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Clay Minerals; June 2004; v. 39; no. 2; p. 151-162; DOI: 10.1180/0009855043920127
© 2004 Mineralogical Society of Great Britain and Ireland
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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

M. BELMAR1, D. MORATA1, F. MUNIZAGA1, C. PÉREZ DE ARCE2, S. MORALES3 and F. J. CARRILLO3

1 Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile, 2 Servicio Nacional de Geología y Minería, Santa Maria 0104, Providencia, Santiago, Chile, and 3 Departamento de Mineralogía-Petrología, Facultad Ciencias, Universidad de Granada, Avenida Fuentenueva s/n., Granada, 18002, Spain

* E-mail: mbelmar{at}ing.uchile.cl

(Received 4 June 2003; revised 5 December 2003)

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 µm 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 17435 Ma is interpreted as belonging to the contact metamorphism due to the intrusion of Jurassic plutons (16535 Ma to 17535 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: pelites, K-Ar dating, very low-grade metamorphism, Costal Range, Chile




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A. P. WILLNER, S. N. THOMSON, A. KRONER, J.-A. WARTHO, J. R. WIJBRANS, and F. HERVE
Time Markers for the Evolution and Exhumation History of a Late Palaeozoic Paired Metamorphic Belt in North-Central Chile (34{degrees}-35{degrees}30'S)
J. Petrology, September 1, 2005; 46(9): 1835 - 1858.
[Abstract] [Full Text] [PDF]


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