A magmatic barcode for the São Francisco Craton: Contextual in-situ SHRIMP U[sbnd]Pb baddeleyite and zircon dating of the Lavras, Pará de Minas and Formiga dyke swarms and implications for Columbia and Rodinia reconstructions

Abstract

Eoarchean to Rhyacian crust is preserved in the São Francisco Craton of eastern Brazil. To position this crustal segment in paleocontinental reconstructions, precise, accurate and robust geochronological data are necessary, especially for the diverse regional-scale mafic dyke swarms that crosscut the cratonic basement. This geochronological database can then be used to construct a magmatic barcode and compare it to the barcode of other cratons around the world, in search of similarities that might help to position these pieces in the paleocontinental puzzles. New UPb SHRIMP contextual in-situ (thin section) dating of baddeleyite and zircon from six samples of three different dyke swarms in the southern São Francisco Craton, in addition to novel lithogeochemical and NdSr isotopic data, allow to pinpoint dyke emplacement at ca. 2.55 Ga (Lavras I swarm; εNd(t) = −6 to +2; TDM not calculable), ca. 1.8–1.7 Ga (Pará de Minas I and II dyke swarms; εNd(t) = −10 to −5; TDM = 2.5–3.0 Ga) and at ca. 900 Ma (Formiga dyke swarm; εNd(t) = −7 to 0; TDM = 1.4–2.3 Ga). The new geochronological data suggest a link between the regional dyke swarms and extensional stresses during the onset of crustal rifting related to the evolution of the Minas, Espinhaço and Macaúbas basins, respectively. A barcode comparison shows strong similarity between the São Francisco and North China cratons (Lavras-Taipingzhai/Naoyumen swarms, Pará de Minas-Taihang/Miyun swarms, Formiga/Pedro Lessa-Sariwon/Dashigou swarms; and possible correlations of the poorly dated 2.2–2.0 Ga Paraopeba swarm with similar aged swarms in North China), suggesting proximity of those two cratonic blocks, whether they were part or not of Proterozoic paleocontinents such as Columbia and Rodinia. The novel geochronological data support previous interpretations based on paleomagnetic data and provide further refinements of the geochronological record of the southern hemisphere cratonic blocks, allowing for better-tied global correlations.