Geophysical and morpho-tectonic study of the transition between seafloor spreading and continental rifting, western Woodlark Basin, Papua New Guinea

Abstract

Two major morpho-tectonic domains, separated by a major transfer zone, are described at the transition between seafloor spreading and continental rifting in the western Woodlark Basin, off-shore eastern Papua New Guinea. The oceanic domain comprises new oceanic crust formed during the Bruhnes Epoch, older transitional crust and the rifted continental margins. Two rift branches are recognized within the continental domain. The southern rift branch has failed while the northern branch is a locus of maximum extension with initial development of oceanic crustal accretion. Based on magnetic data, seafloor spreading in the western part of the Woodlark Basin commenced between 3.5 and 2.5 Ma along the northern margin of the basin and maintained its position adjacent to this margin up to 0.8 Ma (Jaramillo event). Just prior to the Bruhnes Epoch, the seafloor spreading axis jumped southward to its current position. Frequent jumps of seafloor spreading centers and relocation of paleoaxes indicate the instability of the Woodlark extensional system. The transition between the two domains is characterized by differential localization of extensional strain. Variations in the localization can result from progressive change of extensional mode when the initial rifting evolves into seafloor spreading and/or from differences in lithospheric rheology as the rift propagates into the continental margin. A consequence of such variations is the massive production of new oceanic crust during seafloor spreading which is being balanced across the transfer zone by broadly distributed deformation within continental lithosphere.