桂北地区丹洲群碎屑锆石LA-ICP-MS U-Pb年龄和Hf同位素特征及其地质意义  

LA-ICP-MS U-Pb dating and Hf isotopes of detrital zircon grains from siltstone of Danzhou Group in northern Guangxi and their geological significance

作　　者：寇彩化[1] 刘燕学[1] 李廷栋[1] 黄河[1] 张恒[1] KOU Caihua;LIU Yanxue;LI Tingdong;HUANG He;ZHANG Heng(Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质通报》2017年第8期1393-1406,共14页Geological Bulletin of China

基　　金：国家自然科学基金项目<江南造山带西段桂北新元古代基性-超基性岩岩石成因研究及其对构造演化的约束>(批准号:41402052);中国地质科学院基本科研业务<湘西新元古代基性-超基性岩岩石年代学及成因研究>(编号:J1602);中国地质调查项目<中国区域地质志>(编号:1212011120117)

摘　　要：桂北丹洲群顶部拱洞组粉砂岩的碎屑锆石的阴极发光图像和Th/U(0.2~2.4)值显示,它们均为岩浆成因的锆石。锆石^(206)Pb/^(238)Pb年龄分布在730~769Ma和771~850Ma之间,这些锆石的Hf同位素成分范围较大,ε_(Hf)(t)值和二阶段Hf模式年龄(T_(DM2))分别为-18.4~11.4和1020~2812Ma。此外,样品中还有一些年龄较老的锆石颗粒,^(207)Pb/^(206)Pb年龄为1910~3140Ma,ε_(Hf)(t)值和二阶段Hf模式年龄(T_(DM2))分别为-13.6~3.4和2740~3635Ma。结合前人的研究推测,桂北丹洲群拱洞组沉积年龄小于等于706±10Ma,物源主要由扬子板块新元古代岩浆岩组成,也有少量太古宙岩浆岩的加入。推测中国华南地区存在对应于Rodinia超大陆聚合相关的格林威尔运动的响应。根据已测锆石的ε_(Hf)(t)值和Hf二阶段模式年龄推断,研究区地壳生长主要经历3个阶段:(1)3.64~3.25Ga,初生地壳出现在3.64Ga;(2)2.98~2.37Ga;(3)2.19~1.28Ga,地壳生长的主要时期。This paper reports LA-ICP-MS U-Pb dating and Hf isotopes for detrital zircon grains of siltstone from Gongdong Formation at the top of the Danzhou Group.The majority of zircon grains are transparent,euhedral and prismatic crystals with oscillatory zoning in CL images and have high Th/U ratios of0.2~2.4,indicating an igneous origin for the zircon.The206Pb/238Pb age distributions for the detrital zircon grains mainly range from730Ma to769Ma and771Ma to850Ma,andεH(f t)and two-stage Hf model ages(TDM2)range from-18.4to11.4and from1020Ma to2812Ma,respectively.Moreover,there are some detrital zircon grains with relatively older ages with206Pb/238Pb ages from1910Ma to3140Ma,andεH(f t)and TDM2from-13.6~3.4and2740~3635Ma,respectively.Combined with previous researches,the authors infer that the maximum depositional age of the Gongdong Formation from Danzhou Group is706±10Ma.The source region was predominated by Neoproterozoic magmatic rocks from Yangtze Block(ca.750~830Ma)with the mixture of minor Archean magmatic rocks.There was developed the Greenville movement in South China resulting from the assembly of Rodinia supercontinent.In addition,on the basis of theεH(f t)and TDM2data of the detrital zircon grains,the authors hold the existence of three stages for the crust growth in the study area:①3.64Ga to3.25Ga,with the juvenile crust at3.64Ga;②2.98Ga to2.37Ga;③2.19Ga to1.28Ga.

关 键 词：桂北丹洲群 碎屑锆石LA-ICP-MSU-Pb定年 HF同位素 RODINIA超大陆 地壳生长 

分 类 号：P597.3[天文地球—地球化学] P534.3[天文地球—地质学]