info:eu-repo/semantics/article
OS ANFIBOLITOS DA REGIÃO MORRETES-ANTONINA (PR)
OS ANFIBOLITOS DA REGIÃO MORRETES-ANTONINA (PR)
Autor
GIRARDI, VICENTE A. V.
Institución
Resumen
Two metamorphic zones have been established for rocks of the Morretes-Antonina área, State of Paraná, Brazil. The first one is composed chiefly of oligoclase-andesine gneisses interbedded with gondites, oligoclase-andesine amphibolites, and andesine-labradorite amphibolites. The second, which has been affected by retrograde metamorphism exhibits albite gneisses, albite amphibolites, magnesian schists, chlorite schists, and magnetite quartzites. The mineral assemblages for those zones are consistent respectively with the amphibolite facies and greenschist facies of metamorphism. The andesine-labradorite amphibolites, showing no evidence of retrogressive metamorphism, are composed essentially of brown hornblende and plagioclase An40-54. The oligoclase-andesine amphibolites exhibit plagioclase An25-35, as well as brown and green hornblende. Albite (An0-5, epidote, and actinolite are major minerals on the albite amphibolite group. Mineralogical breakdowns from hornblende to actinolite, or to biotite plus chlorite, and from calcic plagioclase to sodic plagioclase plus epidote, are common features of these rocks. No significant chemical variations have been registered for the low and high-grade amphibolites. The Niggli numbers si, alk, and k are only slightly greater for the albite amphibolites than for the andesine amphibolites, whereas the mg value is lower for the former. The chemical data for major elements indicate that the amphibolites are of igneous parentage. Two metamorphic zones have been established for rocks of the Morretes-Antonina área, State of Paraná, Brazil. The first one is composed chiefly of oligoclase-andesine gneisses interbedded with gondites, oligoclase-andesine amphibolites, and andesine-labradorite amphibolites. The second, which has been affected by retrograde metamorphism exhibits albite gneisses, albite amphibolites, magnesian schists, chlorite schists, and magnetite quartzites. The mineral assemblages for those zones are consistent respectively with the amphibolite facies and greenschist facies of metamorphism. The andesine-labradorite amphibolites, showing no evidence of retrogressive metamorphism, are composed essentially of brown hornblende and plagioclase An40-54. The oligoclase-andesine amphibolites exhibit plagioclase An25-35, as well as brown and green hornblende. Albite (An0-5, epidote, and actinolite are major minerals on the albite amphibolite group. Mineralogical breakdowns from hornblende to actinolite, or to biotite plus chlorite, and from calcic plagioclase to sodic plagioclase plus epidote, are common features of these rocks. No significant chemical variations have been registered for the low and high-grade amphibolites. The Niggli numbers si, alk, and k are only slightly greater for the albite amphibolites than for the andesine amphibolites, whereas the mg value is lower for the former. The chemical data for major elements indicate that the amphibolites are of igneous parentage.