大兴安岭中北段老道口闪长岩锆石U-Pb年龄、地球化学特征及构造意义

发布时间：2019-01-08 10:57

【摘要】：鄂伦春自治旗老道口闪长质岩体位于兴蒙造山带东段、大兴安岭中北段,原定义为老道口单元的老道口岩体主要由闪长岩、石英二长岩和闪长玢岩组成。锆石SIMS U-Pb定年测定闪长岩年龄为(126.09±0.95)Ma,属于早白垩世岩浆活动的产物,并非前人认为的形成于寒武纪。闪长岩的w(SiO_2)为56.13%~57.91%,w(TiO_2)为0.97%~0.99%,w(MgO)和w(TFe_2O_3)分别为2.00%~2.12%和6.73%~7.41%,Mg#值为36.00~38.00,w(Na_2O)为4.29%~4.53%,w(K2O)为1.38%~1.59%,K_2O/Na_2O为0.31~0.37,w(Al_2O_3)为17.95%~18.36%,相对富钠高铝,稀土元素球粒陨石标准化曲线显示其具有富含轻稀土元素(LREE)、贫重稀土元素(HREE)以及Eu(0.85~0.87)弱负异常的特点。老道口闪长岩强不相容元素Th、U、K显著富集和高场强元素Nb、Ta明显亏损,其岩浆源区可能为俯冲流体交代的岩石圈地幔。闪长岩富集Ba、K、Rb、Th、U等大离子亲石元素,高场强元素Nb、Ta、Ti、P等明显亏损,指示了与俯冲作用相关的地球化学特征。结合老道口岩体地球化学特点和区域构造背景,认为该岩体很可能形成于蒙古—鄂霍茨克洋闭合造山后的岩石圈伸展构造环境。
[Abstract]:The Laodokou diorite is located in the eastern part of the Xingmeng orogenic belt and the northern part of the Daxingan Mountains. The Laodokou rock mass, which was originally defined as the Laodokou unit, is mainly composed of diorite, quartz monzonite and diorite porphyrite. Zircon SIMS U-Pb dating of diorite ages of (126.09 卤0.95) Ma, is a product of early Cretaceous magmatism and is not considered to have been formed in the Cambrian. The SiO_2 of the diorite is 56.13 and the TiO_2 is 0.970.99.The (MgO) and TFe_2O_3 are 2.12% and 6.737.41%, respectively. The Mg# value of 36.00 and 38.00 (Na_2O) was 4.293.The value of K2O was 1.38 and the value of K2O was 1.59. the Mg# value was 0.310.37W (Al_2O_3) 17.9556.36. Compared with the rich sodium and high aluminum, the normalized curves of chondrites show that chondrites are rich in (LREE), rich in light rare earth elements, poor in (HREE) and weak negative anomalies in Eu (0.85 ~ 0.87). In Laodokou diorite, strong incompatible element Th,U,K is significantly enriched and high field strength element Nb,Ta is depleted. Its magmatic source may be subducted fluid metasomorphic lithospheric mantle. The diorite is rich in large ion lithophile elements such as Ba,K,Rb,Th,U, and the high field strength element Nb,Ta,Ti,P is depleted, indicating the geochemical characteristics related to subduction. Based on the geochemical characteristics and regional tectonic setting of the Laodokou rock body, it is considered that the rock body was probably formed in the lithospheric extensional tectonic environment after the closed orogenic of the Mongolia-Okhotsk Ocean.
【作者单位】：吉林大学地球科学学院;东北亚矿产资源评价国土资源部重点实验室;黑龙江省区域调查研究所;
【基金】：国家重点基础研究发展计划项目(“973”计划项目)(2013CB429802) 中国地质调查局项目(12120115001001-08) 东北亚矿产资源评价国土资源部重点实验室开放基金项目~~
【分类号】：P597.3;P588.122

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