Antônio Gilberto Costa

The Granulite-Facies Rocks of the Northern Segment of the Ribeira Belt, Eastern Minas Gerais, SE Brazil

Abstract Granulite rocks are exposed in eastern Minas Gerais, Brazil. Its early neoproterozoic evolution is characterised by a history of an active continental margin, including the accretion of suspect terranes. The Manhuacu Terrane is one of those which is represented by a granitic continental plutonic arc and terrigeneous metasediments reflecting a continental margin. A metasedimentary gneiss belt at this margin with shallow to deep marine clastic lithologies as well as metavolcanic and metaplutonic mafic rocks was interpreted as an extensive tectonic segment with suspect development in a back-arc setting. Fragments of a volcanic arc are identified and interpreted as an evidence for a probable island-arc domain. The granulites occur as massive rocks as well as high-grade gneisses and show lithological, structural and metamorphic attributes consistent with their host belt type. In the western portion granulites derived from sedimentary protoliths, have been deposited, deformed and metamorphosed together with the mafic intrusions and as well as with their crystallization. Regional uplift exposed these rocks probably immediately after the metamorphism. In these belts the metamorphic grade is not uniform, especially where uplifting has exposed oblique cross sections over the granulitic rocks. Geothermobarometric calculations indicate that the granulites has been generated under T conditions between 800 and 990 ± 50 C and from medium (4.8 kb) to relatively high (10.0 kb) pressures.

Stone Materials, Constructions Techniques and Alterations in Historic Buildings: Examples from Minas Gerais, in Brazil and from the Braga and Viseu Districts in Portugal

The use of stone materials in constructions and in the art of sculpture in Brazil, as well as the related constructions techniques employed, was strongly influenced by Portugal between the mid-sixteenth century and the early nineteenth century. One of those techniques consisted of erecting the whole constructions using stone materials, without the use of mortar, by solely juxtaposing smaller and larger stones. Some remaining buildings and descriptions dating back to the beginning of the twentieth century, involving the use of carved stone in “mineiro” – or Minas Gerais – constructions, known as minhota, or made in the fashion of Minho, bear proof to the use of that technique and, specially, to the influence this ancient Portuguese province had on the constructing style and on the way of working the stones in Minas Gerais. However, when we consider the frequency with which that technique was used, there is evidence that the use of “stone blocks” was much more common in certain regions of Portugal such as in constructions situated in the district of Braga, in the old province of Minho. Also from Portugal, from the old province of Beira Alta, there should be considered beautiful examples of constructions featuring the use of the dry stone technique which involved utilizing blocks of granitic rock as those seen in the Viseu district. In addition to the description of the stone materials utilized in these buildings, both Brazilian and Portuguese, and in the production of several sculptural elements associated with some of these architectural sets, evidence is provided which shows the occurrence of very similar deterioration processes which are responsible for the imprinting of certain features into these cultural assets, identified by the loss of materials and formation of crusts due to biological colonizations.