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Significance of 40Ar–39Ar encapsulation ages of metapelites from late Palaeozoic metamorphic complexes of Aysén, Chile

Published online by Cambridge University Press:  17 December 2007

ELISA RAMÍREZ-SÁNCHEZ ,
KATJA DECKART  and
FRANCISCO HERVÉ
ELISA RAMÍREZ-SÁNCHEZ*
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Santiago, Chile
KATJA DECKART
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Santiago, Chile
FRANCISCO HERVÉ
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Santiago, Chile
*
*Author for correspondence: eramirezs@cenizas.cl
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Abstract

The ages obtained by the 40Ar–39Ar encapsulation technique (retention and total gas ages) on <2 μm fractions of five metapelites from the Eastern Andean Metamorphic Complex and two from the Chonos Metamorphic Complex allow discussion of the latest recorded metamorphic event in each zone. The Kübler Index (KI) of illite/muscovite (principal component of the metapelites) varies between 0.15° and 0.45° Δ°2θ, indicating regional variation from diagenetic to epizonal metamorphic grade. The 40Ar–39Ar encapsulation analyses reveal 39Ar loss varying between 21 and 25%, which shows a limited positive correlation with KI values. The obtained retention and total gas metapelite ages reflect distinct metamorphic conditions. Retention ages most probably indicate burial or regional metamorphic events without plutonic influence in the southern Eastern Andean Metamorphic Complex. Total gas ages reflect contact ages for metapelites close to intrusions in the northern and southern Eastern Andean Metamorphic Complex and in the Chonos Metamorphic Complex. The thermal overprinting of metapelites occurred in Early Cretaceous times at 130 Ma and 145 Ma and is related to the contact metamorphism of an emplacement pulse of the North Patagonian Batholith. Total gas metapelite ages obtained from the western belt of the Chonos Metamorphic Complex suggest a thermal event related to a distinct pulse of the North Patagonian Batholith.

Keywords

40Ar–39Ar encapsulationmetapelitemetamorphic complexes of AysénChile
Type
Original Article
Information
Geological Magazine , Volume 145 , Issue 3 , May 2008 , pp. 389 - 396
Copyright
Copyright © Cambridge University Press 2007

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