Lithologic units from lavras county minas gerais state brazil
Bueno, C.R.P.; Bahia, V.G.; Curi, N.; Dias Junior, M.D.S.
Ciencia e Pratica 14(3): 352-364
1990
Accession: 007516812
The main objective of this work was to detail the mineralogical composition of the lithologic units from Lavras county, Minas Gerais state, Brazil. Based on 1:60,000 scale aerial photos and IBGE (Instituto Brasileiro de Geografia) topographic maps, the area was studied at field conditions with sampling for macro- and microscopic petrographic analyses, and the 1:100,000 scale geologic map was used. The region is dominated by metamorphic rocks which were subdivided into distinct lithologic units defined following petrologic criteria. There is a mineralogical composition variability into these units, where in some cases pyroxene dominates as the essential mafic mineral, being altered, and in some circumstances giving place to biotite and hornblende (granulitic and migmatitic unit). Under other conditions there is a dominance of quartz-feldspar mass, being the feldspar represented by microline or plagioclase (leucocratic gneiss unit). In the migmatite unit there is an increase of porphyritic types. Many times these minerals demonstrate high degree of recrystallization, giving a diffuse aspect to the samples, evidencing the cataclasis (cataclastic gneiss unit). Hornblende or tremolite-actinolite is the essential mineral in the basic intrusions classified as amphibolites. Quartzite and mica-schist dominate the south part of the county. Generally the quartzites are pure but some times they are micaceous (muscovite), whereas there is occurrence of feldspar and quartz schists, as well as biotite and muscovite. These lithologic units can serve as bases for future studies involving parent materials, pedogenesis, geomorphologic aspects, and inter-related others.