Andrew Goodliffe, B. Taylor, F. Martinez and R. N. Hey (SOEST, University of Hawaii, 2525 Correa Road, Honolulu, HI, 96822; andrew@mano.soest.hawaii.edu)
The Woodlark Basin is actively propagating westwards into the continental crust of the Papuan Peninsula by rifting and seafloor spreading. Magnetic, gravity, multichannel seismic and HAWAII MR1 bathymetry and sidescan data have been used to derive the evolution of this ocean basin.
Initial rifting is accomplished by extension along low angle detachment faults, giving a strong sense of asymmetry to the youngest parts of the basin. This form of extension gives rise to magnetization contrasts within continental crust between hanging wall rocks and the exhumed footwall rocks as they cool below the Curie point.
The most recently formed spreading segments nucleated in areas of large crustal extension. West of 153E the extension is shared between the margins and the spreading segments, as evidenced by numerous margin earthquakes with normal fault plane solutions. Between 152.5E and 154E the spreading center is growing by ridge propagation events as evidenced by seafloor fabric and numerous continental slivers that have been rifted from the margins. Moresby Transform has formed at 154.2E, offsetting by 50 km the two easternmost spreading segments in the survey area.
Within the last 0.78 Ma there has been a change in the orientation of the spreading segments east of 153E, resulting in transtension along Moresby Transform and the propagation of the spreading center at 153E into the southern continental margin. The difference in orientation between the spreading segments either side of 153E can be partly attributed to distributed deformation.