Optimization Of OSL-Thermochronology And Its Application To Icy Point,Alaska

Low temperature thermochronology has been widely used in the study of orogenic belt exhumation,topography and geomorphology,and sedimentary basin evolution,and has played an important role in constraining the exhumation rate and topographic changes.OSL-thermochronology is a new method of low temperature thermochronology,which studies the thermal history of minerals such as quartz and Kfeldspar by measuring their OSL signals accumulated under the control of temperature changes.OSL-thermochronology has low closure temperature(100-40℃),which is sensitive to surface processes,and the accumulated time scale of measurable signals is short.It is easy to obtain a variety of different thermal stability signals for different research purposes;the minerals used(such as quartz or K-feldspar)are widely distributed in various geological bodies.So OSL-thermochronology is a promising method.The OSL-thermochronology model describes the time evolution of the luminescence signal controlled by temperature,including many parameters such as characteristic saturation dose,environmental dose rate and trap depth.The inversion of mineral thermal history by the luminescence signal depends on the determination of these parameters by experiments.The accuracy and uncertainty of experimental measurement and the characteristics of samples bring uncertainty to parameters,which affect the accuracy of thermal history reconstruction.In order to quantitatively evaluate the effects of different parameters,Sobol ’method based on variance decomposition is used to analyze the global sensitivity of the parameters of luminescence thermochronology model,which provides a theoretical basis for the optimization of the measurement method of key parameters.On this basis,we apply the OSL-thermochronology method to sandstone samples form Icy Point of Alaska that have undergone rapid exhumation for hundreds of thousands of years constrained by the apatite(U-Th)/He method.In order to simplify the pretreatment process of OSL-thermochronology samples,the slice OSL dating technology developed in recent years was introduced.Based on the slice OSL dating technology,the OSL-thermochronology age and related parameters of 8 samples in the Icy Point area were measured systematically.The results show as follows: 1.The cooling age range of K-feldspar IRSL signal from the Icy Point in Alaska is 80-280 ka,which is significantly lower than the AHe age(280-730 ka),and the cooling age difference of the same sample can be up to 0.2-0.45 Ma,which may be related to the difference in the closure temperature of the two thermochronology methods.2.Comparing the cooling paths of different samples,it is found that the Icy Point of Alaska has been in a rapid exhumation state since 0.4Ma,and there may be a more rapid shortscale exhumation event since 0.13 Ma.