浙西北建德地区休宁组沉积时限的厘定:来自凝灰岩锆石U-Pb年代学的制约  

Depositional age of the Xiuning Formation in the Jiande Area,northwestern Zhejiang Province:constraints from U-Pb zircon tuff geochronology

作　　者：邓奇[1,2] 汪正江 杨菲[1] 崔晓庄[1] 王剑[1,2] 任光明[1] 周效华 熊小辉[1] 蔡娟娟[1] DENG Qi;WANG Zhengjiang;YANG Fei;CUI Xiaozhuang;WANG Jian;REN Guangming;ZHOU Xiaohua;XIONG Xiaohui;CAI Juanjuan(Chengdu Center,China Geological Survey,Chengdu,610081;Key Laboratory for Sedimentary Basin and Oil and Gas Resources,Ministry of Land and Resources,Chengdu,610081;Nanjing Center,China Geological Survey,Nanjing,210016)

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]自然资源部沉积盆地与油气资源重点实验室,成都610081 [3]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2期414-427,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(批准号:41772115;41372124;41502114;41672112);中国地质调查局项目(编号:DD20160193)联合资助的成果

摘　　要：浙西北建德地区休宁组(原称志棠组)是华南新元古代的重要地层单元之一,但其沉积时限和区域对比关系长期存在争论。本文对采自休宁组下部和上部的凝灰岩进行了LA-ICP-MS锆石U-Pb定年,获得两件凝灰岩样品的形成年龄分别为785.0±2.8Ma(MSWD=0.85,n=37)和727.5±7.3Ma(MSWD=0.64,n=7)。结合前人研究成果认为,休宁组沉积时限为～800Ma至～728Ma;野外沉积学研究表明,休宁组沉积构造发育,主体属于正常气候条件下的冲积扇和滨浅海(湖)沉积,非南华冰期地层;区域上,休宁组与板溪群及其相当地层的中上部、莲沱组、苏雄组/开建桥组、澄江组沉积时限基本相当,与下冰期(Sturtian冰期)长安组不存在对比关系,应明确为华南"四堡造山运动"不整合面之上、南华冰期之下的一套裂谷充填序列。The Xiuning Formation(formerly known as the Zhitang Formation)developed in Jiande area,northwestern Zhejiang Province,is one of the most important Neoproterozoic stratigraphic units in South China block.However,its depositional age and regional correlation have been debated for a long time.Our LA-ICP-MS zircon U-Pb dating results show that tuff samples from Lower and Upper part of the Xiuning Formation produce U-Pb ages of 785.0±2.8 Ma(MSWD=0.85,n=37)and 727.5±7.3 Ma(MSWD=0.64,n=7),respectively.A synthesis of available data suggests that the sedimentary time interval of the Xiuning Formation spans ca.70 Ma from?800 Ma to?728 Ma.Field observations show that shallow water sedimentary structures occur abundantly in the Xiuning Formation,suggesting a dominant alluvial fan and offshore to shallow sea(lake)rather than glacial depositional environment.Regionally,the depositional period of Xiuning Formation is synchronous with the Banxi Group,Liantuo Formation,Suxiong Formation(Kaijianqiao Formation),and Banxi Group but predates the glaciogenic Chang’an Formation.It should be defined as a set of rifting filling sequences overlying the unconformities of the Sibao Orogeny and underlying the Nanhua glaciogenic strata in South China.

关 键 词：浙西北 休宁组 凝灰岩 锆石U-PB定年 新元古代 

分 类 号：P534.3[天文地球—古生物学与地层学] P588.2[天文地球—地质学] P597.3