Application of the (U-Th)/He thermochronometry to the tectono-thermal evolution of sedimentary basin - A case history of well KQ1 in the Tarim basin

The (U-Th)/He thermochronometry of apatite or zircon has been used as a new technique to study the structural uplift and thermal history of sedimentary basins in recent years. Based on the tested apatite and zircon He ages data from drilling wells samples, an evolution model of apatite He ages with depth and/or temperature is built, which illustrates that the He closure temperature in apatite is about 85°C in the Tarim basin. However, the zircon He ages reveals that these samples hadn t undergone its higher closure temperature. The thermal history since Ordovician in Well KQ1 has been modeled by using the He ages, AFT and R_o data. The modeling result shows that the thermal gradient was about 35. 5°C/km in the end of Ordovician, and 33. 3∼34. 5°C/km during the period of Silurian to Devonian, and it decreased to 27. 6°C/km in the end of Cretaceous. Therefore, the (U-Th)/He ages may provide a newly tool to rebuilt the thermal history of sedimentary basins, especially to the Low Paleozoic carbonate stratum in Tarim basin which is lack of normal thermal indicators.