Study on the detrital zircon fission‐track ages from natural borehole samples in the Bohai Bay and Tarim basins with different thermal backgrounds

Abstract

Zircon fission‐track thermochronometry was used as an effective indicator to investigate the thermal history of sedimentary basins with high temperatures, and fission‐track ages and annealing temperatures were very important parameters. We measured fission‐track ages and discussed the annealing behaviour of zircon fission track from natural borehole samples in the Bohai Bay and Tarim basins. The annealing temperature of the zircon fission track was approximately 220°C in the deep borehole samples of the Bohai Bay Basin with a high thermal background. However, the annealing temperature was approximately 170°C in the deep borehole samples of the Tarim Basin with a low thermal background. In Neogene–Quaternary, the heating rate ranged from 2 to 7°C/Ma in the Sk1 samples, and 4 to 18°C/Ma in the K1 samples. This explained that zircon fission track with different thermal backgrounds existed different annealing temperatures due to the different heating rates. The uranium concentration of the K1 samples mostly ranged from 16 to 1,500 ppm, with a few grains spread from >1,500 to 3,000 ppm, while the Sk1 samples mainly distributed between 4 ppm and 350 ppm. The K1 samples with high uranium contents tended to accumulate much radiation damages and were less resistant to annealing and appeared to have a lower annealing temperature compared to zircons of lower uranium contents in the Sk1 samples. By properly understanding annealing behaviour and annealing temperature, zircon fission‐track thermochronometry could provide a correct explanation for fission‐track ages.