Flexural versus dynamic processes of subsidence in the North American Cordillera foreland basin

Abstract

[1] Dynamic subsidence related to subduction is an important process in retroarc foreland basin systems. Dynamic subsidence in the North American retroarc foreland has been proposed as dominant in the Late Cretaceous; however, questions remain about the nature of the subcrustal load and the basin response to such processes. We present new isopach data using 130 data points covering a large portion of the U.S. and a revised flexural analysis of the Sevier foreland. Higher rigidity associated with the Wyoming craton can best model flexural subsidence directly prior to~81 Ma. We constrain the transition from flexural to nonflexural subsidence to~81 Ma and correlate this with large Late Cretaceous progradation. The locus of subsidence and the location of the subducted Shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the North American Cordillera. Citation: Painter, C. S., and B. Carrapa

Early Inception of the Laramide Orogeny in Southwestern Montana and Northern Wyoming: Implications for Models of Flat‐Slab Subduction

“…Onset of a regional, dynamic component of subsidence at ca. 81 Ma (Painter & Carrapa, ) is consistent with mantle convection above a shallowly subducting Farallon plate (Gurnis, , Liu & Nummedal, ; Liu et al, ; Mitrovica et al, ; Pang & Nummedal, ; Spasojevic et al, ). Numerical models show that the northeastward progression of a flat slab can fit with the eastward shift of the foreland depocenter (Liu et al, , ; Heller & Liu, ).…”

“…Numerical models show that the northeastward progression of a flat slab can fit with the eastward shift of the foreland depocenter (Liu et al, , ; Heller & Liu, ). Although this large‐scale episode has been dynamically related to flat‐ or shallow‐slab subduction (Gurnis, ; Heller & Liu, ; Liu et al, , Mitrovica et al, ; Pang & Nummedal, ; Painter & Carrapa, ), identifying a real dynamic subsidence component is challenging as it can be related to different processes. For example, regional dynamic subsidence can be caused by penetration of the subducting slab into the lower mantle (Faccenna et al, ; Yang et al, ).…”

Late Cretaceous–early Eocene Laramide uplift, exhumation, and basin subsidence in Wyoming: Crustal responses to flat slab subduction

“…We interpret the first stage of Laramide deformation during the Maastrichtian and early Paleocene as a simple northeastward migration of strain in the greater Cordilleran orogenic system as the flat subduction proceeded (Figure a). This stage of deformation corresponds to when the center of the hypothetical Shatsky conjugate plateau on the Farallon plate entered southern Wyoming after it passed beneath the Colorado Plateau between 84 and 68 Ma [ L. Liu et al ., ; Liu and Gurnis , ; Painter and Carrapa , ]. The suction force in the asthenosphere wedge between the flat slab and Archean keel caused subsidence on the overriding plate along the southwestern edge of the Wyoming craton and produced a localized deep depocenter in southeastern Wyoming during the late Campanian and Maastrichtian [ Jones et al ., ; Painter and Carrapa , ].…”

Southwestward weakening of Wyoming lithosphere during the Laramide orogeny

“…The subducted Farallon oceanic plate dipped steeply during most of the Sevier deformation, but became gently inclined during the very late stage (ca. 81 Ma) [ Liu et al , ; Jones et al , ; Painter and Carrapa , ]. The bending stresses induced by the topographic load of the Sevier fold‐and‐thrust belt combined with crust‐mantle decoupling initiated by the overthickened Sevier hinterland and the end loads due to the low‐angle subduction at the western edge of the thick Wyoming craton, caused the southwestward decrease of lithospheric stiffness in Wyoming at the beginning of Laramide deformation.…”

“…Localized T e of Wyoming lithosphere varies between 6 and 46 km during the Laramide deformation (Table ). Temporally, the lithospheric stiffness was smaller during the Laramide deformation compared to the stiffness during the Sevier deformation and at present, both of which have flexural rigidities in the range of 10 23.0 –10 24.0 N m [ Lowry and Smith , , ; Painter and Carrapa , ], corresponding to a T e range of 25–55 km. Spatially, the stiffness of the Wyoming lithosphere gradually decreases from northeast ( T e = 32–46 km) to southwest ( T e = 6–9 km), but remains nearly constant throughout the Laramide deformation in each basin (Table and Figures b and ).…”