金沙江大具盆地碎屑堆积体的土壤碳酸盐铀系测年  

U-SERIES DATING OF PEDOGENIC CARBONATES FROM DAJU BASIN,JINSHA RIVER VALLEY

作　　者：胡晓 游洋 焦亚诺 邵庆丰[2] 孔兴功[2] HU Xiao;YOU Yang;JIAO Yanuo;SHAO Qingfeng;KONG Xinggong(School of Earth Sciences and Engineering,Nanjing University,Nanjing 210093,Jiangsu;School of Geography,Nanjing Normal University,Nanjing 210023,Jiangsu;University of Chinese Academy of Sciences,Beijing 100049;State Key Laboratory of Lake Science and Environment,Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences,Nanjing 210008,Jiangsu)

机构地区：[1]南京大学地球科学与工程学院,江苏,南京210093 [2]南京师范大学地理科学学院,江苏,南京210023 [3]中国科学院大学,北京100049 [4]中国科学院南京地理与湖泊研究所湖泊与环境国家重点实验室,江苏,南京210008

出　　处：《第四纪研究》2022年第5期1287-1296,共10页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41877430)资助。

摘　　要：金沙江大具盆地中堆积着巨厚的碎屑沉积物,覆盖于6级阶地之上,拔河高度可达300 m以上,其成因和年代都是我国地貌学的研究热点。由于大具盆地的碎屑堆积体岩性简单、分选性差,缺乏合适的测年材料(如炭屑、火山灰、动物化石等),此前仅有宇生核素^(10)Be和^(26)Al暴露测年和光释光测年获得绝对测年数据。野外调查发现大具盆地碎屑堆积体中广泛发育着土壤碳酸盐,而且其质地纯净致密,适合于铀系测年,可约束堆积体形成的最小年龄。为此,采集了海拔高度分别在1859 m、 1809 m、 1738 m和1721 m的4处堆积体(DJ1、 DJ2、 DJ3和DJ4)中的34个土壤碳酸盐样品进行铀系测年。多接收器电感耦合等离子体质谱(MC-ICP-MS)的铀系测年结果显示这4处堆积体中土壤碳酸盐的最大年代分别为14.72±1.08 ka、 11.30±0.17 ka、 15.08±0.70 ka和16.34±1.22 ka都对应于末次冰消期。因此,推测大具盆地中巨厚的碎屑沉积事件可能发生于末次冰消期或稍早时段,最小年龄为16.34±1.22 ka。Daju Basin( 27° 16’ ~ 27° 19’N,100° 12’ ~ 100° 16’E),located between Yulong Snow Mountains and Haba Snow Mountains,is formed by the junction of the Songpan-Garze fold system with Yangtze platform,and Sanjiang fold system,and is controlled by Longpan-Qiaohou Fault,the eastern piedmont fault of Yulong Mountains,Zhongdian-Daju Fault and Lijiang-Jianchuan Fault. Influenced by the continuous and periodic uplift of the QinghaiTibetan Plateau since the Cenozoic,the neotectonic movement in the Yulong-Haba block was intense,mainly manifested as the differential uplift of fault blocks and the formation of fault subsidence basin. Daju Basin presents extremely thick detrital sediments covering on the terraces( T1~ T6),with a height up to 300 m above the Jinsha River level. The detrital sediments filled in the Daju Basin are mainly composed of poorly sorted limestone breccia,with the size varying from a few centimeters to 2 ~ 3 meters. Due to the lack of suitable dating materials( such as charcoal,volcanic ash,and fossil remains),these deposits were only dated by the cosmogenic^(10)Be and^(26)Al exposure dating method and OSL method. Field expeditions lead to the discovery of the widely developed pedogenic carbonates in the detrital sediments in the Daju Basin,which concentrated at the depth of 1 ~ 2 m below ground.Furthermore,the pedogenic carbonates are pure and condensed,making them datable by the U-series method. The pedogenic carbonates were certainly formed after the deposition of the detrital sediments,hence,their U-series ages allow constraining on the minimum age of the deposition events. In this study,a total of 34 pedogenic carbonate samples were collected from DJ1( 27° 17’36. 94″N,100° 12’30. 1″E;1859 m a.s.l.;6 samples were collected from within the thickness of 3. 5 ~ 5. 0 m),DJ2( 27° 17’30. 6″N,100° 12’53. 67″E;1809 m a. s. l.;11 samples were collected from within the thickness of 3 ~ 4 m),DJ3( 27° 17’55. 64″N,100° 13’48. 93″E;1738 m a.s.l.;9 samples were collected from

关 键 词：大具盆地 碎屑堆积体 土壤碳酸盐 铀系测年 

分 类 号：P597.3[天文地球—地球化学]