Parts of the deep trenches in the Pacific Ocean are much “younger”—by as much as 50 million years—than previously believed. Scientists say the findings could change current thinking about how such deep-ocean trenches form.
Using the research ship JOIDES Resolution, researchers examined core samples extracted from a subduction zone south of Japan. The samples were taken from water about 4,800 feet deep in the Pacific floor.
A subduction zone is a huge underwater boundary that marks the collision between Earth’s tectonic plates. They are pieces of crust that slowly move across the planet’s surface over millions of years. When two tectonic plates meet at a subduction zone, one bends and slides underneath the other.
[Pacific’s tectonic plates aren’t all that rigid]
Such subduction zones weren’t identified until the 1960s, but they occur all around the Pacific Ocean, and are often referred to as the “ring of fire” because they are responsible for many of the world’s largest earthquakes, tsunamis, and volcanic eruptions.
“From the core samples, we were able to date the sediments both with fossils and records of Earth’s past magnetic field reversals,” says Kara Bogus, who serves as an expedition project manager and staff scientist at Texas A&M University’s International Ocean Discovery Program (IODP).
“We found that this igneous crust is much younger—about 50 million years—than we originally thought. The fact that it is younger, coupled with its chemical composition, tells us how the subduction zone began.”
Only half the story
The discovery is significant, researchers say, because “one of the biggest questions remaining in plate tectonics is how subduction zones start, or ‘initiate.’ When these plates push under each other into the Earth, hot magma is created that erupts from volcanoes on the surface plate, such as has occurred in the Northern Mariana Islands.
“It’s half the story in plate tectonics. We understand well the other half (how the plates move apart from each other and create new crust), but we are just beginning to understand this half. Overall, our results mean that we need to modify our subduction inception models.”
The work is published in the journal Nature Geoscience.
Source: Texas A&M University
