Paper No. 38-21
Presentation Time: 8:00 AM-12:00 PM
THE TECTONIC EVOLUTION OF THE BRASILIANO/PAN-AFRICAN BRASÍLIA BELT: INSIGHTS FROM SEDIMENTARY BASINS
DIAS, Paulo H. A.1, REIS, Humberto, S2, VALERIANO, Claudio, M3, ALKMIM, Fernando F4, RODRIGUES, Joseneusa, B5, SILVA, Marcio, A6, MEIRELES LEITE, Mariana7, SILVA, Wilker S.4, ARMOND, Pedro, V.4 and PIRES, Ana, C.8, (1)School of Mines, Universidade Federal de Ouro Preto, Minas Gerais, WA CEP 35400-000; GEREMI-BH, Geological Survey of Brazil, Avenida Brasil 1731, Belo Horizonte, Minas Gerais 30140-002, Brazil; Department of Earth and Space Sciences, University of Washington, Johnson Hall 070, Box 351310, 1707 NE Grant Lane, Seattle, WA 351310, (2)School of Mines, Universidade Federal de Ouro Preto, Ouro Preto, Minas Gerais 35400-000, Brazil, (3)Instituo de Geologia, Rio de Janeiro State University, R. São Francisco Xavier, 524 - Maracanã,, Rio de Janeiro, Rio de Janeiro 20550-013, Brazil, (4)School of Mines, Universidade Federal de Ouro Preto, Minas Gerais, WA CEP 35400-000, (5)DIGEOD, Geological Survey of Brazil, Avenida Brasil 1731, Belo Horizonte, Minas Gerais 30140-002, Brazil, (6)GEREMI-BH, Geological Survey of Brazil, Avenida Brasil 1731, Belo Horizonte, Minas Gerais 30140-002, Brazil, (7)Univerisade Federal de Minas Gerais, Instituto de Geociencias, Av. Pres. Antônio Carlos, 6627, Belo Horizonte, 31270-90, Brazil, (8)Instituo de Geologia, Federal University of Minas Gerais, Av. Pres. Antônio Carlos, 6627, Belo Horioznte, Minas Gerais 31270901, Brazil
The Brasília Belt is a crucial component of the Brasiliano/Pan-African Orogeny, shaped by the convergence of the Amazon, São Francisco, and Paranapanema cratonic blocks. This convergence led to the partial inversion of Meso-Neoproterozoic RIFT-SAG and marginal passive basins, culminating in an Ediacaran fold-and-thrust belt that encompasses a series of collisional basins. The history and structure of an orogenic system are revealed through the study of igneous rocks associated with accretionary and collisional phases, as well as through the organization and provenance of sedimentary basins that were formed. Extensive geochronological data on detrital zircon U-Pb (ca. 9,000 analyses) from the rift-sag basin, passive margin basin, forearc basin, and orogenic basin were utilized, in addition to some unpublished new data from the Geological Survey of Brazil.
Rifting initiation occurred during the Statherian characterized by bimodal volcanic activity (1.77-1.78 Ga) often interlayered with a sedimentary siliciclastic sequence with the youngest zircon at 1.74 Ga. This basin transitioned to a flexural stage during the Calymmian, representing a shallow marine succession with the youngest zircon peak at 1.55 Ga. The passive margin is marked by over 800 km of sedimentary belt along the western margins of the São Francisco craton, comprising a siliciclastic and pelite-carbonate proximal succession with a maximum age of 1.0 Ga. The distal sediments are represented by a shale succession, including intercalations of mafic-ultramafic rocks, indicative of ocean floor development between 750 and 870 Ma. The forearc basin presents a complex assortment of sediments showing some ultramafic volcanic bodies. These rocks exhibit lithochemical characteristics, Sm-Nd isotopic data, and a U-Pb zircon age spectrum consistent with sediments and volcanic rocks associated with a magmatic arc. Its maximum depositional age is 650 Ma, with a primary zircon age peak at 780 Ma. The syn-collisional orogenic basin forms a discontinuous Cryogenian-Ediacaran basin that unconformably overlaps the sediments of the inverted passive margin. It is primarily composed of a uniform succession of graywackes, with the maximum depositional age at 650 Ma, linked to sources from syn-collisional granites.
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