Revisiting the Paleomagnetism of the Ghost Rocks Formation of the Kodiak Islands, Alaska

The Paleocene Ghost Rocks Formation is the second youngest unit in the accretionary complex that comprise the Kodiak Islands, AK, part of the Chugach terrane, and consist of a sequence of turbidites interbedded with pillow lavas. Most workers agree that the anomalous near trench magmatism is a result of the passage of a trench- ridge-trench (TRT) along the margin of North America. However, it remains controversial as to the location where this interaction took place relative to the ancient North American margin. Plumley et al. (1983) conducted a paleomagnetic study on the pillow lavas of the Ghost Rocks Formation and concluded that they had formed at a latitude of 40° N. Discordant locality mean directions at the two localities of the study, Alitak and Kiliuda Bays and a complex two-stage structural correction used at Alitak Bay have cast doubt on the strength of this conclusion. This collaborative structural and paleomagnetic study seeks to resolve the location where the Ghost Rocks Formation formed using more detailed sampling and structural analysis. A total of 176 sites were sampled in 2006 and 2007, from four localities in the Kodiak Islands. This abstract will focus on samples collected from the Jap Bay locality, where sedimentary rocks were sampled. Preliminary results of sites taken at Jap Bay have two components of magnetization. The second-removed component has dual polarity and an improvement in clustering is observed upon tilt correction. These results are consistent with preliminary result of samples collected at two other sites of this study, Alitak and Kiliuda bays, suggesting the magnetic character recorded in the Ghost Rocks Formation is primary in origin. The inclinations are shallow relative to those expected for North America and at this time support models that place the Chugach terrane >1000km south of their present location.