Along the northwest coast of North America, a sinuous crack in the Earth’s crust tells the story of catastrophic tectonic activity that shook the region millions of years ago.
Because of this massive disruption, geological formations that once formed together in a common area are now separated by approximately 997 kilometers.
This separation occurred along the 2,011-kilometer-long Denali Fault, which crosses the southern tip of the Alaska Peninsula, runs through the lower part of the state, and extends into southwestern Canada’s Yukon Territory.
In a new study, geologists at the University of Alaska Fairbanks scrutinized features along the fault and found evidence that three locations—the Clearwater Mountains in south-central Alaska, Kluane Lake in the Yukon, and the Coast Mountains near the city Juneau – were once part of a single geological feature. The new study was published in the journal Geology.
Previously, researchers assumed that all three locations formed separately, but the new study concluded that they were part of a common area, formed during the final collision of land masses that led to the formation of North America.
This formation probably occurred when the Wrangellia composite terrane, an oceanic plate, gradually collided with the western edge of North America between 72 and 56 million years ago.
This idea was first mentioned in a 1993 paper, but recent research provides more evidence to support it by analyzing samples of monazite – a mineral containing rare earth elements such as lanthanum, cerium, neodymium and sometimes yttrium – from these locations.
The geology of these three locations showed clear signs of reverse metamorphism – a geological phenomenon where rocks formed at higher temperatures and pressures lie on top of those formed at lower temperatures and pressures (contrary to what is commonly expected).
“We have shown that each of these three independent inverted metamorphic belts formed at the same time under similar conditions. And they are all in a very similar structural context. Not only are they the same age, but they behaved in a similar way. Their age decreases structurally as we advance in depth,” Sean Regan, lead author of the study and associate professor at the University of Alaska Fairbanks Institute of Geophysics, said in a statement.
“Our understanding of the growth of the lithosphere or plates along the western margin of North America is becoming clearer, and much of this is related to the reconstruction of transform faults, such as the Denali fault. “We are beginning to recognize the major features that are involved in the sticking or attachment of once distant land masses to the North American plate,” added Regan.
