Duplex structure and Paleocene displacement of the Toyuk thrust zone near the Dalton Highway, north-central Brooks Range

• The Toyuk thrust zone is a regional tectonic boundary in the central Brooks Range of northern Alaska that has been interpreted previously as a single large-displacement fault. Just west of the Dalton Highway, the thrust zone is defined by several north-vergent imbricate thrust faults. These faults have cut detachment folds formed in the competent Kanayut Conglomerate between detachments in the underlying Hunt Fork Shale and overlying Kayak Shale, thereby forming a duplex. The exposed structural geometry suggests two endmember models of duplex geometry. In model one, each linking thrust has roughly the same small displacement and the roof thrust is overlain by a normal stratigraphic succession. In model two, the uppermost and hindmost fault has greater displacement than the other faults and so forms a duplex roof above which the stratigraphic section is duplicated. Discrimination between these models is not possible because the duplex roof has been eroded in the field area.Apatite fission-track analyses of samples collected within the Toyuk thrust zone record two distinct episodes of cooling interpreted to represent unroofing in response to tectonic deformation. The initial episode occurred at ~100 Ma, while the later episode occurred at ~60 Ma. These two cooling/denudation events have been documented previously in the region, but the samples from the thrust zone are the first to document displacement on a specific fault during the ~60 Ma event so far south of the front of the central Brooks Range. The results suggest that at least part of the growth of the Toyuk thrust zone accommodated structural thickening within the orogenic wedge coeval with deformation at the range front.

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NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

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