白银厂矿田玄武岩地球化学特征及其形成地质环境  

GEOCHEMICAL CHARACTERISTICS OF BASALTS IN BAIYINCHANG ORE-FIELD AND ITS FORMATION GEOLOGICAL SETTING

作　　者：郭原生[1] 王金荣[1] 解宪丽[2] 邱红英[1] 胡沛青[1] 傅善明[1] 

机构地区：[1]兰州大学资源环境学院地质系,甘肃兰州730000 [2]南京师范大学地理系,江苏南京210008

出　　处：《甘肃地质学报》2001年第2期29-34,共6页Acta Geologica Gansu

摘　　要：白银厂矿田玄武岩主要由玄武岩和碱性玄武岩组成 ,其中玄武岩属于钙碱性系列和拉斑系列 ,碱性玄武岩属于钾质碱性玄武岩系列和钠质碱性玄武岩系列。相对于N -MORB ,本区钙碱性系列和拉斑系列玄武岩明显富集Ba、Rb、Th、U ,而亏损Ti;碱性系列玄武岩高度富集K、Ba、Rb、Th、U ,而Ti、Zr、Ce相对亏损 ,表明该区玄武岩的形成与板块俯冲作用有关。钙碱性玄武岩系列和拉斑玄武岩系列玄武岩具有低的REE含量和亏损的LREE配分型式 ,表明它是由LREE亏损和HREE略有富集的地幔部分熔融形成 ;碱性系列玄武岩的REE含量和 (La/Yb) N 比值高 ,LREE和HREE的分馏程度较高 ,表明其形成于演化的岩浆 ,可能来自于富集LREE的地幔源区或地幔橄榄岩较低程度的熔融。痕量元素地球化学特征表明 ,本区玄武岩应是与板块俯冲作用有关的地幔部分熔融形成 ,成岩环境为火山弧环境 ,是岛弧向成熟岛弧转化过程中的产物。Basalt series in Baiyinchang ore-field are consist of basalts and alkali-basalts,in which basalts belong to calc-alkalic basalts and tholeiite, alkali basalts belongs to kali-alkali series. Compared with N-MORB,calc-alkalic basalt and tholeiite, it is obviously rich in Ba?Rb?Th?U and depleted in Ti,the alkali-basalt is highly rich in K, Ba, Rb, Th, but depleted in Ti, Zr and Ce, and showing the generation of the basalts was related to plate subduction. The REE of calc-alkali basalt and tholeiite are characterized by lower amounts of REE and LREE-depleted distribution pattern and which reflect that the basalts were formed by the partial melting of LREE-depleted and slightly HREE-rich mantle. Alkalic basablts contain higher amounts of REE with higher (La/Yb) N ratios and higher degree fraction between LREE and HREE, which indicate that alkalic basalts developed from evolved magma deriving from the LREE-rich mantle sources or lower degree partial melting of mantle peridotite. Trace-element geochemical features show basaltes in Baiyinchang ore-field formed by mantle partial melting relative to plate subduction in vocanic arc-a production in transposition processes of island-arc into mature island-arc.

关 键 词：玄武岩 地球化学 地质环境 微量元素 稀土元素 板块俯冲作用 

分 类 号：P588.1[天文地球—岩石学]