Evidence for Subduction of the Solomon Sea Plate at the Trobriand Trough, Papua New Guinea

The Solomon Sea plate is bounded to the north and south by subduction zones and to the east by a major strike slip fault. On the northern side of the Solomon Sea plate, the New Britain Trench is associated with a well-defined north-dipping Benioff zone. In contrast, on the southern side of the Solomon Sea plate, the south dipping subduction zone at the Trobriand Trough is poorly defined seismologically, and its existence has been debated. There is much evidence to suggest that the Trobriand Trough represents a subduction zone that is either active or was active in geologically recent times. This includes: 1) newly collected multibeam bathymetry data that clearly defines the deformation front that has formed as a result of southward subduction of the Solomon Sea plate; 2) a clear gravity signature that is similar to, but not as strong as that seen at the New Britain Trench; 3) modern subduction zone volcanism (e.g. Mt. Lamington, Mt Victory and smaller volcanoes to the east); 4) calc-alkaline volcaniclastic material recovered during ODP Leg 180 that records nearby volcanic eruptions between 1.5 Ma and 3.8 Ma; 5) plate motion reconstructions that require southward subduction of the Solomon Sea plate at the Trobriand Trough; and 6) low heat flow (~30 mW m^-2) in the forearc directly overlying the southward subducting Solomon Sea plate.