AN: T71E-02TI: 3-D Seismic Reflection Interpretations Along the Fiords Crossing the    Boundaries of the Alexander Accreted Terrane, Northern British    ColumbiaAU: Triparna DasAF: Dept. of Geosciences Princeton University Princeton New Jersey    08544-1003 USAEM: das@geo.princeton.eduAU: John DieboldAF: Lamont-Doherty Columbia University Rt. 9W P.O. Box 1000 Palisades New    York  10964 USAEM: johnd@lamont.ldgo.columbia.eduAU: Kristin RohrAF: Pacific Geoscience Center 9860 W. Saanich Road P.O. Box 6000 Sidney    British Columbia  V8L 4B2 CanadaEM: rohr@pgc.emr.caAU: Chris AndronicosAF: Dept. of Geosciences Princeton University Princeton New Jersey    08544-1003 USAEM: cla@princeton.eduAU: Keith KlepeisAF: Dept. of Geology and Geophysics Bldg. F05 The University of Sydney NSW    2006 AustraliaEM: keith@es.su.oz.auAU: Lincoln S. HollisterAF: Dept. of Geosciences Princeton University Princeton New Jersey    08544-1003 USAEM: linc@geo.princeton.eduAB:     The ACCRETE project acquired seismic reflection    profiles across the major terrane boundaries of the    Pacific Northwest. A loose grid of lines was collected    over the northern end of the Tertiary Queen Charlotte    Basin, which is thought to overlie the boundary between    the Wrangellia and Alexander terranes, as well as the    more recent Alexander - North America suture. The    existence, nature, and age of these boundaries are highly    controversial. Observed reflections may be the result of    recent basin formation as well as the older terrane    accretion events.        Under the Alexander terrane, several bands of    pronounced southwest dipping seismic reflections    obliquely cut a generally highly reflective crust. They    extend from about 3 seconds 2-way travel time to about    1 sec from Moho, which is at 8-9sec. Reflections in the    upper crust (1-3 sec) dip gently east and are consistent    with the attitude of the structural fabric observed along    the shorelines of the nearby islands and mainland. The    combination of these two reflecting zones produces    wedge-shaped structures, opening to the southwest.    Under the prominent southwest dipping reflecting zones,    Moho appears to be about 1 sec shallower than to either    end. The bands of reflecting horizons do not cross the    Coast shear to the east, and they diminish over a few    tens of kilometers to the west, under Wrangellia.        The absence of mapped southwest dipping structures in    the exposed Alexander terrane suggests that the    southwest dipping reflectors might be relatively late, and    thus they can be interpreted as kilometer scale    detachment zones related to the known late Miocene    extension of Queen Charlotte Basin. However,    previously discovered half-grabens in western Dixon    Entrance, which are bound by east-dipping faults, are not    associated with the crustal scale reflectors seen in the    ACCRETE data set. Therefore, an alternative    explanation for the southwest dipping reflectors is that    they represent east vergent thrust decollements produced    during accretion of the Alexander terrane.    SC: TDE: 7245DE: 8110DE: 8155MN: Fall Meeting 1996