“Shattered Alliances: The Denali Fault’s Role in the Collision of Ancient Landmasses”

The investigation, spearheaded by associate professor Sean Regan at the University of Alaska Fairbanks Geophysical Institute and UAF College of Natural Science and Mathematics, is highlighted on the front cover of the December issue of Geology, the journal of The Geological Society of America.

Regan serves as the principal author of the research paper. Co-authors from UAF include doctoral candidate McKenzie Miller, recent master’s degree holder Sean Marble, and research assistant professor Florian Hofmann. Additional co-authors come from St. Lawrence University, South Dakota School of Mines and Technology, and the University of California, Santa Barbara.

“Our comprehension of lithospheric expansion, or plate development, along the western edge of North America is becoming more lucid, and a significant aspect of that pertains to the recreation of strike-slip faults such as the Denali Fault,” Regan stated. “We are beginning to identify those fundamental characteristics involved in the joining, or suturing, of once-distant land masses to the North American plate.”

The study concentrated on formations located at three sites: the Clearwater Mountains in Southcentral Alaska, the Kluane Lake area in Canada’s southwestern Yukon, and the Coast Mountains near Juneau. Previous perspectives among geologists vary, with some proposing that the three sites originated separately.

Regan’s historical reconstruction regarding 300 miles of horizontal displacement on the Denali Fault over millions of years revealed that the three sites at one point constituted a terminal suture zone. A terminal suture zone signifies the ultimate amalgamation of tectonic plates or crustal fragments into a more extensive mass.

Regan’s research delineates one of several locations where the Wrangellia Composite Terrane, an oceanic plate that formed far from its current location, was integrated into the western edge of North America between 72 million and 56 million years ago.

“When you consider geologists traversing the Earth’s surface attempting to grasp what transpired, it is logical that they may not associate features that are so separated,” Regan mentioned in reference to the three locations he examined. “With various geologists operating in distinct regions, connections typically do not emerge until one can reconstruct deformation along the Denali Fault.”

Regan’s reconstruction emphasized the inverted metamorphism of the three sites, a geological phenomenon wherein rocks formed under elevated temperatures and pressures are discovered overlying rocks formed under lower temperatures and pressures. This contrasts with the typical sequence seen in regional metamorphism, where temperature and pressure commonly increase with depth.

Inverted metamorphism is a crucial indicator of tectonic intricacy and aids geologists in reconstructing crustal deformation processes and orogeny.

“We demonstrated that each of these three distinct inverted metamorphic belts formed concurrently under comparable conditions,” Regan affirmed. “Furthermore, they all occupy a remarkably similar structural environment. Not only are they of the same age, they all exhibited analogous behavior. They diminish in age, structurally, as you go deeper.”

Regan linked the three sites by investigating their monazite, which is composed of the rare earth elements lanthanum, cerium, neodymium, and occasionally yttrium. He gathered monazite from the two Alaskan locations and utilized Kluane data published earlier that year by another researcher.

“It is truly a remarkable little mineral,” Regan expressed. “It can participate in a multitude of reactions, allowing us to use it as a tool to trace the mineralogical development of a rock.”

Regan commenced his investigation after perusing a 1993 publication by researchers at the University of Alberta and University of British Columbia, published in Geology. That article posited similarities in the Denali Fault region later evaluated by Regan, yet only classified them as a single metamorphic-plutonic belt.

A metamorphic-plutonic belt is a zone characterized by the close relationship of metamorphic and plutonic rocks that form as a result of intense tectonic activity, usually during mountain-building episodes. Such belts are often located in regions where tectonic plates converge.

“It astounded me that the 1993 article had not garnered more attention in its time,” Regan noted. “I had that paper displayed on my wall for the past four years, as I believed it was genuinely ahead of its era.”