Geology, Mantle Tomography, and Inclination Corrected Paleogeographic Trajectories Support Westward Subduction During Cretaceous Orogenesis in the North American Cordillera

Abstract

Geological evidence, including the presence of two passive margin platforms, juxtaposed and mismatched deformation between North America and more outboard terranes, as well as the lack of rift deposits, suggest that North America was the lower plate during both the Sevier and Laramide events and that subduction dipped westward beneath the Cordilleran Ribbon Continent (Rubia). Terranes within the composite ribbon continent, now present in the Canadian Cordillera, collided with western North America during the 125–105 Ma Sevier event and were transported northward during the ~80–58 Ma Laramide event, which affected the Cordillera from South America to Alaska. New high-resolution mantle tomography beneath North America reveals a huge slab wall that extends vertically for over 1000 km, marks the site of long-lived subduction, and provides independent verification of the westward-dipping subduction model. Other workers analyzed paleogeographic trajectories and concluded that the initial collision took place in Canada at about 160 Ma – a time and place for which there is no deformational thickening on the North American platform – and later farther west where subduction was not likely westward, but eastward. However, by utilizing a meridionally corrected North American paleogeographic trajectory, coupled with the geologically most reasonable location for the initial deformation, the position of western North America with respect to the relict superslab parsimoniously accounts for the timing and extents of both the Sevier and Laramide events. SOMMAIRELes indications géologiques, en particulier la présence de deux marges de plateforme passives, de déformations adjacentes non-conformes entre l’Amérique du Nord et les terranes extérieurs, ainsi que l’absence de gisements de rift, permet de croire que l’Amérique du Nord était la plaque sous-jacente durant les événements de Sevier et de Laramide et que la subduction plongeait vers l’ouest sous le continent rubané de la Cordillères (Rubia). Les terranes du continent rubané composite, maintenant au sein de la Cordillère canadienne, sont entrés en collision avec l’ouest de l’Amérique du Nord durant l’événement Sevier (125-105 Ma), et ont été transportés vers le nord durant l’événement Laramide (~80–58 Ma), laquelle a affecté la Cordillère, de l’Amérique du Sud à l’Alaska. Une nouvelle tomographie haute résolution du manteau sous l’Amérique du Nord montre la présence d’un gigantesque mur de plaques vertical qui s’étend sur 1 000 km, marque le site d’une subduction de longue haleine, et offre une validation indépendante du modèle d’une subduction à pendage vers l’ouest. D’autres chercheurs ont analysé les trajectoires paléogéographiques et conclu que la collision initiale s’est produite au Canada vers 160 Ma – un moment et un endroit sans épaississement par déformation sur la plateforme d’Amérique du Nord – et plus tard plus à l’ouest, là où la subduction n’était vraisemblablement pas vers l’ouest, mais vers l’est. Cela dit, en considérant une trajectoire paléogéographique de l’Amérique du Nord corrigée longitudinalement, avec la position géologique la plus probable de la déformation initiale, la position de la portion ouest de l’Amérique du Nord par rapport aux restes de la super-plaque explique alors facilement la chronologie et l’étendue des épisodes Sevier et Laramide.

Arc and Slab-Failure Magmatism in Cordilleran Batholiths I – The Cretaceous Coastal Batholith of Peru and its Role in South American Orogenesis and Hemispheric Subduction Flip

“…It has not escaped our attention that the deformational scheme outlined here for South America is strikingly similar to that of the North American Laramide event (Hildebrand 2013(Hildebrand , 2014, but before discussing the North American geology, we need briefly mention some new tomographic advances arising from improved computing power and high-resolution seismic arrays, such as USArray (Williams et al 2010), and also from recently developed kinematic models for plate motions in deep mantle reference frames based on seafloor spreading history, hotspot migration, paleomagnetism, and moving continents (Müller et al 1993;O'Neill et al 2005;Torsvik et al 2008a, b;Doubrovine et al 2012;Shepard et al 2012;Seton et al 2012). …”

“…Orocopia and Pelona schist (Jacobson et al 2007) is associated with this zone, which suggests that it had once been joined with the similar Swakane gneiss of the North Cascades (Matzel et al 2004;Hildebrand 2013Hildebrand , 2014. Similarly, a major swarm of Late Cretaceous-Early Tertiary post-collisional plutons -considered by Hildebrand (2013) to have been generated by slab failure -trending through the Transverse Ranges, the Mojave and Sonoran deserts, and on through western Mexico would also match with similar age plutons of the Cascades and Idaho (Figure 12).…”

“…Eastward subduction beneath North America during westerly migration of North America as the Atlantic Ocean opened implies that both the trench and continent would have been coupled and migrated westward together, and thus have left an inclined, not vertical, slab. Hildebrand (2014) found that the Sigloch and Mihalynuk (2013) model, once corrected for paleomagnetic inclination errors (Kent and Irving 2010), matched the time and place for initial impingement of the Cordilleran Ribbon Continent in the Great Basin region during the Sevier Åberg et al 1984;Levi and Aguirre 1981. Map compiled from sources cited in text.…”

Arc and Slab-Failure Magmatism in Cordilleran Batholiths II – The Cretaceous Peninsular Ranges Batholith of Southern and Baja California

“…The collision marks the closure of an ocean along the western margin of the Cordilleran Ribbon Continent some 20-25 m.y. prior to the Laramide event, which reflects terminal collision of the ribbon continent with North America (Hildebrand 2013(Hildebrand , 2014.…”

“…12). The ~125-105 Ma Sevier deformation of the western US and its hinterland, now located in the Canadian Cordillera (Hildebrand 2014 units that post-date the Oregonian event and predate the Laramide appear to be relatively common within western and central Mexico (Fig. 14).…”