Geologists challenge a widely held theory

Jim Martyka

A long-unsolved case of geological assault might now be resolved, thanks to the efforts of two University graduates.
For years, geologists have been mystified by the formation of the Rocky Mountains, the nation’s largest mountain range. The peaks show all the signs of having been formed by the collision of two tectonic plates, but direct evidence of the collision or the plate that could have caused it has so far been lacking.
Basil Tikoff and Julie Maxson, who both graduated from the University with degrees in geology, have developed a “hit-and-run” theory about the formation of the Rockies, claiming a large plate pushed up the mountains during a collision and then fled the scene.
But even more amazing is how the two geologists, who were conducting different types of geological research more than 1,000 miles apart from each other, discovered the coincidences that led to their theory.
“The Rocky Mountains have always looked like collision mountains, like the Himalayas and such,” said Maxson, an assistant professor of geology at Carleton College. “But, never before had anyone put forth a (formation) theory based on this.”
Tikoff, a research associate in the Department of Geology and Geophysics at the University, said that it was this problem that intrigued him.
“It’s been a problem because usually (mountains) form when you collide two plates that won’t subduct,” he said. “However, with the Rockies, there is only evidence of one plate.”
Tikoff and Maxson’s theory, however, claims that a collision did take place. They say the tectonic plate, “Baja BC,” which stretches from northern Washington state to southeast Alaska, collided with southeastern California, forming the Rocky Mountains nearly 90 million years ago. This constitutes “the hit.”
The plate then changed direction and moved, during the course of 50 million years, to it’s current location, thus constituting “the run.”
While Maxson’s studies led her to discover “the run,” Tikoff’s work revealed “the hit.”
Tikoff was studying the cessation of volcanic activity in the southwestern part of the country. He determined that the inactivity had to have been caused by a collision some 90 million years ago. The collection of paleomagnetic data also confirmed his theory that a collision took place.
At the same time, Maxson was studying Baja BC and determined that it was in the south and started to move north around the same time as the collision. The two put their work together and proposed the “hit and run” caused the formation of the Rockies.
“It was kind of an ‘Aha!’ moment,” said Maxson.
Their theory conflicts with the established story of the formation of the mountain range, which came from geologists’ studies in the early 1980s.
This widely accepted theory states that part of the Farallon plate, which is located off the east coast of California and Mexico, sank below North America, pushing up the Rockies in the process.
Geologists believe the plate’s descent changed as it sank, rubbing the bottom of North America and pushing up the mountains.
However, Tikoff said there are several problems with this theory.
One of problems is evidence that the bottom layers of North America still exist.
“If the plate rubbed the bottom of the continent, it should scrape some of it off,” said Tikoff. “However, we have evidence that it is all still there.”
Tikoff also said that there is too much evidence that supports that a collision took place. The popular theory does not account for that.
Despite the problems, Tikoff said geologists accepted the old theory mostly for lack of a better explanation.
Now Tikoff and Maxson both hope their theory gains support. “There are just too many coincidences in our findings,” said Maxson.
However, both also said problems do exist with their theory, such as inconsistencies in the plate movement and evidence that Baja BC may have collided at its current location.
Their most serious problem, however, is the lack of a fault line. When two plates collide, the largest piece of evidence left behind is a fault line. Tikoff and Maxson have thus far been unable to find one for their collision theory.
“There should be one there among the several that exist in that area,” said Maxson. “It’s just a matter of finding which one.”
Maxson said this search is the next step in their research. She said she hopes they can start work on this search next summer.
“Now we’re going from what happened to how it happened,” said Tikoff.
For the time being, both said they will work on promoting their theory.
Tikoff and Maxson will present the theory at the next meeting of the Geological Society of America later this year.
“We’ll see if it’s accepted or not,” he said. “Only time will tell.”