Abstract

An intense structural-metamorphic event of probable Permian-Triassic age is inferred from petrologic and field observations of low-grade schists from the Coast Ranges of central Chile between latitudes 38°S and 43°S. Relict almandine-rich garnet, biotite, and aluminous amphibole in mafic schists are replaced by a pervasive assemblage consisting of albite + chlorite + epidote + actinolite + sphene ± quartz: ± stilpnomelane ± white mica ± iron oxide. Chemographic analysis of phase compatibilities based on electron microprobe analyses suggests a regional retrogradation from earlier upper greenschist and/or epidote amphibolite to lower greenschist facies. A regional northwest-southeast-trending fabric within the terrane was imposed during the lower greenschist metamorphism which involved widespread reintroduction of fluids into the system. This major orogenic event is thought to be the culminating episode in a subduction-related accretionary process along the late Paleozoic margin of South America. Convergence may have been markedly oblique to the present north-south-trending continental margin.

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