Los mármoles de alto grado del Macizo de San Carlos (Río Hondo, Cuchi Yaco y Sagrada Familia), Sierras de Córdoba, Argentina

GUERESCHI, ALINA BEATRIZ; MARTINO, ROBERTO DONATO

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1999 vol. 54 p. 36 - 46

0004-4822

The Sierras Pampeanas near Córdoba consist mainly of medium- to high-grade metamorphic rocks (tonalitic gneisses, amphibolites and marbles) in contact with trending NNW migmatitic belts represented by homogeneous and heterogeneous cordierite-bearing migmatites. The San Carlos Massif located in the northwestern part of the Sierras represents the largest of these belts. It is mainly formed by homogeneous migmatites (plagioclase - quartz - biotite - garnet - cordierite ± K-feldspar) with septa of quartz-feldespathic gneisses, amphibolites, calc-silicate gneisses and marbles. In the southeastern part of the San Carlos Massif, at Río Hondo, Cuchi Yaco and Sagrada Familia, there are bodies of forsterite- and clinohumite-bearing calcodolomitic and serpentinized calcitic marbles, all with spinel and phlogopite as accesory mineral phases. Estimated metamorphic peak P-T conditions give around 700°C and 5 Kb, with variable XCO2 (< 0.45). These conditions are consistent with the previously determined in migmatites at San Carlos Massif (5.6 Kb and 700-750°C). Clinohumite occurring as corona around forsterite would have been produced during later decompression and rehydration with HF-rich fluids, which were presumably present in the original sedimentary protolith. Pressure lowering would be related to a regional tectonic extension and exhumation recorded in the migmatites and mirrored in the marbles at the same scale. After that, a progressive hydration affects the prograde mineralogy during a static cooling event that preserves delicate corona textures. The metamorphic reactions and evolution followed by the marbles are correlated with the associated migmatites in which they are hosted. Summarizing, a sedimentary sequence composed of carbonates and pelites undergo high-grade metamorphism which produces partial melting in pelites and solid-solid reactions in the carbonates. This latter lithology would behave like resisters and became like rafts in the partial melted environment.