东昆仑南缘布青山构造混杂带得力斯坦南MOR型玄武岩地质、地球化学特征及岩石成因  

Geological and Geochemical Features of Delisitannan Basalts and Their Petrogenesis in Buqingshan Tectonic Mélange Belt,Southern Margin of East Kunlun Orogen

作　　者：李瑞保[1,2] 裴先治[1,2] 李佐臣[1,2] 陈有炘[2] 刘成军[2] 裴磊[3] 徐通[2] 刘战庆[4] 魏博[2] 

机构地区：[1]长安大学西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [2]长安大学国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [3]中国地质大学地球科学与资源学院,北京100083 [4]桂林理工大学地球科学学院,广西桂林541004

出　　处：《地球科学（中国地质大学学报）》2015年第7期1148-1162,共15页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(Nos.41172186;41472191;40972136);中央高校基本科研业务费专项资金项目(Nos.CHD2011TD020;2013G1271091;2013G1271092);青海省国土资源厅--中国铝业公司公益性区域地质矿产调查基金项目(No.200801)

摘　　要：东昆仑南缘布青山构造混杂带发育有较多OIB型玄武岩,这类玄武岩成因与地幔柱密切相关.与灰岩密切伴生的具有MOR型特征的基性火山岩亦是东昆仑南缘古特提斯洋盆一类重要的海山玄武岩.为了查明布青山构造混杂带中不同类型洋岛或海山玄武岩的岩石成因,对得力斯坦南玄武岩进行了详细的地质、地球化学和岩石成因研究.布青山地区得力斯坦南出露的玄武岩岩石类型复杂多样,主要由枕状玄武岩、气孔-杏仁状玄武岩、角砾状玄武岩和块状玄武岩组成.主量元素地球化学特征表明,该套玄武岩属于深海拉斑玄武岩和洋脊拉斑玄武岩系列.得力斯坦南玄武岩∑REE介于34.51×10-6~61.60×10-6,LREE/HREE介于0.89~1.37,（La/Yb）N介于0.30~0.56,δEu介于0.90~1.18.球粒陨石标准化稀土元素配分图呈现轻稀土元素亏损的左倾型,与NMORB型玄武岩稀土元素配分曲线基本相同.得力斯坦南玄武岩Zr、Hf、Nb和Ta含量均相当于NMORB的相应元素的丰度值.Zr/Nb值介于24.59~57.69,Nb/La值介于0.45~0.94,Hf/Ta值介于18.29~31.94.在原始地幔标准化微量元素蛛网图上,曲线右侧高场强元素基本未分异（Nb、Ta、Zr、Hf等）,并贴近于NMORB标准线,具有与NMORB玄武岩相似而明显不同于EMORB和OIB型玄武岩的特征.微量元素判别表明其形成于洋中脊或由于洋脊扩张向两侧后移的洋中脊构造环境,结合其上覆盖有深水硅泥岩及浅水厚层状碳酸盐岩的地质事实,认为其在地形地貌上属于古海山.岩石成因研究表明该套玄武岩起源于亏损地幔（DM）,并估算其为地幔二辉橄榄岩发生约10%部分熔融的产物.OIB-type basalts outcropped in the Buqingshan tectonic melange belt, southern margin of East Kunlun, are closely related to mantle plume petrogeneticly. The MOR-type basalts are also another types of seamount basalts developed in the Pal- eotethys ocean. The Delisitannan basalts in Buqinshan area are located in the southern margin of the East Kunlun region. Field investigations show that the basalts are composed of pillow basalts, fumarolic-amygdaloidal basalts, breccia basalts and massive basalts, which are covered by lamellar fuchsia silicon mudstone. Geochemical data show that the basalts are subdivided into abyssal tholeiite and oceanic ridge tholeiite series. The contents of REE range from 34.51× 10^-6-61.60× 10^-6 , LREE/HREE =0.89-1.37, （La/Yb）N =0.30-0.56. The chondrite-normalized REE pattern shows left-dipped incline and weak negative Eu abnormity （δEu=0.90-1.18）, which is identical to NMORB REE distribution pattern. The Delisitannan basalts are aschistic in HSFE （Nb,Ta,Zr, Hf）, and Zr/Nb ratios range from 24.59-57.69, Nb/La ratios range from 0.45-0.94, Hf/Ta ratio ranges from 18.29-31.94, which are all similar to those of NMORB basalts, and are obviously different from EMORB and OIB basalts. All of the trace element characteristics indicate that the basalts formed in an NMORB tectonic environment. The petrogenesis study shows that the rocks originated from depleted mantle, and are the product of 10% partial melting of mantle lherzolite roughly.

关 键 词：东昆仑 玄武岩 布青山 古特提斯洋 地球化学 岩石学 

分 类 号：P588[天文地球—岩石学]