BASAMENTO PALEOPROTEROZOICO DEL ÁREA DE SAN MIGUEL, SIERRAS SEPTENTRIONALES DE LA PROVINCIA DE BUENOS AIRES. REGISTRO DE UNA CUENCA DE RETROARCO EN EL MARGEN SUR DEL CRATÓN DEL RÍO DE LA PLATA

LAJOINIE, MARÍA FLORENCIA; LANFRANCHINI, MABEL ELENA; ETCHEVERRY, RICARDO OSCAR

San Miguel de Tucumán

Congreso; XX Congreso Geológico Argentino; 2017

Asociación Geológica Argentina

New information obtained from the characterization of biotite gneises and migmatites from the San Miguel area allowed the interpretation of metamorphic processes that formed a portion of the Paleoproterozoic basement of the Tandilia Belt.Biotite gneiss shows a compositional S1 banding (N35°E/60°NW) and a mineral composition: microcline, (oligoclase-andesine), quartz and biotite. Migmatites occur as differentiated bodies with stromatic structure with S1 orientation and quartz, oligoclase, microcline leucosomes. Also almandine garnet appears in voluminous leucosomes. Chemical analyses indicate that the gneiss derived from a sedimentary protolith (wacke) while the migmatites would have formed from partial melting of the gneiss through decomposition of biotite in presence of quartz and plagioclase. This fact must have generated the garnetiferous phase with potassic feldspar and a peraluminous granitic melt in imbalance: low ratio (La/Yb)N