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Significance of K-Ar dating of very low-grade metamorphism in Triassic-Jurassic pelites from the Coastal Range of central Chile

Published online by Cambridge University Press:  09 July 2018

M. Belmar ,
D. Morata ,
F. Munizaga ,
C. Pérez de Arce ,
S. Morales  and
F. J. Carrillo
M. Belmar*
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
D. Morata
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
F. Munizaga
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
C. Pérez de Arce
Affiliation:
Servicio Nacional de Geología y Minería, Santa Maria 0104, Providencia, Santiago, Chile
S. Morales
Affiliation:
Departamento de Mineralogía-Petrología, Facultad Ciencias, Universidad de Granada, Avenida Fuentenueva s/n., Granada, 18002, Spain
F. J. Carrillo
Affiliation:
Departamento de Mineralogía-Petrología, Facultad Ciencias, Universidad de Granada, Avenida Fuentenueva s/n., Granada, 18002, Spain
*
*E-mail: mbelmar@ing.uchile.cl
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Abstract

K-Ar isotopic dating of very low-grade metamorphism affecting Triassic-Jurassic rocks in the Coastal Range of central Chile was carried out on whole rocks and their <2 mm size fractions. In the study area, a regional-burial low-grade metamorphism at anchizone conditions (T ≤190°C) and low-pressure conditions (P ≥1.3 kbar) has been described. The highest observed temperatures are related to a contact metamorphism produced by nearby Jurassic intrusions, with a P-T estimate at the immediate contact zone of ~650–690°C and 4 kbar.

The whole-rock K-Ar age of 174±5 Ma is interpreted as belonging to the contact metamorphism due to the intrusion of Jurassic plutons (165±5 Ma to 175±5 Ma). A time-interval of ~20 Ma between the diagenesis (206 Ma) and the anchizonal very low-grade metamorphism (181–184 Ma) is obtained, and a rate of subsidence of ~120 m/Ma is proposed for these Triassic-Jurassic basins. A thermal influence on the burial, very low-grade, regional metamorphism is invoked.

Keywords

pelitesK-Ar datingvery low-grade metamorphismCostal RangeChile
Type
Research Article
Information
Clay Minerals , Volume 39 , Issue 2 , June 2004 , pp. 151 - 162
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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