The common theory of plate tectonics that is taught in classrooms across the country states that when a a plate is pushed, or subducted, under another plate, the subducted plate gets pushed into the Earth's core where it is essentially melted down. New evidence coming from coast of California, however, shows that this may not be entirely accurate.
The basic theory is still intact for now, but researchers are rethinking how long it takes for such a process to occur, along with entertaining the idea that plates can stay intact for millions of years after they slide under other plates. Though of little consequence to your average person, this is big news for geologists.
"Many had assumed that these pieces would have broken off quite close to the surface," said Brown geophysicist Donald Forsyth, who led the research with Yun Wang, a former Brown graduate student now at the University of Alaska. "We're suggesting that they actually broke off fairly deep, leaving these large slabs behind."
This amendment to the currently held theory all started when Forsyth took a closer look at a popular effect in the geological community known as the "Isabella Anomaly". The anomaly represents a significant cooler section of Earth located in central California, and for years it befuddled the scientists who tried to explain it.
Forsyth noticed that the Isabella Anomaly had the same temperature at the same depth as several other anomalies. It was also at the same depth as fragments from the Farallon plate that had not subducted and were still near the surface off the coast of California. The conclusion then became obvious: if all the anomalies and known fragments were at the same depth, they are probably still connected.
What Forsyth now wants to say is that instead of the Farallon plate subducting under the North American plate and melting deep in the Earth's mantle, it has instead survived almost completely submerged under California and Mexico for close to 100 million years. This equates to a gigantic fossil lurking right beneath our continent, one that nobody thought could've possibly existed.
"This work has radically changed our understanding of the makeup of the west coast of North America," says co-author of the study Brian Savage. "It will cause a thorough rethinking of the geological history of North America and undoubtedly many other continental margins."
