Eastern Paranapanema and southern São Francisco orogenic margins: Records of enduring Neoproterozoic oceanic convergence and collision in the southern Brasília Orogen

Abstract

The late Neoproterozoic processes of western Gondwana assembly are well-preserved in most Brazilian orogens. In the southern edge of the São Francisco Craton, a syn-metamorphic pile of nappes is the result of the closure of the Goiás-Pharusian Ocean through the collision between the São Francisco (passive margin) and Paranapanema (active margin) paleoplates. The inner segments of the orogen suggest active margin- to syn-collisional-type sedimentation and magmatism recorded by the Andrelândia and Liberdade Nappes, among others.The Liberdade Nappe metasedimentary rocks, which have a maximum depositional age of 760 Ma, suggest a source area in an evolved Tonian-Cryogenian continental magmatic arc located in the east-northeastern Paranapanema margin. The Santo Antonio Unit (maximum depositional age of 680 Ma) of the lower Andrelândia Nappe for the same age interval instead presents a source primarily in an island arc. The Serra da Boa Vista, the upper unit of the Andrelândia Nappe, seems to record the beginning of continental collision because of its Rhyacian source, recognized as being in the São Francisco Craton, and no important evidence for Neoproterozoic arc magmatism. Grenville- and Rondonian-San Ignacio-type source areas, as well as Statherian ages, are observed in all units.Metabasic rocks interlayered in the Liberdade Nappe metasedimentary rocks have chondritic to suprachondritic εNd(t) (−1.86 to 1.75) and 1.09–1.48 Ga Nd TDM model ages, suggesting juvenile magmatism. Retroeclogitic and metavolcaniclastic rocks of Calymmian age (1.46–1.48 Ga) occur as exotic blocks within the same metasedimentary rocks.The complete ocean closure and the beginning of continental collision must have occurred at approximately 670 Ma, which corresponds to the maximum depositional age of the syn-collisional unit (Serra da Boa Vista) and to the age of the eclogitic rocks. The Andrelândia Nappe System migration was probably restricted to the 635–600 Ma interval, followed by the thinning of the orogenic crust.