The formation and evolution of the Qiaojia pull-apart basin,North Xiaojiang Fault Zone,Southwest China |
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Authors: | Tian-tao Li Xiang-jun Pei Run-qiu Huang Long-de Jin |
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Institution: | 1.State key Laboratory of Geohazard Prevention and Geoenvironment Protection,Chengdu University of Technology,Chengdu,China;2.Georgia Institute of Technology,Atlanta,USA |
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Abstract: | Sedimentary sequences with drastic thickening over short distances have been observed in Qiaojia County, Yunnan Province, Southwest China. These are related to a pull-apart basin controlled by the Xiaojiang strike-slip fault. Our field investigations include determining the surface characteristics of the Qiaojia basin which consists of three terrace sequences and a series of alluvial fans. Several drill holes were used to reveal the internal structure of the basin. The results suggest that the basinal sediments are over 300 m thick. From bottom to top, they can be classified into five different units. We inferred that the units of lacustrine sediments are deposited in a paleo-lake which was formed by a paleo-landslide. Accelerator mass spectrometry radiocarbon dating (AMS 14C dating) was used to estimate the ages of the terrace and lacustrine sediments. We use the results to infer that the paleo-lake has existed about 15,000 years and that the Qiaojia basin was uplifted at an average rate of 3.3 mm/a. Furthermore, we then model the evolution process of the basin and interpreted 6 phases of development. |
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