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| Geology of Santiago Metropolitan Region | |
|---|---|
| Name | Santiago Metropolitan Region |
| Country | Chile |
| Area km2 | 15361 |
| Capital | Santiago |
Geology of Santiago Metropolitan Region
The Santiago Metropolitan Region occupies the Chilean Central Valley and adjacent ranges within the Andes, hosting a complex record of sedimentary, volcanic, and tectonic processes tied to the convergence of the Nazca Plate, South American Plate, and remnants of the Pacific Plate. Its geology integrates Paleogene to Quaternary stratigraphy exposed around urban Santiago, the Maipo River, and the Huasco River headwaters, shaped by orogenic, magmatic, and glacial episodes recorded in rock, structure, and landscape.
The region sits within the Andean orogeny influenced by the subduction of the Nazca Plate beneath the South American Plate and modulated by the presence of the Juan Fernández Ridge, the Chile Triple Junction farther south, and past interactions with the Farallon Plate. Key physiographic elements include the Cordillera de la Costa, the Central Valley, and the Principal Cordillera of the Andes Mountains, with major drainage systems like the Mapocho River, Maipo River, and tributaries draining volcanoes such as Cerro El Plomo. Regional mapping and synthesis have been conducted by institutions including the Servicio Nacional de Geología y Minería (SERNAGEOMIN), the Universidad de Chile, and the Universidad Católica de Chile.
Stratigraphic sequences range from Mesozoic basement of the Chañarcillo Basin-related successions to Cenozoic volcanic and sedimentary cover. Basement units include metamorphic rocks correlated to the Coastal Cordillera Complex and plutonic suites linked to the Batholith of the Andes and the Coquimbo Metamorphic Complex. Overlying Paleogene and Neogene units contain the Abanico Formation-equivalent volcanic-sedimentary sequences, rich in tuffs associated with episodes preserved near Farellones and Lo Valdivia. Quaternary alluvium and terraces along the Maipo River overlie Miocene continental deposits and Paleozoic to Mesozoic marine strata known from exposures in the Melipilla and Rancagua areas.
Active shortening and crustal thickening manifest in thrust faults, fold systems, and high-angle reverse faults within the Principal Cordillera and adjacent basins. Major structural features include the San Ramón Fault, the El Arrayán Fault, and the Pudahuel Fault system, which relate to regional stress fields documented during studies by the National Geophysical Data Center collaborators at the International Seismological Centre. Paleoseismic records along these structures and paleostress reconstructions connect to historic earthquakes such as the 1730 Valparaíso earthquake and the 1985 Algarrobo earthquake affecting central Chile. Crustal-scale processes have been interpreted through seismic profiles from the Andean Geophysical Transect and GPS networks maintained by the Centro Sismológico Nacional.
Volcanism is dominated by andesitic to dacitic stratovolcanoes and rhyolitic domes aligned with the active volcanic arc. Prominent volcanic centers include Cerro El Plomo, Cerro Tupungato on the border with Argentina, and the San José complex, part of volcanic chains imaged in petrological work at the Smithsonian Institution Global Volcanism Program. Magmatic products comprise calc-alkaline plutons and porphyries of the Central Andean metallogenic belt, with intrusive bodies such as the Coya pluton and the Farellones Granite contributing to uplift and mineralization. Geochemical studies link arc magmatism to slab-derived fluids from the Nazca Plate and to variations induced by the Juan Fernández Ridge subduction.
Quaternary records preserve glacial advances in the upper Maipo and Aconcagua catchments, with moraines, cirques, and U-shaped valleys at localities like Cajón del Maipo, studied in paleoclimate reconstructions alongside work at Glacier San Francisco and Miami Glacier-adjacent sites. Fluvial terraces along the Mapocho River and Maipo River archive uplift and incision histories tied to seismic cycles, and alluvial fans at the piedmont reflect episodic debris flows linked to extreme precipitation and volcanic ash deposition from centers such as San José. Cosmogenic nuclide dating and optically stimulated luminescence applied at sites like Lo Prado and Puente Alto resolve late Pleistocene-Holocene incision rates and paleoflood events contemporaneous with documented climatic oscillations recorded in Lake Chungará and Laguna del Inca cores.
The region hosts skarn, porphyry, and epithermal mineralization within the Central Andean metallogenic province. Known deposits include copper-gold occurrences proximal to the El Teniente district influence, polymetallic veins near Rancagua, and industrial aggregates mined around Melipilla and Curacaví. Exploration and extraction have been undertaken by companies such as Codelco, Antofagasta Minerals, and exploration firms collaborating with the Comisión Chilena del Cobre (Cochilco). Water-bearing unconsolidated deposits supply groundwater for Santiago's supply infrastructure, while geothermal prospects have been investigated in the high Andes near Farellones and the Cajón del Maipo area.
Seismic hazard stems from shallow crustal faults (e.g., San Ramón Fault) and subduction megathrust earthquakes linked to the Peru–Chile Trench; historical impacts include the 1647 Santiago earthquake and the 2010 Chile earthquake consequences informing building codes administered by the Instituto Nacional de Normalización (INN). Volcanic hazards from the active arc—ashfall, lahars, and pyroclastic flows from centers like San José—pose risks to communities in Cajón del Maipo and infrastructure along the Pan-American Highway. Landslides and debris flows affect steep slopes in the Principal Cordillera and urbanized foothills near La Florida and Puente Alto, assessed through hazard mapping by SERNAGEOMIN, municipal emergency services, and research at the Pontifical Catholic University of Chile.