110 OCEANIA (INCLUDING FIJI, PNG AND SOLOMONS) Figure Physiographic map of the south west Pacific Reproduced with permission from Smith WHF and Sandwell DT (1997) Global seafloor topography from satellite altimetry and ship depth soundings Science 277: 1957 1962 Available on the Internet at http:// topex.ucsd.edu/marine_topo/mar_topo.html sediments; and locally extensive Oligocene gabbro There is no indication of a continental or cratonic basement, though such may exist The Paleocene and much of the Eocene sediments were deposited in a deep marine environment and probably have been added to the mainland by accretion above a north-dipping subduction system Collisional Zone Figure The map shows earthquakes with magnitude or greater, recorded during 1963 2002 Red indicates hypocentre depth of 70 km, green 70 300 km, blue 300 500 km and black >500 km Features of the map are the west dipping seismic zone beneath Tonga in the east, the north dipping seismic zone be neath New Britain in the north west, and the steeply dipping seismic zone beneath Vanuatu Shallow seismic zones (red dots) mark the spreading ridges and transforms in the Bismarck and Solomon seas and the North Fiji Basin Map prepared by Emile Okal in turn are transitional northwards into greenschist facies graphitic schists The sediments of the stable platform and foldbelt comprise the Papuan Basin The foldbelt changes character east of the Aure Fault (Figure 3) Beyond this point, the foldbelt comprises fault-bounded segments of Late Cretaceous, Paleocene, and Eocene fine siliceous siliciclastic and calcareous sedimentary rocks, associated with faulted slivers of ultramafic rock; Oligocene and younger coarser, partly volcanogenic, dominantly clastic The western part of the central collisional zone comprises fault-bounded terranes of Jurassic to Eocene sedimentary, igneous, metamorphic, and ultramafic rock, and younger (Eocene to Miocene) dioritic intrusive bodies The association of ultramafic rocks with eclogite, blueschists, submarine volcanic rocks, and volcanogenic sediments indicates a former volcanic arc environment Sediments associated with the volcanic rocks are of two ages, mid-Eocene and Oligocene This suggests a history of successive development of volcanic arcs and successive collisions; the Oligocene volcanic rocks are found only on the north side of the northern ranges Also included in the western part of the central collisional zone are two faultbounded blocks of Palaeozoic basement One of these lies on the border with Indonesian Papua and the other extends northward from the Kubor Range, to underlie the Jimi valley (Figure 3) These Palaeozoic terranes lie outward (northward) of younger accreted terranes and thus appear to be ‘out of sequence’