摘要
龙泉群区域变质岩系的时代一直被归属于震旦纪—早古生代(闽北的相当层位被置于震旦系)。笔者首次获得该群的全岩等时线年龄为1376.5±82.1Ma(Sm-Nd)和988.6±40.2Ma、951.7±11.4Ma(Rb—Sr),由此确定龙泉群的时代为中元古晚期(1000—1400Ma),其主期区域变质年龄约为950±50Ma。龙泉群副变质的Nd模式年龄t_(DM)=1.8—2.0Ga,其主要蚀源区为早前寒武纪陆壳。变质基性火山岩的ε_(Nd)(t)=1.63±0.63,反映其岩浆源自壳下亏损地幔并经古老硅铝壳的污染。结合基础地质研究成果分析,龙泉群系早元古代浙闽克拉通内地槽(裂陷糟)火山—沉积产物,属内硅铝壳造山带而非洋壳残块。
The high greenschist--facies regional metamorphic series of the LongquanGroup has been long inferred to be of Sinian--Early Paleozoic age. But the whole-rock isochron ages of the group obtained by the authors for the first timc are1376.5±82. 1 Ma(Sm--Nd), 988.6 ±40.2 Ma (Rb-Sr) and 951.7± 11 .4 Ma (Rb--Sr),from which it is suggested that its rock formation age is late Middle Proterozoic(1.0-1.4 Ga), and its regional metamorphic age is about 950±50 Ma. According tothe isochron of the metabasic volcanics ε_(Nd)(t) = 1.63 ± 0.63, the authors considerthat the primordial magma was derived from the depleted mantle below the crustand contaminated by old silica crust. On this basis coupled with an analysis of thegeological setting, the Longquan Group is the volcano--sedimentary product of ataphrogenic trough within the early Proterozoic Zhejiang--Fujian craton.
出处
《地质论评》
CAS
CSCD
北大核心
1992年第3期271-278,共8页
Geological Review
关键词
中元古界
龙泉群
地质
年代学
isotopic age
metamorphic basement
Zhejiang
