北山造山带中部早古生代伸展构造体制:来自石板井辉长岩的年代学及地球化学证据

发布时间：2018-08-19 09:05

【摘要】：北山造山带位于华北板块、塔里木板块和哈萨克斯坦板块交汇部位。为了研究北山地区早古生代大地构造属性,基于1∶5万区域地质矿产调查,采用LA-ICP-MS锆石U-Pb同位素定年法对分布于石板井地区的辉长岩体进行了年龄测定和岩石地球化学测试。结果表明:辉长岩体锆石U-Pb年龄为498.9±2.4Ma,属晚寒武世。地球化学数据显示:岩石具有较低的SiO_2(40.39%~53.62%)和较高的Al_2O_3(12.56%~19.26%)、CaO(8.09%~10.93%)含量和Mg#值。稀土总量较高(∑REE=62.69×10~(-6)~250.62×10~(-6)),轻重稀土分异明显[(La/Yb)N=4.89~16.94],无明显Eu异常,δEu=0.82~1.28。岩石富集大离子亲石元素Rb、Ba、K等,亏损高场强元素Nb、Ta、P、Zr、Ti等。Rb/Nb-Rb/Zr、(Ce/Yb)N-(Yb)N、Zr-Y和Zr-Nb图解显示该岩体岩浆起源于过渡型岩石圈地幔的部分熔融,并且在上升侵位过程中发生明显的地壳混染。辉长岩体具有相对高的TiO2(0.65%~1.98%)、Nb(4.47×10~(-6)~18.56×10~(-6))、Ta(0.44×10~(-6)~1.86×10~(-6))、Zr(48.07×10~(-6)~386.86×10~(-6))、Hf(2.17×10~(-6)~21.23×10~(-6))含量,相近于板内玄武岩。此外,在辉长岩体南侧发育同期二长花岗岩,二者构成双峰式岩浆岩组合。综合上述特征,辉长岩产出构造背景为板内伸展构造体制,并推测在晚寒武世古亚洲洋未发生俯冲,仍处于扩张期。
[Abstract]:Beishan orogenic belt is located in North China plate, Tarim plate and Kazakhstan plate. In order to study the early Paleozoic tectonic attributes in Beishan area, based on the 1: 50 000 regional geological and mineral survey, LA-ICP-MS zircon U-Pb isotopic dating method was used to determine the age and geochemistry of gabbro bodies distributed in Shibanjing area. The results show that the zircon U-Pb age of gabbro is 498.9 卤2.4 Ma, which belongs to the late Cambrian. Geochemical data show that rocks have lower SiO_2 (40.3953.62%) and higher Al_2O_3 (12.56 ~ 19.26%) Cao (8.0910. 93%) content and Mg# value. The total amount of rare earth elements is higher (鈭，

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