Neoproterozoic crustal accretion in central Brazil

Recent geochronological studies have demonstrated the existence of several Neoproterozoic orthogneiss and metavolcanic are suites (ca. 900 to 600 Ma) in the southern part of the Tocantins province, a major Neoproterozoic orogenic area in central Brazil, exposed between the Amazon and São Francisco cratons. Nd and Sr isotopic characteristics of these metamorphic suites are primitive: initial ⁸⁷Sr/⁸⁷Sr ratios vary from ∼0.7024 to ∼0.7042 and initial ɛ_Nd values are positive, varying between +0.2 and +6.9. The most primitive initial Sr and Nd isotopic compositions are very similar to model depleted- mantle compositions at the time of formation of the original magmas. The mantle- like characteristics of these are suites in western Goiás contradict previous ensialic evolution models for the Tocantins province and reveal that crustal accretion processes were important in large areas of central Brazil during Neoproterozoic time.