【摘要】 依据陇山群片麻岩的Sm-Nd同位素资料,认为片麻岩形成于中元古代,等时线年龄为1451±190Ma,是裂谷作用初始阶段的火山沉积岩系。结合斜长角闪岩的地质、地球化学资料及Sm-Nd同位素资料,认为斜长角闪岩的原岩是侵入陇山群的辉绿岩墙或基性岩脉,不同于陇山群的主体岩系,是800～1000Ma(晋宁期)裂谷作用的产物;源区为亏损的类似于现在大洋中脊型地幔,裂谷活动的扩张速率为2～5cm/a,说明裂谷作用具有相当的规模。由于该区位于祁连—秦岭造山带和贺兰裂谷的交叉位置,上述认识具有区域构造意义。更多还原

【Abstract】 Based on new Sm-Nd isotope data of gneisses in the Longshan Group , the authors come to a conclusion that the Longshan Group was formed in the Middle Proterozoic with an Sm-Nd isochron age of 1451 ± 190Ma, indicating an initial rift magmatism in the region. Two more basic magmatic events took place afterwards with amphibolite Sm-Nd isochron ages of 983 ± 22Ma and 756 ± 97Ma respectively, namely during the Jinning Movement (800～1000Ma). The mantle source is depleted and similar to the MORB-type one, reflecting intensive rifting. The paper also points out that owing to the special geological site of the studying area where the Qilian-Qinling orogens and Helan rift meet, all the above results are of great significance in respect to regional tectonic.更多还原