Post-orogenic structural style and reactivation in the northern Bowen Basin, eastern Australia

Abstract

The northern Bowen Basin in eastern Australia was affected by the middle Permian–Late Triassic Hunter--Bowen Orogeny, but the effect of the post-orogenic deformation events is less well understood. 2D seismic surveys and field observations were utilised to the east of Moranbah to understand structural style and reactivation in the northern Bowen Basin. Large-scale faults include the Daunia and New Chum thrusts, and the Daunia Graben bounding faults. These faults displace the upper Permian–Triassic lithological units with throws larger than 30 m. Large-scale thrusts are parts of the Late Triassic north-northwest-striking Jellinbah Thrust Zone in the northern Bowen Basin. The Daunia Graben comprises normal faults, parallel to the thrusts, with a maximum 80 m throw. Small-scale faults affect one or two lithological units with throws less than 30 m. Small-scale reverse faults mainly strike north-northwest, whereas small-scale normal faults strike northeast–southwest, east-northeast–west-southwest and north-northeast–south-southeast. The Daunia Graben and some small-scale normal faults developed during a regional extensional regime either in the Late Triassic or in the mid-Cretaceous to early Cenozoic. A series of small-scale faults probably developed during the Hunter--Bowen Orogeny as subsidiary structures associated with the Jellinbah Thrust Zone, whereas some small-scale reverse faults propagated during the Late Jurassic–Early Cretaceous and middle–late Cenozoic. Post-orogenic reactivation phases affected east of Moranbah through: (1) the development of the Daunia Graben within the hanging wall of the New Chum Thrusts, possibly owing to the negative inversion of pre-existing structures; (2) its subsequent partial inversion associated with small-scale reverse faults; and (3) the reactivation of small-scale normal and strike-slip faults. The driving mechanisms of these reactivation phases are related to far-field stress fields associated with episodic Late Triassic to late Cenozoic extensional and contractional regimes at Australian Plate boundaries. In contrast to the middle Permian–Late Triassic Hunter--Bowen Orogeny phases, post-orogenic deformation events in the Bowen Basin were not robust enough to produce a large number of large-scale faults. This probably reflects the retreat of the active subduction zone from eastern Australia since the Late Triassic. KEY POINTS Large-scale faults in the northern Bowen Basin affected upper Permian–Triassic units with throws >30 m, whereas small-scale faults displaced one or two lithological units with throws <30 m. Some large-scale and small-scale faults are part of the Late Triassic north-northwest-striking Jellinbah Thrust Zone, which deformed the northern Bowen Basin in response to the Hunter--Bowen Orogeny. Some large-scale and small-scale reverse and normal faults developed during post-orogenic reactivation phases from the Late Triassic to late Cenozoic.