甘肃北山白山堂矿区流纹斑岩的U-Pb年代学、地球化学特征及其地质意义  

U-Pb Geochronology and Geochemical Characteristics of the Rhyolite Porphyry in the Baishantang Mine,Gansu and Their Geological Implications

作　　者：惠卫东[1] 朱江[2,1] 邓杰[3,1] 吕新彪[1] 莫亚龙[1] 李春诚[1] 

机构地区：[1]中国地质大学资源学院,湖北武汉430074 [2]中国地质调查局武汉地质调查中心,湖北武汉430223 [3]湖北省地质调查院,湖北武汉430034

出　　处：《地质与勘探》2013年第3期484-495,共12页Geology and Exploration

基　　金：国家科技支撑计划重点项目(编号2007BA25B04和2011BAB06B04-05)

摘　　要：LA-ICP-MS锆石U-Pb定年结果表明,甘肃北山南部白山堂矿区流纹斑岩的形成年龄为374.9±2.3Ma(MSWD=1.5)。地球化学特征显示流纹斑岩呈钙碱性、过铝质,具高硅(70%～74%)、高钾(4.34%～8.75%)和低钙(0.13%～1.16%)含量特点,铝饱和指数A/CNK为1.12～1.65,稀土配分曲线上表现为左高右低,负Eu异常明显,大离子亲石元素相对富集,Nb,Ta,Sr,P,Ti亏损。结合前人Sr-Nd同位素分析认为,该岩体起源于古老的地壳物质部分熔融。非常低Sr、高Yb的特征表明岩体形成时的压力较低,深度较浅,全岩锆石饱和温度约为750℃。结合区域地质分析认为,该岩体与北山南部柳园埃达克岩、墩墩山地区岛弧火山岩具有一致的成岩年龄,形成于陆缘火山弧环境。The LA - ICP - MS zircon U - Pb dating yields a 2o6 pb/23s U age of 394.9 ~ 2.3 Ma （ MSWD = 1.5 ） for rhyolite porphyry in the Bais- hantang mine, Gansu, implying its Late Devonian intrusion. Geochemistry analyses show that the rocks are typically potassium - rich （ K2O = 4.34% - 8. 75 % ） and peraluminous （ A/CNK = 1.12 - 1.65 ）. REE is characterized by obvious negative Eu anomalies. The elements K, Rb, Ba, U and Pb are rich in the rhyolite while Nb, Ta, Sr, P, Ti are depleted. The geochemical data, coupled with the published Sr-Nd isotopic analysis, indicate that the Baishan- tang rhyolite was most likely generated by partial melting of the old crust material. We propose that the rhyolite was formed at a continental volcanic arc that was closely related to subduction.

关 键 词：U-PB年龄 地球化学 流纹斑岩 岩石成因 白山堂 甘肃 

分 类 号：P581[天文地球—岩石学]