重口味SM

U of T geoscientists shed new light on plate tectonics

The researchers found that the Pacific plate is scored by large undersea faults that are pulling it apart
view of the pacfic ocean from space

Researchers have discovered undersea faults on the Pacific plate, some of which are hundreds of kilometres long (image by NOAA/NASA GOES Project)

A team of geoscientists from the 重口味SM is shedding new light on the century-old model of plate tectonics, which suggests the plates covering the ocean floors are rigid as they move across the Earth鈥檚 mantle.

The researchers found that the Pacific plate is scored by large undersea faults that are pulling it apart. The newly discovered faults, described in a paper , are the result of enormous forces within the plate tugging it westward.

Some of the faults are thousands of metres deep and hundreds of kilometres long.

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Erkan G眉n (photo by Don Campbell)

鈥淲e knew that geological deformations like faults happen on the continental plate interiors far from plate boundaries,鈥 says Erkan G眉n, a post-doctoral researcher in the department of physical and environmental sciences at U of T Scarborough. 鈥淏ut we didn't know the same thing was happening to ocean plates.鈥

Russell Pysklywec, a professor in the department of Earth Sciences in the Faculty of Arts & Sciences, adds that the research contributes to a fuller understanding of the field.

鈥淲hat we're doing is refining plate tectonics 鈥 the theory that describes how our planet works 鈥 and showing those plates really aren't as pristine as we previously thought.鈥

Other researchers involved in the study include Phil Heron, an assistant professor in the department of physical and environmental sciences at U of T Scarborough, as well as researchers from the Eurasia Institute of Earth Sciences at Istanbul Technical University.

For millions of years, the Pacific plate 鈥 which constitutes most of the Pacific Ocean floor 鈥 has drifted westward to plunge down into the Earth鈥檚 mantle along undersea trenches or subduction zones that run from Japan to New Zealand and Australia. As the western edge of the plate is pulled down into the mantle, it drags the rest of the plate with it like a tablecloth being pulled from a table.

The newly discovered plate damage at the faults occurs within extensive, sub-oceanic plateaus formed millions of years ago when molten rock from the Earth鈥檚 mantle extruded onto the ocean floor; the faults tend to run parallel to the closest trench.

鈥淚t was thought that because the sub-oceanic plateaus are thicker, they should be stronger,鈥 says G眉n. 鈥淏ut our models and seismic data show it鈥檚 actually the opposite: the plateaus are weaker.鈥

In other words, if the Pacific plate is like a tablecloth being pulled across a tabletop, the plateaus are patches of weaker cloth that are more prone to tearing.

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Russell Pysklywec on the south slope of Mount Tongariro in New Zealand (supplied image)

The researchers studied four plateaus in the western Pacific Ocean 鈥 the Ontong Java, Shatsky, Hess and Manihiki 鈥 in a vast area roughly bounded by Hawaii, Japan, New Zealand and Australia. They made their discovery using supercomputer models and existing data 鈥 some collected in studies done in the 1970s and 鈥80s.

鈥淭here is evidence that volcanism occurred at these sites in the past as a result of this type of plate damage 鈥 perhaps episodically or continuously 鈥 but it isn鈥檛 clear if that鈥檚 happening now,鈥 says G眉n. 鈥淪till, we can鈥檛 be certain because the plateaus are thousands of metres below the ocean surface and sending research vessels to collect data is a major effort. So, in fact, we鈥檙e hopeful our paper brings some attention to the plateaus and more data will be collected.鈥

The theory of plate tectonics has been refined over many decades by numerous Earth scientists, including U of T鈥檚 John Tuzo Wilson, .

鈥淏ut the theory鈥檚 not carved in stone and we鈥檙e still finding new things,鈥 says Pysklywec. 鈥淣ow we know this fault damage is tearing apart the centre of an ocean plate 鈥 and this could be linked to seismic activity and volcanism.

鈥淎 new finding like this overturns what we鈥檝e understood and taught about the active Earth,鈥 he says. 鈥淎nd it shows that there are still radical mysteries about even the grand operation of our evolving planet.鈥

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