Tectonic evolution of the Sevier and Laramide belts within the North American Cordillera orogenic system

Abstract

The thin-skin Sevier and thick-skin Laramide belts of the North American Cordillera provide a long-term record of the interrelations between evolving styles of mountain building and plate dynamics over a complete tectonic cycle, from onset of rapid subduction, to protracted growth of a composite orogenic system, to final collapse. Primary architecture of basement and sedimentary cover rocks, which included a thick passive margin section deposited along the western continental margin, influenced patterns of subsequent deformation. The Cordilleran orogenic system, comprised of an interrelated forearc accretionary complex, magmatic arc, retroarc hinterland, Sevier fold-thrust belt, and foreland basin locally deformed by Laramide arches, developed during Jurassic to Paleogene Andean-style subduction and terrane accretion. The Sevier belt formed as a foreland-propagating (west to east) wedge mostly during Cretaceous to Paleogene time, and included a western thrust system with aerially extensive thrust sheets that carried thick passive margin strata, and an eastern thrust system that carried thinner strata. Within the Wyoming salient of the Sevier belt, major thrust and fold traces display systematic map-view curvature about an average N-S structural trend, reflecting a component of primary curvature related to sedimentary prism architecture, followed by 60-80% vertical-axis rotation of thrust sheets related to curved fault slip and interaction with Laramide arches at the salient ends. Internal deformation in the western thrust sheets was limited within strong shallower levels, whereas deeper levels underwent shear and vertical flattening near a weak basal fault zone. Internal deformation in the eastern thrust sheets included widespread early layer-parallel shortening (LPS), followed by concentration of slip onto weak fault zones. Approximately 200 km of thin-skin shortening in the Sevier belt was transferred into lower crustal thickening and uplift of an orogenic plateau in the hinterland to the west. Synorogenic strata were deposited in an evolving foreland basin to the east that formed 11 Jurassic with deposition of marine carbonates and evaporites in the Twin Creek Formation and correlative strata (Imlay, 1967), synchronous with early terrane accretion along the western plate margin (Dickinson, 2008). These evaporites subsequently formed detachments during Sevier thrusting (Coogan and Yonkee, 1985). Late Jurassic and Cretaceous to Paleogene strata deposited in the foreland are described in section 4.5. 2.3. Accreted terranes The western part of the Cordilleran orogenic system was constructed on accreted terranes that included: (1) peri-cratonic rocks with fossil and detrital zircon (DZ) signatures typical of North America (Roberts Mountain and Golconda allochthons, Kootenay terrane); (2) Paleozoic to Mesozoic arc and ophiolite rocks of the Intermontane terrane group in Canada, and the Sierra Foothills, Klamath Mountains, and Blue Mountains provinces; and (3) Paleozoic to Mesozoic distal arc and ophiolite rocks of t...

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…The cross-section in Figure 26A, located at about 50°N, summarizes these data schematically and highlights the crustal scale structure of the orogen. A comparison with the traverse of the cordilleran system from Wyoming to California by [225] yields similarities, albeit the Laramide belt which is absent in the Canadian traverse.…”

“…This antiform is caused by the ramp through the Palaeozoic in the underlying unit, which rests on the autochthonous Palaeozoic sequence. In contrast to the Sevier belt of Wyoming-Idaho-Utah [225] frontal ramp anticlines in the Palaeozoic carbonates are not exposed but may have been eroded.…”

“…For example, Early Cretaceous décollement was coeval with the Purcell thrust, the Gwillim Creek shear zone was coeval with the Bourgeau thrust, the Monashee décollement with the McConnel thrust, and the Basal décollement with the Foothill thrusts, and these four pairs evolved sequentially in this order. It is interesting to note that the equivalent structures in the Sevier belt of Wyoming-Idaho-Utah (Paris to Prospect thrust) evolved by in-sequence thrusting as well and in exactly the same time interval [225]. Figure 24B is a more detailed cross-section displaying the internal structure of the most external part of the North American cordillera in the traverse of southern Canada.…”

“…The North American Cordillera evolved from a complex set of processes that involved subduction, the accretion of terranes and strike-slip faulting in mainly Mesozoic -Cenozoic times [223][224][225]. Three transects are presented here which together yield a comprehensive view of the thick-and thin-skinned tectonic styles encountered in this orogen.…”

“…The activity of these thrust faults was dated using Cenozoic synorogenic clastics by [15,225,233,234], and the time intervals of activity are labeled in Figure 25A. It clearly follows from these age dates that the thrust faults formed in-sequence from the hinterland toward the foreland from the Early Cretaceous (Paris thrust) to the Palaeogene (Prospect thrust).…”