Termal metamorphism of marbles from Caçapava do Sul, RS, Southern Brazil

Olavo José Bortolotto

Abstract


The Caçapava do Sul region, State of Rio Grande do Sul, is characterized by the occurrence of a granitic batholith (Caçapava Granite) that is surrounded by a belt of metamorphites belonging to the Porongos Group, assigned to Upper Precanbrian by RIBEIRO et alii (1966). Among the metamorphites occur a carbonatic rock body, lens shaped, with clear contacts, interpenetrated by granitic apophises and with an outcrop of about 17 km2. The study of the metamorphism showed that these rocks were affected termically by the Caçapava Granite and its apophises, as become evident by the metamorphic zoneation in rocks belonging to a Piroxene Hornfels Facies, near the contact, and Albita-Epidoto Hornfels Facies, placed farther away. The structure generaly isotropic, the preservation of the polimorphous orthoclase, the contemporariness of the granitic body and its wall rocks (Brazilian Cicle) and having in view hat the wall rocks belong to a Green Schists Facies (BITENCOURT, 1983), make evident the shallow emplacement of the Caçapava Granite and allow to estimate the highest metamorphic temperatures at about 560°C. The total pressure and the pressure of fluid phase were estimated at 1.000 bars, which also conforms to the shallow emplacement (3 - 4 km) of the granitic body. The analyses of the metamorphism of these rocks, based on T – XCO2 diagrams for the CaO-MgO-SiO2-CO2-H2O system, maked evidente equilibrium and disequilibrium paragenesis which conforms to the Caçapava granitic magma that didn't favour an homogeneous termic distribution and of long duration.


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DOI: https://doi.org/10.5902/2179460X25479

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