西秦岭三叠纪大河坝组砂岩构造背景与物质来源  

Tectonic Setting and Provenance of Sandstones from Triassic Daheba Formation in the West Qinling Orogenic Belt

作　　者：李康宁 汤庆艳 栾晓刚 王玉玺 邓小华 杨宗枫 LI Kangning;TANG Qingyan;LUAN Xiaogang;WANG Yuxi;DENG Xiaohua;YANG Zongfeng(School of Earth Sciences,Lanzhou University,Lanzhou 730000,Gansu,China;Third Institute Geological and Mineral Exploration of Gansu Provincial Bureau of Geology and Mineral Resources,Lanzhou 730050,Gansu,China;Binghua Mining Limited Liability Company of Xiahe County,Gannan 747100,Gansu,China;School of Earth Science and Resources,Chang’an University,Xi’an 710064,Shaanxi,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃兰州730000 [2]甘肃省地质矿产勘查开发局第三地质矿产勘查院,甘肃兰州730050 [3]夏河县冰华矿业有限责任公司,甘肃甘南747100 [4]长安大学地球科学与资源学院,陕西西安710064

出　　处：《西北地质》2024年第3期113-127,I0002,共16页Northwestern Geology

基　　金：甘肃省重点人才项目(2023)“金川超大型铜镍硫化物矿床钴元素赋存状态及成矿机制研究”;自然资源部黄河上游战略性矿产资源重点实验室开放课题资助项目(YSMRKF202201);甘肃省科技计划(22YF7GA050);甘肃省地质勘查基金项目(202202-D01);甘肃省自然资源厅科技创新项目(202201)联合资助。

摘　　要：大河坝组是西秦岭夏河–碌曲地区出露最晚的一套海相地层,记录了印支期海退事件。笔者基于大河坝组层序特征、砂岩主微量元素成分和碎屑锆石U-Pb年龄基础上,探索其物质来源特征和构造背景指示意义。大河坝组主体为砂板岩复理石建造,包括长石砂岩、岩屑长石砂岩、含砾岩屑长石砂岩等。其中,砂岩具有中等SiO_(2)(64.11%~68.27%,平均为65.45%),较高Al_(2)O_(3)(13.61%~15.19%,平均为14.51%),较低Fe2O_(3)(0.82%~1.72%,平均为1.25%)、CaO(2.39%~3.32%,平均为3.06%)、MgO(0.06%~0.10%,平均为0.08%)特征。稀土元素总量较高,ΣREE值为184×10^(-6)~434×10^(-6),平均为252×10^(-6)。球粒陨石标准化图解中显示Eu负异常,具有与活动大陆边缘环境相似的Th、Zr、Ti、Co、Ni等微量元素含量。砂岩中碎屑锆石U-Pb年龄主要为2204~2520 Ma、1536~2067Ma、253.3~448.7Ma等3个阶段,在2445Ma、1986.4Ma、1757.6Ma、448.5Ma、278.2Ma等5个年龄段出现峰值,锆石最小年龄为253.3 Ma。砂岩主微量元素分析和碎屑锆石U-Pb年代学谱系显示,大河坝组源区构造环境为活动大陆边缘,碎屑物质来自上地壳中性火成岩,主要物源区为研究区北部北秦岭构造带、祁连造山带东段和华北板块南缘基底,少部分碎屑来自西秦岭同期岩浆岩和多旋回沉积物。The Daheba formation is the latest strata exposed in the Xiahe-Luqu area of the West Qinling Oro-genic Belt(WQOB),with recording the Indosinian regression event.In this study,based on the stratigraphic se-quence characteristics,major and trace element compositions and zircon U-Pb dating of the sandstone,we traced the origin of the sandstone and explored the tectonic settings of the Daheba Formation.The Daheba Formation consists of feldspar sandstone,lithic feldspar sandstone,conglomerate clastic feldspar sandstone.The SiO_(2) con-tent of sandstone range from 64.11%to 68.72%with an average of 65.45%.The sandstones are also character-ized by high Al_(2)O_(3)(13.61%~15.19%),lower Fe2O_(3)(0.82%~1.72%),CaO(2.393%~3.32%)and MgO-6(0.06%~0.1%)contents.They have high rare earth elements(REE)range from 184.13×10 to 434.06×10^(-6),and show negative Eu anomaly in the chondrite normalized diagram.They also have similar Th,Zr,Ti,and Co,Ni compositions with that of active continental margin sediments.The detrital zircon U-Pb ages from the sand-stones are mainly concentrated in 253.3~448.7 Ma,1536~2067 Ma and 2204~2520 Ma,and show five age peaks at 278.2 Ma,448.5 Ma,1757.6 Ma,1986.4 Ma and 2445 Ma,with the youngest ages at 253.3 Ma.These indicates that the Daheba Formation was deposited in an active continental margin setting,and the detritus origi-nated from the upper crust igneous rocks.The main sources for the detritus is possibly of the basement of the northern Qinling,the eastern part of the Qilian,and the southern edge of the North China Plate in the northern parts of the study area with small parts from the magmatic rocks and polycyclic sediments in the West Qinling.

关 键 词：大河坝组 碎屑锆石 构造环境 物源 西秦岭造山带 

分 类 号：P597[天文地球—地球化学]