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Abstract

Preliminary results on the regional metamorphism of the Sierra Chica (Sierras Pampeanas) are reported. The work is based on a detailed textural and mineral study of high-grade cordierite-garnet metapelitic migmatites of diatexitic type. Three events are recognized on the basis of garnet textural and chemical zoning: M7 probably represents an older metamorphism and took place under subsolidus conditions; M2 is synchronous to the main regional foliation (Sn+1). The peak of metamorphism was reached at this stage under granulite facies conditions (P1= 5.7 ± O.4kb, T= 820 ± 25°C). This event is assigned to the Pampean Orogeny; M3 represents a lower P-T event which is temptatively assigned to the uplift of the previously thickened continental crust. Registered P-T conditions for this retrograde event have been determined at 4±0.5kb and 775 ± 75°C respectively.