摘要
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。
Neoproterozoic granitoids are widespread in the northern part of the western margin of the Yangtze block. They have low concentrations of Rb, U, Th, Nb, Hf and REE, low values of A/NKC (<1. 03) , Sδ18O(<7. 6%) and initial 87Sr/86Sr ratio (<0. 7069) , high Sr, Ba and Zr concentrations and *Nd values (> -5. 0). The fractionation between LREE and HREE is not significant. These characteristics are similar to those of syntexis-type granitoids in South China. Their Nd model ages (1. 81-1. 14 Ga) are between the ages of the old crust (>2. 0 Ga) and juvenile crust (≈1. 0 Ga). These features suggest that the sources of the granitoids should be mixtures derived from the mantle and crust. The formation of the magmas may be associated with the subduction of the early Neoproterozoic Yunnan-Qinghai-Tibet oceanic plate under the Yangtze block.
出处
《地质论评》
CAS
CSCD
北大核心
2000年第5期512-519,共8页
Geological Review
基金
教育部博士点基金 (编号96028429)
关键词
花岗岩类
新元古代
扬子板块西缘
地球化学特征
isotope
granitoids
Neoproterozoic
northern part of the western margin of the Yangtze block
