辽西义县晚白垩世大兴庄组流纹岩的地球化学特征及其成因  

Geochemistry Characteristics of the Late Cretaceous Adakitic Rhyolites of Daxingzhuang Formation and its Genesis in Yixian Area,Western Liaoning Province

作　　者：李伍平[1] 

机构地区：[1]广州大学土木工程学院,广东广州510006

出　　处：《地球科学（中国地质大学学报）》2011年第3期429-439,共11页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.90714002);国家重点基础研究"973"项目(No.2006CB403501)

摘　　要：辽西义县晚白垩世大兴庄组流纹岩具有埃达克质火山岩的特征.这些流纹岩SiO2≥68.62%、Al2O3≥14.40%、MgO<1.2%(Mg#<0.45)、Sr>360μg/g、Yb<1.1μg/g、Y<12μg/g、La/Yb>40、Sr/Y≥39和Nb/Ta>17.5;轻稀土元素富集,重稀土元素和高场强元素(如Nb、Ta、Ti)明显亏损,轻重稀土元素强烈分馏,具有弱的负铕异常;Nd、Sr同位素具有较低的143Nd/144Nd(0.511 376~0.511 441,εNd(t)=-23.45^-22.16)和适中的87Sr/86Sr(0.707 3~0.707 4,εSr(t)=32.38~32.8)比值,具有富集地幔端员(EMI)特点.这些特征表明,大兴庄组流纹质岩浆起源于较厚下地壳榴辉岩部分融熔,也说明中生代晚期局部仍残留较厚的下地壳,这为进一步理解燕山造山带中生代到新生代岩石圈减薄提供了重要信息.The study of the geochemistry of the Late Cretaceous rhyolites of Daxingzhuang Formation in Yixian area,western Liaoning Province,shows that these rocks demonstrate characteristics of adakitic rocks with SiO2≥68.62%,Al2O3≥14.40%,MgO〈1.2%（Mg#〈0.45）,Sr〉360 μg/g,Yb〈1.1 μg/g,Y〈12 μg/g,La/Yb〉40,Sr/Y≥39,Nb/Ta〉17.5 and with δEu weak negative anomaly,LREE enrichment,HREE depletion,HFSEs（Nb,Ta,Ti） strong depletion,lower 143Nd/144Nd ratios（0.511 376 to 0.511 441,-23.45 to-22.16 in εNd（t））,moderate 87Sr/86Sr ratios（0.707 3 to 0.707 4,32.38 to 32.8 in εSr（t）） which have the features of the enriched mantle EMI.The above geochemical features of the rhyolites indicate the magmas originated from the partial melting of eclogite of the lower thicken basaltic crust of the North China craton and perhaps also represent the thicken crust still existed in partial area of Yanshan orogenic belt.It falicitates the understanding of the processes of the lithosphere thinning of the North China craton during the Mesozoic and Cenozoic period.

关 键 词：埃达克质流纹岩 部分熔融 晚白垩世 地球化学 大兴庄组 辽西. 

分 类 号：P588.14[天文地球—岩石学]