Sedimentation in a complex convergent margin: the Papua New Guinea collision zone of the western Solomon Sea

Abstract

Bathymetric, sidescan and `groundtruthed' acoustic facies maps incorporating 50,000 km 2 of HAWAII MR1 swath and 3.5 kHz data have been used to construct a tectono-sedimentary model for sedimentation along the western Solomon Sea region of the Papua New Guinea collision zone. The southern underthrust plate along the collision zone includes the Morobe and Trobriand tectono-sedimentary provinces. This region has an extensive platform to the east, a narrow shelf, and a moderately steep slope descending to the plate margin. Along the edge of the underthrust plate sediment accumulates mainly in numerous isolated slope basins and several canyon-fed slope fans. The former are 5 to 20 km across and filled with fine-grained hemipelagic sediment. The latter are larger (40 to 70 km across), coarser-grained and elongate along the margin. The overriding plate along the Papua New Guinea collision zone includes the Huon, Finsch, Siassi and New Britain tectono-sedimentary provinces. The edge of this plate has no shelf, is very steep, and sediments accumulate in fewer isolated slope basins and more numerous canyon-fed slope fans, which are also elongate along the margin. The basin floor is constrained along two elongate deep sea trenches (separated by oceanic lithosphere). Sediment supply from the northern overriding plate to the basin floor is limited, as most submarine canyons terminate at slope fans, slope basins or terraces. Sediment supply from the southern underthrusting plate is also believed to be low, as approximately half of the tributary submarine canyons debouch onto slope fans before joining the axial Markham Canyon. The sediment supplied to the western end of the trench is delivered axially down the collisional suture, much of it apparently derived from emergent landmasses to the west. This pattern of sediment delivery implies that the fill in ancient deep water collisional basins may be largely unrelated to terranes on either side of the basin, but derived from terranes further afield.