阿尔金断裂东端白垩纪火山岩地球化学特征及其地质意义  

Geochemical characteristics and tectonic significance of the Cretaceous volcanic rocks in the Eastern Terminal of the Altyn Tagh fault zones

作　　者：汤文豪[1,2] 张志诚[1,2] 李建锋[1,2] 晨辰 李可[1,2] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室 [2]北京大学地球与空间科学学院,北京100871

出　　处：《地学前缘》2012年第4期51-62,共12页Earth Science Frontiers

基　　金：国家自然科学基金项目(41072148;40672130)

摘　　要：在阿尔金断裂与祁连山北缘逆冲断裂交汇处的昌马盆地和酒西盆地内,产出一套中基性火山岩,多为玄武岩和粗面玄武岩,属于碱性玄武岩系列。火山岩富集轻稀土元素,(La/Yb)N比值为7.28～18.01,富集大离子亲石元素(K、Rb和Ba等),亏损高场强元素(Nb、Ta等),显示出与OIB类似的地球化学特征。阿尔金断裂带东端火山岩的Sr同位素较高,87Sr/86Sr值在0.706～0.708,Nd同位素较低,εNd(t)值多为负值(0.53～-6.13),显示出EMⅡ型富集地幔来源的特征。K-Ar同位素年代学测试结果表明,阿尔金断裂带东端火山岩形成于(120.1±2.5)～(102.2±2.9)Ma,属于早白垩世晚期。火山岩的地球化学特征反映其形成于一个广泛的陆内伸展环境中,区域上可能受到阿尔金断裂带的影响,是阿尔金断裂白垩纪再活化的重要佐证。The volcanic rocks in the Changma Basin and Jiuxi Basin are intermediate-mafic volcanic rocks,which are located at the intersection of the Altyn Tagh fault（ATF） and the North Marginal Fault of the Qilian Mountains（NMFQ）,northern of the Tibetan Plateau.They are mostly basalt and trachy-basalt and belong to alkaline basalt series.The basalts are characterized by enriched light rare earth elements（LREE,（La/Yb）N is 7.28-18.01） and large ion lithophile elements（LILE）（K,Rb,Ba,etc.）,and by loss of high field strength elements（HFSE）（Nb,Ta,etc.）,showing similar geochemical characteristics to OIB.The volcanic rocks of the eastern terminal of ATF have higher Sr isotope and lower Nd isotope,their 87Sr/86Sr ranges between 0.706-0.708,and their εNd（t） was more negative（0.53——6.13）,showing that they are from EMⅡ-type enrichment mantle.K-Ar isotopic dating result is that the volcanic rocks formed in（120.1±2.5）-（102.2±2.9）Ma,the late Early Cretaceous.The geochemical characteristics of the basalts suggest that they formed in a wide range of extensional environment,and they may have undergone the impact of the ATF.The Cretaceous volcanic rocks are important evidence of the ATF reactivation.

关 键 词：火山岩 早白垩世 K-Ar年代学 阿尔金断裂带 祁连山西端 

分 类 号：P588[天文地球—岩石学] P597[天文地球—地质学]