Los mármoles cálcicos de El Escorial (Complejo Metamórfico Cushamen, Macizo Norpatagónico): caracterización isotópica de 87Sr-86Sr y edad de sedimentación

The El Escorial marbles (Cushamen Metamorphic Complex) along with amphibolites form metamorphic septa within the permian granitoids of the Mamil Choique Formation (261-286 Ma). The metamorphism, determined in granulite facies migmatic gneisses septa cropping out 120 km southwest of El Escorial, occurs at 311 ± 27 Ma (CHIME method in monazite). The marbles are calcitic (calcite > 95%, R.I.: 0.5 to 2.5%) and show 87Sr/86Sr values between 0.70768 and 0.70825 (n = 10). The data provided in this work, added to previous contributions, allow to constraints the sedimentation age of the silicic-carbonate successions of the Cushamen Metamorphic Complex between ca. 385 and 335 Ma. This suggests the existence of a mixed carbonate-siliciclastic platform at least in the southernmost portion of southwestern Gondwana between Middle Devonian and early Carboniferous (Middle Mississippian).