Brazilian Journal of Geology · 2013 · 17 citations · 30 references
The Carmpolis de Minas Layered Suite is situated in the Campo Belo Metamorphic Complex domain, Minas Gerais, SE Brazil, which, together with other metamorphic complexes in the surroundings of the Quadriltero Ferrfero, composes the Archean sialic crust of the southern part of the So Francisco Craton. This suite encompasses a remaining segment of a magmatic arc, which is deformed and metamorphosed to upper amphibolite-granulite facies. It shows layered and massive strata, constituted by rock types with lithogeochemical signature equivalent to low-K 2 O tholeiitic series. Both tholeiitic and calc-alkaline magmatism phases were identified. Amphibolite and metarhyolite samples were used for zircon U-Pb dating using MC-LA-ICP-MS. The amphibolite zircons yielded 232 Th/ 238 U ratios 0.17 -0.83 and a Concordia age of 2,752 18 Ma. This interval yields an approximation to minimum age of the calc-alkaline phase. The metarhyolite zircons yielded 232 Th/ 238 U ratios 0.25 -0.66 and ages of 2,713 9.9 and 2,710 31 Ma. This variation was interpreted as the minimum age interval of the calc-alkaline phase. One of the metarhyolite samples yielded two inherited zircon populations. These populations were dated at 3,374 30 and 2,859 23 Ma, suggesting the contribution of older crusts in the genesis of the suite. The results showed that the genesis of this suite represents an episode of juvenile arc crust formation during the Rio das Velhas Tectonotermal Event (2,780 Ma). This syn-to late-orogenic episode involved arc development, tholeiitic to calc-alkaline magmatism, metamorphism, and crustal recycling.
30