The Woodlark Basin is located in the Solomon Sea southeast of Papua New Guinea (Fig. F1). The present-day tectonics of the region are the result of interactions between microplates caught in and formed during oblique convergence between the Pacific and Indo-Australian plates (Benes et al., 1994; Tregoning et al., 1998). Counterclockwise rotation of the Solomon microplate within this plate boundary zone led to the development of an oceanic spreading center. Magnetic anomalies indicate that the seafloor spreading center has propagated westward into eastern Papua New Guinea since at least 6 Ma (Weissel et al., 1982; Benes et al., 1994; Taylor et al., 1995, 1999; Goodliffe et al., 1997). Progressive opening of the western Woodlark Basin due to seafloor spreading led to separation of the formerly contiguous crust of the Pocklington and Woodlark Rises. The seafloor spreading tip is currently located at 9.8°S, 151.7°E. West of the seafloor spreading center, continental extension is manifested by full and half grabens, active metamorphic core complexes, and rift-related peralkaline volcanism (e.g., Smith and Simpson, 1972; Davies, 1973; Smith, 1976; Hegner and Smith, 1992; Davies and Warren, 1988; Hill et al., 1992, 1995; Hill and Baldwin, 1993; Baldwin et al., 1993; Stolz et al., 1993; Hill, 1994).
The Moresby Seamount is a bathymetric high located ~20-30 km west of the spreading tip and east of the D'Entrecasteaux Islands active metamorphic core complexes. Earthquake and seismic reflection data indicate that the seamount is bounded on its northern side by a seismically active, low-angle normal fault that strikes east-west and dips 25°-30° toward the north (Abers et al., 1997; Taylor, Huchon, Klaus, et al., 1999). The location of the fault within kilometers of the spreading tip allows for continental extension to be studied just prior to the transition to seafloor spreading.