Thermal history of the Hodgkinson Province and Laura Basin, Queensland: multiple cooling episodes identified from apatite fission track analysis and vitrinite reflectance data

Apatite fission track analysis and vitrinite reflectance data from outcrop and well samples in the Hodgkinson Province and Laura Basin reveal regional Cretaceous cooling. Apatite fission track analysis appears to define two d iscrete cooling episodes, in the mid-Cretaceous (110-100 Ma) and Late Creta ceous (80-70 Ma), although in most samples data allow only definition of a single episode. Rocks now at outcrop cooled from Cretaceous palaeotemperatu res generally between 50 and 130 degrees C in the south of the region, and from >100 degrees C in the north. Some samples from the Hodgkinson Province also show evidence for an Early Jurassic cooling episode, characterised by maximum palaeotemperatures varying from at least 95 degrees C (from apatit e fission track analysis) to similar to 200-220 degrees C (from vitrinite r eflectance), with cooling beginning at around 200 Ma. Apatite fission track analysis data do not reveal the earlier event in the Laura Basin, but on t he basis of vitrinite reflectance data from Permian? units this event is al so inferred to have affected the pre-Jurassic basin units in this region. T he regional extent of the Cretaceous cooling episode in the Hodgkinson Prov ince suggests that the elevated palaeotemperatures in this region were most likely due to greater depth of burial. with subsequent cooling due to kilo metre-scale denudation. For a palaeogeothermal gradient of 30 degrees C/km and a palaeosurface temperature of 25 degrees C the total degree of Cretace ous cooling experienced by the samples corresponds to removal of between si milar to 0.8 and >3.0 km of Triassic and younger section removed by denudat ion, beginning some time between ca 110 and 80 Ma. Higher palaeogradients w ould require correspondingly lower amounts of removed section. The geology of the Laura Basin suggests that an explanation of the observed Cretaceous palaeotemperatures in this region in terms of deeper burial may be untenabl e. Heating due to hot fluid flow may be a more realistic mechanism for prod ucing the observed Cretaceous palaeothermal effects in the Laura Basin.