Active Continental Extension of Eastern Papua New Guinea: Geologic Studies of Emerged Coral Reefs and Marine Sedimentary Rocks

University Of Texas At Austin, Austin TX

Investigators

Abstract

0106518 Mann The lateral transition from seafloor spreading at a narrow, well defined plate boundary to diffuse rifting of continental crust occurs today in three localities worldwide: the Red Sea, the Gulf of Aden, and eastern Papua New Guinea. These three areas are critical for understanding how continents rupture because the spatial progression from seafloor spreading to continental rifting provides insights into the temporal and structural evolution of an oceanic spreading ridge to a continental rift. Such insights are not readily apparent from the more widespread zones of active intracontinental extension like the U.S. Basin and Range province where extension has not - and may not - eventually proceed to the point of seafloor spreading. Of these three seafloor spreading to rift transition areas, only Papua New Guinea exhibits a close spatial association between the tip of the propagating spreading ridge and low-angle normal fault earthquakes, active, low-angle normal faults in a submarine setting, and late Neogene metamorphic core complexes. The D'Entrecasteaux Islands and Papuan Peninsula, fringed by late Neogene sedimentary rocks and late Quaternary coral reefs, occupy the transition area between oceanic spreading and continental rifting. These accessible land areas provide an ideal geologic setting to test several contrasting tectonic models for spreading ridge-rift transitions proposed on the basis of earthquakes, radiometric and structural studies of core complexes, and marine geophysical studies. The main elements of these previously proposed models include oceanic propagating ridge models applied to this region of continental crust, localization of metamorphic core complexes and topographic uplift adjacent to areas of propagating ridges, and lateral shifts in the location of rifting and subsequent spreading. We are using a combination of geologic studies of late Quaternary coral reefs and late Neogene sedimentary sections along hundreds of kilometers of eastern PNG coastlines to determine the pattern of late Neogene to late Quaternary vertical tectonic history, style of deformation, and tectonic mechanisms in order to test the tectonic models described above. Key questions that we are addressing in these studies include: 1) Where is the area of maximum late Quaternary coral reef uplift in the D'Entrecasteaux Islands and Papuan Peninsula and what structures have affected them? 2) Are there detectable spatial migrations in the uplift pattern of this region? and 3) Are low angle normal faults present in the late Neogene marine rocks and the coral terraces themselves in the area of low angle normal fault earthquakes near Sanaroa and Fergusson Islands? Our results will aid interpretations of the tectonic effects of active ridge propagation or jumping in other active rift areas including the Red Sea, East African rifts, and Gulf of Aden where a detailed reef record such as in Papua New Guinea is not available.