Title of Oral/Poster Presentation

Exhumation and fluid flow history of the eastern Denali fault zone, Yukon, Canada, from multi-method thermochronometry

Class

Article

Graduation Year

2018

College

College of Science

Department

Geology Department

Faculty Mentor

Alexis Ault

Presentation Type

Poster Presentation

Abstract

Reconstructing the spatial and temporal patterns of deformation along fault zones is a critical component of understanding the long-term evolution and seismic hazard of major faults. The ~2,000-km-long Denali fault zone (DFZ) extends from the Bering Sea, through south-central Alaska, and into Yukon, Canada. The 2002 Mw 7.9 earthquake on the DFZ indicates there are significant modern seismic hazards. We examine the timing, tempo, and spatial variation of rock exhumation within the DFZ-bounded Kluane Range in southeastern Yukon with new and previously published low-temperature thermochronology data from different locations and elevations within a zone of DFZ-related distributed deformation. Zircon (U-Th)/He (He), apatite fission-track, apatite He, and hematite He thermochronometers record exhumation from depth and cooling through temperatures of 220-20 °C, 120-80 °C, and 90-30 °C, and 250-25 °C, respectively. All thermochronometric dates increase in a non-linear fashion with distance from the modern-day trace of the DFZ. The youngest dates from the highest temperature thermochronometers are immediately adjacent to the DFZ. Thermal history models of thermochronometric dates suggest episodes of apparent rapid cooling in the Cretaceous and Late Oligocene. Cretaceous cooling is temporally coincident with documented magmatism and contractional tectonism in the area and likely reflects rapid post-magmatic cooling and/or accelerated exhumation. Spatial patterns of thermochronometric dates require a ≥2x increase in the magnitude of Late Oligocene differential exhumation over a ≤3 km-width zone. Alternatively, date patterns may be explained by localized circulation of hydrothermal fluids that perturbed and variably reset thermochronometric dates adjacent to the fault. Brittle faults within this locality exhibit evidence for extensive fluid flow and hematite mineralization, supporting this notion. Hematite He dates from fault surfaces hosted within this zone suggest fluid circulation may have occurred at ~7 Ma, in-tandem with fault activity. Ongoing apatite, zircon, and hematite He dating will further test and refine this hypothesis.

Location

North Atrium

Start Date

4-13-2017 12:00 PM

End Date

4-13-2017 1:15 PM

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Apr 13th, 12:00 PM Apr 13th, 1:15 PM

Exhumation and fluid flow history of the eastern Denali fault zone, Yukon, Canada, from multi-method thermochronometry

North Atrium

Reconstructing the spatial and temporal patterns of deformation along fault zones is a critical component of understanding the long-term evolution and seismic hazard of major faults. The ~2,000-km-long Denali fault zone (DFZ) extends from the Bering Sea, through south-central Alaska, and into Yukon, Canada. The 2002 Mw 7.9 earthquake on the DFZ indicates there are significant modern seismic hazards. We examine the timing, tempo, and spatial variation of rock exhumation within the DFZ-bounded Kluane Range in southeastern Yukon with new and previously published low-temperature thermochronology data from different locations and elevations within a zone of DFZ-related distributed deformation. Zircon (U-Th)/He (He), apatite fission-track, apatite He, and hematite He thermochronometers record exhumation from depth and cooling through temperatures of 220-20 °C, 120-80 °C, and 90-30 °C, and 250-25 °C, respectively. All thermochronometric dates increase in a non-linear fashion with distance from the modern-day trace of the DFZ. The youngest dates from the highest temperature thermochronometers are immediately adjacent to the DFZ. Thermal history models of thermochronometric dates suggest episodes of apparent rapid cooling in the Cretaceous and Late Oligocene. Cretaceous cooling is temporally coincident with documented magmatism and contractional tectonism in the area and likely reflects rapid post-magmatic cooling and/or accelerated exhumation. Spatial patterns of thermochronometric dates require a ≥2x increase in the magnitude of Late Oligocene differential exhumation over a ≤3 km-width zone. Alternatively, date patterns may be explained by localized circulation of hydrothermal fluids that perturbed and variably reset thermochronometric dates adjacent to the fault. Brittle faults within this locality exhibit evidence for extensive fluid flow and hematite mineralization, supporting this notion. Hematite He dates from fault surfaces hosted within this zone suggest fluid circulation may have occurred at ~7 Ma, in-tandem with fault activity. Ongoing apatite, zircon, and hematite He dating will further test and refine this hypothesis.