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滇西保山地块大地构造上位于藏-滇-泰-马中间板块中段,西以怒江-瑞丽断裂为界,东以澜沧江-柯街-南汀河断裂为界.由于缺乏出露的新生代花岗质岩石,传统上认为,在喜马拉雅期该地块花岗质岩浆活动微弱.因此,双脉地晚始新世隐伏花岗岩的发现,改写了该地块无喜马拉雅期花岗质岩浆活动的记录.对取自研究区ZK7-1和ZK0-1钻孔岩芯花岗岩样品锆石U-Pb年代学、地球化学和Sr-Nd-Pb同位素研究表明:(1)双脉地隐伏花岗岩岩石类型为中粗粒二云母正长花岗岩,岩体以高SiO2低CaO为特征,总碱量(K2O+Na2O)为5.22%～8.03%,K2O/Na2O比率0.24～1.79;K,Rb,U,Th和Pb显示清晰正异常,Ba,Sr,Ti和Nb显示清晰负异常;具中等稀土元素含量(85～125μgg-1),中度富集轻稀土元素((La/Yb)=4.77～7.22),以及中度负Eu异常(δEu=0.29～0.39),属于高钾钙碱性-钙碱性强过铝S型花岗岩.(2)利用SHRIMP锆石U-Pb同位素定年获得上述两类岩石的岩浆结晶年龄分别为(36.27±0.48)和(35.78±0.49)Ma,成岩年代为晚始新世.(3)Sr-Nd-Pb同位素组成表明双脉地二云母正长花岗岩源岩来自成熟大陆地壳物质,具有典型S型花岗岩特征.(4)花岗岩样品w(CaO)/w(Na2O)和w(Al2O3)/w(TiO2)比值及其在w(CaO)/w(Na2O)-w(Al2O3)/w(TiO2)图上分布表明,其岩浆来自地壳富粘土质物质的部分熔融,其熔融温度约为900～950℃;依据锆浓度饱和温度计计算岩浆结晶温度775～795℃;在Hf-Rb-Ta微量元素判别图解上,花岗岩样品分布于后碰撞构造环境.(5)在喜马拉雅后碰撞造山阶段,伴随印度大陆向欧亚大陆的持续楔入,印支地块(或保山地块)向南东方向逃逸,作为地块西界的高黎贡断裂带发生大规模走滑剪切作用,并触发加厚地壳减压部分熔融形成过铝花岗质岩浆,然后冷凝结晶形成双脉地二云母正长花岗岩.
The Baoshan block in western Yunnan is located in the middle section of the Tibet-Yunnan-Tai-Ma intermediate plate, bordered by the Nujiang-Ruili fault in the west and the Lancang-Kejie-Nandinghe fault in the east. Due to the lack of exposed Cenozoic Granitic rocks have traditionally been thought to have a weak activity of granitic magmatism during the Himalayan period.Therefore, the discovery of the Late Eocene horizonal granitoid in the Himalayas altered the Himalayan granitic magmatic activity in the block The zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotopic studies of zircons from core samples of ZK7-1 and ZK0-1 boreholes from the study area indicate that (1) the two-veined buried granitic rock type Is medium-coarse-grained mica-hosted granite. The rock mass is characterized by high SiO2 and low CaO. The total alkali content (K2O + Na2O) is 5.22% ~ 8.03% and the K2O / Na2O ratio is 0.24 ~ 1.79. K, Rb, U, Th And Pb showed clear positive anomalies, and Ba, Sr, Ti and Nb showed clear negative anomalies. With moderate REE content (85 ~ 125μgg-1) and moderate REE content ((La / Yb) = 4.77 ~ 7.22) , And moderately negative Eu anomalies (δEu = 0.29 ~ 0.39), belonging to high K calc-alkaline-calc-alkaline Al-rich S-type granites. (2) The above two types of zircons were obtained by dating SHRIMP zircon U-Pb isotope The magmatic ages of the rocks are (36.27 ± 0.48) and (35.78 ± 0.49) Ma, respectively, and the diagenetic age is late Eocene. (3) The Sr-Nd-Pb isotopic composition indicates that the dual- (4) The ratio of w (CaO) / w (Na2O) and w (Al2O3) / w (TiO2) to the content of w (CaO) / w The distribution of w (Al2O3) / w (TiO2) shows that the magma comes from the partial melting of crustally clay - rich matter and the melting temperature is about 900-950 ℃. The magma crystallization temperature is 775-795 ℃ according to the zirconium saturation thermometer. In the Hf-Rb-Ta trace element discrimination scheme, the granite samples are distributed in the post-collision tectonic setting. (5) During the post-collision orogeny of the Himalayas, with the continuous wedging of the Indian continent to Eurasia, the Indo-China block Massif) to the south-easterly direction as a large-scale strike-slip shear of the Gaoligong fault zone in the western boundary of the block and triggered the partial melting of the thickening crust to form peraluminous granitic magma and then condense and crystallize Two-pulse to two mica is the long granite.