本文選題：閃長巖 + 鋯石U-Pb年齡��； 參考：《地質學報》2017年10期

【摘要】：本文對牛鼻子梁鎂鐵質-超鎂鐵質雜巖體中產(chǎn)出的閃長巖進行了詳細的U-Pb年代學、巖石地球化學和Hf同位素分析,以便對巖石的成因及南祁連造山帶對柴達木盆地的俯沖效應予以研究。閃長巖中鋯石LAICP-MS U-Pb定年結果表明,閃長巖的形成時代為361±3 Ma(MSWD=0.049),即晚泥盆世。巖石地球化學方面,SiO_2含量為53.44%~58.27%,Na_2O+K_2O為4.80%~6.39%,K_2O/Na_2O比值為0.33~0.97,顯示出富鈉的特征,巖石由鈣堿性序列向高鉀鈣堿性序列過渡。微量元素原地地幔標準化蛛網(wǎng)圖上顯示相對富集大離子親石元素(Rb、K)及輕稀土,相對虧損高場強元素(Ta、Nb、Zr),同時Th含量介于2.03×10~(-6)~6.57×10~(-6)之間,Th/Ta比值為2.73~12.82之間,顯示為殼幔混染作用的產(chǎn)物,另外據(jù)閃長巖中發(fā)現(xiàn)的輝長巖包體也表明了殼幔巖漿的混合。閃長巖Hf同位素顯示,巖石的ε_(Hf)(t)值和二階段模式年齡(TDM2)分別介于±6.41~±9.36和714~878Ma之間。上述結果表明,巖體的原始巖漿是一種幔源物質為主,混合新生陸殼部分熔融的產(chǎn)物。綜合區(qū)域巖石構造背景的研究,認為牛鼻子梁閃長巖巖體形成于南祁連向柴達木板塊俯沖碰撞后伸展的環(huán)境。
[Abstract]:In this paper, U-Pb geochronology, geochemistry and HF isotopic analysis of the diorite produced in the Niunoliang mafic ultramafic complex have been carried out. In order to study the genesis of rocks and the subduction effect of South Qilian orogenic belt on Qaidam Basin. The zircon LAICP-MS U-Pb dating results of diorite indicate that the age of diorite formation is 361 鹵3 Ma (MSWD0. 049), that is, the late Devonian. In terms of rock geochemistry, the content of Sio _ 2 is 53.44 and 58.27%, and that of Na _ 2O / S _ 2O is 4.80 and 6.39% respectively. The ratio of K _ 2O / Na _ 2O is 0.33 ~ 0.97, which shows the characteristics of sodium enrichment and the transition of rocks from calc-alkaline sequence to high-potassium calc-alkaline sequence. The trace elements in situ mantle-normalized cobwebs show that they are relatively enriched in large ion lithophile elements (RbPK) and light rare earths, and relatively depleted in high field strength elements (Ta-Nb-Zr), and the Th content is between 2.03 脳 10 ~ (-6) and 6.57 脳 10 ~ (-6). The ratio of Th / Ta is 2.7312.82, indicating that it is the product of crust-mantle mixing. In addition, the gabbro inclusions found in diorite indicate the mixing of crust and mantle magma. The HF isotope of diorite shows that the 蔚 _ (HF) (t) and the two-stage model age (TDM2) of the diorite are between 鹵6.41 ~ 鹵9.36 and 714 ~ 878 Ma, respectively. The above results indicate that the primitive magma of the rock mass is the product of partial melting of the mantle source material mixed with the new continental crust. Based on the study of the regional tectonic background, it is considered that the Niunose Liang diorite rock body was formed in the extensional environment of the southern Qilian subduction and collision to the Qaidam plate.
【作者單位】： 中國地質科學院礦產(chǎn)資源研究所國土資源部成礦作用與資源評價重點實驗室;北京大學地球與空間科學學院;吉林大學地球科學學院;山東省第六地質礦產(chǎn)勘查院;
【基金】：“青海省牛鼻子梁地區(qū)銅鎳硫化物礦床控礦條件及找礦突破研究”項目 “青海省柴達木周緣銅鎳硫化物礦成礦規(guī)律及找礦預測研究”項目聯(lián)合資助的成果
【分類號】：P588.122;P597;P618.63

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