The most recent period of orogenesis in southern Alaska began in late Neogene time with the collision of the Yakutat microplate, which is partially accreted to and partially subducted beneath the Alaskan margin to form the St. Elias Mountains. One of the most dynamic areas within the orogen is the Eastern syntaxis where the Dangerous River Zone (DRZ), a significant structural and lithologic boundary, partitions deformation between dextral transpressive structures associated with the Queen Charlotte-Fairweather fault and the Yakutat fold and thrust belt. The DRZ originated as a suture zone between an oceanic plateau and the continental margin or a previously unrecognized structure within the Chugach accretionary complex, which has implications for the crustal structure beneath the western third of the Yakutat microplate.
Neotectonic studies suggest significant spatial and kinematic variation in active deformation during the collision of the Yakutat microplate. The St. Elias orogen experienced a widespread structural reorganization in the Quaternary with oblique convergence accommodated by an en echelon thrust array. The new tectonic configuration also includes the continuing development of an incipient indentor corner, significant retrothrust motion, and shifting deformation fronts. Reorganization is temporally linked to intense glacial erosion in the core of orogen and rapid sedimentation in offshore depocenters during the Pleistocene.
Near the end of the Pleistocene, large tidewater and piedmont glacial complexes began to break up and retreated from the continental shelf resulting in significant isostatic adjustments. Marine to terrestrial sedimentary deposits in the Gulf of Alaska provide constraints on the timing and magnitude of glacial rebound as well as changes in relative sea-level at the end of the Last Glacial Maximum. Drastic ice retreat resulted in rapid isostatic uplift, which was locally exceeded by equally rapid sea-level rise.
