白云鄂博中二叠世巴音珠日和岩体地球化学特征及构造意义  

Geochemical Characteristics of Bayinzhurihe Pluton and Its Tectonic Significance,Bayan Obo,Inner Mongolia

作　　者：罗红玲[1,2] 吴泰然[1] 赵磊[1,3] 贺元凯[1] 荆旭[1] 

机构地区：[1]教育部造山带与地壳演化重点实验室(北京大学),北京100871 [2]中国矿业大学地球与测绘工程学院,北京100083 [3]中国地质科学院地质研究所,北京100037

出　　处：《高校地质学报》2013年第1期123-132,共10页Geological Journal of China Universities

基　　金：国家自然科学基金项目(40902065和40672146);中央高校基本科研业务费资助

摘　　要：白云鄂博巴音珠日和岩体位于华北板块北缘中段的东升庙—太仆寺旗岩浆岩带上。该岩体由角闪辉长岩和石英闪长岩组成,其地球化学性质显示:低硅高铝,SiO2=49.72%～59.34%,Al2O3=15.79%～19.50%,Mg#=38～44;大离子亲石元素(LILE)富集(如Ba=829×10-6～1104×10-6,Sr=502×10-6～726×10-6)、高场强元素(HFSE,Nb,Ta等)亏损、轻稀土(LREE)富集(La/Yb)N=5.0～11.4,多数样品为弱负铕异常(δEu=0.63～1.09);低Sr/Nd(12～24)和La/Nb(1.33～2.39)比值显示了板内岩浆作用特征。两个角闪辉长岩的高Nb/Th(9.6～18.4)比值显示了非弧玄武质岩浆特征。岩体的锆石LA-ICP-MSU-Pb年龄为(265±2)Ma,代表岩体侵位年龄。锆石εHf(t)=-13.0～-17.2、tDMC=2.12～2.38Ga,显示了较明显的下地壳基底组分的加入。巴音珠日和岩体可能为后碰撞背景下,地壳的伸展减薄造成基性下地壳的部分熔融,熔体与来自富集地幔的玄武质岩浆发生部分混合,随后经进一步分异结晶作用形成。The middle segment of northern margin of the North China Plate was influenced by intense tectonic and magmatic activity during the Permian. Dozens of intrusions formed an E-W trending magmatic belt that extended from the Dongshenmiao to Xianghuang Qi, Inner Mongolia, with a length of 400 km and width of 30 km. As a representative, Bayinzhurihe Pluton consists of quartz diorite and hornblende gabbro, which belong to high-potassium calc-alkaline series. They are characterized by low SiO2 （49.72%～59.34%） and high Al2O3 （15.79%～19.50%） contents, with Mg#=38～44, enrichment in large ion lithophile elements （LILE, e.g., Ba=829×10^-6～1104×10^-6, Sr=502×10^-6～726×10-6）, relative depletion in high field strength elements （HFSE, e.g.,Nb, Ta） in primitive mantle-normalized spidergrams, and right-inclined rare earth element patterns, mostly with slightly negative Eu anomalies （δEu=0.63～1.09）. Their low Sr/Nd ratios （12～24） and La/Nb ratios （1.33～2.59） may reflect intraplate magmatism involved. Hornblende gabbro shows non-arc-like （Nb/Th =9.6-18.4） basalt affinity compositions. LA-ICP-MS U-Pb zircon dating of the Pluton yielded an intrusive age of 265 ± 2Ma. Its zircons have eHf（t）=-13.0～-17.2 and tDM^C=2.12-2.38 Ga, mainly show the characteristics of lower continental crust. These features lead us to conclude that Bayinzhurihe Pluton was generated by mixing of lower crustal-derived mafic melt and minor enriched mantle-derived mafic magma, followed by fractional crystallization,due to crustal extension in post-collisional setting.

关 键 词：锆石LA—ICP—MS U—Pb定年 HF同位素组成 后碰撞 华北板块北缘 

分 类 号：P59[天文地球—地球化学]