大兴安岭北部新林地区大乌苏混杂岩锆石U-Pb年代学、地球化学及其地质意义

新林地区位于大兴安岭北部，处在塔源-新林-喜桂图断裂之上，西侧为额尔古纳地块，东侧为兴安地块。前人研究认为本区的“倭勒根群”为有序地层，通过野外观察及综合分析，认为本区地层是经历了多期次的变质变形作用，由多个构造岩块堆叠和拼贴起来的非史密斯地层单位。对新林地区大乌苏混杂岩的基质及岩块进行了碎屑锆石LA-ICP-MS U-Pb定年。测试结果显示，岩块中细碧岩的岩浆结晶年龄为（477.3±2.7）Ma，基质中变质石英砂岩的最小峰值年龄为468 Ma，限定其沉积时间为早奥陶世。而本地区二长花岗岩测年的结果为300 Ma，综合文献资料并结合本区构造特点，认为大乌苏混杂岩实际上是一套时间跨距从早奥陶世到晚石炭世的非史密斯地层。地球化学特征上，蛇绿岩残片低SiO₂，属钙碱性或拉斑玄武岩系列玄武岩；稀土元素球粒陨石标准化图解中Eu无异常或弱正异常，稀土元素总量变化较大；在微量元素原始地幔标准化图解中，富集Ba、K、Sr等大离子亲石元素，相对亏损Nb、Ta、Zr等高场强元素。可以推测在兴隆-呼玛弧后盆地进一步拉伸过程中，本区形成具有洋壳性质的大洋，同时在岛弧上形成细碧-角斑岩及中基性火山岩，在弧前形成砂泥质浊积岩。

Dawusu Complex of Xinlin District in Northern Greater Hinggan Mountains Zircon U-Pb Chronology,Petrogeochemistry,and Its Geological Implication

Xinlin district located in the Tayuan-Xinlin-Xiguitu fracture where the west side of Erguna block, the east side of Xing'an block, in northern Greater Hinggan Mountains. Previous research suggests that "Wolegen Group" belongs to the orderly strata. Through field observation and comprehensive analysis, this paper considers that the strata in this area belongs to Non Smith stratigraphic unit by a plurality of tectonic block stacked and collaged, that experienced many times of metamorphic deformation. This paper conducted detrital zircon LA-ICP-MS U-Pb dating on matrix and rock mass of Dawusu complex in Xinlin district. The test results show that the magmatic crystallization age of rock mass in the spilite is (477.3±2.7)Ma,and the minimum peak age of metamorphic quartz sandstone in the matrix is 468 Ma, limiting the deposition time of Early Ordovician. Then, the two granite of local district dating results for 300 Ma, the paper considers that the Dawusu complex is actually a set of Non Smith stratigraphy that age from the Early Ordovician to Late Carboniferous,by based on the literatures and combined with the structural characteristics of the area. Geochemical characteristics show that the the content of SiO₂ in ophiolite fragments is low, and it belongs to calc-alkaline or basalt of tholeiite series; The plots of chondrite-normalized REE patterns shows that Eu element is no abnormal or weak positive anomaly; The plots of primitive mantle-normalized trace element patterns shows that the oceanic crust is enriched in Nb,Ta,Zr and other large ion lithophile elements, depleted in Ba,K, Sr and other high field strength element. And it can be speculated that the nature of oceanic crust of the ocean formed in the area,the spilite-keratophyre and intermediate-basic volcanic rock formed in the island arc, and the sandy muddy turbidite formed in the fore-arc during Xinglong-Huma back-arc basin further stretching process.