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本文为确定临江市八道沟地区二长花岗岩的成因及形成时代,进而揭示区域构造背景,对其进行了地球化学、锆石U-Pb年代学及Hf同位素研究.岩石样品中的锆石主要为长柱状,自形程度较好,发育较清晰的韵律生长环带结构,具岩浆锆石特征;测年结果表明,该岩石形成于早侏罗世(176±1 Ma,MSWD=0.92).岩石Si O2含量介于68.93%~70.02%之间,贫Mg O(1.27%~1.45%)、Ca O(1.80~2.78%),A/CNK=0.92~1.02,轻稀土元素明显富集,铕异常不明显(0.96~1.03),属于准铝质高钾钙碱性花岗岩,显示为I型花岗岩特征。岩石εHf(t)值为-20.21~-24.08,二阶段模式年龄TDM2(Hf)=2 498~2 740 Ma,且富集大离子亲石元素,亏损高场强元素Nb、Ta、P、Ti,Mg#值介于45~47之间,推断岩石样品源于新太古代下地壳熔融。结合区域同时代岩浆岩展布,认为八道沟地区二长花岗岩的形成与古太平洋板块向欧亚大陆俯冲有关。
In order to reveal the genesis and formation age of the monzonitic granites in the Badaogou area of Linjiang and to reveal the regional tectonic setting, geochemical and zircon U-Pb geochronology and Hf isotope studies were carried out.The main zircons in the rock samples The results show that the rock was formed in the Early Jurassic (176 ± 1 Ma, MSWD = 0.92). The content of Si O2 in the rock ranged from 68.93% to 70.02%, with poor MgO (1.27% -1.45%), CaO (1.80-2.78%) and A / CNK = 0.92-1.02. The anomaly is not obvious (0.96 ~ 1.03), belongs to the quasi-aluminum high-K calc-alkaline granite, showing the characteristics of type I granite. The εHf (t) values of rocks range from -20.21 to -24.08, and the TDM2 (Hf) = 2 498 to 2 740 Ma in the second-stage model is enriched in large ion lithophile elements, depleted in high field strength elements Nb, Ta, P, Ti , And the Mg # values ranged from 45 to 47, suggesting that the rock samples were derived from the Lower Archean crustal melting. Combined with the contemporaneous magmatic distribution in the area, it is considered that the formation of the monzonitic granites in the Badoudou area is related to the subduction of the Paleo-Pacific plate to the Eurasian continent.