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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 style deformation
mechanism.
Regional map with free-air gravity image overlay with MCS ship tracks 
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