Paleomagnetism of 1.79 Ga Pará de Minas mafic dykes: Testing a São Francisco/Congo-North China-Rio de la Plata connection in Columbia

Abstract

Paleogeographic connections between São Francisco/Congo, North China and Rio de la Plata Cratons through the Paleoproterozoic have been proposed on the basis of geological and paleomagnetic data. We conducted new paleomagnetic analyses for mafic dykes of the 1790 Ma Pará de Minas swarm, occurring in the southern São Francisco Craton. The data revealed south/southwestern, low inclination magnetic directions after alternating field (AF) and thermal demagnetization, providing a paleomagnetic pole at 39.8°S, 196.8°E (A95 = 17.0°). The characteristic remanent magnetization is interpreted as a thermo-remanent magnetization carried by stable ‘pseudo-single domain’ magnetite grains, being acquired during the cooling of the dykes at 1790 Ma, as attested by a positive baked contact test performed on one of the dykes. The new pole in conjunction with 1790–1750 Ma paleomagnetic poles available for other blocks allowed an improved reconstruction of Columbia/Nuna supercontinent at this time frame. Laurentia, Baltica, Siberia, proto-Amazonia, West Africa and proto-Australia were positioned as in previously proposed models. The main difference from our reconstruction concerns the link of the São Francisco/Congo, North China and Rio de la Plata cratons, implying that much of the Columbia supercontinent had already agglutinated around 1850–1800 Ma ago. This configuration is consistent with the onset of eventual taphrogenic episodes over most blocks, accompanied by the emplacement of mafic dyke swarms and granitic intrusions at 1790–1750 Ma.