江南造山带中段冷家溪群沉积物源及构造背景:以岳阳地区黄浒洞组为例  

Provenance and Tectonic Setting of Lengjiaxi Group in the Central Jiangnan Orogen: A Case Study of Huanghudong Formation, Yueyang Area

作　　者：田洋[1,2] 金巍 王晶 柯贤忠[1] 龙文国[1] Tian Yang;Jin Wei;Wang Jing;Ke Xianzhong;Long Wenguo(Wuhan Center of China Geological Survey,WwAaw 430205,China;Hubei Key Laboratory of Paleontology and Geological Environment Evolution,Wuhan 430205,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]古生物与地质环境演化湖北省重点实验室,湖北武汉430205

出　　处：《地球科学》2021年第4期1328-1348,共21页Earth Science

基　　金：中国地质调查局地质调查项目(Nos.DD20160031,DD20190050)。

摘　　要：为揭示江南造山带中段冷家溪群沉积物源与构造背景,选取湖南东北部岳阳地区黄浒洞组为研究对象,开展岩石学、沉积学、地球化学及锆石年代学研究工作.结果显示,黄浒洞组杂砂岩杂基含量高(常>25%),碎屑颗粒贫石英(25%~40%),富含长石(15%~25%)与岩屑(15%~30%),分选差,磨圆差-中等.全岩SiO_(2)含量(63.39%~72.88%,平均70.14%)中等,(Fe_(2)O_(3)^(T)+Mg O)*(6.04%~8.29%,平均6.81%)与TiO_(2)*(0.67%~0.92%,平均0.74%)含量较高,K_(2)O/Na_(2)O(0.84~2.35,平均1.43)比值高,Al_(2)O_(3)/SiO_(2)(0.17~0.28,平均0.20)比值低,最接近形成于大陆岛弧环境杂砂岩的特征值.样品具有中等ICV值(平均0.86)与CIA值(70~80),指示物源包含再循环的古老沉积物与第1次循环物质,且源区经历了中等化学风化作用.杂砂岩样品稀土元素含量较高(REE平均173.02×10^(-6)),具有与上地壳及PAAS相似的球粒陨石标准化配分型式,呈现轻稀土富集((La/Yb)_(N)平均7.32)、重稀土平坦、中度Eu负异常(Eu/Eu*0.58~0.70,平均0.66)特征,但与上地壳相比,明显富集重稀土((La/Yb)_(ucc)平均0.70).1件凝灰岩夹层样品的锆石LA-ICP-MS U-Pb年龄为824±3.1 Ma,指示黄浒洞组沉积于新元古代.结合前人研究成果,黄浒洞组杂砂岩低的结构与成分成熟度,北东东-南东向的古水流,特征元素含量、比值及各类物源与构造环境判别图解,综合表明江南造山带中段岳阳地区冷家溪群沉积于弧后盆地,接受来自北侧构造相对稳定、物源成熟度较高的扬子陆块内部与南侧构造活动较强烈、物源成熟度较低的大陆岛弧的双向物源供给.For revealing provenance and tectonic setting of Lengjiaxi Group in the central Jiangnan orogen,a synthetic study on petrology,sedimentology,geochemistry and zircon geochronology of Huanghudong Formation in Yueyang area was carried out.All greywacke samples are rich in matrix (mostly more than 25%),feldspar (15%-25%) and lithic fragments (15%-30%),poor in quartz (25%-40%),with poor sorting and poor-medium rounding.These samples are characterized by medium SiO_(2)(63.39%-72.88%,mean:70.14%) contents,high (Fe_(2)O_(3)^(T)+MgO)*(6.04%-8.29%,mean:6.81%) and TiO_(2)*(0.67%-0.92%,mean:0.74%) contents,high K_(2)O/Na_(2)O (0.84-2.35,mean:1.43) ratios,and low Al_(2)O_(3)/SiO_(2)(0.17-0.28,mean:0.20) ratios,resembling those of continental island arc greywackes.Their medium index of compositional variation (ICV,mean:0.86) and chemical index of alteration values (CIA,mean:70-80) demonstrate that the source contains recycled ancient sediments and first-cycle materials which underwent moderate chemical weathering.Greywackes have high contents inΣREE (mean:173.02×10^(-6)),with chondrite-normalized REE patterns similar to upper crust and PAAS,showing enriched LREE ((La/Yb)_(N) mean:7.32),subhorizontal HREE curves and moderate Eu (Eu/Eu*:0.58-0.70,mean:0.66) negative anomalies.However,compared to the upper crust,greywackes HREE contents are significantly enriched with an average (La/Yb)_(ucc)value of 0.70.LA-ICP-MS zircon U-Pb dating of one layered tuff sample yields zircon U-Pb age of 824±3.1 Ma.Low textural and compositional maturity,NEE-SE paleocurrent,contents and ratios of characteristic elements,provenance and tectonic discrimination diagrams of Huanghudong Formation greywackes,and combined with other geological observations,suggest that the Lengjiaxi Group of Yueyang area in the central Jiangnan orogen might be formed in a back-arc basin.The sources are of high compositional maturity from interior Yangtze block in stable tectonic setting in the north,and of low compositional maturity from continental island arc with str

关 键 词：物源 构造背景 地球化学 冷家溪群 江南造山带 

分 类 号：P534[天文地球—古生物学与地层学]