Structural analysis of the Southern Peninsular, Southern Wrangellia, and Northern Chugach Terranes Along the Trans‐Alaska Crustal Transect, Northern Chugach Mountains, Alaska

Abstract

Structural and tectonic analysis of the southern Peninsular, southern Wrangellia, and northern Chugach terranes, along the Trans‐Alaska Crustal Transect in the northern Chugach Mountains documents a long succession of Early Jurassic through Cenozoic deformational events. The deformational events are generally characterized by distinctive structural fabrics and metamorphisms. Most of the events are interpreted to be related to subduction‐related accretion or terrane accretion along the Border Ranges fault system (BRFS) and companion faults, and the Contact fault system (CFS). Each period of subduction‐related accretion consisted of underplating of the outboard unit beneath the adjacent inboard unit. The fabric associated with each subduction‐related accretion consisted of folding, intense shearing, and local rolling of planar structures. Age and structural relationships suggest migration of the zone of subduction‐related accretion from the BRFS to the north, through each accreting unit, to younger bounding thrust faults to the south. Other older and younger deformational events are also recognized and are interpreted to have formed before and after, respectively, accretions along the BRFS and CFS. The main younger deformational events are (1) early Tertiary north verging folding of portions of the northern Chugach and southern Wrangellia terranes and (2) broad folding and rotation of major and minor structures related to subduction‐related accretion or terrane accretion during early and middle Tertiary oroclinal bending of Alaska.