TECTONICS OF RIFT PROPAGATION INTO A CONTINENTAL-MARGIN - WESTERN WOODLARK BASIN, PAPUA-NEW-GUINEA

Oblique convergence along the irregular boundary between the Pacific a nd Indo-Australian plates in the SW Pacific has resulted in a transpre ssional regime. The drag of the overriding Pacific plate has produced a breakup of the Solomon microplate from the Indo-Australian plate and has induced its rotation within the mega-shear zone between the two m ajor plates. The microplate is being separated from the Indo-Australia n plate by passive rifting and seafloor spreading in the Woodlark Basi n which is propagating westward along the continental margin of Papua New Guinea. The present-day pole of the microplate rotation with respe ct to Indo-Australian plate is estimated to be near the Owen Stanley F ault Zone which represents the suture after Paleocene-Eocene arc-conti nent collision. The average rate of the seafloor spreading propagation is estimated to be 150 mm yr-1 over the last 3.4 Ma. The transition b etween seafloor spreading and continental rifting is characterized by a dramatic reduction in the production of new oceanic crust and by a c hange from localized deformation within oceanic lithosphere to distrib uted continental extension. Variations between the two structural styl es are being balanced by an accommodation zone and a newly developing transform fault. The style of continental deformation progressively ch anges due to a gradual decrease in lithospheric thinning along the rif t axis toward the pole of opening. Three accommodation zones are propo sed to balance differential extension and slippage between individual series of tilted blocks.