Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizario ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702 ± 21 Ma during a greenschist facies event M2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257 ± 12 Ma) and Camboriu Orogeny (∼ 1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702 ± 21 Ma) of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.

[1]  J. Santos,et al.  Duration of the Trans-Amazonian Cycle and Its Correlation within South America Based on U-Pb SHRIMP Geochronology of the La Plata Craton, Uruguay , 2003 .

[2]  L. Hartmann,et al.  Cratons and orogenic belts of the Brazilian Shield and their contained gold deposits , 2001, Mineralium Deposita.

[3]  J. Santos,et al.  Zircon U–Pb SHRIMP dating of gneissic basement of the Dom Feliciano Belt, southernmost Brazil , 2000 .

[4]  D. Groves,et al.  Advances in SHRIMP geochronology and their impact on understanding the tectonic and metallogenic evolution of southern Brazil , 2000 .

[5]  D. Groves,et al.  A New Understanding of the Provinces of the Amazon Craton Based on Integration of Field Mapping and U-Pb and Sm-Nd Geochronology , 2000 .

[6]  A. Rust,et al.  U-Pb and Pb-Pb age constraints on Paleoproterozoic magmatism, deformation and gold mineralization in the Omai area, Guyana Shield , 2000 .

[7]  F. Almeida,et al.  The origin and evolution of the South American Platform , 2000 .

[8]  M. Formoso,et al.  Magmatism and Metallogeny in the Crustal Evolution of Rio Grande do Sul Shield, Brazil , 1999 .

[9]  L. Hartmann.  Deepest Exposed Crust Of Brazil-Geochemistry Of Paleoproterozoic Depleted Santa Maria Chico Granulites , 1998 .

[10]  N. McNaughton,et al.  SHRIMP U/Pb zircon geochronology of Neoproterozoic juvenile and crustal-reworked terranes in southernmost Brazil , 1998 .

[11]  J. B. Smith,et al.  The Sholl Shear Zone, West Pilbara: evidence for a domain boundary structure from integrated tectonostratigraphic analyses, SHRIMP UPb dating and isotopic and geochemical data of granitoids , 1998 .

[12]  J. Kirschvink,et al.  Zircon U-Pb ages for the Early Cambrian time-scale , 1992, Journal of the Geological Society.

[13]  L. Fernandes,et al.  Relações Embasamento/"Cobertura" na Porção Ocidental do Cinturão Dom Feliciano: um Esboço Estrutural , 1990 .

[14]  A. Tommasi,et al.  Deformation patterns in the southern Brazilian branch of the Dom Feliciano Belt: A reappraisal , 1992 .