206 Strain and Displacement: Patterns, Gradients, Partitioning, and Reconstructions
This session aims to bring together researchers from structure-related disciplines to facilitate discussions of approaches that inform our understanding of strain and displacement. We welcome contributions from observations, experiments, theory, and modeling that characterize deformation from micro to tectonic scales.
Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 217C
Linking long-term Denali fault displacement gradients with curvature of the southern Alaska margin
Paper number: 206-5
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM
Authors
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Sean ReganGeophysical Institute-University of Alaska Fairbanks, Fairbanks, AK
Abstract
The Denali fault is an active right-lateral strike-slip fault that transects the northern North American Cordillera from British Columbia to Bristol Bay in southwestern Alaska. Along its >2500 km length, multiple bedrock and surficial geologic markers are offset by the fault and record an east-to-west decrease in net right lateral displacement that appears to have persisted since the Late Cretaceous. The fault also displays a ~100° change in strike along its length, referred to as the Alaskan Orocline, that has been interpreted to facilitate the Quaternary slip (rate) gradient. However, the effect of the orocline on Denali fault slip over longer timescales (106-7 yr) remains less clear. Here, we review the bedrock geologic assemblages used to record long-term displacement on the Denali fault and link dissection of those geologic markers to development of the Alaskan orocline over the Late Cretaceous and Cenozoic. Our analysis results in two key outcomes: 1) The section of the Denali fault west of the orocline hinge displays an older slip history, but has accumulated less net right-lateral slip than the section of the fault to the east of the orocline hinge; and 2) Oroclinal bending of southern Alaska overlapped in time with intense shortening and inverted metamorphism in the Canadian Cordillera to the south, which extruded western Alaska along strike slip faults, including the western Denali fault. These outcomes demonstrate that the Quaternary strand of the Denali fault links at least two bedrock fault strands and evolved independently prior to linkage: an older strand in the west that accommodated Late Cretaceous-Paleogene extrusion and oroclinal bending of Alaska, and a post-50 Ma strand in the east that translates lithosphere through the orocline hinge from east to west. Our work indicates that the variable displacement of bedrock slip markers along-strike of the Denali fault is well-explained by integration of fault strands with variable slip history. We propose that displacement gradients resulting from linkage of pre-existing fault strands should be expected along long-lived continental fault systems and should be considered along with more commonly evoked mechanical or slip partitioning explanations.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-414174
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