Brandon Shuck and his colleagues provide us with an updated view on one of the key ongoing potential SZI events:
Geoscientists have proposed that the process of forming a new subduction zone takes advantage of weaknesses such as buoyancy contrasts and re-using older weak plate boundaries. To test these ideas, new seismic images are used to document tectonic structures at the Puysegur margin, which might be an SZI event south of New Zealand. The images reveal that the upper plate of the Puysegur margin consists mostly of stretched continental lithosphere that formed during an Eocene-Oligocene extension phase. Following extension, a translational phase juxtaposed thin and high-density oceanic lithosphere against thick and low-density continental lithosphere in a wide damage zone. Convergence across this zone led to underthrusting of the Australian Plate beneath the Pacific Plate and the development of an incipient Puysegur subduction. The results demonstrate that incipient subduction was aided by lithospheric buoyancy contrasts and weak zones inherited from earlier phases of tectonic activity. Moreover, these findings argue that pre-existing plate boundaries, weakening mechanisms, and strike-slip can be key components of the subduction initiation process in general and have likely prevailed throughout Earth's history.
Shuck et al. (2021, Tectonics)
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Tectonic setting of the Australia (AUS)—Pacific (PAC) plate boundary south of New Zealand.