Pace and Process of Active Folding and Fluvial Incision Across the Kantishna Hills Anticline, Central Alaska

• Published in: Geophysical research letters 2019-03, Vol.46 (6), p.3235-3244
• Main Authors: Bender, A. M., Lease, R. O., Haeussler, P. J., Rittenour, T., Corbett, L. B., Bierman, P. R., Caffee, M. W.
• Format: Article
• Language: English
• Subjects: Alaska; Anticlines; Bedrock; bedrock river incision; Beryllium 10; Chronology; Climate change; Climate control; continental neotectonics; cosmogenic nuclide dating; Deformation; Deformation mechanisms; Earth; Earth surface; Earthquakes; Folding; Geomorphology; Glacial advances; Glaciers; Hills; Landscape; luminescence dating; Plate tectonics; Pleistocene; River channels; Rivers; Seismic activity; Strain rate; tectonic geomorphology; Tectonics; Terraces; Topography (geology); Uplift; Water depth; Width
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL081509

Rates of northern Alaska Range thrust system deformation are poorly constrained. Shortening at the system's west end is focused on the Kantishna Hills anticline. Where the McKinley River cuts across the anticline, the landscape records both Late Pleistocene deformation and climatic change. New optically stimulated luminescence and cosmogenic 10Be depth profile dates of three McKinley River terrace levels (~22, ~18, and ~14–9 ka) match independently determined ages of local glacial maxima, consistent with climate‐driven terrace formation. Terrace ages quantify rates of differential bedrock incision, uplift, and shortening based on fault depth inferred from microseismicity. Differential rock uplift and incision (≤1.4 m/kyr) drive significant channel width narrowing in response to ongoing folding at a shortening rate of ~1.2 m/kyr. Our results constrain northern Alaska Range thrust system deformation rates, and elucidate superimposed landscape responses to Late Pleistocene climate change and active folding with broad geomorphic implications. Plain Language Summary Where plate tectonics deforms Earth's surface, river landscapes hold information about the distribution and rate of earthquake‐related deformation over thousands of years. The processes that form these landscapes remain uncertain. Here we study the landscape where the McKinley River cuts across the Kantishna Hills anticline to quantify previously unknown rates of earthquake‐related tectonic deformation in intracontinental Alaska, and investigate the mechanisms by which this landscape evolved. We date McKinley River terraces that were the river channel ~22, ~18, and ~14–9 ka; the ages match independent ages of regional glacial advances and hence indicate climatic control on river terrace formation. Digital topography analysis shows that the terraces have been folded and uplifted above the channel at rates up to ~1.4 m/kyr associated with shortening at ~1.2 m/kyr. The McKinley River channel narrows and slightly steepens across the fold where uplift rates are highest, indicating that the river adjusts to uplift primarily by reducing channel width and not by steepening as common incision models assume. Kantishna Hills anticline shortening accounts for ~10% of the total ~13‐mm/year plate strain rate; ~6 mm/year remains unaccounted for at this latitude and is likely distributed across structures south of the Denali Fault. Key Points Luminescence and 10Be terrace ages (~22 to ~9 ka) reflect climatic modula