LATE CENOZOIC COLLISION OF THE YAKUTAT TERRANE, GULF OF ALASKA, AS IMAGED IN DEEP-CRUSTAL SEISMIC-REFLECTION DATA: A POSSIBLE ANALOG OF EARLIER CORDILLERAN TERRANE INTERACTIONS

During the past 5-10 Ma in the northern Gulf of Alaska region, the Yakutat terrane has been colliding with part of the northern Cordillera. Tectonic effects of this collision apparently span the entire width of the Cordillera, according to recent computer modeling done by others, and the collision may drive the westward tectonic escape of parts of southern Alaska. The Yakutat collision has been implicated as a driving force for such diverse earth processes as seismogenesis and climate change. For these reasons, this terrane’s collision may provide insight into how pre-late Cenozoic terrane collisions deformed Cordilleran rocks. We use marine deep-crustal seismic-reflection data to investigate two of the Yakutat terrane’s boundaries. The first boundary lies along the Kayak Island zone (KIZ), where crustal delamination at a depth of about 10 km split the Yakutat terrane into subducted igneous oceanic crust and accreted sedimentary rocks. Delamination along the KIZ apparently ceased during the middle Pleistocene. We also investigated the Transition fault zone, the southern tectonic boundary separating the Yakutat terrane from the oceanic Pacific plate. Sedimentary rocks at the most likely location of this fault zone are complexly deformed, and reflections from the oceanic crust are interrupted, so that near the Aleutian trench this fault zone may be absorbing some of the Yakutat-Alaska convergence.