岩石表层释光暴露年龄及侵蚀速率的相关参数影响分析

Effect of related parameters on exposure age and erosion rate obtained via rock surface luminescence dating

近十年,岩石表层释光测年方法自提出以来发展迅速,表现出广泛的应用前景和潜力,但该方法相关的参数对暴露年龄和侵蚀速率结果的影响却鲜有研究。本文通过模拟光衰减系数μ、晒退速率σφ_(0)、环境剂量率D及特征饱和剂量D_(0)这些相关参数与半饱和深度(量化释光信号晒退深度的指标)之间的关系,分析研究了上述参数对暴露年龄和侵蚀速率的影响,以及在不同参数σφ_(0)及D_(0)下获得暴露年龄和侵蚀速率的极限。结果表明μ和σφ_(0)对释光信号晒退和侵蚀速率的影响非常显著,当增加相同的暴露时间或侵蚀速率时,μ值越小,对应半饱和深度变化的速率更大,而不同σφ_(0)值对应半饱和深度变化的速率相同。浅色透光性(μ值较小)岩石是较为理想的定年材料,野外作业中应优先采集。一般情况下,环境剂量率D和特征饱和剂量D_(0)的大小对暴露年龄和侵蚀速率的值基本不产生影响,故在实际应用中可忽略岩石表面和内部的D值差异。该方法测年范围为10^(-3)~10^(2)ka,获得侵蚀速率范围为10^(-2)~10^(3)mm·ka^(-1)。

[Background]Rock surface luminescence dating has developed rapidly in the past decade.It has been widely used to obtain exposure ages and erosion rates of various rocks in archaeology,geology,and geography,such as stone artifacts,glacier bedrock,gravel,and bedrock fault surfaces.However,these is little study on the effect of parameters related to this method,such as attenuation coefficientμ,decay rate of the trapped charge at the rock surfaceσφ_(0),environmental dose rate Ḋ,and characteristic saturation dose D_(0)on exposure age and erosion rate results.[Purpose]This study aims to quantitatively investigate the impact of relevant parameters on exposure age and erosion rate,and examine the limits of exposure age and erosion rate obtained by the method under different parameters.[Methods]First,parameters that might have an impact on age and erosion rate results were determined through theoretical analyses.Then,the relationship among the parameters,depth of half saturation and exposure age(erosion rate)were studied using numerical simulations.The impact of each relevant parameter on exposure age and erosion rate was observed for varied parameter values.Finally,the dating limit was determined from the inflection point in the simulated profiles.[Results]The smallerμvalue is,the greater the rate of change in the depth of half saturation would be when increasing the same exposure time.However,the rate of change in the depth of half saturation remains constant for differentσφ_(0) values when the same erosion rate is increased.[Conclusions]Among the parameters,σφ_(0) and,more remarkably,μsignificantly affect the dating result.In general,Ḋand D_(0)have little effect on the exposure age and erosion rate;therefore,the differences in Ḋbetween the surface and interior of rocks may be ignored.The growth rate of depth of half saturation of granite gneiss is significantly higher than that of sandstone for the same exposure time increment.Therefore,light-colored rocks such as granite should be prioritized for collection during field work.The ranges of dating and obtaining erosion rate using this method are 10^(-3)~10^(2) ka and 10^(-2)~10^(3) mm∙ka^(-1),respectively.