HR: 16:45h
AN: T14B-04    [Abstracts]
TI: Along Strike Variation in Response to Tectonic Processes Within a Long Lived Accretionary Orogen, Coast Mountains, British Columbia
AU: * Israel, S
EM: Steve.Israel@gov.yk.ca
AF: Yukon Geological Surve, 2099 second ave, Whitehores, YT Y1A 1B5, Canada
AU: Kennedy, L A
EM: lkennedy@eos.ubc.ca
AF: University of British Columbia, Earth and Ocean Sciences,6339 Stores Rd, Vancouver, BC V6T 1Z4, Canada
AU: Ullrich, T D
EM: tullrich@eos.ubc.ca
AF: University of British Columbia, Earth and Ocean Sciences,6339 Stores Rd, Vancouver, BC V6T 1Z4, Canada
AU: Friedman, R M
EM: rfriedman@eos.ubc.ca
AF: University of British Columbia, Earth and Ocean Sciences,6339 Stores Rd, Vancouver, BC V6T 1Z4, Canada
AB: Jurassic to Tertiary tectonic interactions between two large superterranes of the Canadian Cordillera are preserved within the Atnarko complex. The complex is located within the Coast plutonic complex, a belt of plutonic and metamorphic rock that occurs near the western margin of the present North American margin. Pre-Early Jurassic metavolcanic and metasedimentary rocks are structurally interleaved with Late Triassic to Early Cretaceous orthogneiss and record several phases of deformation that include: poorly characterized Jurassic deformation; Early to mid-Cretaceous southwest to west directed compression; mid-Cretaceous north to northeast directed compression; mid- to Late Cretaceous dextral and sinistral ductile/brittle shearing; and post latest Cretaceous brittle faulting. Along strike of the Atnarko Complex, deformation is partitioned into compressive and translational regions with the Atnarko complex area defining the transition between the two types of crustal deformation. To the northwest of the Atnarko complex post mid-Cretaceous deformation is expressed as southwest-directed compression while to the southeast, large dextral strike-slip faults formed. It is proposed that compression in the northwest led to increased crustal thickness and partial melting of lower and middle crust in the Tertiary. In contrast the cessation of compression in the southeast lead to a more stable crustal lithosphere (i.e. cooler). A change in relative plate motions in the early Tertiary triggered full-scale orogen- perpendicular collapse in the northwest, facilitated by decoupling between the middle and lower crusts along thermally weakened layers. Localized orogen-parallel extension occurred in the southeast, which was kinematically linked to large dextral strike-slip faults where the upper crust remained coupled to the middle and lower crust.
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting