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| Sevier orogenic belt | |
|---|---|
| Name | Sevier orogenic belt |
| Period | Late Jurassic–Eocene |
| Type | Thrust belt |
| Location | Western North America |
| Orogeny | Sevier Orogeny |
| Length | ~2000 km |
| Width | variable |
Sevier orogenic belt
The Sevier orogenic belt is a continental-scale thrust belt that developed along the western margin of North America during the Late Jurassic through Eocene, producing a north–south–trending system of thin-skinned contractional structures that influenced the evolution of the North American Cordillera, the Rocky Mountains, and the Great Basin. The belt records interactions among the Farallon Plate, microplates such as the Kula Plate, and continental lithosphere, and it is integral to understanding contemporaneous tectonic events including the Laramide orogeny and the development of the Western Interior Seaway. Classic study regions include thrust systems exposed in Idaho, Wyoming, Utah, Nevada, and Montana.
The Sevier orogenic belt comprises a stack of thin-skinned nappes and regional thrust sheets that transported sedimentary cover rocks eastward over deformed foreland strata, shaping the Sevier orogeny deformation front and the hinterland to the west. Pioneering work by researchers associated with institutions such as the United States Geological Survey and universities including University of Utah, Stanford University, and Caltech established the belt as a type example of Cordilleran thin-skinned thrusting, comparable in process significance to the Alps and the Himalayas in conceptual models. Field areas that illustrate key structural elements include the Teton Range, Wasatch Range, and exposures in the Marysvale volcanic field.
Sevier deformation is plate-driven, tied to the subduction of the Farallon Plate beneath the North American margin and to changes in convergence direction associated with the inferred migration of the Kula Plate and episodic slab rollback. Initiation in the latest Jurassic corresponds with accretionary and magmatic episodes observed in sections of the Sierra Nevada and Coast Ranges, while peak shortening during the Cretaceous is synchronous with high rates of sedimentation in the Western Interior Basin and contraction documented adjacent to the Laramide orogeny_affected interior. Temporal and spatial relationships with events recorded in the Sevier fold-and-thrust belt (Utah) and the Idaho-Wyoming thrust belt indicate diachronous propagation of thrust fronts and links to plate reorganization episodes such as microplate capture documented in paleogeographic reconstructions.
The Sevier belt involves largely Mesozoic and Paleozoic stratigraphic sequences including platform carbonates, clastic successions, and evaporite layers sourced from depositional domains like the Western Interior Seaway, the Permian Basin, and shelf environments offshore of the craton. Structural styles are dominated by thin-skinned thrusting with detachments on mechanically weak horizons such as Jurassic evaporites and shales, producing imbricate thrust slices, duplexes, and regional décollement surfaces analogous to those described from the Canadian Rockies and the Rocky Mountain foreland fold and thrust belt. Exposures in the Sevier fold-and-thrust belt show backthrusts, fold-thrust interference patterns, and klippen formations comparable to classical models proposed by geologists affiliated with the Geological Society of America.
Metamorphic effects in the Sevier belt are generally low-grade and dominated by burial and tectonic heating in thrust sheets, with localized contact metamorphism where magmatic rocks intruded sedimentary sequences during Cretaceous and Tertiary magmatic pulses correlated with arcs documented in the Sierra Nevada batholith and the Mojave Desert arc complex. Magmatism related to slab dynamics produced volcanic and plutonic suites recorded in the Marysvale volcanic field, the Idaho batholith, and dispersed ash layers that provide marker beds for regional correlation. Metamorphic mineral assemblages and intrusive ages provide constraints on thermal structure during shortening and on fluid-flow histories analogous to those inferred for other Cordilleran orogenic belts.
East of the deformational front, lithospheric flexure produced foreland basins that captured thick wedges of clastic sediment shed from uplifting thrust sheets; notable depocenters include parts of the Western Interior Basin and synorogenic basins now exposed in Utah and Wyoming. Foreland basin stratigraphy consists of conglomerates, sandstones, and fine-grained mudstones deposited in alluvial, fluvial, and shallow marine systems, with provenance links to uplifted source regions traced using heavy-mineral suites and isotopic systems compared with rocks of the Sierra Nevada and Wind River Range. Sedimentary architecture and unconformity-bounded sequences record pulses of shortening, sediment supply changes, and regional sea-level variation related to the Cretaceous greenhouse intervals.
Absolute dating methods including U-Pb zircon geochronology on volcanic tuffs and detrital grains, Ar-Ar dating on volcanic and metamorphic phases, and low-temperature thermochronology such as (U-Th)/He and fission-track measurements on apatite and zircon have constrained the timing and rates of Sevier contraction, thrust migration, and exhumation. Detrital zircon provenance studies linking samples to source terranes like the Sierra Nevada batholith and the Canadian Shield have refined sediment dispersal models, while thermochronometric transects across thrust fronts quantify cooling histories and burial depths, enabling calibration against regional kinematic models developed by researchers at institutions such as University of Colorado Boulder and University of Michigan.
The structural and sedimentary architectures of the Sevier belt host hydrocarbon plays in foreland basins with reservoir rocks including Cretaceous sandstones and Paleozoic carbonates, and traps associated with thrust-imbricate geometries documented in petroleum assessments by the USGS and industry partners. Mineral resources associated with magmatic and hydrothermal episodes include porphyry-related copper and associated gold-silver mineralization in regions with igneous centers, as well as sediment-hosted ore deposits and gypsum/anhydrite extracted from evaporitic units. Groundwater reservoirs and aggregate resources in folded and faulted strata support municipal and industrial uses across states such as Utah and Nevada.
Category:Orogenic belts Category:Geology of North America