As continental crust is thicker and more buoyant, the extensional forces working at the plate boundary couldn't crack Zealandia. Zealandia was perched over the north end of this extensional zone. Zealandia is a submerged section of continental crust the size of Australia around New Zealand. This process is called seafloor spreading, and it's how new oceanic crust forms.īut there was a catch: The secret continent of Zealandia. The oceanic crust at the plate boundary responded to this extension predictably: As the crust thin, magma from the mantle pushed up through fractures, hardening into new rock. It all started about 45 million years ago, when a new plate boundary between the Australian and Pacific plates began to form because of a force called extension - basically, tectonic forces pulled the two plates apart like putty. The new data allowed the researchers to put together a history of the young subduction zone, which Shuck presented at the virtual meeting of the Seismological Society of America on April 22, the same day the study was published in the journal Tectonics. The collision pushed the dense oceanic crust under the lighter continental crust, a process called subduction.
A strike-slip fault brought this weakened continental crust and denser oceanic crust from the Australian Plate side-by-side. Seafloor spreading starting 45 million years ago stretched out the submerged continental crust of Zealandia on the Pacific Plate, creating a thinned region at the Solander Basin. The making of a subduction zoneĪ schematic showing the Puysegur margin south of New Zealand. In spite of the weather, the researchers were able to deploy seafloor seismometers and to take seismic surveys of the subsurface, a method which uses reflected sound waves to see underground structures. "Our boat was rolling side to side by like 20 degrees at one point," Shuck said. The crew had to spend almost a quarter of the time sheltering behind islands to avoid gales. Scientists aboard the research vessel Marcus Langseth set out to this region in 2018 as part of the South Island Subduction Initiation Experiment. Studying the Puysegur margin is no easy feat, though, because it's in the "Roaring Forties," the latitudes between 40 degrees south and 50 degrees south where the winds and currents are brutal. Related: In photos: Ocean hidden beneath Earth's surface There's not yet any good explanation of how tectonic plates break open and start subducting. That makes it an ideal spot to answer the question of how subduction zones form in the first place, Shuck told Live Science. The subduction zone in the Puysegur margin is young enough that this history has not yet been erased.
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