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| Chonos Metamorphic Complex | |
|---|---|
| Name | Chonos Metamorphic Complex |
| Type | Metamorphic complex |
| Period | Neoproterozoic–Mesozoic (varied) |
| Region | Aysén Region, Los Lagos Region, Chile |
| Country | Chile |
| Lithology | Schist, gneiss, amphibolite, migmatite, metasedimentary rocks |
| Namedfor | Chonos Archipelago |
| Namedby | Early Chilean geological surveys |
Chonos Metamorphic Complex The Chonos Metamorphic Complex is a widespread metamorphic terrane in southern Chile known for high-grade tectonostratigraphic assemblages, pervasive metamorphism and complex deformational histories. It crops out across the Chonos Archipelago, Aysén Region, and parts of the Los Lagos Region, and records interactions among major plates and terranes such as the Nazca Plate, South American Plate, and accreted microcontinental fragments. The complex has been studied in the context of regional correlations with the Patagonia Metamorphic Complex, Antarctic Peninsula, and other southern hemisphere orogens.
The complex comprises a mosaic of metasedimentary and metavolcanic units including garnet-bearing schists, paragneisses, amphibolites, and migmatites that interdigitate with granitoid bodies and ultramafic lenses. Key lithologies include mica schist, quartzite, calc-silicate rocks, and layered amphibolite reminiscent of units mapped in the Cordillera Darwin, Magallanes Province, and the Sierra de la Ventana in Argentina. Country rocks host crosscutting plutons related to granitoid suites similar to those dated in the Patagonian Batholith, North Patagonian Batholith, and plutons correlated with the Famatinian belt. Metasedimentary sequences show provenance links to terranes like the Cuyania Terrane, Río de la Plata Craton, and fragments comparable to the Gondwana margin.
Metamorphic grades range from greenschist to granulite facies, with distinct isograds marked by minerals such as chlorite, biotite, garnet, kyanite, sillimanite, and orthopyroxene. Petrographic studies document prograde and retrograde fabrics, partial melting textures, and migmatitic leucosomes comparable to those observed in the Coastal Batholith of Peru and the Sierra de San Luis. Mineral assemblages and reaction textures record high-pressure amphibolite to granulite conditions analogous to metamorphism recorded in the Taitao Peninsula and the Fuegian Andes. Accessory phases include zircon, monazite, titanite, and rutile used in isotopic studies linking to research on Jack Hills zircons and detrital zircon programs across South America.
The structural framework displays tight folds, pervasive foliation, mylonitic shear zones, and thrust fault systems consistent with accretionary orogeny and continental collision. Major structures align NW–SE and NE–SW, reflecting multiple deformation phases comparable to those documented in the Western Paleozoic Fold Belt, the Andean Orogeny propagation, and terrane accretion events described for the Kerguelen Plateau-adjacent margins. Shear zones show kinematic indicators like S-C fabrics and stretching lineations that parallel findings from the Liquiñe-Ofqui Fault Zone, Beagle Channel, and the Magallanes Fault System. The tectonic setting implicates interactions among the Nazca Plate, Phoenix Plate, and Antarctic Plate through Mesozoic–Cenozoic time.
U–Pb zircon and monazite ages constrain metamorphism and magmatism from Neoproterozoic through Mesozoic intervals; detrital zircon spectra reveal contributions from the Amazonian Craton, Laurentia, and recycled sources similar to those in the Mawson Craton and East Antarctica Shield. Radiometric ages tie metamorphic pulses to regional events such as the Ross Orogeny, Famatinian Orogeny, and the emplacement of the Patagonian Batholith. Provenance studies using Sm–Nd and Lu–Hf isotopes link sediment sources to the Arequipa-Antofalla Shield, Pampean Orogen, and older basement akin to the Sierra de la Ventana and Sierra Chica de Córdoba.
Metallogenic prospects include base metal and gold occurrences associated with hydrothermal metamorphic fluids, skarn-type mineralization in calc-silicate horizons, and sulfide mineralization within metavolcanic units. Mineral assemblages include chalcopyrite, pyrite, sphalerite, galena, and scheelite-bearing skarns analogous to deposits in the El Teniente, Escondida, and Cerro Negro districts. Metamorphic-hosted gold occurrences recall models applied to the Dudypta Gold Field and the Greenstone Belts of West Africa and Western Australia, while intrusive-related systems show parallels to porphyry provinces evaluated by organizations like the Servicio Nacional de Geología y Minería (SERNAGEOMIN) and companies such as Codelco and Anglo American.
Exposures extend across the western margin of southern South America, from the archipelagos near the Moraleda Channel and Guafo Island to mainland belts around Coyhaique and the Aysén Fjord system. Outcrops are commonly masked by Quaternary glacial deposits such as those studied in the Patagonian Icefields, San Rafael Glacier, and the Northern Patagonian Ice Field, affecting mapping efforts similar to those in the Fjords of British Columbia and the South Georgia region. Coastal geomorphology and marine platforms adjacent to the complex interface with ecosystems studied in the Juan Fernández Islands and along the Pacific Ring of Fire.
Initial descriptions arose from Chilean geological surveys and early explorers linking the complex to regional metamorphic belts catalogued by figures like Eduardo de los Ríos and institutions such as the Universidad de Chile and Instituto de Investigaciones Geológicas. Subsequent work by international teams from universities including University of Buenos Aires, University of Cambridge, University of California, Universidad de Concepción, and research agencies like CONICYT advanced mapping, geochronology, and petrology. Collaborative programs involving the Natural History Museum, London, Smithsonian Institution, US Geological Survey, and continental projects comparing the complex with the Antarctic Peninsula and Patagonia have produced the modern framework for ongoing exploration and resource assessment.
Category:Geology of Chile Category:Metamorphic complexes