Delayed Subsidence After Rifting and a Record of Breakup for Northwestern Zealandia

Abstract

Continental rifting and breakup of eastern Gondwana during the Cretaceous separated northern Zealandia from eastern Australia, but the processes leading to this highly extended and largely submerged block of continental crust are unknown. We acquired and processed multichannel seismic reflection data across northern Zealandia and examine the stratigraphy of the Middleton Basin. We identified a two‐phase formation process for the basin, as evidenced by an unconformity separating two postrift units. After initial basin formation and slow deposition of the lower postrift unit, deposition rates within the Middleton Basin rapidly increased in response to the latest stage of subsidence and to create the modern basin. We propose a tectonic model wherein the Middleton Basin initiated through oceanic spreading and the subsequent postrift subsidence of the newly created oceanic lithosphere was delayed due to thermal buoyancy associated with nearby oceanic spreading in the Tasman Basin. Our results provide new constraints on rifting and breakup processes of wide, magma‐poor, and asymmetric margins and indicate that multiple regions of weak lithosphere may have influenced the breakup.

Crustal Structure Across the Lord Howe Rise, Northern Zealandia, and Rifting of the Eastern Gondwana Margin

“…In the multichannel seismic data, the crust of the Middleton Basin displays some characteristics of oceanic crust. The crust has a thickness of ~2‐s twt and a Moho reflection imaged at 9.5‐s twt (Figure a; Boston et al, ).…”

“…A multichannel seismic reflection (MCS) survey was also conducted along the survey line using a 444‐channel hydrophone streamer with a 6‐km length and the same air gun array but fired at 50‐m intervals. The MCS data provide detailed seismic images of the sedimentary section and underlying crust (Boston et al, ).…”

“…To better constrain these variations, we ran a second traveltime tomography using an updated starting model incorporating the MCS time‐migrated data. On the time‐migrated MCS profile, many sedimentary basins are imaged with varying thicknesses and widths (Figure a; Boston et al, ). The goal of this second‐step tomography was to include these sedimentary basins in the starting model to allow the generation of a more realistic traveltime tomography model.…”

“…(a) Time section showing coincident multichannel seismic reflection (MCS) data along the Ocean Bottom Seismometer (OBS) line (Boston et al, ). The top of the basement is shown by the thick black dotted line.…”

Early Cretaceous subsidence of the Naturaliste Plateau defined by a new record of volcaniclastic-rich sequence at IODP Site U1513

“…The lack of substantial post-rift thermal subsidence on the southwest Australian rifted margin could be induced by the effects of mantle plume (e.g., thermal buoyancy, mantle instability, small-scale convection; Boston et al, 2019;Dafoe et al, 2017). During this period, the margin might be located within a large influence radius of a mantle plume (500-1,000 km; White and McKenzie, 1989).…”