甘肃天水地区红土堡变基性岩的地球化学特征及其构造意义  

Geochemical characteristics of the Hongtubao metabasic rocks in the Tianshui area, Gansu, and their tectonic significance

作　　者：胡波[1] 裴先治[1] 丁仨平 杨吉[1] 赵小明[1] 李佐臣[1] 

机构地区：[1]长安大学地球科学与国土资源学院,陕西西安710054

出　　处：《地质通报》2005年第3期258-263,共6页Geological Bulletin of China

基　　金：国家自然科学基金重点项目(编号:40234041);教育部科学技术研究重点项目(编号:104175);中国地质调查局<1:25万天水市幅区域地质调查>项目(编号:200013000154)资助成果。

摘　　要：红土堡变基性岩以灰绿色变质玄武岩为主,有少量同时代同成分的辉绿岩墙顺层侵入其中。变基性岩属于拉斑玄武岩系列。稀土元素分布型式呈LREE弱富集型,具有较高的∑REE,无明显的Eu异常或弱的正异常,有明显的Ce负异常。弱富集大离子亲石元素(K、Rb、Sr、Ba),富集Th,贫Cr、Ni,具有Nb、Ta负异常,La/Nb比值大于1,无明显的Ti负异常。这些微量元素特征及其构造环境判别显示该基性岩可能形成于汇聚板块边缘的弧后裂陷—小洋盆构造环境。The Hongtubao metabasic rocks are mainly composed of grayish green metabasalt, intruded along the bedding by some contemporaneous diabase dikes of the same composition. The metabasic rocks are of tholeiitic series. Their chondrite-normalized REE patterns are of weakly LREE-enriched type, with relatively high ∑REE. There is no pronounced Eu anomaly or there are only weak positive anomalies; there is a pronounced negative Ce anomaly. Their MORB-normalized trace element spidergram shows that the rocks are slightly enriched in large-ion lithophile elements (K, Rb, Sr, Ba), enriched in Th and depleted in Cr and Ni. Nb and Ta show negative anomaly, La/Nb>1, and Ti anomaly is not pronounced. The characteristics of these trace elements and their discrimination of tectonic environments show that the metabasic rocks formed in a back-arc rift-small ocean basin tectonic environment at convergent plate margins.

关 键 词：甘肃天水地区 红土堡 变基性岩 地球化学 弧后盆地 

分 类 号：P588.124[天文地球—岩石学] P595[天文地球—地质学]