| 10Be和26Al在地表形成和演化研究中的应用 |
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| 引用本文： | 顾兆炎,刘东生,D．Lal.10Be和26Al在地表形成和演化研究中的应用[J].第四纪研究,1997,17(3):211-221. |
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| 作者姓名： | 顾兆炎 刘东生 D．Lal |
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| 作者单位： | 中国科学院地质研究所!北京,100029(顾兆炎,刘东生),加利福尼亚大学斯克里普斯海洋研究所!圣迭戈(D．Lal) |
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| 基金项目： | 中国科学院留学经费择优支持回国工作基金,国家教委留学回国人员科研启动基金 |
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| 摘 要： | 地球表面丰富多样的地形、地貌是地球内外动力相互作用的结果。宇宙射线辐射地表岩石、沉积物等产生的10Be和26Al放射性核素（半衰期分别为1．5Ma和0．71Ma）,它们的浓度主要取决于由地理位置和地形、地貌条件所决定的宇宙射线辐射的通量和时间,从而能够记录地表的形成和演化历史。因此,宇宙成因核素是研究地表形成历史和作用过程的有力工具。
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| 关 键 词： | 宇宙成因核素 10Be 26Al 曝露年龄 风化-侵蚀速率 |
| 收稿时间： | 1997-05-10 |
| 修稿时间： | 1997-05-29 |
APPLICATION OF THE IN SITU COSMOGENIC NUCLIDES 10Be AND 26Al FOR STUDIES OF FORMATION AND EVOLUTIONARY HISTORIES OF THE EARTH SURFACE |
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| Gu Zhaoyan,Liu Tungsheng.APPLICATION OF THE IN SITU COSMOGENIC NUCLIDES 10Be AND 26Al FOR STUDIES OF FORMATION AND EVOLUTIONARY HISTORIES OF THE EARTH SURFACE[J].Quaternary Sciences,1997,17(3):211-221. |
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| Authors: | Gu Zhaoyan Liu Tungsheng |
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| Institution: | 1. Institute of Geology, Chinese Academy of Sciences, Beijing 100029;
2. Scripps Institution of Oceanography. University of California, San Diego |
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| Abstract: | The surface of the earth is continuously undergoing changes as a result of weathering and erosion, plate tectonics and volcanic processes. Continental denudation with its complex rock-water interactions is the central process of global biogeochemical cycling of elements. Rates of denudation depend on variety of factors,in particular rock properties and chemical composition, climate (especially rainfall),structure, and elevation. Thus they are quite variable on a regional scale. A primary step in most geomorphological studies is to gain understanding of the location-specific weathering and erosional processes. An important recent contribution to the Earth sciences has been made with the development of a cosmogenic nuclide method applicable for the study of divers geomorphic processes and histories. The basic principle of application of the in situ cosmogenic radionuclides ~(10)Be (half-life = 1. 5Ma)and ~(26)Al (half-life = 0.71Ma) in quartz for study of the processes on the earth surface is given in this paper.The basis of the application of the in situ cosmogenic nuclides in the Earth sciences is their production in solids by particles of the cosmic rays. The production rates of the in situ cosmogenic nuclides depend on the cosmic ray flux at their situation as well as composition and density of the target material. They are different under different irradiation conditions, such as altitude, latitude, irradiation geomeny,and type of rock. Relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons~3]. Absolute nuclide production rates cannot generally be predicted with any accufacy because of lack of data on excitation functions of nuclides. Based on a natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for about 11 ka were sampled in Sierra Nevada, USA, the absolute production rates of ~(10)Be and ~(26)Al in quartz have been accurately estimated for different mountain altitudes~11]. Therefore, the absolute production rates of ~(10)Be and ~(26)Al in quartz on surface can be estimated fairly accUrately for any given latitude and altitude~5]. Within a rock, the production rates decrease exponentially with depth. The absorption mean-free-path of cosmic ray in common rock types is of the order of 150 - 170g cm~(-2), about 50 - 60cm in typical rocks. This is the distance in which the cosmic ray flux is reduced by a factor of "e",due to nuclear interactions which absorb the cosmic radiation energy.For a given rock (or mineral) and its location, the concentration of a nuclide produced by cosmic ray depends only on (1) the half-life of the nuclide, (2) the geometry of cosmic ray irradiation of the rock during the rock's exposure history, and (3) the exposure duration.Based on the production rates of ~(10)Be and ~(26)Al and their decay consents, their concentrations can be modeled with rock's exposure duration, erosion and sedimentation ates, and elevation change. The ~(10)Be and ~(26)Al concentrations in the quartz of rocks and sediments~4] can be used to study specific problems in the earth surface processes,including the estimates of the effective surface exposure age, the time-averaged erosion rate, elevation change, and the erosion-sedimentation evolutionary history. A growing number of studies have proved that cosmogenic nuclides ~(10)Be and ~(26)Al are supper powerful for studies of formation and evolutionary histories of the earth surface. A light will be shed from application of the cosmogenic nuclide ~(10)Be and ~(26)Al in Chinese Quaternary researches. |
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| Keywords: | cosmogenic nuclide ~(10)Be ~(26)Al exposure age erosion rate |
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