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Andean geology

On-line version ISSN 0718-7106

Abstract

MURRA, Juan A. et al. El Escorial calcitic marbles (Cushamen Metamorphic Complex, Macizo Norpatagónico): 87Sr/86Sr isotopic characterization and age of sedimentation. AndGeo [online]. 2022, vol.49, n.1, pp.77-93. ISSN 0718-7106.  http://dx.doi.org/10.5027/andgeov49n1-3387.

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 ratios 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).

Keywords : Marble; Sr isotopes; Norpatagonian Massif; Southwest Gondwana.

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