Scientists reveal that the tectonic plate under the Pacific Ocean is tearing apart
Although it is now the prevailing theory, the road to acceptance has been long and bumpy for plate tectonics, which describes how large portions of the Earth’s crust slide, grind, rise, and sink very slowly through its clay mantle.
But even now, more than half a century after gaining scientific approval, the theory still needs some improvement.
A new study looking at four plateaus in the western Pacific Ocean suggests that these extensional regions are not solid plates, but weak spots being yanked away by forces far away at the plate edge.
“The theory is not set in stone, and we are still discovering new things,” says Russell Biskelewic, a geophysicist at the University of Toronto, who co-authored the study.
“We knew that geological deformations such as faults occur in the interior of continental plates far from plate boundaries,” adds first author Erkan Gun, also an earth scientist at the University of Toronto. “But we didn’t know that the same thing was happening to ocean plates.” .
For decades, scientists have been rewriting their understanding of the seafloor, so this new study is just a continuation of their efforts to map the ocean’s rugged terrain.
In the 1950s, oceanographer Mary Tharp’s pioneering work to map large portions of the seafloor using sonar data from warships showed that ocean basins were not at all as flat-surfaced as scientists had suspected.
Instead, the sea floor was carved by vast trenches and huge mountains – no larger than the Mid-Atlantic Ridge, which Tharp discovered, and which is now known to be the longest mountain range on the planet, dividing the Atlantic Ocean in two.
Such mountain ranges form when two tectonic plates collide and the Earth’s crust buckles, or one plate subsides beneath the other, pushing the upper plate upward. Underwater, however, submarine mountains typically form when two plates drift apart at so-called divergent boundaries and magma is released.
But away from these plate boundaries, at the center of the oceanic plates, scientists thought that large parts of the Earth’s crust remained fairly rigid as they drifted over the mantle, and did not deform like plate edges.
To test this thinking, Gunn, Biskelewic and their colleagues collected data on two oceanic plateaus located between Japan and Hawaii, called the Shatzki Ridge and the Hesse Ridge; Ontong Java Plateau, northern Solomon Islands; The Manihiki Plateau, to the northeast of Fiji and Tonga.
Given the challenges of seafloor surveying, their study was limited to the four plateaus in the western Pacific Ocean for which data were available.
Oceanic plateaus are located hundreds to thousands of kilometers from the nearest plate boundaries. However, Gunn and his colleagues found that the plateaus share deformational and magmatic features, suggesting that they were torn apart by gravitational forces at the edge of the Pacific Plate, where plates are subducted beneath neighboring plates.
The fissures, or fault lines, identified by researchers tend to run parallel to the nearest trench, as you can see on the map above.
The team also modeled the plate tectonic dynamics of four hypothetical plateaus located between 750 and 1,500 kilometers (466 to 932 miles) from the nearest subduction zone, to gain a better understanding of the mechanisms driving this distant deformation.
Regardless of their distance from the plate edge, these hypothetical plateaus have extended over millions of years and become thinner on the side closer to the trench.
“It was thought that because the plateaus under the ocean are thicker, they must be stronger,” Gunn says. “But our seismic models and data show that it is actually the opposite: the plateaus are weaker.”
While acknowledging that they only analyzed four plateaus in the Pacific Ocean, the researchers hope their findings will stimulate further exploration to map the seafloor.
“Sending out research ships to collect data is a huge effort,” Gunn says. “So, actually, we hope that our research will draw some attention to plateaus and that more data will be collected.”
The study was published in Geophysical Research Letters.