[J08-1] Imaging and interpreting lithospheric structures using seismic and geodetic approaches I

[J08-1-02] First insights into the deep structure of the eastern Australian passive margin using wide-angle seismic data: Crustal segmentation from the Tasman Basin to the northern Lord Howe Rise

^○Flora Gallais¹, Gou Fujie¹, Shuichi Kodaira¹, Seiichi Miura¹, Brian Boston¹, Yasuyuki Nakamura¹, Ron Hackney², Saneatsu Saito¹, Kazuya Shiraishi¹, Yuka Kaiho¹, Yasuhiro Yamada¹, Scott Nichol², Georges Bernardel², Cameron Mitchell² (1.JAMSTEC, CEAT, Yokohama, Japan, 2.Geoscience Australia, Canberra, Australia)

The eastern Australian margin was shaped by the fragmentation of eastern Gondwana during the Late Cretaceous. This led to the opening of the Tasman Basin and to the formation of sub-parallel ridges and basins, including the Lord Howe Rise. To image the deep structure of the region, a large-scale crustal experiment was conducted by JAMSTEC and Geoscience Australia onboard the R/V Kairei with the deployment of 100 ocean-bottom seismometers (OBS) along a 680 km profile at 27.2S. The OBSs register clear refracted arrivals from the crust and the mantle that are recorded at very large offsets, as great as 300 km. Both pre- and post-critical reflected phases from the Moho (PmP) are also very clearly recorded by the OBSs. We performed first-arrival tomographic inversion to analyze the data. An initial layered P-wave velocity model was built using the two-way travel time reflection from the basement interpreted from coincident multi-channel seismic data to constrain the thickness of the sedimentary layer. During the inversion, the PmP arrivals are used to add constraints on the thickness of the crust. The uncertainty in the final P-wave velocity model is tested by applying Monte Carlo analysis. The final Vp model shows large variations in crustal thickness and allows the identification of distinct crustal domains along the profile from the Tasman Basin to the northern Lord Howe Rise: the Tasman Basin is an oceanic domain with ~7km thick crust; further east, a 15km crust is present below the Dampier Ridge; the crust again thins to 8km below the Middleton Basin; and the northern Lord Howe Rise is floored by a 21km thick crust. Further work will compare the modeled P-wave velocities with previously published results from the southwest Pacific region and other well-known tectonic provinces from around the world to discuss the variation of nature of the crust along the profile. This will help to better understand the processes that led to the fragmentation of eastern Gondwana.