The Issues of Application for the Fission Track Dating and Its Geological Significance
ZHANG Zhicheng 1) WANG Xuesong 2) ( 1)Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,School of Earth and Space Sciences,Peking University, Beijing, 100871; 2)Laboratory and Research Center of Petroleum Geology, Research Institute of Petroleum Exploration and Development, Beijing, 100083)
Unlike most methods of radiometric dating, fission track dating measures the effect, rather than the products, of radioactive decay events. External detector dating method can calculate individual grain ages. There are three assembled ages for single sample, which are pooled age, mean age and central age. It is very important that the fission track ages have no unambiguous geological significance. Tracks are randomly oriented in three-dimensional space. However, the measurements of track density used in age determinations are based on a two-dimensional sample of tracks intersecting an internal surface. With the increasing of the temperature, the fission tracks are progressively shortened from their ends,resulting in a reduction in the observed area density of the tracks and therefore a reduction in the measured fission track age. Because the fission track age is associated with the length of tracks, the length and distribution of tracks are the most important parameters in the fission track analysis. By modelling of thermal histories from apatite fission track data, the thermal histories of samples can be reconstructed.