Progressive deformation associated with mid-Cretaceous to Tertiary contractional tectonism in the Juneau gold belt, Coast Mountains, southeastern Alaska

The Juneau gold belt in northern southeastern Alaska is composed of a disparate assemblage of lithotectonic terranes ranging in age from Paleozoic and perhaps older to Cretaceous. Four progressive deformational events (D ₁-D₄) associated with metamorphism and contractional tectonism began in mid-Cretaceous time, and continued well into the Tertiary. Structures associated with these events are overprinted by Eocene vein systems (D5) that contain gold mineralization. The final recognized deformation event (D6) formed brittle contractional structures and strike-slip faults. The geometry of deformed sedimentary and volcanic clasts outside of shear zones indicates that a flattening style of strain developed during contraction. Clast orientations, associated mineral lineations, folds, and asymmetric fabrics are interpreted to indicate flattening and top-to-the-west shear associated with D₁-D₄. The distinct D5 faulting and fluid-flow event occurred over a short time period (56.5-52.8 Ma) and produced a series of economically important auriferous quartz vein deposits that characterize the 160-km-long Juneau gold belt. Gold vein mineralization may have been initiated by changes in the far-field stress regime and/or rapid exhumation. Structural relations are interpreted to indicate that the deformation regime initiated as contractional and ultimately developed into transpressional.