西藏雄村铜金矿区侏罗系砂岩地球化学特征:对构造背景的约束

发布时间：2018-05-30 09:36

本文选题：雄村 + 岛弧　；参考：《地质学报》2017年09期

【摘要】：西藏雄村铜金矿区位于冈底斯造山带中段南缘,其南紧邻雅鲁藏布缝合带(IYS)和日喀则弧前盆地,北为谢通门始新世大岩基。通过对雄村矿区砂岩进行系统的镜下鉴定,主量、微量元素分析,揭示雄村组砂岩构造背景和物源属性。研究结果显示,雄村砂岩样品SiO_2含量53.27%~66.13%,平均含量58.27%,与古生代杂砂岩(66.1%)相近。Al_2O_3含量较高(14.53%~24.04%),平均20.12%,指示砂岩长石矿物较多且黏土化较强。综合微观特征,雄村砂岩为长石岩屑砂岩。主量元素中特征氧化物组合Fe2O3+MgO(7.3%~17.6%)、TiO_2(0.68%~1.25%)、Al_2O_3/SiO_2(0.22%~0.45%)与大洋岛弧成因砂岩值相似;微量元素蛛网图上雄村砂岩相对亏损Ta、Nb、P、Ti及HREE等高场强元素而富集K、Rb、U、REE等大离子亲石元素,REE球粒陨石标准化后具有轻稀土富集而重稀土元素较平坦的右倾分布模式。特征微量元素Th(2.5×10~(-6))、Zr(114×10~(-6))、Hf(3.6×10~(-6))、Ce(27.95×10~(-6))、Ti(0.54×10~(-6))含量及Th/U(2.9)、Zr/Th(46)、La/Sc(0.72)、Th/Sc(0.11)比值表明雄村砂岩具有大洋岛弧成因性质,La-Th-Sc、Th-Sc-Zr/10、Th-Co-Zr/10等判别图解显示砂岩形成源区可能位于大洋岛弧环境。稀土元素页岩标准化后具有弱负Ce异常及正Eu异常,指示砂岩受海水及深部热液双重影响,同样与大洋岛弧环境页岩标准化后特征相似。Co/Th-La/Sc和La/Th-Hf图解表明雄村砂岩物源区为长英质中酸性火山岩源区和安山质火山弧源区,结合他人对砂岩中碎屑锆石的年龄研究,认为雄村矿区砂岩没有早于晚三叠世的碎屑锆石,具有岛弧火山岩源区特点。
[Abstract]:Xiongcun copper and gold deposit area in Tibet is located in the southern margin of the Gangdis orogenic belt, adjacent to the Yalu Zangbo suture zone (IYS) and Xigaze forearc basin, and to the north is the large Eocene rock base of Xetongmen. The structural background and provenance attributes of Xiongcun formation sandstone are revealed by means of systematic microscopic identification, principal quantity and trace element analysis of the sandstone in Xiongcun mining area. The results show that the SiO_2 content of Xiongcun sandstone sample is 53.270.66.13 and the average content is 58.27, which is similar to that of Paleozoic impurity sandstone (66.1). The content of Al _ 2O _ 2O _ 3 is higher. The content of Al _ 2O _ 2O _ 3 is higher, with an average of 20.12, indicating that the sandstone has more feldspar minerals and stronger clay. Comprehensive microscopic characteristics, Xiongcun sandstone is feldspar lithic sandstone. The characteristic oxide assemblage Fe2O3 MgO7.3in the principal elements is 17.6T / TiO2S / 0.68 / 1.25 / T / T / Al2O3 / SiO20.22T / 0.45T), which is similar to the value of oceanic island arc origin sandstone; The sandstones of Xiongcun on the cobweb of trace elements are relatively depleted of high field strength elements such as Tahln NbPU Ti and HREE, and enriched with large ion lithophile elements, such as HREE, etc. After standardization, the REE chondrites have a pattern of light rare earth enrichment and flat right-dip distribution of heavy rare earth elements. The characteristic trace element Th(2.5 脳 10 ~ (10) ~ (-6) and the ratio of Th / T ~ (2. 9) ~ (2. 9) ~ (2. 9) La ~ (Sc) ~ (0.72) ~ (2) ~ (2) 2 ~ (2) O ~ (2 +) ~ (1) ~ (0. 11) indicate that the sandstone of Xiongcun has the genetic properties of oceanic island arc, La-Th-Sctc / Thc-Th10Zr-Zr10, and so on, indicating that the source area of the sandstone may be located in the oceanic arc environment, such as La-Th-Sctr. Th-Zr-Zr10 / Zr10. 10% -Zr10 / Zr10. The results show that the source area of the sandstone may be located in the oceanic arc environment, and the results show that the source area of the sandstone may be located in the oceanic arc environment. The REE shale is characterized by weak negative ce anomaly and positive EU anomaly after standardization, indicating that sandstone is affected by both seawater and deep hydrothermal solution. Also similar to the characteristics of shale normalized in oceanic island arc environment. Co-% Th-La-Sc and La/Th-Hf diagrams show that the source of Xiongcun sandstone is the source of felsic intermediate-acid volcanic rock and the source of Anshan volcanic arc. The age of clastic zircon in sandstone is studied in combination with others. It is considered that the sandstone in Xiongcun mine has no clastic zircon earlier than the late Triassic and has the characteristics of island arc volcanic source.
【作者单位】：成都理工大学地球科学学院;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;西藏天圆矿业资源开发有限公司;西藏大学工学院;中国地质调查局成都地质调查中心;中国地质大学地球科学与资源学院;
【基金】：大陆构造与动力学国家重点实验室开放基金重点项目(编号K201401) 国家自然科学基金项目(编号41502079;41172077) 四川省青年基金项目(编号2014JQ0047) 四川省教育厅自然科学重点项目(编号15ZA0073) 地调项目(编号12120114068401)联合资助成果
【分类号】：P618.41;P618.51

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