Research findings change understanding of central Idaho geology

Kathleen Durk, an Idaho State University geological sciences undergraduate student, helped solve the mystery of the source for “ghost” zircon grains in Idaho’s Big Lost River system. Her findings fundamentally change understanding of the geological history of central Idaho.

After completing her high-mountain detective work as part of her ISU senior thesis, the former Century High School student also traveled to Australia this spring to obtain uranium-lead geochronology (rock-aging) data using one of the world’s most powerful Ion Microprobes.

“My senior research project and field work with the ISU geological sciences department was a good capstone learning experience to my undergraduate career,” said Durk, who will be working as a teaching assistant at this summer’s ISU Geological Field Camp, based north of Mackay within sight of Mount Borah, Idaho’s tallest peak. That camp runs for five weeks from May 29 through July 2.

“It’s unusual,” added Durk, “for any undergraduate to get the kind of opportunity for research that I was able to at ISU. It was a really awesome opportunity that doesn’t happen very often.”

Durk spent last summer doing fieldwork for her senior thesis in the Wildhorse Creek drainage of Idaho’s Pioneer Mountains. She was assisting her major advisor, Paul Link, PhD, ISU geosciences professor, working on a National Science Foundation grant.

Several years earlier, Link and students had obtained ages from grains of the mineral zircon, in the sands of the Big Lost River system, that were a “ghost” age. Zircon is a mineral that contains small amounts of uranium, and thus provides a geologic clock or measure of absolute age. Zircons are found in all granitic rocks, and can be recycled through sediments in streams, and preserve their original age of crystallization. These grains were about 700 million years old, but no rocks of that age had been mapped anywhere upstream in the Big Lost River system. The 700 million year old zircons were traced to Wildhorse Creek in the Pioneer Mountains west of Mackay

In summer 2006 Durk spent four weeks in the field sampling rock formations to find the possible source of the ghost zircon grains. She worked out of a backpack tent for her base camp at about 10,000-feet elevation. She and ISU geoscience field assistants spent each day hiking and taking samples.

“I covered the area and studied the rock and went around the entire drainage,” Durk said. “I got to know the rocks and looked for something that didn’t look like something else, and I sampled that rock.  And then I determined that it contained zircon grains that were 700 million years old.  I found it.”

This spring, Durk traveled to Canberra, the national capital of Australia, to determine the age of the zircon grains in her rock samples. She worked eight-hour days for about four weeks at the Australian National University Sensitive High Ion Microprobe. The lab analysis confirmed that the metamorphosed granite rock Durk had sampled was indeed the source of the unknown grains.  

“Kathleen completed high-quality research that is very impressive for an undergraduate student,” Link said. “And her findings change our understanding of the geological history of central Idaho, which is pretty significant.”

“Until now,” Link continued, “the core of the Pioneer Mountains is thought to have crystallized about 2,300 million years ago. We just found rock one-third that age. This has serious implications for our understanding of how North America rifted away from Siberia about 700 million years ago”.  

Durk, Link and Mark Fanning, PhD, Research School of Earth Sciences, Australian National University, collaborated on the study. They will now submit the results to scientific journals.

“It was all pretty fun, but really challenging,” Durk said. “I am fortunate for all these life-changing opportunities.”