingly subdivided into Kedoushan,Chiasha and Zhongfeneun formations.Three age data are obtained.The biotite separated from dacite collected from Kedoushan formation which represen-tied the last extrusion episode in this area is measured and yields an age of 115.4 Ma,which is assigned to Early Cretaceous.The sequence of volcanic sediments in Shou-t’ltang basin of western Zhejiang is divided downwards into Shouchang,Huaiigjiari and Laoeun formations.The Rb-Sr isochron age of rhyolitic welded tuff from the Shouchang formation is 118±4 Ma.Although different opinions of Late Jurassic and Early Cretaceous on the geological ages of these strata in above-stated areas are held by biostratigraphers,the radiometric data that is between 110 and 137 Ma should support the later conclusion of Early Cretaceous.更多还原