| 滇西北剑川盆地新近系地层时代的新认识及构造意义 |
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| 引用本文： | 王书兵,蒋复初,田国强,傅建利,李朝柱.滇西北剑川盆地新近系地层时代的新认识及构造意义[J].第四纪研究,2020(1):28-39. |
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| 作者姓名： | 王书兵 蒋复初 田国强 傅建利 李朝柱 |
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| 作者单位： | 活动构造与地壳稳定性评价重点实验室;中国地质科学院地质力学研究所 |
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| 基金项目： | 国家自然科学基金项目(批准号:41472327);中国地质调查局项目(批准号:1212011120165)共同资助。 |
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| 摘 要： | 地处板块接触地带的滇西北剑川地区是研究新构造运动的重要场所。剑川盆地保留有较为完整的新生代地层,在1:250000地质图上,新生界自下而上为古新统勐野井组、始新统宝相寺组、渐新统金丝厂组、中新统双河组和上新统剑川组;其中双河组为一套含可采煤层的砂泥岩夹泥灰岩沉积,剑川组为一套火山-沉积岩组。近期的研究揭示双河组和剑川组均属始新世,但发表的年龄相互包含,并没有清楚的把两者分开。本文采用Ar-Ar和锆石U-Pb方法测试了双河组和剑川组顶、底凝灰岩的年龄,辅以岩体、岩脉的年龄,重新厘定了两个组的顶、底年龄。剑川组顶部凝灰岩锆石SHRIMP U-Pb年龄为34 Ma±;底部凝灰岩黑云母Ar-Ar坪年龄为36 Ma±,与底部侵入岩脉的锆石SHRIMP U-Pb年龄一致;中上部侵入岩脉的黑云母Ar-Ar坪年龄在34~36 Ma之间。同时,老君山岩体、玉召块岩体和沙帽山岩体的锆石SHRIMP U-Pb年龄在34~35 Ma之间。剑川火山-沉积岩组的年龄集中在34~36 Ma之间,属始新世晚期。剑川双河煤矿矿部至三家村及五家村一带,双河组之下新发现一套凝灰岩,其黑云母Ar-Ar坪年龄和锆石SHRIMP U-Pb年龄均为37 Ma±,表明双河组的起始年代不超过37 Ma;双河组形成于36~37 Ma之间,也属始新世晚期。新的结果表明剑川盆地始新统地层应包括宝相寺组、金丝厂组、双河组和剑川组,缺失渐新统沉积。结合其他盆地的年龄数据,表明剑川乃至整个云南地区在渐新世期间为褶皱隆起期。
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| 关 键 词： | AR-AR年龄 锆石SHRIMP U-PB年龄 始新世 剑川组 双河组 剑川盆地 |
NEW INSIGHTS INTO NEOGENE STRATIGRAPHIC AGE IN THE JIANCHUAN BASIN,NORTHWEST YUNNAN AND ITS TECTONIC SIGNIFICANCE |
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| Institution: | (Key Laboratory of Active Tectonics and Crustal Stability Assessment,Beijing 100081;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081) |
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| Abstract: | Jianchuan area,located in plate contact zone in northwest Yunnan,with relatively complete Cenozoic strata in the Jianchuan Basin,is an important place for neotectonics study.According to the 1:250000 geological map,from bottom to top,the Cenozoic is composed of the Paleocene Mengyejing Formation,Eocene Baoxiangsi Formation,Oligocene Jinsichang Formation,Miocene Shuanghe Formation and Pliocene Jianchuan Formation.The Shuanghe Fm is formed with a set of sand-shale mixed with marl deposits,containing minable seam,and the Jianchuan Fm is a set of volcanic-sedimentary rocks.Recent studies have revealed that both the Shuanghe Fm and Jianchuan Fm belong to Eocene;however,the published ages are overlapped,and they don't separate the two.We use Ar-Ar and zircon U-Pb methods to test the ages of the tuff at the top and bottom of the Shuanghe Fm and Jianchuan Fm.Associating with the ages of the rock mass and dike,the ages of the two groups at the top and bottom are redetermined.In the Jianchuan Fm,the zircon SHRIMP U-Pb age of the tuff at the top is 34 Ma±;the Ar-Ar plateau age of the bottom tuff biomica is 36 Ma±,which is consistent with the zircon SHRIMP U-Pb age of the bottom intrusive dike;the biotite Ar-Ar plateau age of the upper middle intrusive rock dyke is between 34~36 Ma.In addition,the zircon SHRIMP U-Pb ages of the Laojunshan rock mass,Yuzhaokuai rock mass and Shamaoshan rock mass range from 34 Ma to 35 Ma.The age of the Jianchuan Fm is between 34~36 Ma,belonging to the Late Eocene.There is a set of newly discovered tuff under the Shuanghe Fm in the area from Jianchuan Shuanghe Coal Mining Department to Sanjia village and Wujia village,which clearly indicates that the Shuanghe Fm overlays it,and it can limit the initial age of the Shuanghe Fm.The biotite Ar-Ar plateau age and zircon SHRIMP U-Pb age of the tuff are both 37 Ma±,showing the initial age of the Shuanghe Fm is earlier than 37 Ma.The Shuanghe Fm was formed between 36~37 Ma,also belonging to the Late Eocene.Our research results show that the Eocene strata in the Jianchuan Basin include the Baoxiangsi Fm,Jinsichang Fm,Shuanghe Fm and Jianchuan Fm,and lack of the Oligocene deposits.Combined with the age data of other basins in Yunnan,it shows that the Jianchuan area and even the whole Yunnan are in the fold-uplift period during the Oligocene. |
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| Keywords: | Ar-Ar age zircon SHRIMP U-Pb age Eocene Jianchuan Formation Shuanghe Formation Jianchuan Basin |
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