Active continental rifting, metamorphic core complex development, and seafloor spreading makes the western Woodlark Basin of Papua New Guinea an ideal area to study processes associated with the initial rupture of continental lithosphere (e.g., Hill et al., 1995; Taylor et al., 1999, and references therein). Ocean Drilling Program (ODP) Leg 180 was designed to examine processes associated with continental rifting, including low angle normal faulting, sedimentary basin evolution, and the movement of footwall blocks during the final stages of rifting and prior to seafloor spreading initiation (Taylor, Huchon, Klaus, et al, 1999).
One of the objectives of ODP Leg 180 was to determine the pressure-temperature-time (P-T-t) history of recovered igneous and metamorphic rocks to constrain the tectonic evolution of the Moresby Seamount, a bathymetric high bounded on its northern flank by a seismically active low-angle normal fault (Abers et al., 1997). The north-south transect drilled just west of the spreading tip recovered diabase, gabbro, basalt, and sedimentary rocks. We present results of a thermochronologic study of diabase and felsic igneous clasts recovered from sites drilled on the hanging wall and footwall of the normal fault bounding the Moresby Seamount. Results allow us to constrain, in part, the prerifting tectonic evolution of the region and the geologic setting prior to the onset of crustal extension and seafloor spreading in the vicinity of the Moresby Seamount. Results are interpreted in the context of the present-day tectonic setting and the geologic evolution of the Papuan Peninsula.