【摘要】：北山造山帶位于華北板塊、塔里木板塊和哈薩克斯坦板塊交匯部位。為了研究北山地區(qū)早古生代大地構(gòu)造屬性,基于1∶5萬區(qū)域地質(zhì)礦產(chǎn)調(diào)查,采用LA-ICP-MS鋯石U-Pb同位素定年法對分布于石板井地區(qū)的輝長巖體進(jìn)行了年齡測定和巖石地球化學(xué)測試。結(jié)果表明:輝長巖體鋯石U-Pb年齡為498.9±2.4Ma,屬晚寒武世。地球化學(xué)數(shù)據(jù)顯示:巖石具有較低的SiO_2(40.39%~53.62%)和較高的Al_2O_3(12.56%~19.26%)、CaO(8.09%~10.93%)含量和Mg#值。稀土總量較高(∑REE=62.69×10~(-6)~250.62×10~(-6)),輕重稀土分異明顯[(La/Yb)N=4.89~16.94],無明顯Eu異常,δEu=0.82~1.28。巖石富集大離子親石元素Rb、Ba、K等,虧損高場強(qiáng)元素Nb、Ta、P、Zr、Ti等。Rb/Nb-Rb/Zr、(Ce/Yb)N-(Yb)N、Zr-Y和Zr-Nb圖解顯示該巖體巖漿起源于過渡型巖石圈地幔的部分熔融,并且在上升侵位過程中發(fā)生明顯的地殼混染。輝長巖體具有相對高的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,相近于板內(nèi)玄武巖。此外,在輝長巖體南側(cè)發(fā)育同期二長花崗巖,二者構(gòu)成雙峰式巖漿巖組合。綜合上述特征,輝長巖產(chǎn)出構(gòu)造背景為板內(nèi)伸展構(gòu)造體制,并推測在晚寒武世古亞洲洋未發(fā)生俯沖,仍處于擴(kuò)張期。
[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 鹵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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