Sea-floor spreading in the Lau back-arc basin

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 < 75% of the opening rates determined geodetically. In the absence of earthquake evidence for significant off-axis deformation between 18–21°S, we infer that opening rates have recently increased on the central and east Lau spreading centers.