Evidence of Fission Track Data for Thermotectonic Evolution History of the Lower Yangtze Area

In order to reveal characteristics of the tectono-thermal evolution of the outcrops of south Lower Yangtze area and its regional controls, detailed apatite fission track analysis (AFT) on seven Palaeo-Mesozoic clastic rocks has been carried out. The results show that the Palaeo-Mesozoic clastic rocks have apatite fission-track ages ranging from 105.7 to 50.9 Ma, much younger than corresponding strata ages. Mean fission track length ranges from 13.19 μm to 13.70 μm, with a single-peak distribution. The AFT heat history modeling curves show that the cooling history since Late Cretaceous can be divided into three phases. The first phase was rapid basin uplifting and cooling (1.7 to 15℃/Ma), the second phase was stable basin uplifting and cooling (0.27 to 0.81℃/Ma) and the third phase was rapid basin uplifting and cooling (2.8 to 5.6℃/Ma).The 113 Ma to 100 Ma transformation corresponding to Huangqiao transform event (110 Ma to 90 Ma) was related with the tectono-thermal change from the Yanshan magmatism to extensional faulting. The 75 Ma to 68 Ma transformation corresponds to Yizheng tectonic event(70 Ma to 60 Ma).The 18 Ma to 10 Ma transformation represents the uplifting and erosion process during the late Himalayan period.