A comparison of continental extension estimates across the margins of the Woodlark Basin, Papua New Guinea

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Previous studies have shown that depth dependent extension is common across rifted margins. A discrepancy exists between the estimates of extension made through whole lithosphere/crust vs fault heave calculations (for example, northwest Australia, South China Sea, Galicia). Although this discrepancy is also observed in the Woodlark Basin (~111 (23) from brittle extension and ~115 (47) from subsidence [Kington and Goodliffe, 2008]), the location of this study, including sub-seismic resolution and poly-phase faulting reduces this mismatch. What makes the Woodlark Basin unique is that a third measure of continental extension is available, Euler pole kinematics. Previous studies show that this predicts almost double (~220 km) the extension calculated from subsidence and brittle extension [Kington and Goodliffe, 2008]. Extension in the Woodlark Basin began at ~8.4 Ma and transitioned to sea-floor spreading in the east at ~6 Ma [Kington and Goodliffe, 2008]. The basin is an ideal place to study the extension discrepancy because of its young age and thin sediments. Seismic reflection data provide good images of basement and fault structures. High-resolution bathymetry permits tracing of major faults on the seafloor. A previous study focused on the extension discrepancy at the rifting to spreading transition. This study will focus on the discrepancy further east where seafloor spreading began at ~1.8 Ma and opening rates are faster. Using high resolution bathymetry, magnetics, gravity, and low-fold 2-D seismic reflection data allowed me to estimate the amount of extension through brittle extension and subsidence. Euler pole derived extension rates from previous studies were used for comparison. The results of this study show that the amount of extension increases towards the east as is expected from having a Euler pole to the west. Subsidence derived extension estimates yielded 95.6 (38) km at 153.0E with a maximum stretching factor of 1.8. This increased to 145.3 (52) km with a maximum stretching factor of 1.89 to the east. Brittle extension estimates yielded between 107.1 (26.8) and 143.1 (35.8) km of extension between 153.0E and 154.0E. Both estimates of extension are far lower than the ~235 km of extension predicted by Euler Pole kinematics for the same area. As in the Kington and Goodliffe [2008] study, brittle faulting and subsidence derived extension estimates match (within the error limits).

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Geophysical engineering, Geophysics, Geology