Unravelling complicated basin thermal histories from apatite and zircon (U-Th)/He systematics: An example from the Drummond Basin, Queensland (Australia)

The thermal history of sedimentary basins is commonly interpreted in terms of burial and exhumation. Apatite and zircon (U-Th)/He data obtained from five drill core samples (Campaspe DDH-1) from the Drummond Basin are used to construct a continuous, post-depositional thermal history of this Late Devonian-Early Carboniferous rift basin. Detrital zircon U/Pb ages indicate a maximum depositional age of 340 Ma, however, most apatite (U-Th)/He (AHe) analyses yielded apparent ages of 30 - 100 Ma (n=35) and zircon (U-Th)/He (ZHe) analyses gave ages of 200-340 Ma (n=67). Double dated (U-Th)/(He-Pb) zircons show no correlation between (U-Th)/He and U/Pb ages. Also, most of the ZHe ages are younger than the depositional age, indicating disturbance of the ZHe and AHe systems after deposition. Transdimensional inverse thermal history modeling using the QTQt software suggests the samples experienced two post-depositional heating-cooling cycles: (1) rapid heating to 280 ⁺¹⁶⁰/_-120 °C (95% confidence interval) at 300 Ma followed by rapid cooling to near-surface temperatures of 50 ⁺⁵⁰/_-30 °C between 270 and 240 Ma, and (2) gradual heating to 105 ⁺¹⁵/_-10 °C until the Late Cretaceous, and then rapid cooling beginning 90 Ma. To better constrain the first heating event, inverse modeling was performed using the HeFTy software with basic input parameters deduced from the QTQt modeling. The results suggest peak temperature conditions of the first heating event to be 150-195 °C, corresponding to the lower bound of the 95% confidence interval from the QTQt modeling. We relate the 300 Ma heating to the large Kennedy-Connors-Auburn igneous province, revealing that major regional igneous events can significantly perturb a basin thermal history. In contrast, the slow temperature increase between 270 and 100 Ma is related to progressive burial by sediments of the Galilee and Great Australian basins. Finally, rapid cooling beginning 90 Ma was synchronous with rift margin exhumation.