CRUSTAL ZONING OF NEOPROTEROZOIC PRE-COLLISIONAL GRANITOIDS IN THE PARAÍBA DO SUL BELT, RIO DE JANEIRO, BRAZIL

RÔMULO MACHADO, MICHEL DEMANGE, IAN MCREATH, JACQUES MOUTTE

Resumo


In the Rio de Janeiro State granites with associated charnockites or charnockitic suites are present in the Litorâneo domain in the internal part of the Paraíba do Sul belt, while plutons without charnockitic rocks occur in the Serra dos Órgãos and Paraíba domains in the external part. In both groups the linear and foliated batholiths are structurally concordant with the regional trends. The two associations usually have slightly expanded compositions with orogenic geochemical features, which are comparable with those for Cordilheran I-type batholiths, but are more evolved. Chemical differences found in the less-differentiated rocks of the two associations disappear in the most evolved terms. The lateral compositional zoning of the less-evolved terms across the belt could have been produced either by magma genesis above a NWdipping subduction zone, or by lateral migration of magmatism during tectonic evolution. The plutons were either emplaced at different, deep crustal levels under amphibolite or granulite facies conditions, or evolved in the presence of different fluids. The pre-collisional magmatism occurred between 560 and 634 Ma ago.

Palavras-chave


Crustal zoning; Pre-collisional; Neoproterozoic; Granites; Charnockites.

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