Detrital apatite fission track analysis and geomorphologic evolution of the Nujiang River area
Sun Dongxia1,2, Ji Jianqing2, Liu Yiduo1, Li Baolong2, Chen Jianjun2, Zhong Dalai1
1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
2. Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871
River sand as an averaged product of catchment can reflect the regional thermal histories of the entire river basin.Sampling in different segments of one river is able to obtain more accurate information of the thermal history evolutions.Seven detrital sand samples were collected from different locations of the Nujiang River in western Yunnan to attempt to reveal the thermal history of the entire river basin through the apatite fission track(AFT) method.The samples show the main age peaks of 12.2 Ma,12.8 Ma,7.7 Ma,5.3 Ma,4.4 Ma,4.9 Ma,7.3 Ma respectively,presenting an interesting and extremely special pattern of 'old on the sides and young in the center’. The younger results in the center means the middle segment of Nujiang River got through relative quicker thermal histories.The youngest and special region lies in the three rivers parallel flowing area and water vapor channel of southwest monsoon,resulting in the significantly difference in precipitation patterns between the different segments.We therefore conclude that climate led to its rapid landscape evolution and then caused the youngest samples exposed in the middle segment of Nujiang River.All the AFT age peaks can be divided into five groups: 5.3～4.4 Ma,7.7～7.3 Ma,12.8～10.7 Ma,26.8～22.2 Ma and 48.7～30.1 Ma,documenting the main stages of Cenozoic thermal histories in Nujiang River Basin,western Yunnan.Furthermore,the prominent characters of the detrital river sand are identified,as an indication of segmentation to get more accurate thermal information.