EVOLUTION OF THE SEVIER AND LARAMIDE BELTS WITHIN AN INTEGRATED OROGENIC SYSTEM

The thin-skin Sevier (SB) and thick-skin Laramide (LB) belts of the North American Cordillera provide a long-term record of mountain building and plate dynamics. Primary architecture of the sedimentary prism along the continental margin and cratonic lithosphere in the foreland influenced subsequent deformation. Interrelated components of the orogenic system included a forearc accretionary complex, magmatic arc, hinterland, retroarc fold-thrust belt (SB), and foreland basin, modified by basement arches (LB). The SB formed as an eastward-propagating wedge mostly during the Cretaceous to Paleogene. The SB trends overall N-S, along with map-view curvature that partly primary shape of the sedimentary prism, followed by 60-80% vertical-axis rotation during curved thrust slip and interaction with foreland arches. Approximately 200 km of shortening in the SB was transferred into lower crustal thickening and uplift of a hinterland plateau. Large-scale shortening and LPS directions in the SB were oriented overall W-E with refraction about curved thrusts, related to increased gravitational potential energy in the hinterland and topographic slope along the wedge front. Synorogenic strata accumulated in a foreland basin that formed by flexural loading of the thrust wedge and dynamic subsidence during shallowing subduction. The foreland LB developed during later Cretaceous to Paleogene time, partly overlapping with SB deformation, but with a different style and stress field. The LB comprises an overall NW-SE trending network of basement-cored arches and intervening basins, but individual arch trends vary, partly related to primary basement heterogeneities, with limited vertical-axis rotation. Shortening in the LB was oriented overall WSW-ENE at low angles to relative plate motion and was spatially and temporally correlated with a sector of flat-slab subduction. An integrated model for evolution of the SB and LB includes influence of primary sedimentary and basement architecture, enhanced plate coupling from increased subduction rates, linkage of upper crustal shortening in the SB with lower crustal thickening of a hinterland plateau and topographically influenced stress transmission, and thick-skin foreland deformation in the LB partly related to bottom-up stress transmission during flat-slab subduction.