Rock star: Montana State Earth sciences professor receives grant to study geologic history of the Rockies
BOZEMAN – Though the rock you idly kick along that mountain trail isn’t sentient, it does have a long memory – one that a Montana State University researcher is tapping to reveal the geologic history of southwest Montana dating from hundreds of millions to billions of years ago.
Devon Orme, assistant professor of geology in MSU’s Department of Earth Sciences in the College of Letters and Science, has been awarded a grant from the National Science Foundation to apply techniques she helped develop to unlock the unknown “deep-time” history of western North America.
Along with collaborators from Idaho State and Columbia universities, who will work in the Teton and Uinta ranges respectively, Orme and her students will analyze rocks in the mountains of southwest Montana to better understand the continent’s ancient tectonic activity. Some of the rocks they will study are more than 3 billion years old.
Montana State University Professor Devon Orme poses for a portrait in her Traphagen Hall lab on Friday, Feb. 10, 2023, in Bozeman, Montana. The rocks she is holding were found together but their difference in age is over 2 billion years. MSU photo by Colter Peterson
All the ranges in the study are part of the Rocky Mountains, which stretch 3,000 miles from the provinces of Alberta and British Columbia in Canada to west-central New Mexico. The development of the Rockies is believed to have begun about 100 million to 80 million years ago, when the eastern edge of the Pacific oceanic plate continued to slide beneath the western edge of the block of Earth’s crust known as the North American Craton, which – in southwest Montana – sits “in our backyard,” Orme said.
The exact timing of this mountain-building event in southwest Montana is debated, and parts of what happened prior to that remain a mystery, as eons of erosion stripped away layers of rock and left a 2 billion-year gap in the geologic record known as the Great Unconformity. But now, Orme said, scientists can reconstruct the story by analyzing geochemical properties in rock that existed through the ages and is exposed in the Rocky Mountains.
“Rocks in the Beartooth, Bridger, Gallatin and Tobacco Root ranges hold the history and memory of geologic processes,” Orme said of the mountain ranges near Bozeman.
The research will build on a previous MSU study of the Beartooth Mountains in south-central Montana and northern Wyoming. A recently published paper in the journal Tectonics describes how the geologic history of the range was reconstructed with deep-time thermochronology using the mineral zircon, a process which Orme helped develop nearly 10 years ago. The technique exploits various degrees of damage to the crystalline structure of zircon and its uranium, thorium and helium content to find out when and how many times the rock was exposed to heat after being buried under sediment, then cooled after being uplifted during periods of faulting and erosion. The paper’s lead author, Chance Ronemus, conducted the work in Orme’s lab at MSU as a master’s student from 2019 to 2021.
Ronemus and the MSU team applied the method to rocks collected throughout the Beartooth range, including 2.8-billion-year-old samples taken from the top of Montana’s highest mountain, 12,807-foot-tall Granite Peak. The peak is well-known for being difficult to climb, so it wasn’t just the laborious sample analysis that “was a heroic effort by Chance,” Orme said.
The work proved that some of the rock comprising the Beartooths rose and fell many times before taking the shape we see today. It also helped validate the deep-time thermochronology method, which is being adopted by geologists around the globe who are excited by its potential, Orme said.
“In the last three years, use of the technique has exploded,” Orme said. Outside of North America, “researchers in China and India, for example, are applying it – it’s really cool to see the global ripple effect.”
Closer to home, the NSF funding will allow researchers to apply the technique to samples taken from a 400-mile segment of the Rocky Mountains. The three-year grant will provide opportunities for students from each institution to gain field and laboratory experience at all the study sites. From MSU, one graduate student and four undergraduate students will participate.
Primary objectives of the study are to fill a billion-year gap in the rock record along the western margin of the North American Craton, also known as Laurentia, and contribute to knowledge about Laurentian tectonics and the breakup of the supercontinent Rodinia, which occurred between 750 and 630 million years ago.
The teams also will collaborate with the Idaho Museum of Natural History to create a mobile exhibit highlighting the ancient history of the charismatic mountain ranges in the study. The exhibit will visit museums that serve rural, Rocky Mountain communities and tell the stories the rocks on that mountain path have stored in their ancient memories.
"The mountains have a much longer geologic history than the geologic processes that shaped the topography we see today,” Orme said. “My goaI is to reconstruct this entire history.”
