800 MA RIFTING IN THE PARAGUAY BELT, CENTRAL BRAZIL: U-PB SHRIMP AGE DETERMINATION, RODINIA BREAK-UP AND IMPLICATIONS FOR A CONNECTION WITH AVALONIAN PERI-GONDWANA TERRANES

The history of peripheral orogens in Gondwana reconstruction models, at the end of the Precambrian and beginning of the Paleozoic, generally do not consider the Tocantins Province, at the eastern margin of the Amazonian craton, in central Brazil. In all models, West Gondwana is shown as a static unit consolidated since 630 Ma, whereas subduction processes along active continental margins are common in East Gondwana between ca. 630 and 540 Ma. However, recently recognized 570-540 Ma old mafic granulites and arc magmatism in the Tocantins Province suggest an alternative hypothesis about the regional geological evolution in central Brazil as well as a different scenario for the amalgamation of West Gondwana. In the central part of the Tocantins Province, between the Brasília and Paraguay sedimentary fold belts, remnants of juvenile primitive island arcs (Goiás Magmatic Arc) were accreted to the São Franscisco craton, after Rodinia break-up. These terranes are interpreted as remnants of a large Neoproterozoic ocean basin, destroyed between c. 890 and 630 Ma. The precursor sediments of the Paraguay belt were deposited in a passive margin at the southeast margin of the Amazonian craton.Absolute age of the Paraguay belt was determined by U-Pb SHRIMP analysis in a metavolcanic rock from Nova Xavantina. Sample MAT 1 is an acid tuff containing prismatic, elongate, clear zircon grains which present a complex pattern. Several zircon populations present ages of 2.0, 1.4 - 1.2 Ga, which are interpreted as inherited components derived from continental sources. A mean 822 ± 9 Ma U-Pb age determined for three zircon grains is considered to be the best estimate for the crystallization age of the rock, and consequently, the age of explosive volcanism during the rifting event. Isotopic evidence suggests that portions of Avalonia basement rocks are of Amazonian Provenance and were assembled in Rodinia at ca. 12-1.0 Ga.Several models of supercontinent reconstructions could be simplified if the Transbrasiliano lineament is considered as a transform fault, playing a major role in the final amalgamation of West Gondwana, as the geodynamic link between peri-Gondwana terranes at the Proterozoic-Cambrian boundary in South and North America.