Detrital Zircon Low-temperature Thermochronology In Sedimentary Basin

Zircon fission track and(U-Th)/He thermochronometry has been used as an effective method to study thermal history of the deep sedimentary basin with high temperature.Previous studies proposed the thermal simulation experiment to investigate fission track annealing model and He thermal dynamics model of igneous zircon.However,basic research of detrital zircon low temperature thermochronology is relatively weak.In this paper,the evolutionary pattern of zircon fission track annealing temperature and He closure temperature are established by zircon fission track ages,fission track lengths,He ages and zircon burial depth of natural borehole samples obtained from the Cenozoic strara in the Bohai Bay and Tarim basins,which have different thermal settings.Meanwhile,zircon FT annealing behavior and He diffusion characteristic are also discussed.The initial track length of detrital zircon obtained from natural evolution samples is determined as 12.97 ?m by the maximum value,average value and correction value methods.Zircon fission track from different thermal setting exist different annealing temperature and annealing behavior due to the different heating rate.Zircon fission track annealing temperature is about 220 °C in the deep borehole samples of the Bohai Bay basin with high thermal background.However,the zircon fission track annealing temperature is about 160 °C in the deep borehole samples of the Tarim basin with low thermal background.The total annealing temperature is higher than 240 °C by establishing the evolutionary pattern between zircon fission track ages and burial depth.In addition,conventional zircon fission track annealing model established by thermal simulation experiment is corrected on the basis of functional form of fission track length,temperature and time from natural borehole samples.We also point out that heating rate,uranium concentration,and track angle to C-axis have apparent influence on the zircon fission track ages and lengths.Zircon He closure temperature is studied by the evolutionary pattern between zircon He ages and burial depth based on the data of natural borehole samples.The results show that zircon He closure temperature of natural evolution samples is approximately 200 °C,higher than the temperature obtain from the thermal simulation experiments(183°C).The temperature range of 140 °C ~ 200 °C is zircon helium partial retention zone.The high He closure temperature of detrital zircon results from long term low radiation damage accumulation,the effective uranium concentration and sufficient grain radius.The forward models of possible timetemperature paths are proposed that produce positive and negative correlation results between zircon He ages and eU concentration.Zircon thermochronology ages from the drilling samples in the shalow which older than the corresponding stratigraphic ages are used to reveal the provenance information.The Paleogene West Shandong Rise and Mesozoic volcanic activities are the chief provenance to Cenozoic strata of the Jiyang Depression.South Tianshan orogen and volcanic activity in Permian Tarim basin are the provenance of the Kuqa Depression.Tectonic uplift event of West Kunlun orogen is the main source of Southwestern Depression.This study is a revaluation of the conventional zircon fission track annealing temperature and zircon He closure temperature using nature evolution detrital zircon samples from different thermal setting.Zircon fission track and(U-Th)/He dating can be used as an effective thermal indicator to study thermal history of the deep sedimentary basin at high temperature,also has a great guiding significance in the studying of the evolution process of source rocks and hydrocarbon accumulation in the deep sedimentary basin.