2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 5
Presentation Time: 9:00 AM


HARTMANN, Léo A., Geologia, Campus do Vale, Geociências/UFRGS, Bairro Agronomia, Porto Alegre, RS, 91.509-900, Brazil and SANTOS, João Orestes, Geology, Geol Survey of Brazil, Av. Borges Medeiros 3200 - 1905, Praia de Belas, Porto Alegre, 90110-150, Brazil, leo.hartmann@ufrgs.br

The Paleoproterozoic crust of South America was subjected to several orogenic episodes between 2.5-2.0 Ga, particularly during the Trans-Amazon Cycle. Localized stable platform conditions led to the deposition iron formations in the Quadrilátero Ferrífero during the Siderian and large orogenic gold deposits were formed in the juvenile belts of northern Amazon Craton, and in cover sedimentary rocks of eastern Brazil during the Trans-Amazonian Cycle. The present contribution emphasizes mapping by the Geological Survey of Brazil (CPRM) integrated with U-Pb SHRIMP data of zircon, titanite, and baddeleyite (>170 rocks) by the authors and a review of the literature.

Siderian rocks are known in the southern (Minas Supergroup, 2580-2420 Ma), and western (Almas and Riachão do Ouro complexes, 2400 Ma) São Francisco Craton (Minas Supergroup) and north of the Carajás Province (Bacajá Domain, 2320 Ma) of the Amazon Craton. Two Siderian age peaks are identified in several detrital zircon populations of southern (Porongos Complex), northern (Roraima Supergroup, Jacareacanga Group and Castelo dos Sonhos Formation) and northeastern (Granja Massif) Brazil at 2.45 and 2.35 Ga.

The major crust-building event of South America was the Trans-Amazonian Cycle, which involved three or more accretionary orogenies at 2.26 Ga, 2.15 Ga and 2.08 Ga, succeeded by a major collisional orogeny at 2.03-2.01 Ga. Trans-Amazonian rocks form a large continuous belt from Venezuela to Amapá in northern Brazil and discontinuous belts in the São Francisco and La Plata cratons. Those events and resulting belts have been characterized in Venezuela, Guyana, Surinam, French Guiana, northern, eastern and southern Brazil, Uruguay and Argentina.

The large Omai (Guyana) and Las Cristinas (Venezuela) gold deposits were formed in the final stages of the orogenic cycle, while the Quadrilátero Ferrífero ore was formed earlier at the beginning of the Paleoproterozoic (2.58-2.45 Ga).

This novel, extensive, intense, advanced technology-based study of the Paleoproterozoic crust of South America between 2.5-2.0 Ga has identified the sequential growth of the continent through the amalgamation of juvenile terrains, succeeded by a major collisional orogeny. No zircon ages younger than 2.0 Ga are known in Trans-Amazonian belts of South America.