Neotectonics of the Yakutat Collision: Changes in Deformation Driven by Mass Redistribution

Structural relationships in the eastern syntaxis of the St. Elias orogen, Alaska

“…The interpretation of structure at depth has considerable implications for structural reconstructions and estimates of total shortening. Berger et al, 2008a;Chapman et al, 2008). Shortening estimates from published structural reconstructions are lower, generally <100 km (Meigs et al, 2008;Chapman et al, 2008;Wallace, 2008).…”

“…Offshore, the deformation front is defi ned by the Pamplona zone, an active fold-and-thrust system that accommodates ~6 mm/yr of shortening Chapman et al, 2008). The Pamplona zone trends onshore into the Malaspina fault, the active deformation front in the eastern syntaxis area (Fig.…”

“…Apatite U-Th/He ages (Berger et al, 2008a(Berger et al, , 2008bSpotila and Berger, 2010), zircon fi ssion-track ages (Enkelmann et al, 2010), and structural restorations (Meigs et al, 2008;Wallace, 2008), however, suggest that much of the sedimentary cover exposed at the surface today was never buried >5 km, indicating that none of the rocks now exposed in the YFTB were deeply buried beneath thrusts prior to exhumation. Previous interpretations of the YFTB structure at depth include a series of duplexes and imbricate thrusts in Cenozoic sedimentary rocks alone (Berger et al, 2008a;Chapman et al, 2008) or also including structurally thickened basement rocks (Wallace, 2008). The interpretation of structure at depth has considerable implications for structural reconstructions and estimates of total shortening.…”

The Quaternary thrust system of the northern Alaska Range

“…deformation is the subduction and accretion of the eastern and central Yakutat terrane (Fig. 1), which began in the late Miocene to Pliocene (e.g., Bruns, 1983;Plafker and Berg, 1994;Chapman et al, 2008). The strain from this collision is transferred into central Alaska through the translation and counterclockwise rotation of south-central Alaska .…”

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“…During the past several million years, the Aleutian megathrust has stepped eastward within the Yakutat microplate, from the western segment of the orogen where the Kushtaka and Martin Lake trenching sites are located, to the Pamplona zone and its onshore continuation, the Malaspina thrust system (Plafker, 1987;Chapman et al, 2008;Enkelmann et al, 2010;L.L. Worthington, 2010, personal commun.…”