Paleomagnetic Constraints Upon the Displacement History of the Alexander Terrane, Alaska

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The collision and accretion of allochthonous terranes dominates the Mesozoic and Cenozoic history of the Pacific Northwest and Alaska. The largest terrane to dock was the amalgamated terrane sometimes referred to as "Baja British Columbia", so-called because included terranes such as Wrangellia have apparent primary Paleomagnetic vectors indicating low latitudes. However, available data from another included terrane (Alexander terrane) indicates no latitudinal movement since the late Triassic. As Alexander terrane lies to the south of Wrangellia, a severe spatial and timing problem exists. This project will attempt to resolve the paradox by extensive paleomagnetic analysis of sample collections from these terranes, including removal of overprints and determination of ages by 40Ar/39Ar techniques. Results offer the potential to resolve the tectonic sequence of assembly of the Pacific north- west terranes.