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Strike-Slip Enables Subduction Initiation Beneath a Failed Rift: New Seismic Constraints from Puysegur Margin, New Zealand

Subduction zones are fundamental to Earth’s plate tectonic history, yet the details of how they initiate remain enigmatic. It is thought that subduction initiation often takes advantage of previously weakened lithosphere and may preferentially nucleate along pre-existing plate boundaries. To evaluate how past tectonic regimes and inherited lithospheric structure might facilitate underthrusting and lead to self-sustaining subduction, we present an analysis of the Puysegur Trench, a young subduction zone with a rapidly evolving tectonic history. The Puysegur Margin, south of New Zealand, has experienced a transformation from continental rifting to strike-slip, and most recently to incipient subduction, all in the last ~45 million years. Here we present deep-penetrating multichannel reflection (MCS) and ocean-bottom seismometer (OBS) tomographic images to document crustal structures and their evolution along the margin. Our images reveal that the overriding Pacific Plate contains stretched continental crust with magmatic intrusions, which formed from Eocene-Oligocene rifting between Zealandia continental plateaus. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading as previously thought. Subsequent strike-slip deformation translated continental crust northward causing an oblique collisional zone, with trailing ~10 Myr old oceanic lithosphere. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust the continent-collision zone. We suggest that subduction initiation at the Puysegur Trench was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the plate boundary. The Puysegur Margin demonstrates that forced nucleation along a strike-slip boundary is a viable subduction initiation scenario and should be considered throughout Earth’s history.

Presenting Author: Brandon Shuck

Student Presenter: Yes

Day: 4/22/2021

Time: 9:45 AM - 11:00 AM Pacific

Additional Authors