U-Pb and Hf isotope analysis of detrital zircons from the Banks Island assemblage (coastal British Columbia) and southern Alexander terrane (southeast Alaska)
Clare J. Tochilin et al., Department of Geology, University of Arizona, Tucson, Arizona, USA. Published online ahead of print on 2 Apr. 2014; http://dx.doi.org/10.1130/L338.1.
The Banks Island assemblage (BIA) consists of metasedimentary rocks that are exposed on the outer islands of coastal British Columbia. These rocks are enigmatic in that quartz-rich metasedimentary components accumulated near a continent, whereas the surrounding Alexander and Wrangellia terranes have little continent-derived material. In an effort to learn more about the origin of the BIA, the authors have conducted U-Pb and Hf isotope analyses on detrital zircons from metasedimentary rocks of the BIA and from nearby strata of the southern Alexander terrane. These data confirm that the BIA consists largely of continent-derived material, whereas the southern Alexander terrane formed far from a continental margin. Comparison with previously published data from other regions of the Cordillera suggests that the BIA resembles rocks of the northern Alexander terrane. The authors accordingly suggest that the BIA formed adjacent to the northern Alexander terrane and was offset southward by approximately 1000 km to now reside adjacent to the southern portion of the terrane. This southward motion was accommodated along the Early Cretaceous Kitkatla shear zone. Comparison of these U-Pb ages and Hf isotope signatures with other
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