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| West Andean Thrust System | |
|---|---|
| Name | West Andean Thrust System |
| Country | Peru, Ecuador, Chile, Bolivia |
| Region | Andes, Western Cordillera (Andes) |
West Andean Thrust System
The West Andean Thrust System is a major crustal-scale thrust and fold belt along the western flank of the Andes that accommodates shortening related to the convergence of the Nazca Plate beneath the South American Plate. It links offshore and onshore structural domains across the forearc and retroarc between the coastal basins of Peru and the Altiplano of Bolivia, influencing deformation in the Central Andes and interacting with older structures preserved in the Western Cordillera (Andes), Cordillera Occidental (Peru), and the Coastal Cordillera (Chile). Studies of the system integrate field mapping, seismic reflection, geodesy, and thermochronology employed by teams from institutions such as the United States Geological Survey, Instituto Geofísico del Perú, and university groups at University of São Paulo, University of Chile, and Massachusetts Institute of Technology.
The West Andean Thrust System forms a linked series of thrust fronts, hinterland folds, and detached thrust sheets that extend from the Peruvian margin through Ecuador into northern Chile and southern Bolivia; it interacts with the Peruvian forearc basin, the Maracaibo Basin to the north, and the Puna Plateau to the south. Major structural segments are named regionally as the Morro Solar Anticline sector, the Ica Basin front, and the Coquimbo–Atacama corridor, and are spatially associated with features like the Nazca Ridge subduction anomaly and the Muisca and Inca cultural landscapes. The thrust system is a key element in models of Andean orogeny that incorporate inputs from researchers at Geological Society of America, Sociedad Geológica del Perú, and the Geological Society of London.
The system developed during Mesozoic to Cenozoic shortening as the Nazca Plate converged with western South America, with important modulations during the Cretaceous and the Neogene. Its stratigraphic package includes Mesozoic marine shales and carbonates correlated with units described in the Talara Basin, Marañón Basin, and the Coquimbo Formation; Cenozoic synorogenic sediments equivalent to deposits in the Moquegua Basin and Pisco Basin record foredeep evolution. Tectonic drivers include slab geometry variations linked to the Nazca Ridge and the Juan Fernández Ridge, changes in convergence rate documented by studies at Scripps Institution of Oceanography, and interactions with lithospheric structures such as the Ancash Fault and pre-Andean cratonic blocks like the Amazonian Craton.
Structurally, the West Andean Thrust System comprises imbricate thrust slices, duplex systems, and long-wavelength ramps and flats mapped along the western Andean margin near the Cordillera Blanca, Cordillera Negra, and the Chiloe Island region. Detailed cross-sections integrate seismic reflection interpretations from surveys linked to Petroperú, ENAP, and academic consortia, revealing basement-involved thrusting in segments adjacent to the Precambrian shields and thin-skinned thrusting over evaporite detachment horizons in areas analogous to the Salta Basin and the Magallanes Basin. Major mapped faults include front-parallel thrusts that merge with blind ramp structures and out-of-sequence thrusts that locally uplift Neogene basin fills, comparable to structures documented in the Altiplano-Puna Volcanic Complex region.
Seismic behavior along the system reflects both shallow crustal earthquakes and coupling with megathrust events on the slab interface associated with the 1868 Arica earthquake, the 1940 Lima earthquake, and the 2007 Pisco earthquake sequences, with historical catalogs maintained by Instituto Geofísico del Perú, Servicio Sismológico Nacional (Chile), and the U.S. Geological Survey. Paleoseismic trenching studies near the Ica earthquake-affected zones and geodetic inversions using GPS networks from UNAVCO and Instituto Geográfico Nacional (Argentina) indicate episodic rupture on west-verging thrusts, with recurrence intervals that vary along strike and that are modulated by stress transfer from subduction earthquakes like the 1960 Valdivia earthquake.
Surface expression of the thrust system includes uplifted coastal scarps, river knickpoints on drainages such as the Río Santa, the Rímac River, and the Loa River, and tilting of forearc terraces observed near the Sechura Desert and Atacama Desert. The thrust-related topography influences sediment routing to the Peruvian continental margin, controls locations of alluvial fans and marine terraces studied by geomorphologists from Universidad Nacional Mayor de San Marcos and Pontificia Universidad Católica de Chile, and interacts with Quaternary glacial deposits in the Cordillera Blanca affecting hazard exposure in regions tied to the Huaraz and Arequipa urban areas.
The West Andean Thrust System affects hydrocarbon prospectivity in basins such as the Talara Basin, Marañón Basin, and marginal plays offshore explored by companies like Petroperú and ENAP, where thrust geometries control trap formation. It also controls groundwater flow and geothermal gradients exploited or assessed by agencies including Codelco and national energy ministries. Hazard mitigation efforts involve seismic microzonation undertaken by municipal authorities in Lima, Quito, Valparaíso, and La Paz, building-code updates influenced by studies from International Association for Earthquake Engineering, and early-warning systems coordinated across Andean Community member states.
Research on the West Andean Thrust System spans classical field mapping by geologists affiliated with institutions like Servicio Geológico Colombiano and British Geological Survey to modern integrative studies employing 2D and 3D seismic reflection, balanced cross-section construction used by researchers at Imperial College London and Universidad de Buenos Aires, thermochronology (apatite fission-track and (U–Th)/He) conducted at laboratories such as Arizona State University and GFZ German Research Centre for Geosciences, and crustal-scale geodynamic modeling by groups at ETH Zurich and Caltech. Interdisciplinary programs involving paleoseismology, geomorphology, and space geodesy use datasets from COSMO-SkyMed, Landsat, and Sentinel missions to resolve timing, rates, and linkages between surface processes and deep structural evolution.