How veins record progressive faulting and folding, a case study of the lower Cook Inlet basin, Alaska

Elisabeth Nadin, University of Alaska Fairbanks
Paul Betka, Lamont-Doherty Earth Observatory
Jacob Rosenthal, Oregon Department of Transportation
Robert Gillis, Alaska Department of Geological and Geophysical Surveys

Regionally persistent vein sets (i.e., filled fractures) cut Early Jurassic through late Paleogene(?) strata throughout a study area >2000 km2 in the lower Cook Inlet forearc basin of Alaska. We documented vein orientations using field, aerial, and GIS–based studies, and grouped them into four dominant sets using Sterenoet 9.8. We restored the vein orientations about regional folds by first removing the bedding dip, and then rotating the bedding strike into parallelism with the regional structural trend (as indicated by fold trend/plunge). 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 documented abutting and crosscutting relations between sets, and present relative timing observations to demonstrate that veins developed with regional faulting and fold growth of Cook Inlet basin strata during Paleogene deformation along the southern margin of Alaska. Our results may serve as a case study for linking vein growth to tectonic events in other ancient and modern forearc basins. The data set also constitutes a potential teaching module for defining vein sets, applying Fisher statistics, and applying the strike test to vein orientations to evaluate orogen-scale curvature of deformed strata.


Teaching Structural Geology and Tectonics