The project is a follow-on to the discovery that there are very young UHP rocks exposed on islands near the eastern tip of Papua New Guinea (PNG). A major objective is to use detailed study of this area to better understand how UHP rocks get to the surface from great depth. Because the rocks are in a tectonically active region, it can be argued that there is a good chance of improving models for UHP exhumation because this example is still in its tectonic context. There is evidence that the process is ongoing. Related to this objective is the study of the overall tectonic evolution of this area, which is needed in order to help understand how the UHP rocks got where they are and from whence they came.
Within this framework, this project involves a range of studies that can contribute to piecing together the UHP exhumation history and the tectonic evolution. One large study involves passive seismic data acquisition to image the crust and mantle beneath the area where partially exhumed HP/UHP rocks may occur at depth; a large fraction of the studies involve petrology, geology, mineral physics and geochemistry. In addition, GPS work and geodynamic modeling are included.
The Woodlark rift of eastern Papua New Guinea (PNG) is one of a few places where an active oceanic spreading center intersects with a continent landmass, tearing it open with incipient continental rifting. There, in a region of active and rapid continental extension, high-pressure and ultra-high-pressure (HP/UHP) rocks from deep in the earth’s crust and upper-most mantle have been exhumed from ~100 km depth to the surface at cm/yr rates. This study seeks to better understand the underlying forces that drive the overall continental extension, as well as the faulting mechanisms and driving forces that enable rapid uplift of the HP/UHP rocks. Seismic imaging of the crust and mantle structure beneath eastern PNG suggests that N-S extension associated with warm, upwelling mantle extends westward under PNG from the tip of the oceanic spreading center. Inferred mantle flow and thermal structure do not suggest a major buoyant upwelling localized in the region of the HP/UHP exhumation. Numerical models of extensional fault evolution in imply that the faults bounding HP/UHP exhumation must have a narrow range of strengths to produce the observed deformation. These results are being integrated with additional geophysical and geological constraints determined through ongoing collaborative projects to build a more complete understanding of continental rifting and HP/UHP exhumation in eastern PNG. In addition to these scientific outcomes, the project had important societal benefits. The field area occupies a volcanic and seismically hazardous region, and field activities and resulting maps of earthquake locations significantly improved the local understanding of seismic hazard. Scientific training associated with this grant included the education of two post-doctoral associates, four graduate students, and a collaborator from the PNG Division of Mineral Resources. All seismic data collected during this experiment is openly available to the public via the IRIS Data Management Center (www.iris.edu).
