FIRST INVENTORY OF GRENVILLIAN ROCKS IN SOUTH AMERICA

Grenvillian rocks of Brazil and South America are present in three cratons: the Amazon, São Francisco, and La Plata. Grenvillian rocks of the Amazon craton have a direct correlation with the Grenvillian of North America (Kroonemberg, 1982; Priem et al., 1971; Renne et al., 1996; Santos et al., 2003), whereas the Grenvillian belts of the São Francisco and La Plata cratons probably are more closely associated with the Namaqua and Kibaran cratons of western Africa.

On the Amazon craton, four collisional belts of the Sunsás orogeny formed between 1450-1100 Ma: the Sunsás, Candeias, Nova Brasilândia, and Santa Helena. Foreland basins younger than 1100 Ma derived from these belts occur in the craton’s interior (Palmeiral, Pacaás-Novos, Prainha, and Dardanelos). Mylonitic belts occur in the Complexo Jamari and the Providência Suite. Late Grenvillian mafic rocks extend from the state of Para, underneath the Solimões basin to southeastern Columbia (Yaca-Yaca and Piraparana) and appear to have formed concurrently with the Nova Brasilândia orogeny between 1180-1100 Ma. Grenvillian crustal fragments are common in the eastern Andean Cordilllera in Columbia (Garzón, Santa Marta) and Venezuela (Mérida) and in the western Cordillera in Peru (Aerquipa) showing that the Andean orogen north of 16°S developed on a Grenvillian continental margin.

One felsic intrusion, the 1317 Ma Saracura Granite, is known near the Central Guyanan Belt, but the presence of detrital zircons with ages of 1450-1000 Ma in the Orinoco (Goldstein et al., 1997) and Apiaú Rivers suggest important additional Grenvillian felsic magmatism in the Guyanan Shield. Grenvillian deformation is recorded by N-NE trending mylonite belts that occur in the upper Rio Negro basin with mica Ar ages between 1336-1184 Ma.

In the two Atlantic cratons affected by the Brasiliano Cycle, Grenvillian rocks are mostly low-grade meta-sediments known stratigraphically as pre-Bambuí (>900 Ma). Examples occur in the São Francisco craton at Paranoá and Canastra in the west; at Chapada and Rio Preto in the north; and at Belém do São Francisco, Cabrobó, and Marancó in the Borborema Province in Brazil. There are a group of rocks of about 1000 Ma in Uruguay, intermediate granites near San Juan in Argentina, and the San Juan Bautista granite of Paraguay.