江南造山带九岭南缘宜丰岩组火山岩锆石SHRIMP年代学及Hf同位素特征  

Zircon SHRIMP geochronology and Hf isotopic characteristics of volcanic rocks from the Yifeng Formation in the southern margin of the Jiuling uplift in the Jiangnan orogen

作　　者：周效华[1] 陈荣[1] 张炜[1] 李春海[1] 高天山[1] 马雪[1] 朱清波[1] 靳国栋[1] ZHOU Xiaohua;CHEN Rong;ZHANG Wei;LI Chunhai;GAO Tianshan;MA Xue;ZHU Qingbo;JIN Ouodong(Nanjing Center,China Geological Survey,Nunjing,210016)

机构地区：[1]中国地质调查局南京地质调查中心,南京210016

出　　处：《地质学报》2019年第5期1069-1080,共12页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号121201008000160903;12120114039001);国家重点研发计划(编号2016YFC06002000)资助成果

摘　　要：赣西北九岭南缘宜丰岩组是江南造山带的一个重要地层单元,但其沉积时限和区域地层对比关系尚不确定。本次1∶5万区调工作中,在万载—宜丰一带宜丰岩组地层中发现有呈夹层产出的变英安岩、变凝灰岩。SHRIMP锆石定年表明,变英安岩、变凝灰岩分别形成于835.0±7.8Ma和830.3±9.5Ma。结合宜丰岩组底部凝灰质砂岩最年轻的一组碎屑锆石U-Pb年龄852.9±2.6Ma,认为宜丰岩组沉积时限为～853 Ma至～830Ma,表明宜丰岩组主体形成于新元古代早期。锆石Hf同位素显示,ε_(Hf)(t)变化范围较大,为-16.02～+12.04,总体以正值为主。最为接近亏损地幔成分的5个锆石颗粒的ε_(Hf)(t)变化范围为+9.65～+12.04,具有最年轻的Hf二阶段模式年龄0.95～1.09Ga,与成岩年龄差距不大,表明源区中可能有新生地壳物质的加入。野外沉积学研究表明,宜丰岩组浊流沉积构造发育,主体属于半深海大陆斜坡沉积。区域上,宜丰岩组与溪口岩群、双桥山群、冷家溪群、西村岩组、南桥岩组、苍溪岩组沉积时限基本相当,沉积环境相似,应明确为华南"晋宁运动"不整合面之下的一套弧后盆地环境产物。The Yifeng Formationin the southern margin of the Jiuling uplift in northwestern Jiangxi is an important stratigraphic unit in the Jiangnan orogen,South China,but its depositional age and regional stratigraphic correlation is uncertain.During the 1∶50000 regional geological survey,intercalated metamorphic andesite and tuff was discovered in the Yifeng rock formation in the Wanzai-Yifeng area.SHRIMP zircon dating indicates that the metamorphic dacite and metamorphic tuff formed at 835+7.8 Ma and 830.3+9.5 Ma respectively.Combined with the youngest detrital zircon U-Pb age of 852.9+2.6 Ma for the tuff from the bottom of the Yifeng Formation,it can be believed that the Yifeng Formation deposited at ~853 Ma,indicating that the main rocks of the Yifeng Formation formed in the early Neoproterozoic.Zircon Hf isotope composition shows thatεHf(t)has a wide variation range from-16.02 to+12.04 and is generally positive.TheεHf(t)values of five zircons with most similar compositions of mantle-depleted mantle range from +9.65 to +12.04,and have the youngest Hf two stage mode age(TDM2)of 0.95~1.09 Ga,which is close to the diagentic age,indicating the new crustal materials may be involved in the provenance.Regionally,the field sedimentology study shows that the turbidite sedimentary structure of the Yifeng rock formation is well developed with the main rocks belonging to the bathyal deposition of continental slope.The Yifeng Group basically has similar sedimentary ages and similar sedimentary environment as the Xikou,Shuangqiaoshan,the Lengjiaxi,Xicun,Nanqiao and Cangxi groups have.It can be concluded that they should be the one set of back-arc basin sequence underlying the unconformities of the Jinning orogeny and overlying the Shuangxiwu arc strata in South China.

关 键 词：九岭南缘 宜丰岩组 火山岩 SHRIMP定年 Hf同位素 新元古代 江南造山带 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]