Thermotectonic evolution history of the lower Yangtze area based on detrital zircon fission-track analysis

It is difficult to acquire a corresponding relationship between temperature and time using reflectance of vitrinite as a major geothermometer. In order to reveal characteristics of the tectono-thermal evolution of the outcrops of south Lower Yangtze area and its regional controls, detailed zircon fission track analysis (ZFT), which can depict a good corresponding relationship between temperature and time, on fifteen Palaeo-Mesozoic clastic rocks was carried out. The results show that the Palaeo-Mesozoic clastic rocks have zircon fission-track ages ranging from 214 to 75 Ma. These ZFT ages (pooled ages or central ages) coupled with ZFT grain ages show characteristics of regional thermal variation, corresponding to the difference of tectonothermal reconstruction and differential ZFT annealing properties. The ZFT ages dominantly concentrate on the period of 157 to 95 Ma, as a magnificent feature, according with the time of 160-100 Ma for large-scaled magmatism that ocurred in the Lower Yangtze and Southeast China. It follows that this magmatism is considered to exert appreciable influence upon sample ZFT thermochronology. Two younger ZFT results (ZFT10 and ZFT11) of 75 and 76 Ma from the Nanhua Series are associated with faulting of the NW-SE structural zone.