Metamorphic evolution of the Sierras de San Luis, Argentine: granulite facies metamorphism related to mafic intrusions.

CHRISTOF HAUZENBERGER,; ABERRA MOGESSIE,; GERARD HOINKES,; ANYA FELFERNIG,; ERNESTO BJERG,; JOSÉ KOSTADINOFF,; SERGIO DELPINO,; LUIS DIMIERI

MINERALOGY AND PETROLOGY

Springer-Verlag

Lugar: Viena; Año: 2001 vol. 71 p. 95 - 126

0930-0708

The Sierras de San Luis, which are part of the Sierras Pampeanas, are located in CentralArgentina. The crystalline basement of the Sierras de San Luis is built up of three mainblocks (western block, central block, and eastern block), which are separated bymylonite zones. The western and the eastern block are dominated by migmatites,whereas the central block is mostly lower in metamorphic grade ranging fromgreenschist facies to amphibolite facies, and locally to granulite facies in the vicinity ofnumerous ma®c bodies. Most parts of the central block is built up of amphibolite faciesrocks. These were formed during a ®rst metamorphic event (M1-A) which ischaracterized by a mineral assemblage of stauroliteÿgarnetÿbiotiteÿmuscoviteÿ plagioclaseÿquartzÿilmenite®brolitechlorite. The PT conditions of M1-A are about570 C to 600 C and 5 to 5.7 kbar. A ma®c intrusion, now seen as numerous ma®clenses included in the basement rocks caused local granulite facies metamorphism. Theobserved mineral assemblage consists of garnetÿcordieriteÿsillimaniteÿbiotiteÿKfeldsparÿplagioclaseÿquartzÿrutileÿilmeniteorthopyroxene (M2-G). The PT estimatesfor granulite facies conditions are 740 C to 790 C and 5.7 to 6.4 kbar. Duringcooling a mylonite zone developed within the central block retrograding most of thegranulite facies rocks to amphibolite facies conditions. The newly formed mineralassemblage consists of garnetÿbiotiteÿsillimaniteÿplagioclaseÿmuscoviteÿquartzÿ rutileK-feldspar (M3-A). The PT estimates of the locally overprinting secondamphibolite facies event (M3-A) are about 590 C to 650C and 5.4 to 6.0 kbar. Thededuced PT path shows a near isobaric heating from M1-A to M2-G.The mylonitemineral assemblage M3-A equilibrated at pressures close to M2-G. The PT path can be explained best by heating of an amphibolite facies middle crust by a ma®c intrusion.During near-isobaric cooling tectonic activity in discrete parts of the basement causedmylonitization at amphibolite facies conditions.