The Lord Howe Rise (LHR) is located to the east of Australia in water depths up to 3,000 m. The LHR is a 600 km wide and 1,600 km long continental ribbon that detached from eastern Gondwana by the Late Cretaceous. The driving forces that led to the breakup between the LHR and eastern Gondwana are not fully understood, but span two end-member processes: (1) slab rollback associated with back-arc extension; (2) a plume impinging the lithosphere.
To better understand the driving mechanism, a large set of marine geophysical data were acquired onboard the JAMSTEC vessel R/V Kairei in March–May 2016, in collaboration with Geoscience Australia. These data include:
* A 680 km long east-west oriented profile at ~27.2°S along which wide-angle seismic refraction data (~100 ocean-bottom seismometers (OBS)) were acquired conjointly with multi-channel seismic (MCS) reflection data;
* ~600 km of high-resolution 2D seismic reflection data at seven sites being
considered for IODP drilling;
*Multibeam bathymetry, gravity and magnetic data.
We present preliminary results obtained from a combined interpretation of OBS modeling and MCS along the east-west profile. The MCS profile produced a good image of the rift-fill sedimentary deposits and the acoustic basement from the Tasman Sea across the Dampier Ridge, the Middleton, Capel and Faust basins and the Lord Howe Platform to the east. With the OBS data, clear reflected arrivals from the basement and the mantle (Pn) are recorded at a very large offset (up to 250 km), with a strong Moho reflected arrival (PmP). Preliminary interpretation of these datasets suggests that the nature of the basement varies from oceanic crust to (thin?) continental crust, in agreement with previous geophysical studies of the area.
Further processing and modeling of the data will constrain the geometry of the main sedimentary basins and the nature of basement. This ongoing work is in support of an IODP proposal to drill through a rift basin and into the basement of the LHR. The processes of LHR crustal ribbon development will be investigated using rock cores recovered from up to 3,500 m below the seafloor.
Presented at the 2016 Seismological Society of Japan (SSOJ) Fall Meeting