U–Pb and Sm–Nd geochronology of amphibolites from the Curaçá Belt, São Francisco Craton, Brazil: Tectonic implications

Abstract

The Curaçá terrane is part of the Itabuna-Salvador-Curaçá (I-S-C) Paleoproterozoic orogen in the São Francisco craton, northeastern Brazil, and comprises supracrustal rocks, gneisses of their probable basement, amphibolites, and mafic-ultramafic Cu-bearing bodies (including the Caraíba Cu-Mine), all affected by D1-D3 deformation events associated to M1-M3 metamorphism under high-T granulite and amphibolite facies, and assisted by G1-G3 tonalitic-granodioritic-granitic intrusions. U-Pb and Sm-Nd Thermal Ionization Mass Spectrometry (TIMS) isotopic data from amphibolite, tonalite, and granite, sampled in a well-known outcrop, indicate partial reset and heterogeneous modification of the original isotopic systems, attributable to deformation and metamorphism. The ages obtained from these systems agree with each other, and also with other previously published U-Pb data, and imply that 2.6 Ga is the crystallization age of the protolith of the amphibolite. Together with key structural relationships, they also indicate a 2.08-2.05 Ga interval for M3 metamorphism, and make even a less precise age (2.2-2.3 Ga) acceptable, as it suggests contamination in the amphibolite with material in a syn-D2 tonalite crystallized 2248±36 Ma ago. The new data demonstrate the existence of Neoarchean fragments of both oceanic and continental crusts and constrain the Archean-Paleoproterozoic development of the Curaçá belt, the I-S-C orogen, and the São Francisco craton.

Mapping New IOCG Mineral Systems in Brazil: The Vale do Curaçá and Riacho do Pontal Copper Districts

“…Importantly, Itiúba syenite is a syn tectonic to shear zone of 2084 ± 9 Ma. This age is also related to copper mineralization situated along shear zones [26,46].…”

“…Shear zones have been mapped along the Vale do Curaçá district and are often marked by intense biotite-rich rocks related to mylonitic rocks. These zones are characterized by two phases of progressive deformation [34,46]. (a) The first phase (D1) involved transpressive thrust structures showing convergence to the west.…”

“…More recent work shows early (2580 ± 10 Ma; [45]) orthomagmatic mineralization overprinted by a later hydrothermal event that produced IOCG mineralization at ca 2 Ga [20,29,36]. Studies conducted by [46][47][48] show evidence of structural control at the Caraíba mine.…”

“…The north-to northeast-trending magnetic anomalies of the Vale do Curaçá copper district correspond to anastomosed structures that have been geologically mapped throughout the district. The NS-trending structures have been overprinted by at least two cycles of shearing [34,46]. These later shear faults are recorded on the TAHG map (Figure 6a).…”

Geocronologia U-Pb em zircão de ortognaisses e granitoides

“…No ortognaisse granulítico ocorrem idades concordantes em bordas de zircão, sugerindo cristalização cedo-riaciana (~2,3 Ga). D'el Rey Silva et al, (2007) relatam idade de 2248 ± 36 Ma (U-Pb TIMS) para tonalito encaixante das rochas máficas mineralizadas. Não são relatadas unidades com idades U-Pb insitu que possibilitem a franca determinação de magmatismo cedo-riaciano no orógeno, portanto, é coerente relacionar a idade de D'el Rey Silva et al, (2007) a: i) mistura de idades em borda riaciana e núcleo xenocristalino neoarqueano durante a diluição isotópica; ii) ou a discordância relacionada ao reequilíbrio isotópico por recristalização em condições de metamorfismo de alto grau (Figura 2.2b) (Moser et al, 2009;Kröner et al, 2013Kröner et al, , 2014.…”