青海牛鼻子梁镍矿勘查区闪长岩U-Pb年代学、地球化学及Hf同位素研究

发布时间：2018-07-09 10:36

本文选题：闪长岩 + 锆石U-Pb年龄　；参考：《地质学报》2017年10期

【摘要】：本文对牛鼻子梁镁铁质-超镁铁质杂岩体中产出的闪长岩进行了详细的U-Pb年代学、岩石地球化学和Hf同位素分析,以便对岩石的成因及南祁连造山带对柴达木盆地的俯冲效应予以研究。闪长岩中锆石LAICP-MS U-Pb定年结果表明,闪长岩的形成时代为361±3 Ma(MSWD=0.049),即晚泥盆世。岩石地球化学方面,SiO_2含量为53.44%~58.27%,Na_2O+K_2O为4.80%~6.39%,K_2O/Na_2O比值为0.33~0.97,显示出富钠的特征,岩石由钙碱性序列向高钾钙碱性序列过渡。微量元素原地地幔标准化蛛网图上显示相对富集大离子亲石元素(Rb、K)及轻稀土,相对亏损高场强元素(Ta、Nb、Zr),同时Th含量介于2.03×10~(-6)~6.57×10~(-6)之间,Th/Ta比值为2.73~12.82之间,显示为壳幔混染作用的产物,另外据闪长岩中发现的辉长岩包体也表明了壳幔岩浆的混合。闪长岩Hf同位素显示,岩石的ε_(Hf)(t)值和二阶段模式年龄(TDM2)分别介于±6.41~±9.36和714~878Ma之间。上述结果表明,岩体的原始岩浆是一种幔源物质为主,混合新生陆壳部分熔融的产物。综合区域岩石构造背景的研究,认为牛鼻子梁闪长岩岩体形成于南祁连向柴达木板块俯冲碰撞后伸展的环境。
[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 卤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 卤6.41 ~ 卤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.
【作者单位】：中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室;北京大学地球与空间科学学院;吉林大学地球科学学院;山东省第六地质矿产勘查院;
【基金】：“青海省牛鼻子梁地区铜镍硫化物矿床控矿条件及找矿突破研究”项目 “青海省柴达木周缘铜镍硫化物矿成矿规律及找矿预测研究”项目联合资助的成果
【分类号】：P588.122;P597;P618.63

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