Late Cretaceous to Oligocene burial and collision in western Papua New Guinea: Indications from low-temperature thermochronology and thermal modelling

Abstract

Recent field and analytical work have considerably improved our understanding of the structure of the Muller Range along the frontal trend of the Papuan Fold and Thrust Belt (PFTB) in western Papua New Guinea (PNG). However numerous questions remain unresolved concerning the geological evolution of the region. In particular, the Late Cretaceous to Oligocene history of the region is largely unknown due to the absence of a continuous stratigraphic record. Here, we use both new and existing low-temperature thermochronology data to investigate the geological history of the Muller Range. Thermal history models based on these data suggest two major Cenozoic cooling episodes. The youngest, and best constrained, is clearly recorded in the stratigraphic record and relates to Neogene collision at the northern margin of the Australian continent. An older episode of comparable or greater magnitude occurred in the Eocene to Oligocene and may relate to the removal of 1500–3000 m of Late Cretaceous to Eocene section across the Muller Range prior to the widespread deposition of the shelfal Darai Limestone. We suggest that extension along major faults beneath the Muller Range accommodated sedimentation from the Late Cretaceous to the Eocene, consistent with long-lived extensional structures observed in neighbouring regions. In contrast to the Muller Range area, an almost continuous Late Cretaceous to Eocene stratigraphic sequence is preserved in the hinterland <50 km to the northeast. The selective removal of this sequence across the Muller Range suggests it was uplifted in the Eocene to Oligocene, possibly in part facilitated by the inversion of extensional faults in the Muller Range area. We suggest that this inversion was related to the Eocene to Oligocene collision of the expansive Sepik Terrane to the northwest of the PNG margin. The new data and interpretations presented here have significant implications for the evolution of the PFTB and for tectonic reconstructions of PNG.