ARQUITETURA DE PLUTONS ZONADOS DA FAIXA ARAÇUAÍ-RIBEIRA

Résumé

Post-collisional to late orogenic magmatism (570 to 480 Ma) in the Araçuaí-Ribeira Foldbelt is characterizedby the predominance of high-K metaluminous, allanite-sphene-bearing granitoids. Smaller lenses of coroniticgabbro, anorthosite, pyroxenite and phlogopite-peridotite are also common in deeper exposed areas of thisfoldbelt. Several large plutons (³ 100 km2) were mapped by the authors and co-workers in a 1:25,000 scale.In southern Espírito Santo, the deep erosional level associated with a steep topography reveals the internalarchitecture of these intrusions: a tendency to funnel-shaped bodies, with sub-vertical cylindrical roots,grading to shallower angle dipping tops. Associated stocks, sills and dikes of basic and acidic magmasgenerally intrude the enclosing gneisses along the foliation planes, local ductile shear zones and fold axes.The contact to these enclosing rocks is sharp in deeper eroded plutons (Santa Angélica, Venda Nova,Mimoso do Sul and Várzea Alegre). Where higher levels are exposed (Castelo, Pedra Azul and Conceiçãode Muqui), agmatic stoping zones dominate along the borders. The igneous foliation is usually well markedand the schistosity of the surrounding gneisses wrap around the plutons. Each intrusion has a uniquemarble cake (bimodal) internal structure: concentric patterns of more basic to intermediate cores aresurrounded by interfingered lenses of basic to acidic magmatites. Syenomonzonite and granite mark theborders. Widespread evidence of mingling and mixing between contrasting magmas of gabbroic and graniticand/or syenomonzonitic compositions is characteristic for all intrusive complexes. Probably due tolithospheric delamination following collisional orogenesis, the upwelling of hot asthenospheric magmasinduced partial crustal melting. The interaction of these contrasting magmas originated the bimodal plutons.Their emplacement followed older regional paths such as regional fold axes and ductile shear zones.