湖南岳阳-湖北通城地区1∶5万区域地质调查成果与主要进展

New Progress in 1:50000 Reginal Geological Survey in Yueyang,Hunan Province-Hubei Province Tongcheng Area

岳阳-通城地区完成的1∶5万区域地质调查,以国际年代地层表(2018)为指南,重新厘定了研究区地层序列,建立了多重地层划分与对比系统。岩石学、地球化学及年代学研究表明冷家溪群黄浒洞组形成于青白口纪早期(~824 Ma),为弧后盆地沉积。首次于原富禄组中发现一平行不整合面,并根据疑源类化石组合、碎屑锆石年龄,将其修正为五强溪组、多益塘组与富禄组,岳阳刘家庄、张辉山等地于富禄组中首次识别出冰水沉积。根据岩浆岩岩性特征、野外接触关系及同位素年龄将区内岩浆岩体划分为8个填图单位,均获得了高精度锆石U-Pb年龄数据,确定了岩浆岩成岩时代与活动期次,并结合岩石地球化学特征探讨了岩石成因及大地构造背景。按特征矿物差异将幕阜山地区花岗伟晶岩分为:电气石伟晶岩→电气石-绿柱石伟晶岩→绿柱石伟晶岩→绿柱石-铌钽铁矿伟晶岩→铌钽铁矿-锂电气石-锂云母伟晶岩5类,对应稀有金属富集的五个阶段:无矿化→含Be→富Be→富Be、Nb、Ta→富Be、Nb、Ta、Li。断峰山地区部分伟晶岩演化至第四阶段,具有较大的稀有金属找矿潜力。

A sheet of 1:50,000 regional geological survey was recently completed in the Yueyang Hunan Province-Hubei Province Tongcheng area.Guided by the latest international chronostratigraphic chart,the stratigraphic sequences were redefined and multiple stratigraphic division and correlation were established in the study area.Petrology,geochemistry,and chronology indicated that the Huanghudong Formation of the Lengjiaxi Group was deposited in back-arc basin during Early Qingbaikou Period(~824 Ma).A parallel unconformity surface was first found in the previous Fulu Formation,and it was revised into Wuqiangxi,Duoyitang Formation and Fulu Formation according to the provenance fossil assemblage and detrastic zircon age.Aqueoglacial deposits were also newly recognized in the new Fulu Formationat the Liujiazhuang and Zhanghuishan area of Yueyang region.Using the lithologic characteristics,field contact relationships and isotope ages of magmatic rocks,the magmatic rocks can be divided into eight mapping units.In each unit,the high precision zircon U-Pb age were obtained.Furthermore,active periods of magmatic rocks were determined,and the petrogenesis and geotectonic background were demonstrated.There are five types of granite pegmatite in the Mufushan area,which show a transition from tourmaline pegmatite,to tourmaline-beryl pegmatite,to beryl pegmatite,to beryl-niobium-tantalite pegmatite,and niobium tantalite-lithium tourmaline-lithium mica pegmatite,corresponding to the five stages of rare metal enrichment,i.e.,no mineralization,involved Be,rich in Be,rich in Be,Nb and Ta,and rich in Be,Nb,Ta,and Li.Some of granite pegmatites in the Duanfengshan area evolved into the fourth stage,showing a well prospecting potential of rare metal resources.