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ANALYSIS OF EFFECTS OF GEOMAGNETIC INTENSITY VARIATIONS ON EXPOSURE DATING

SHAO Qing-feng,CHEN Shi-tao(College of Geographical Sciences,Nanjing Normal University,Nanjing 210097,China)  
The production rates of in-situ terrestrial cosmogenic nuclides are functions of the cosmic-ray flux that is largely modulated by geomagnetic intensity on time scales of 103 to 105 year range.However,the effects of temporal variations in the geomagnetic field on production rates of cosmogenic nuclides are often neglected in exposure dating researches.According to the available paleogeomagnetic field intensity data,this study simulated instantaneous and time-integrated 10Be production rates over the last 200 ka,and calibrated the assumed model ages with an iterative method.The quantitative analysis suggests that changing production rates due to geomagnetic field intensity variations is one of the major uncertainty sources involved in exposure dating,especially at low latitudes and high altitudes.For example,the exposure ages between 50~200 ka,at 25 N and 2 km altitude,are reduced by 14%~19%,and at 40 N with the same altitude,they are reduced by 8% roughly.So,we should take account of the uncertainty of production rates of in-situ cosmogenic nuclides,and use time-integrated rates in exposure dating research.
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