AN: T71E-08TI: Evolution of the Central Gneiss Complex (CGC), ~54 N lat., British    ColumbiaAU: M E RusmoreAF: Department of Geology Occidental College Los Angeles CA    90041EM: rusmore@oxy.eduAU: G E GehrelsAF: Department of Geosciences University of Arizona Tucson AZ    85721AU: S ShulaAF: Department of Geology Occidental College Los Angeles CA    90041AB:     Three models seek to explain formation of the CGC: thrusting     and crustal thickening, deep level accommodation of     northward-translation of upper crust, or core-complex type     crustal extension.  Our study aims to distinguish between     these models.  The CGC experienced severe early Tertiary     (pre-62 Ma) deformation, metamorphism, and plutonism not     shared by adjacent units.  The oldest deformation preserved,    D1, produced gneissic banding and rare intrafolio folds.      Synkinematic metamorphism produced kyanite and staurolite.      A ~77 Ma metamorphosed sill shares the D1 foliation,     suggesting D1 is Late Cretaceous or younger.  D2 folds are     nearly recumbent, tight, and plunge gently NNW-SSE.  Hinge     lines are subparallel to a mineral elongation lineation.      Sillimanite +cordierite assemblages formed during D2,     suggesting pressure decreased between D1 and D2.  A     synkinematic dike is ~67 Ma and a 62.4 ± 0.8 Ma post-    tectonic pluton cuts D2.  D2 is overprinted by post-    metamorphic D3 folds.        The dramatic contrast between CGC and adjacent blocks     requires major faulting along CGC margins.  Motion on the     western contact (Coast shear zone) largely pre-dated the 62     Ma Quottoon pluton and involved uplift of the CGC.  The east     margin here is a locally mylonitic pluton.  Data in hand     favor N-S directed thrusting within the CGC, perhaps in     response to strike-slip faulting, but cannot rule out other     models.    SC: TDE: 8005DE: 8010DE: 8015MN: Fall Meeting 1996