Structural and Compositional Evolution of Cr-Spinels and Hornblends, Palma Group, Rio Grande do Sul, Brasil

LÉO AFRANEO HARTMANN, MARCOS ANTONIO VASCONCELLOS, MARIA DE FÁTIMA BITTENCOURT, JOÃO CASTRO, JULIANA FABIÃO, ANDRÉIA MONTEIRO, KAREN PIRES

Resumo


One amphibolite facies metamorphic event is registered in chromites and hornblendes from the Palma Group serpentinites and meta-andesites, Brazil's southernmost Rio Grande do Sui Slate. Metamorphism was apparently caused by syntectonic injection of voluminous Cambaí Group meta-granitoids and not by post-tectonic Jaguari Granite intrusion. Regional metamorphic hornblendes are in direct contact with magmatic pargasites, which indicates that it was the first metamorphic event in the area. Both hornblendes in Campestre Formation and Crspinels in Cerro da Cruz Formation are little zoned, an indication that only one metamorphic event was of regional extent. Recrystallization to chlorite + epidote greenschist facies parageneses is restricted to shear zones and volumetrically small.



Palavras-chave


Cr-spinels; hornblende; electron microprobe; backscattered electron.

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DOI: https://doi.org/10.22456/1807-9806.20175

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