Optical Stimulated Luminescence Dating Of Rock Surfaces

A wide variety of fluvial terraces, bedrock fault and other geomorphic surface have developed since the late Quaternary, which is the studying object of tectonic activity and climate change and so on. How to measure the formed or abandoned age of geomorphic surface accurately has been always a difficulty of geology research. The most commonly used method is Terrestrial Cosmogenic Nuclidessuch as 10 Be, 26Al(Gosse and Phillips, 2001; Cockburn and Summerfield, 2004; Huang et al., 2004, in Chinese; Gu et al., 2006, in Chinese; Kong et al., 2009; Yuan et al., 2013). However the pretreatment is complex and samples mostly are sent abroad to measure costly. There are many uncertain factors affecting the dating range and accuracy. Other dating methods also have their own limitations. Thus, for arid and semi-arid regions inour country, the establishment of an appropriate, easy dating method forrocks' exposure and burial ageis the key solution for Quaternary tectonic evolution and climate change.Optical stimulated luminescence(OSL) have been recently proposed as a new methodto date for rock surfaces. The basic principle is that rock surface luminescence signal will soon decay with depth when rock exposes to sunlight. When the rock surface became burial, the OSL signal began to accumulate again. With the variation of residual luminescence with depth, it is possible to estimate exposure and burial history of the rock.We selectedcobblesfrom modern river bed and fluvial terraces with dating results of 10 Be depth profiles of Kezilesu River of Kashgar and normal fault bedrock from Langshan Mountain of Inner Mongolia as research subjects. The main conclusions made in this thesis are summarized as follows:(1) The OSL dating protocol of rock slice in our laboratory have been established initially. Slice thickness is set preferably to 0.75 mm and the actual thickness need to be measured to for determining the depth of the optical stimulated luminescence signal. We had better collect darker sandstone for rocks with a long exposure age or lighter granite for rocks with a shorter exposure age.(2) The depth of sunlight penetration to the OSL signal of cobble from present Kezilesu riverbed was deeper than which from the fluvial terraces. We got 460-9200 years for exposure age of the fluvial terrace gravel, which agreed with 10 Be expose age(Thompson, 2013 Ph.D. thesis). That implied that theoptical stimulated luminescence(OSL) dating for cobbles on fluvial terracewas reasonable.(3) We tried to establish OSL dating model for bedrock normal fault and discussed relationship between residual OSL signal and depth of the samples from different height of fault when active times of fault is zero, one or two. Finally, the model was applied to dating Langshan bedrock. Through OSL residual signal versus depth curve of samples from different heights, it showed that the fault plane recorded faulting twice at least. The seismic displacement of the latest earthquake was at least 210 cm, and the seismic displacement of the penultimate earthquake was at least 20 cm.