New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile

The Coastal Ranges in the western part of the Chiloé Archipelago represent an emerged forearc high at the subduction front of south-central Chile. Prior to the Cenozoic framework of the subducting Farallón and Nazca plates beneath the South American plate, the history of the metamorphic basement in...

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Autores principales: Duhart,Paul, Adriasola,Alberto C
Lenguaje:English
Publicado: Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2008
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Acceso en línea:http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082008000100004
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spelling oai:scielo:S0716-020820080001000042008-04-10New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central ChileDuhart,PaulAdriasola,Alberto C Metamorphic/post-metamorphic thermochronology Chilean forearc Cenozoic magmatism South-Central Andes The Coastal Ranges in the western part of the Chiloé Archipelago represent an emerged forearc high at the subduction front of south-central Chile. Prior to the Cenozoic framework of the subducting Farallón and Nazca plates beneath the South American plate, the history of the metamorphic basement in the Coastal Ranges involves episodes of subduction and/or accretion of oceanic and ensialic material along the proto-Pacific margin of Gondwana. Along different segments of the Main Chiloé Island the thermal record of the metamorphic basement rocks includes regional metamorphism, exhumation and finally magmatism. Detrital zircons conventional U-Pb ages from a pelitic schist of the Central Segment of the Main Chiloé Island constrain the maximum possible sedimentation age to the Carboniferous (310 Ma). Other concordant zircon fractions (360, 390 and 412 Ma) suggest Ordovician primary sources. The sedimentary provenance of zircons could correspond to continental magmatic rocks of similar ages presently exposed in adjacent areas such as Nahuelbuta Mountains and Principal Cordillera and, additionally, from distal areas in the North-Patagonian and Deseado massifs. Widespread metamorphism in greenschist facies is well represented in the basement unit of the Main Chiloé Island. K-Ar and 40Ar/39Ar cooling ages in white mica range between 245 to 220 Ma, interpreted as near the peak of metamorphism during Middle to early Late Triassic times. Zircon and apatite fission-track (FT) central ages in metamorphic rocks range from Late Jurassic (ca. 156 Ma) to Eocene (ca. 38 Ma) and are accompanied by relatively large dispersions. The modelling of the zircon FT single-grain age distributions depicts younger deconvoluted Late Cretaceous peak (ca. 80 Ma) and the apatite modelling shows two populations, an older Late Cretaceous peak (ca. 64-91 Ma) and a younger Eocene peak (ca. 3 8-5 3 Ma). The zircon and apatite Late Cretaceous peaks together with the presence of a marine sedimentary succession of presumably later Late Cretaceous age found at the forearc slope of the Main Chiloé Island, suggest exhumation of the metamorphic unit during the early Late Cretaceous. Magmatic zircons from a granodioritic body (Met alqui Pluton) emplaced in pelitic schists within the Central Segment of the Main Chiloé Island, a differentially uplifted block in relation to the northern and southern segments, gave an Eocene U-Pb crystallization age (39.6±0.3 Ma). Upper Eocene (ca. 37 Ma) biotite-bearing porphyric dacitic sills and dikes (Gamboa Dacite) also occur within the Central Segment. Zircon and apatite FT concordant ages (ca. 36 Ma) indicated rapid cooling for these subvolcanic rocks during Eocene times. According to this data, Eocene apatite central and modelling single-grain FT ages detected in the metamorphic rocks probably represent thermal resetting by shallow magmatism, coeval with the Gamboa Dacite and possibly the Met alqui Plutoninfo:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Revista geológica de Chile v.35 n.1 20082008-01-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082008000100004en10.4067/S0716-02082008000100004
institution Scielo Chile
collection Scielo Chile
language English
topic Metamorphic/post-metamorphic thermochronology
Chilean forearc
Cenozoic magmatism
South-Central Andes
spellingShingle Metamorphic/post-metamorphic thermochronology
Chilean forearc
Cenozoic magmatism
South-Central Andes
Duhart,Paul
Adriasola,Alberto C
New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile
description The Coastal Ranges in the western part of the Chiloé Archipelago represent an emerged forearc high at the subduction front of south-central Chile. Prior to the Cenozoic framework of the subducting Farallón and Nazca plates beneath the South American plate, the history of the metamorphic basement in the Coastal Ranges involves episodes of subduction and/or accretion of oceanic and ensialic material along the proto-Pacific margin of Gondwana. Along different segments of the Main Chiloé Island the thermal record of the metamorphic basement rocks includes regional metamorphism, exhumation and finally magmatism. Detrital zircons conventional U-Pb ages from a pelitic schist of the Central Segment of the Main Chiloé Island constrain the maximum possible sedimentation age to the Carboniferous (310 Ma). Other concordant zircon fractions (360, 390 and 412 Ma) suggest Ordovician primary sources. The sedimentary provenance of zircons could correspond to continental magmatic rocks of similar ages presently exposed in adjacent areas such as Nahuelbuta Mountains and Principal Cordillera and, additionally, from distal areas in the North-Patagonian and Deseado massifs. Widespread metamorphism in greenschist facies is well represented in the basement unit of the Main Chiloé Island. K-Ar and 40Ar/39Ar cooling ages in white mica range between 245 to 220 Ma, interpreted as near the peak of metamorphism during Middle to early Late Triassic times. Zircon and apatite fission-track (FT) central ages in metamorphic rocks range from Late Jurassic (ca. 156 Ma) to Eocene (ca. 38 Ma) and are accompanied by relatively large dispersions. The modelling of the zircon FT single-grain age distributions depicts younger deconvoluted Late Cretaceous peak (ca. 80 Ma) and the apatite modelling shows two populations, an older Late Cretaceous peak (ca. 64-91 Ma) and a younger Eocene peak (ca. 3 8-5 3 Ma). The zircon and apatite Late Cretaceous peaks together with the presence of a marine sedimentary succession of presumably later Late Cretaceous age found at the forearc slope of the Main Chiloé Island, suggest exhumation of the metamorphic unit during the early Late Cretaceous. Magmatic zircons from a granodioritic body (Met alqui Pluton) emplaced in pelitic schists within the Central Segment of the Main Chiloé Island, a differentially uplifted block in relation to the northern and southern segments, gave an Eocene U-Pb crystallization age (39.6±0.3 Ma). Upper Eocene (ca. 37 Ma) biotite-bearing porphyric dacitic sills and dikes (Gamboa Dacite) also occur within the Central Segment. Zircon and apatite FT concordant ages (ca. 36 Ma) indicated rapid cooling for these subvolcanic rocks during Eocene times. According to this data, Eocene apatite central and modelling single-grain FT ages detected in the metamorphic rocks probably represent thermal resetting by shallow magmatism, coeval with the Gamboa Dacite and possibly the Met alqui Pluton
author Duhart,Paul
Adriasola,Alberto C
author_facet Duhart,Paul
Adriasola,Alberto C
author_sort Duhart,Paul
title New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile
title_short New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile
title_full New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile
title_fullStr New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile
title_full_unstemmed New time-constraints on provenance, metamorphism and exhumation of the Bahía Mansa Metamorphic Complex on the Main Chiloé Island, south-central Chile
title_sort new time-constraints on provenance, metamorphism and exhumation of the bahía mansa metamorphic complex on the main chiloé island, south-central chile
publisher Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate 2008
url http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082008000100004
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