Orogenic link ∼41°N–46°N: Collisional mountain building and basin closure in the Cordillera of western North America

Abstract

Polyphase structural mapping and mineral age dating across the Salmon River suture zone in west-central Idaho (Riggins region; ∼45°30′N, ∼117°W–116°W) support a late Mesozoic history of penetrative deformation, dynamothermal metamorphism, and intermittent magmatism in response to right-oblique oceanic-continental plate convergence (Farallon–North America). High-strain linear-planar tectonite fabrics are recorded along an unbroken ∼48 km west-to-east transect extending from the Snake River (Wallowa intra-oceanic arc terrane; eastern Blue Mountains Province) over the northern Seven Devils Mountains into the lower Salmon River Canyon (ancestral North America; western Laurentia). Given the temporally overlapping nature (ca. 145–90 Ma) of east-west contraction in the Sevier fold-and-thrust belt (northern Utah–southeast Idaho–southwest Montana segment), we propose that long-term terrane accretion and margin-parallel northward translation in the Cordilleran hinterland (∼41°N–46°N latitude; modern coordinates) drove mid- to upper-crustal shortening >250 km eastward into the foreland region (∼115°W–113°W). During accretion and translation, the progressive transfer of arc assemblages from subducting (Farallon) to structurally overriding (North American) plates was accommodated by displacement along a shallow westward-dipping basal décollement system underlying the Cordilleran orogen. In this context, large-magnitude horizontal shortening of passive continental margin strata was balanced by the addition of buoyant oceanic crust—late Paleozoic to Mesozoic Blue Mountains Province—to the leading edge of western Laurentia. Consistent with orogenic float modeling (mass conservation, balance, and displacement compatibility), diffuse dextral-transpressional deformation across the accretionary boundary (Salmon River suture: Cordilleran hinterland) was kinematically linked to eastward-propagating structures on the continental interior (Sevier thrust belt; Cordilleran foreland). As an alternative to noncollisional convergent margin orogenesis, we propose a collision-related tectonic origin and contractional evolution for central portions of the Sevier belt. Our timing of terrane accretion supports correlation of the Wallowa terrane with Wrangellia (composite arc/plateau assemblage) and implies diachronous south-to-north suturing and basin closure between Idaho and Alaska.

U-Pb LA-ICP-MS Zircon Dating of Crustal Xenoliths: Evidence of the Archean Lithosphere Beneath the Snake River Plain

“…This magmatism is thought to reflect crustal anatexis in response to crustal thickening coeval with the ca. 75-100 Ma Sevier orogeny, e.g., [48][49][50][51], perhaps coupled with the input of mantle-derived mafic magma [52].…”

Early Cretaceous Provenance, Sediment Dispersal, and Foreland Basin Development in Southwestern Montana, North American Cordillera

“…Some workers have suggested that terranes with island arc affinities, presently located in British Columbia, may have been translated northward along the western Idaho shear zone during middle to Late Cretaceous time (e.g., Giorgis et al, 2008;Wyld et al, 2006). One tectonic reconstruction places the Blue Mountains province very near to its modern day position in northeastern Oregon around ∼112 Ma (Gray et al, 2019). In contrast, other workers have interpreted that the Blue Mountains province may have been as far south as western Nevada around ∼110 Ma, allowing for the possibility that other outboard terranes may have occupied the Oregon-Idaho region during ROSENBLUME ET AL.…”

“…Given that the suture zone plutons represent only the westernmost edge of the present-day extent of the Idaho batholith (Gaschnig et al, 2010), the majority of the batholith is excluded as a potential source. The Blue Mountains province is currently situated to the west of the study area; it is an early Mesozoic collisional island arc and forearc assemblage with a complex accretionary and translational history (e.g., Dorsey & LaMaskin, 2007;Gaschnig et al, 2017;Gray et al, 2019;LaMaskin et al, 2011;Schwartz et al, 2010). Mesozoic plutons of the Blue Mountains province represent a potential sediment source for the 160 Ma detrital zircon grains in the study area.…”

“…In some cases, where portions of the hinterland have been displaced along major strike-slip faults, the foreland basin system may hold key information for unraveling complex geological histories as it remained stationary on the continent during orogenesis (e.g., Wyld et al, 2006). During Early Cretaceous time, the western margin of the Idaho-Montana sector of the North America Cordillera was subject to outboard terrane accretion and translation, decreased arc magmatism, growth of the Sevier orogenic belt, and development of a retroforeland basin system on the stable portion of the continent (Figure 1; DeCelles, 2004;Gehrels et al, 2009;Gray et al, 2019;Wyld et al, 2006). During this time, this foreland basin system expanded to several hundred kilometers in width, developed an asymmetric geometry, and spanned the length of the continent (DeCelles, 2004).Numerous models for North American sediment dispersal during Early Cretaceous time have been proposed.…”

Deciphering the State of the Lower Crust and Upper Mantle With Multi‐Physics Inversion

“…To make it even more difficult to establish relationships between surface geology and deep structure, the SRP is largely covered in volcanics associated with the hotspot migration (e.g., Camp et al., 2015; Ellis et al., 2013). Despite these difficulties, multiple stages of deformation, exhumation of lower crustal material and zones of extensive shear have been reported along the edges of the SRP (e.g., Gray et al., 2020; Konstantinou et al., 2012; Tikoff et al., 2001). Most interestingly, Konstantinou and Miller (2015) postulate the existence of a long‐lived major lithospheric boundary below the SRP similar to the Lewis and Clark Shear zone further north taking up deformation associated with low angle subduction of the Farallon Slab.…”