EVIDENCE OF THE SUPERPRODUCTION OF THE CONTINENTAL CRUST DURING PALEOPROTEROZOIC IN SOUTH AMERICAN PLATFORM. IMPLICATIONS REGARDING THE INTERPRETATIVE VALUE OF THE SM-ND MODEL AGES

KEI SATO, OSWALDO SIGA JÚNIOR

Resumo


The production of juvenile continental crust was larger in the Proterozoic than Archean. During Proterozoic the production was about 64%, while during Archean was around 34% of the total volume. The great accretion from mantle to crust happened between 2,2 to 1,9Ga corresponding 35% of the total volume of the actual continental crust. During Archean an intense recycling between mantle and continental crust took place, while in Paleoproterozoic the rate of mantle accretion to continental crust was larger than the assimilation. During MesoNeoproterozoic little accretion of juvenile material occurred, predominating crustal reworking. Consequently the chemical depletion rate (fractionation) of the upper mantle was smaller in Archean than Proterozoic. The isotopic data show a certain increase of the depletion degree of Sm-Nd and Rb-Sr in the upper mantle that began at 2.2 Ga as a reflex of the strong differentiation of the upper mantle to continental crust.

Palavras-chave


Paleoproterozoic material accretion; South American Platform; Sm-Nd model age.

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