Volatile Pathways of the Denali Fault Zone

Mineral springs are often located along fault zones, and investigating their geochemistry provides insight into the roles of faults, earthquakes, and deeply circulated groundwater in the evolution of tectonically active regions. Dr. Dennis Newell’s research group specifically uses the isotopic composition of thermal springs as windows to deep tectonic processes, revealing the contributions of magmatic activity, metamorphism, and mantle degassing. Newell spearheaded NSF-funded research and a 2023 paper in the journal Geology conducting such analyses along the Denali Fault in Alaska.

The Denali fault zone is a major right-lateral strike-slip system traversing Alaska’s interior, recently giving rise to the 2002 Mw 7.9 Denali Fault earthquake. Newell and colleagues investigated warm springs located along and outside of the 2002-ruptured segments of the Denali and Totschunda faults. Isotope results show the presence of up to 30% mantle-derived helium in segments of the faults that did not rupture in 2002. This supports the presence of deep conduits through the crust, tapping volatiles being released from the upper mantle, similar to observations from other major transform systems like the San Andreas and North Anatolian fault zones. In contrast, the isotopic results from springs located along the 2002 rupture indicate the presence of only atmosphere-derived helium, and no active pathway for mantle volatiles. Although this data indicates that groundwater-flow paths are shallow today, accumulations of older travertine along the faults suggest deeper plumbing in the past. Newell and authors suggest the 2002 earthquake disrupted those mantle flow paths.