Gold Open Access: This paper is published under the terms of the CC-BY-NC license.

Regionally persistent vein sets cut Early Jurassic through late Paleogene(?) strata throughout a study area >2000 km2 in the lower Cook Inlet forearc basin of Alaska. Using field, aerial, and GIS–based studies, we document vein orientations, group them into four dominant sets, and present relative timing observations to demonstrate their development during regional faulting and folding of Cook Inlet basin strata. All veins were restored about regional folds by first removing the bedding dip, and then rotating the bedding strike into parallelism with the regional structural trend (038°). The most dominant vein set strikes ∼310°, orthogonal to the regional structural trend, and is present in all strata in the field area. The other sets strike 210°, 360°, and 260°. Fold-test results show that variations in the vein set orientations throughout the study area are correlated with the changes in bedding attitudes that define regional folds, indicating that the veins formed progressively with the folds. We document abutting and crosscutting relations between sets, and present a new ca. 52 Ma 40Ar/39Ar age of a dike that parallels the dominant set (310°) and is crosscut by others. Based on field relations, relative timing constraints, and the fold-test results, we suggest a sequence of vein development and its relationship to fold growth within the Bruin Bay fault system during Paleogene deformation along the southern margin of Alaska. Our results may serve as a case study for linking vein development to tectonic events in other ancient and modern forearc basins.

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