Ages of protolith and Neoproterozoic metamorphism of Al-P-bearing quartzites of the Veredas formation (Northern Espinhaço, Brazil): LA-ICP-MS age determinations on relict and recrystallized zircon and geodynamic consequences

Abstract

The N-S running Espinhaço fold belt, situated in the São Francisco craton in central-eastern Brazil, separates this craton in a western and an eastern part along the Paramirim Corridor, a Brasiliano-Panafrican (∼650–500Ma) deformation zone. The (meta)sediments of the Espinhaço basin consist of several synthems with dominantly siliciclastic deposits. Among them, Al- and P-rich, lazulite-bearing blue quartzite, the amphibolite-facies equivalent of a phosphatic sandstone, of the Veredas Formation in the Northern Espinhaço form a conspicuous horizon. Zircon crystals from these quartzites have been dated using laser ablation inductively coupled plasma mass spectrometry. The zircon crystals are both detrital and metamorphic in origin, the latter exhibiting highly unusual textures produced by dissolution–reprecipitation reaction and concomitant replacement of metamict areas: (REE, Y, Th, U) zircon+fluid=zircon+xenotime. Detrital zircons reveal relict age groups of 3.1–3.3Ga, 2.6–2.7Ga, 2.0–2.3Ga, and 1.5Ga. The end of sedimentation and erosion of the magmatic and metamorphic rocks of the Sao Francisco craton can be estimated therefore as ≤1.5Ga. The major metamorphic event recorded by reprecipitated zircon is Neoproterozoic and documented by a lower-intercept age of 634±19Ma, which was calculated from analyses of individual spots on19 grains with a common relict Orosirian-Rhyacian age of 2032±31Ma, temporal equivalent to Transamazonian. The Neoproterozoic age of the metamorphosed zircons of the Vereda formation corresponds to the Brasiliano-Panafrican remobilization of the São Francisco-West Congo craton along the eastern side of the Espinhaço fold belt in the Paramirim Corridor.