The eastern Australian margin was shaped during the fragmentation of eastern Gondwana in the late Cretaceous. This led to the opening of the Tasman Basin and to the formation of sub-parallel rises, ridges and basins, including the Lord Howe Rise (LHR). The driving forces controlling the rifting are not fully understood, and two processes are invoked: slab rollback associated with back-arc extension or a plume impinging the lithosphere. To better understand the deep structure of the region, a 680km long seismic profile incorporating 100 ocean-bottom seismometers was acquired conjointly with multi-channel seismic (MCS) reflection data onboard the R/V Kairei at 27.2°S (March ¿ May 2016). Beneath the 4800m deep Tasman Basin, the OBSs register clear refracted arrivals from the crust and the mantle that are recorded at very large offsets of up to 250km. Towards the east, the Dampier Ridge rises abruptly to depths of 2750m. Here the refracted arrival from the crust is recorded at very short offset, suggesting a thin sedimentary cover on the ridge. The large offset (80km) of the triplication point between the refracted arrivals from the crust and the mantle suggests a thick crust. Further east on the MCS profile, three sub-basins are evident: the Middleton, Capel and Faust basins. Here the crust and mantle arrivals are recorded as high-amplitude first arrivals associated with a very strong PmP arrival. The offset of the triplication point between the crust and mantle refracted arrivals ranges from 40km to more than 60km. Towards the Lord Howe Platform the mantle refracted arrivals are recorded as a very low amplitude phase. Preliminary interpretation of the whole wide-angle dataset suggests that strong variations occur in the nature and the thickness of the crust. This will be confirmed by the preliminary Vp seismic velocity structure obtained from a tomographic inversion of the first-arrival traveltimes.
Abstract submitted & presented at the 2016 American Geohpysical Union (AGU) Fall Meeting (https://agu.confex.com/agu/fm16/meetingapp.cgi/)