Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published May 1987 | public
Journal Article

Geology of Annette, Gravina, and Duke islands, southeastern Alaska


Geologic mapping, U–Pb (zircon) geochronometry, and conodont studies indicate that the major pre-Jurassic assemblages on Annette, Gravina, Duke, and adjacent smaller islands include pre-Middle Ordovician metavolcanic and metasedimentary rocks (Wales metamorphic suite); Cambrian metaplutonic rocks; Ordovician – Early Silurian volcanic (Descon Formation), dioritic, and gabbroic rocks; Silurian trondhjemitic plutons; Early Devonian sedimentary (Karheen Formation) and volcanic rocks; Late Triassic sedimentary and volcanic rocks (Hyd Group); and a large body of Late Triassic pyroxene gabbro.Stratigraphic, structural, and intrusive relations record episodes of regional deformation, metamorphism, and uplift during Middle Cambrian – Early Ordovician time (Wales orogeny) and during middle Silurian – earliest Devonian time (Klakas orogeny). Upper Triassic strata were apparently deposited during a latest Paleozoic(?) – Triassic rifting event.Comparison with the geology of Prince of Wales Island indicates that the Annette and Craig subterranes of the Alexander terrane belong to the same tectonic fragment and that the Clarence Strait fault has ~15 km of right-lateral displacement at this latitude. Our geochronologic data indicate that the pyroxene gabbro on Duke Island is Triassic in age and therefore probably unrelated to nearby Cretaceous(?) zoned ultramafic bodies.

Additional Information

© 1987 Canadian Science Publishing. Received January 24, 1986; Revision accepted November 7, 1986. This study was supported by research grants awarded to GEG from the California Institute of Technology, the Geological Society of America, and Sigma Xi and was conducted with logistical assistance from the United States Geological Survey (USGS). Donald Grybeck (USGS) supervised our work during the summer of 1984. We thank Nonnan Savage (University of Oregon) for studying the conodonts from the area and James Chen and Leon Silver (Caltech) and Ken Ludwig (USGS) for assistance in our geochrono logic studies. Terrence Barr and Karl Mueller provided able and enthusiastic assistance in the field. The hospitality and logistical support of Mitchell Hudson of Metlakatla are much appreciated.

Additional details

August 22, 2023
October 17, 2023