长江现代沉积物碎屑锆石U-Pb年龄及Hf同位素组成与物源示踪研究  

DETRITAL ZIRCON U-Pb DATING AND Hf ISOTOPE OF MODERN SEDIMENTS IN THE YANGTZE RIVER:IMPLICATIONS FOR THE SEDIMENT PROVENANCE

作　　者：何梦颖[1] 郑洪波[2] 贾军涛 

机构地区：[1]南京大学地球科学与工程学院表生地球化学教育部重点实验室,南京210093 [2]南京师范大学地理科学学院,南京210023 [3]中国石油大学地球科学与技术学院,青岛266580

出　　处：《第四纪研究》2013年第4期656-670,共15页Quaternary Sciences

基　　金：中国科学院战略性先导科技专项项目(批准号:XDB03020300);国家自然科学基金重点项目(批准号:40830107和41111140016);中国地调局大陆架科学钻探项目(批准号:CSDP2012-05)共同资助

摘　　要：为研究长江沉积物物质来源,对长江流域24个现代沉积物样品进行碎屑锆石U-Pb年龄测试,并对10个样品做Hf同位素分析,结果表明：长江河流沉积物的碎屑锆石多为岩浆成因。碎屑锆石U-Pb年龄主要有6组峰：2.4-2.6Ga,1.8-2.0Ga,700-1000Ma,400-550Ma,200-300Ma 和〈65Ma,其中200-300Ma和700-1000Ma为主要的两组峰。锆石U-Pb年龄谱系可区分出长江4个区段,即金沙江段、川江段、长江中游段和下游段,与地理分段相吻合。结合Hf同位素研究,可认为长江流域沉积物中生代-新生代的锆石主要来自松潘-甘孜褶皱带和秦岭造山带; 古生代的锆石多来自秦岭造山带; 元古代-太古代的锆石则多来自扬子克拉通、华夏地块和大别造山带。A total of 24 sand samples were collected in the mainstream and major tributaries of the Yangtze River drainage basin.The sample sites include the whole drainage,from the source ＂Tuotuohe＂ to the river mouth.Three samples were taken at the confluence of the mainstream and tributaries,avoiding potential contaminates.24 samples were dated by the LA-ICP-MS U-Pb technique and 10 samples were analyzed for Hf isotopes on the same spots of concordant grains.Our results show that most zircons are from igneous rocks,so the ages of these zircons could represent the time of their crystallization.The U-Pb age specturm define six age groups in mainstream of the Jinshajiang：2.4-2.6Ga,1.8-2.0Ga,700-1000Ma,400-550Ma,200-300Ma and 〈65Ma （Fig.7A-7D）,and two in the tributaries：700-900Ma and 100-300Ma（Fig.8A-8D）.There are four age groups in the Chuanjiang：2.4-2.6Ga,1.8-2.0Ga,700-1000Ma and 200-300Ma（Fig.7E-7G,Fig.8E-8F）.Among which,2.4-2.6Ga are enrichment in the Jialingjiang and Wujiang.Five age groups display in the mainstream of the Midstream：2.4-2.6Ga,1.8-2.0Ga,700-1000Ma,400-500Ma and 200-300Ma（Fig.7H-7K）,whereas 〈1Ga age population in the tributaries：700-900Ma,400-500Ma and 200-300Ma（Fig.8G-8I）.400-500Ma age range is the main group in the Midstream.The Downstream is a little similar with the Jinshajiang,and exist ca.1 % age younger than 65Ma,but 2.4-2.6Ga age group is minor（Fig.7L-7N）.According to the zircon U-Pb age,the Yangtze River can be divided into four segments,which is consistent with the geography division.Combined with the Hf isotope,it can be considered that zircons aged Mesozoic-Cenozoic were mainly from the Songpan-Garze terrane,and zircons dating Paleozoic were from Qinling orogenic belt.The Yangtze Craton,Cathaysia Block and Dabie orogenic belt are the main source of Archean-Proterozoic zircons.

关 键 词：长江 现代沉积物 碎屑锆石U-Pb定年 HF同位素 物源示踪 

分 类 号：P578.941[天文地球—矿物学] P597.3[天文地球—地质学]