江西贵溪冷水坑晚侏罗世铁锰白云岩地层年龄及沉积环境  

THE U-Pb ZIRCON DATE AND SEDIMENTARY ENVIRONMENTS OF LATE JURASSIC Fe-Mn DOLOMITE IN LENGSHUIKENG OF GUIXI,JIANGXI PROVINCE

作　　者：钱迈平[1] 张宗言[1,2] 余明刚[1,3] 骆学全[1] 张雪辉[1] 孙建东[1,4] 段政[1] 

机构地区：[1]南京地质矿产研究所,江苏南京210016 [2]中国地质大学地球科学学院,湖北武汉430074 [3]南京大学地球科学与工程学院,江苏南京210046 [4]成都理工大学,四川成都610059

出　　处：《地层学杂志》2015年第4期380-394,共15页Journal of Stratigraphy

基　　金：中国地质调查局工作项目(1212011121099;12120113065200);国家自然科学基金青年科学基金项目(No.41002024)成果之一

摘　　要：江西贵溪冷水坑晚侏罗世打鼓顶组—鹅湖岭组火山碎屑建造中的铁锰白云岩,是一套火山角砾岩或集块岩,以层状或大型透镜体展布,是冷水坑特大型Ag-Pb-Zn矿田的重要赋矿层位。通过对其整合接触的上覆顶板、下伏底板晶屑凝灰岩锆石U-Pb同位素年代学研究显示：顶板年龄160.75±0.96Ma,底板年龄161.30±1.30Ma,确定这套铁锰白云岩形成于晚侏罗世Oxfordian期,成矿作用发生在燕山运动早期的火山喷发及热液作用时。铁锰白云岩中包裹体均一温度测定结果显示,其成岩温度在344.2℃~202.5℃之间。其中螺状硫银矿的存在,说明成矿温度低于173℃。稀土组分总量低,类似正常湖相沉积碳酸盐岩,但却含有大量正长质岩浆岩组分,说明并非正常湖相沉积。碳氧同位素分析显示的平均值：δ13 CPDB-6.108‰、δ18 OPDB-15.667‰、δ18 OSMOW-14.709‰,属无机成因为主的火山-岩浆及陆源碎屑沉积。未见有生物碎屑或动物遗迹,但可见少量微生物沉积构造,而且上、下均与火山岩整合接触,属火山凹地湖泊环境,受火山作用影响强烈,湖水富Fe、Mn、S、Si等,不利于较高等的动植物生存,但铁细菌、硫细菌及蓝细菌等低等微生物可以生存。铁锰白云岩呈磨圆、分选均差的角砾状,是火山爆发炸碎或震碎后原地堆积而成。The Fe-Mn Dolomite layered or large lensoid bodies in volcano clastic formation from Late Jurassic Daguding and Ehuling formations is a volcano breccia or agglomerate,and important ore-bearing strata of the Lenshuikeng Ag-Pb-Zn Ore Field,Guixi city,Jiangxi Province.The U-Pb age of crystal tuffs from the top and bottom of the Fe-Mn Dolomite in Daguding Formation are 160.75±0.96 Ma and 161.30±1.30 Ma respectively,and indicat the Fe-Mn Dolomite formed during Oxfordian Period of Jurassic,and the mineralization occurred during volcano erupting and hydrothermal acting in early Yanshan Movement.The determination results of inclusion homogenization temperature from the Fe-Mn Dolomites breccias revealed that the diagenetic temperature is between 344.2 ℃ and 202.5 ℃,and acanthites in which indicate the mineralization temperature less than 173 ℃.Low content of the rare earth elements in Fe-Mn Dolomite breccias show it is similar to that of conventional lacustrine carbonates,but high content of the syenite magmatites in it suggest their forming is closely related to volcano actions.The average value of carbon and oxygen isopic compositions in the siderite and rhodochrosite ore breccias of Fe-Mn Dolomite areδ13CPDB-6.108‰;δ18 OPDB-15.667‰;δ18 OSMOW-14.709‰ respectively,and suggest that it mainly is a mixed sediments of volcano-magma and terrigenous clasts.There is no any biological detritus and animal remains seen,although a few laminated biogenic sedimentary structures formed by microbial mats.The Fe-Mn Dolomite are conformably contact with overlying and underlying volcanic strata,and it show that formed in volcano crater lakes,in which was rich in Fe,Mn,S,Si et al.,made against plants and animals living,although microbiota such as iron bacteria,sulfur bacteria and cyanobacteria et al.living there.The roundness and sorting of Fe-Mn Dolomite breccias is very poor,and it is an autochthonous cumulate broke by volcanic erupting

关 键 词：年代地层 铁锰白云岩 锆石U-Pb年龄 沉积环境 晚侏罗世 贵溪 江西 

分 类 号：P534.52[天文地球—古生物学与地层学]