AN: T71E-01TI: The Queen Charlotte Basin and Coast Mountains: A Paired Belt of  Subsidence and Uplift Caused by a Low-Angle Normal Fault    AU: Kristin M.M. RohrAF: Geological Survey of Canada  PO Box 6000 Sidney BC V8L 4B2     CanadaEM: rohr@pgc.emr.caAU: Lisel CurrieAF: Geological Survey of Canada  605 Robson ST  Vancouver BC V6B 5J3    CanadaEM: lcurrie@gsc.NRCan.gc.caAB:     The Queen Charlotte Basin and Coast Mountains are a paired     belt of synchronous subsidence and uplift which formed     inboard of the Queen Charlotte Fault in the Neogene,     accompanied by regional basaltic volcanism. We propose that    simple shear on a lithosphere scale low-angle normal fault     is responsible for the observed vertical motions. Extensive    crustal thinning in the basin decreases towards the Coast     Mountains and was probably accomplished by some pure shear.    Net subsidence since 20 Ma is typically 3 km. East of the    basin in the Coast Mountains net uplift since 25 Ma is     approximately 4-5 km.         When subduction gave way to a transform motion about 47 Ma     on the Pacific-North America plate boundary, the over-    thickened continental crust probably became unstable.     Resulting shear stress on the base of the lithosphere may     have triggered gravitational collapse (pure shear) and     initiated a low-angle normal fault (simple shear). Where     the low-angle normal fault broke the upper lithosphere     widespread brittle extension in the crust created the Queen    Charlotte Basin. Farther inland where the fault thinned the    lower lithosphere  the Coast Mountains formed. Throughout     the region extension of the lithosphere and upwelling of     the asthenosphere produced basaltic volcanism by     decompression melting over the last 25 Ma. This is the     first time that a mechanism linking all these phenomena     has been proposed.    SC: TDE: 8109DE: 8105DE: 8158MN: Fall Meeting 1996