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Paul Mann and Frederick W. Taylor, Institute for Geophysics, University of Texas at Austin

The lateral transition from active oceanic spreading to active rifting of continental crust occurs in only three localities worldwide: Red Sea, Gulf of Aden, and eastern Papua New Guinea (PNG). These three areas are critical for understanding a variety of tectonic and sedimentary processes associated with the spatial and temporal transition between oceanic ridge propagation and continental rupture. Of these three rifted zones, only PNG exhibits a close spatial association between: 1) the tip of the propagating Woodlark spreading ridge; 2) low-angle normal fault earthquakes; and 3) late Neogene metamorphic core complexes very similar to those described in ancient exhumed belts of intracontinental extension. We mapped emergent, late Quaternary coral reefs and Neogene sedimentary sections over hundreds of kilometers of coastlines of islands and peninsulas of eastern PNG to determine the pattern and rate of uplift, style of deformation, and tectonic mechanisms of rift propagation. Main results include: 1) the best-known area of core complexes on Goodenough and Fergusson Islands is stable or subsiding and is interpreted as a now abandoned spur of ridge propagation active about 3.5 Ma; 2) the main locus of active rifting associated with rapid uplift of Holocene reefs and late Neogene basinal sedimentary rocks is parallel to the Gwoira north-dipping, normal fault system on the Papuan Peninsula and beneath Goodenough Bay; 3) the Milne Bay "graben" is inactive as previously predicted by GPS results showing the Milne Bay area moving as part of the stable Australian plate; 4) the process of rift propagation in PNG appears presently focussed on the Gwoira fault zone within Goodenough Bay and the Papuan Peninsula and is not diffuse across the entire region as depicted in previous models; GPS predicts about 11 mm/yr of extension across this fault.