Geology of the Camboriú Complex (SC) / Geologia do Complexo Camboriú (SC)

AUTOR(ES)

Angela Pacheco Lopes

DATA DE PUBLICAÇÃO

2008

RESUMO

The anatectic origin evidenced by known macrostructures in migmatites of the Camboriú Complex is supported by petrographical, geochemical and isotopic data, with partial melting under compressional regimen being suggested by the large amount of leucosome bodies at low-pressure sites represented by interboudins and dilation surfaces. Despite the continental origin in a relatively closed system suggested by the isotopic data, small-scale mobilization of elements and its consequent isotopic ratio changes in leucosomes and their associated ultramafic rocks might lead studies unsupported by field, petrographic and geochemical control to erroneous interpretations of the geological evolution of the region. The geochemical and isotopic complexities revealed in the detailed study of one single outcrop bring about how misinterpreted interpretations can be in regional isotopic studies. Generation temperatures of 700 to 800 C are estimated for leucosomes, from melting of quartzofeldspatic rocks in presence of water, biotite having taken part of the anatectic process, with possible participation of muscovite. Anatexis may have been intensified by the geothermal gradient elevation that followed numerous Neoproterozoic granite intrusions in the region. The combined use of different analytical methods on data from one single outcrop and correlation samples from regional units led to a better understanding of the petrogenetic evolution of the Camboriú Complex, recycled under thickened continental crust after mantle extraction circa 2.5 Ga. Migmatites in association with ultramafic rocks, or other compositionally similar combinations at higher pressure and temperature conditions, would be protoliths for the Itapema, Serra dos Macacos, and Corre-Mar granites, that also show evidence of having undergone similar crustal recycling. Negative values of eSr(595 Ma), with initial 87Sr/86Sr (595 Ma) >0.706 and >8 suggest upper-crust generation conditions, as supported by geochemical results. Such conditions, and the relatively low leucosome generation temperatures seem compatible with a geological setting in which the migmatites of the Camboriú Complex would represent pending roofs to granite intrusions.

ASSUNTO(S)

isotopic geology petrogênese petrogenesis complexo camboriú petrografia camboriú complex geoquímica geochemistry geologia isotópica petrography

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