扬子板块西缘北段新元古代花岗岩类分布较广。它们具有准铝质化学成分(A/NKC<1.03);贫Rb、U、Th、Nb、Hf,相对富Sr、Ba、Zr;稀土总量较低,轻、重稀土分馏不明显;ε_(Nd)较高(>—4.3),I_(sr)较低(<0.7050),δ~(18)低(<7.6‰)。这些特征与华南同熔型花岗岩类的值十分相似,反映其源区具有壳-幔混合特点。新元古代花岗岩类的Nd模式年龄(1.81～1.14 Ga)介于该区初生地壳(1.0 Ga左右)和古老地壳(>2.0 Ga)之间,推测这些花岗岩类主要是由上述两端元按不同比例组成的混合源区衍生的。母岩浆的形成可能同新元古代早期(晋宁期)滇青藏大洋板块向扬子古板块的俯冲有关。 The Neoproterozoic granites in the northern segment of the western margin of Yangtze Plate are widely distributed. (A / NKC <1.03); poor Rb, U, Th, Nb, Hf, relatively rich in Sr, Ba, Zr; the total amount of rare earth is low, light and heavy rare earth fractional distillation is not obvious; Nd is higher (> -4.3), I sr is lower (<0.7050) and δ 18 is lower (<7.6 ‰). These features are very similar to the values ​​of the same type of granitoids in South China, reflecting that the source region has the characteristics of crust-mantle mixing. The Neoproterozoic granitoids have Nd mode ages ranging from 1.81 to 1.14 Ga between the primary crust (about 1.0 Ga) and the ancient crust (> 2.0 Ga). It is speculated that these granitoids are mainly composed of the above-mentioned two end- Proportional composition derived from mixed source regions. The formation of parent magma may be related to the subduction of the Qinghai-Tibetan plate from the Early Neoproterozoic (Jinning) to the Yangtze block.