The geological roots of South America: 4.1 Ga and 3.7 Ga zircon crystals discovered in N.E. Brazil and N.W. Argentina

2015

International audience; We present new LA-ICP-MS in situ geochronological results for seven Eoarchean zircons dated at 3.7 Ga coming from Cretaceous ash layers of NW Argentina and one Hadean single crystal sampled within the São Francisco Craton in NE Brazil. This zircon comprises a zoned magmatic core dated at 4.1 Ga surrounded by a 1.9 Ga overgrowth related to Paleoproterozoic reworking. This Hadean age is consistent with previously published Nd model ages on orthogneisses from the same domain. These two results represent among the oldest geological witnesses discovered to date in South America, which demonstrates the occurrence of a primitive crust. The contrasting age patterns recorded …