Collisional orogenesis in the northern Canadian Cordillera: Implications for Cordilleran crustal structure, ophiolite emplacement, continental growth, and the terrane hypothesis Joseph M. English T , Stephen T. Johnston 1 School of Earth and Ocean Sciences, University of Victoria, PO Box 3055, STN CSC, Victoria, British Columbia, Canada VSW 3P6 Received 15 April 2004; received in revised form 28 January 2005; accepted 31 January 2005 Available online 13 March 2005 Editor: R.D. van der Hilst Abstract During Upper Triassic to Lower Jurassic time, arc magmatic rocks of the Stikine terrane, arc-marginal sediments of the Whitehorse Trough, igneous and mantle rocks of the Cache Creek dophioliteT and Kutcho assemblage, and oceanic sedimentary and volcanic rocks of the Cache Creek terrane represented a magmatic arc, forearc basin, forearc basement, and subduction complex, respectively. The Cache Creek subduction complex was thrust to the southwest over the Whitehorse Trough forearc basin and the Stikine terrane in the Middle Jurassic during collision with an inboard continental domain. Interpretation of the various lithotectonic assemblages of the northern Intermontane belt in terms of a new plate tectonic model has a number of important implications for the Canadian Cordillera: (a) the model allows comparisons to be drawn with available seismic reflection interpretations of Cordilleran crustal structure; (b) dophioliteT emplacement was achieved by ramping of forearc oceanic lithosphere onto thick crustal parts of a subducting plate during collisional orogenesis; (c) island–arc collision and accretion were the principal mechanisms for continental growth with relatively minor contributions from dsliced-offT oceanic seamounts and/or plateaux; and (d) some terrane-bounding faults such as the Nahlin Fault do not represent major lithospheric- scale boundaries and their importance in tectonic reconstructions has been overemphasised. D 2005 Elsevier B.V. All rights reserved. Keywords: Canadian Cordillera; Cache Creek; ophiolite; orogenesis; fold-and-thrust belt; magmatic arc; forearc basin; subduction complex; tectonic accretion; continental growth 1. Introduction The terrane hypothesis was developed for, and widely applied to, Cordilleran-type orogens (e.g., [1]), and states that continents grow at accretionary margins by the collision of thickened, buoyant 0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2005.01.025 T Corresponding author. Tel.: +1 403 283 9459. E-mail addresses: joeenglish@canada.com (J.M. English)8 stj@uvic.ca (S.T. Johnston). 1 Tel.: +1 250 472 4481; fax: +1 250 721 6200. Earth and Planetary Science Letters 232 (2005) 333 – 344 www.elsevier.com/locate/epsl