Styles and distribution of continental extension derived from the rift basins of eastern Papua New Guinea

The offshore eastern Papua New Guinea region has been undergoing large-scale extension since 6 m.y. ago, as inferred from the Euler rotation pole using the eastern Woodlark Basin spreading center magnetic anomalies. This area is characterized by unusual tectonic features such as high-grade metamorphic domes assembling the metamorphic core complexes and possibly active low-angle normal faults that have been considered the result of large-scale continental extension. Multichannel seismic (MCS) stratigraphic and kinematic/isostatic rift basin modeling techniques are used to study the distribution and the style of extension in the area and to investigate the interpreted metamorphic core complexes and low-angle normal faults. Our studies based on MCS data indicated that the young continental extension of the region has been located mostly to the south of the metamorphic domes. Low-angle seismic reflections suggestive of low-angle normal faults are not identified within the coverage of the Marice Ewing cruise 9203 seismic data. Our MCS study suggests that large extension is unlikely around the D'Entrecasteaux Islands where high-grade metamorphic domes are found. MCS stratigraphic interpretation study in the western Woodlark Basin reveals five major sediment sequences associated with Miocene forearc rifting and Plio-Pleistocene extension. Correlation of seismic interfaces suggests that much of the subsidence in the northern margin cannot be readily related in space or time with the brittle deformation identified from the seismic sections. Cumulative extension measured using fault heaves is significantly smaller (∼73 km) than the estimate made from the Woodlark spreading system Euler rotation pole (∼200 km for 6 m.y.). To further investigate the style, distribution and amount of extension associated with basin subsidence along the northern margin of the western Woodlark Basin, kinematic and isostatic rift basin models are applied. A model that satisfactorily simulated the observed basin development suggests that times of basin-scale subsidence of the northern margin are not coincident with times of brittle deformation of the crust. The model predicts about 91 km of cumulative extension since Pliocene time for the area, most of which is accommodated by a ductile deformation mechanism.