How does a major subduction zone begin? It may start small.

How does a major subduction zone begin? It may start small.

A long-standing mystery in geology is how one tectonic plate breaks apart the Earth’s hard outer shell and begins to dive into another plate in a process called subduction.

Now, a new study describes how a small crack in a tectonic plate can be squeezed and pulled over millions of years until it unravels and starts a runaway geological process.This learnabout an emerging subduction zone near New Zealand, just published in the journal Natural Geoscience.

“We now know how subduction nucleates and how fast it grows,” said the lead author. Brandon Shook. “It’s important to know this because subduction is the primary driver of plate tectonics. It builds mountains, creates new oceans, and drives chemical cycles from the depths of the Earth all the way to the atmosphere.” Shook in Texas He completed his doctoral thesis work at the University’s Jackson School of Geosciences.He is now a postdoctoral research scientist at Columbia University Lamont-Doherty Earth Observatory.

Earth is thought to be the only planet in the solar system to experience subduction, the key to the carbon cycle that makes life possible. “We do believe that subduction doesn’t always happen on Earth, so understanding how [it] Launching today is a critical step in understanding how our world could eventually become a habitable planet,” said study co-author Harm Van Avendonk, a senior research scientist at the University of Texas.

The study began in 2018 on the research vessel Lamont-Doherty Marcus G.Lanceth Off New Zealand, Shook and his boatmates endured weeks of severe weather to collect detailed undersea seismic images.

On shore, Shuck matched the images with rock samples from other ocean expeditions. This provides a geological timeline to reconstruct a pulled plate. According to his reconstruction, about 16 million years ago, a small fissure developed in the Australian plate, slowly expanding as it collided with other tectonic plates. When the fissures pulled far enough, the heavier parts of the plates broke through the Earth’s rocky crust (called the lithosphere), placing it on a downward conveyor belt that lasted for the past 8 million years. Today, the new subduction edge is about 300 miles long.

In 2018, a researcher recovered a seismic imaging sensor near New Zealand. These sensors are able to create detailed geological images of newly formed subduction zones. (The University of Texas Institute of Geophysics)

“That’s pretty small on a global tectonic scale,” Shook said. “But it will grow all the way to Antarctica,” he predicted. “Once it gets that big, more than 1,000 miles long, it could change the motion of adjacent tectonic plates.”

Currently, the only signs on the surface are several volcanoes near New Zealand’s South Island. Most have emerged in the past 100,000 years. They are likely to grow into longer chains of volcanoes as the splits spread south in the future, Shook said.

Shook’s research reconciles two opposing views on how subduction begins: The plates gradually collide back and forth with each other, or the plates collapse spontaneously and rapidly under their own weight. Sometimes both ideas may be part of the equation, new research suggests.

Swiss geophysicist Fabio Crameri said: “This work shows that there may be multiple scenarios that drive the onset of subduction.” natural geosciences Commentary that accompanies the study“Even though not every subduction zone is the same, their models challenge our current system for classifying the onset of subduction zones and underscore the need for 4D modeling.”

The research was supported by the National Science Foundation.

Adapted from a press release from the University of Texas Jackson School of Geosciences.