Multiple post-depositional thermal events in the Drummond Basin, Australia: Evidence from apatite and zircon (U-Th)/He thermochronology

Multiple phases of extension and contraction in orogens can produce relatively complicated thermal histories for sedimentary basins as recorded by thermochronological datasets. This makes it difficult to determine which tectonic events had the most impact on the thermal state, and were drivers of exhumation, of the upper crust. In this study, 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 similar to 340 Ma for the sampled formations, 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). Zircon (U-Th)/(He-Pb) double dating yielded no correlation between U/Pb and ZHe ages, with all the ZHe ages younger than depositional age. These data indicate disturbance of the ZHe and AHe systems after deposition. Inverse thermal history modeling using the QTQt and HeFTy codes suggests the samples experienced two post-depositional heating-cooling cycles: (1) rapid heating to similar to 150-195 *DEG;C at similar to 300 Ma was followed by rapid cooling to near-surface temperatures of similar to 50(+50)/(-30) *DEG;C between 270 and 240 Ma, and (2) gradual heating until the Early Cretaceous, when temperatures increased to similar to 105(+15)/(-10) *DEG;C followed by rapid cooling beginning similar to 90 Ma. We relate the similar to 300 Ma heating to the Kennedy-Connors-Auburn silicic large igneous province, revealing that major regional igneous events can significantly perturb a basin thermal history. In contrast, the slow temperature increase between similar to 270 and 100 Ma is related to progressive burial by overlying sediments of the Galilee and Great Australian basins. Finally, rapid cooling beginning similar to 90 Ma was synchronous with rift margin exhumation.