Andrew Mark Goodliffe

Sea-floor spreading in the Lau back-arc basin

Abstract We report the first 3-D magnetization inversion of bathymetry and magnetics data for the entire Lau Basin and confirm a history of southward-propagating sea-floor spreading during the past 4 Myr. Magnetic lineations, seafloor fabric and ridge segmentation patterns indicate that lithospheric accretion on discrete spreading centers in this back-arc basin is fundamentally similar to that occurring on mid-ocean ridges. The Brunhes Chron spreading rates (65–100 mm/yr) are

Synchronous reorientation of the Woodlark Basin spreading center

Abstract A sidescan and multibeam bathymetry survey of the Woodlark Basin reveals that its 500 km long spreading center reoriented synchronously, without propagation, about 80 ka. There is no evidence of the V-shaped pseudofault geometry typical of spreading center propagation, nor of the progressive fanning of seafloor fabric characteristic of spreading center rotation. The reorientation is recognized by a sharp contact between two seafloor fabric trends, and ruptured off-axis lithosphere formed up to 0.7 Myr previously. The length of the reoriented spreading segments and the tendency to fault pre-reorientation seafloor fabric are controlled by the strength of the lithosphere, the angle of the reorientation, and the length of pre-existing spreading and transform segments. We document the process of synchronous reorientation in the Woodlark Basin and propose that it may occur in other ocean basins.

Contrasting styles of seafloor spreading in the Woodlark Basin: Indications of rift‐induced secondary mantle convection

The Woodlark Basin in the southwest Pacific is a young ocean basin which began forming by ∼6 Ma following the rifting of continental and arc lithosphere. The N-S striking Moresby Transform divides the oceanic basin into eastern and western parts which have contrasting characteristics. Seafloor spreading west of Moresby Transform began after ∼2 Ma, and although spreading rates decrease to the west, the western basin has faster spreading characteristics than the eastern basin. These include (1) ∼500 m shallower seafloor; (2) Bouguer gravity anomalies that are >30 mGals lower; (3) magnetic anomaly and modeled seafloor magnetization amplitudes that are higher; (4) a spreading center with an axial high in contrast to the axial valleys of the eastern basin; (5) smoother seafloor fabric; and (6) exclusively nontransform spreading center offsets in contrast to the eastern basin, which has transform faults and fracture zones that extend across most of the basin. Overall depth contrasts and Bouguer anomalies can be matched by end-member models of thicker crust (∼2 km) or thinner lithosphere (<1/3) in the western basin. Correlated with these contrasts, the surrounding rifted margins abruptly thicken westward of the longitude of Moresby Transform. We examine alternative explanations for these contrasts and propose that rift-induced secondary mantle convection driven by thicker western margin lithosphere is most consistent with the observations. Although rift-induced convection has been cited as a cause for the voluminous excess magmatism at some rifted margins, the observations in the Woodlark Basin suggest that this mechanism may significantly affect the morphology, structure, and geophysical characteristics of young ocean basins in alternate ways which resemble increased spreading rate.