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| Titel |
Late Paleozoic to Triassic magmatism in the north-central High Andes, Chile: New insights from SHRIMP U-Pb geochronology and O-Hf isotopic signatures in zircon |
| VerfasserIn |
Álvaro Hernández González, Katja Deckart, Mark Fanning, Cesar Arriagada |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093429
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| Publikation (Nr.) |
 EGU/EGU2014-8134.pdf |
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| Zusammenfassung |
| The Chilean High Andes (28o- 31oS) comprises a vast number of late Paleozoic – Triassic
granitoids which give information about the last stages of Gondwana assemblage.
Particularly, previous studies determined two tectonic configurations during this time:
subduction related compressional setting (late Carboniferous – Late Permian) and
non-subduction post-collisional extensional setting (Late Permian – Triassic), as the last stage
of Gondwana assemblage. However, new O-Hf isotopic data along new U-Pb SHRIMP ages
in zircon have shown that this model should be modified and updated to the new analytical
data available. δ18O values indicate a strong change in the tectonic configuration
approximately 270 Ma (earliest middle Permian) and thus, units can be divided
into 2 mayor groups: late Carboniferous to earliest middle Permian and middle
Permian to Triassic. The oldest group shows slightly low values of εHfi (ca. +1 to -4)
with high δ18O (ca. >6.5 o-oo), indicating an elevated supracrustal component and
the addition of less radiogenic continental-like material, which along significant
residence time (TDM2: Mesoproterozoic) can be interpreted as magmas formed at
depth in a subduction-related continental arc, and contaminated with supracrustal
material and/or oceanic sediments transported through the subducted slab to the
mantle-wedge. Subsequently, middle Permian – Triassic rocks show a wider range of
εHfi values (ca. +3 to -3) with relatively low, mantle-like δ18O (ca. 4.5-6.5 o-oo),
indicating a source of magmas without the addition of supracrustal material for some
plutons, whilst for others, a slight input. The higher positive values of εHfi can be
related to the influence of new juvenile material in the source of some magmas. This
isotopic data can be interpreted as rocks formed as the result of melting of an old
thinned mafic crust (with mantle-like δ18O values characteristic of this type of rocks)
with limited addition of supracrustal material; in agreement with regional models,
which postulate an extensional setting during this time, and thus, during the last
stages of Gondwana assemblage. Finally, the result for the late Carboniferous to
earliest middle Permian group shows almost identical O-Hf signatures compared to
those observed in the Chilean Coastal Batholith (33o-40oS) of mid Carboniferous –
early Permian age. This suggests a comparable tectonic configuration for the entire
magmatism, initiating from south-to-north, with magmatism starting from the south. |
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