Structure and kinematic evolution of the Duke River fault, southwestern Yukon

Abstract

In southwest Yukon, the boundary between the Alexander terrane and Wrangellia corresponds with the Duke River fault. In this paper, we report on observations of the Duke River fault from four localities in southwest Yukon, and provide new constraints on (1) Permian regional metamorphism within the Alexander terrane, (2) Cretaceous ductile deformation along the Duke River fault, and (3) post-Miocene brittle deformation along the fault. Within these areas, the Duke River fault juxtaposes imbricated, pervasively foliated and folded greenschist-facies rocks of the Alexander terrane southwest of the fault against sub-greenschist-facies, less deformed rocks of Wrangellia. Multiple lines of evidence from this region indicate the Alexander terrane has been juxtaposed against Wrangellia along a southwest-dipping thrust fault. 40Ar/39Ar dates from muscovite, which grew during faulting or have been reset by motion along the Duke River fault, range from 79 to 105 Ma, suggesting that ductile movement along the fault is at least as old as Cretaceous (Albian to Cenomanian). This phase of faulting is interpreted as the local expression of Cretaceous shortening, which has been documented along the length and width of the Cordillera. Cretaceous structures along the Duke River fault are overprinted by brittle deformation that affects rocks as young as Miocene (or Pliocene?). The Duke River fault appears to be accommodating present-day transpression through uplift and reactivation of the thrust fault.

The 1 May 2017 British Columbia‐Alaska Earthquake Doublet and Implication for Complexity Near Southern End of Denali Fault System

“…The sense of slip is more consistent with that of the Duke River fault, which has been proposed to a southwest dipping reverse fault, in contrast to the mostly strike-slip motion of the eastern Denali fault (Cobbett et al, 2016;Muller, 1967). The sense of slip is more consistent with that of the Duke River fault, which has been proposed to a southwest dipping reverse fault, in contrast to the mostly strike-slip motion of the eastern Denali fault (Cobbett et al, 2016;Muller, 1967).…”

“…Fletcher & Freymueller, 2003). The Duke River Fault adjacent to the Dalton Fault has been mapped as a moderately to steeply southwest-dipping reverse fault (Muller, 1967) and has been inferred to be accommodating transpression through uplift and reactivation of this reverse fault (Cobbett et al, 2016). Thus, the Dalton fault likely has a low slip rate.…”

Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

“…Interpretive models are summarized in Figure with three schematic block diagrams and representative cross sections of TSU and mean topography (i.e., NSU) corresponding to Phases I (line A‐A′), II (line B‐B′), and III (line C‐C′). Block diagrams include major fault and magmatic systems active during each phase based on previous work (Figure ; Andronicos et al, ; Cobbett et al, ; Dodds & Campbell, ; Gehrels et al, ; Ingram & Hutton, ; Israel et al, ; Lowey, ; Rubin et al, ). We assume a component of sustained right‐lateral displacement along the EDFZ such that the Kluane Ranges (southwest of the EDFZ) were juxtaposed against Intermontane terrane (northeast of the EDFZ) features that are presently observed to the southeast of our study area at various times in the past.…”

“…(c) Chronology of local and regional geologic events. References for timeline are the following: 1 Miller et al (); 2 Cobbett et al (); 3 Ingram and Hutton (), Gehrels et al (), and Lowey (); 4 Eisbacher (), Cole et al (), Miller et al (), and Riccio et al (); 5 Erdmer and Mortensen (), Mezger et al (), and Israel et al (); 6,15,16 Eisbacher and Hopkins (), Ridgway et al (), and Ridgway and Sweet (); 7 Nokleberg et al (), Rubin et al (), and Dusel‐Bacon et al (); 8 Haeussler et al (); 9 Falkowski et al (); 10 Finzel et al (); 11,12,13,14 Dodds and Campbell (); 17 Denton et al ().…”

Initiation of the Wrangell Arc: A Record of Tectonic Changes in an Arc-Transform Junction Revealed by New Geochemistry and Geochronology of the ~29–18 Ma Sonya Creek Volcanic Field, Alaska

“…These two volcanoes physically overlap one another, and show a limited areal extent with focused distribution along the Duke River fault. Evidence for Oligocene to Miocene motion on the Duke River Fault (Cobbett et al, 2017) supports the idea that transcurrent faulting can focus arc volcanism along faults (Tibaldi et al, 2010). Shifts in lava chemistry from alkaline, to transitional, to calc-alkaline, and back to transitional affinities record the relative importance of the tectonic processes of leaky transform magmatism over a slab-window (alkaline) and subduction (calc-alkaline).…”