CRUSTAL EVOLUTION OF THE NEOPROTEROZOIC OPHIOLITES IN SOUTH AMERICA

In South America, Neoproterozoic accretionary and collisional terranes developed during the amalgamation of West Gondwana. These terranes contain remnants of oceanic arcs and ophiolite complexes, formed in a time interval between 880 and 650 Ma, with final collisional event at approximately 530 Ma. The Tocantins Tectonic Province (TTP), in central-northern Brazil, is a system of Brasiliano orogens (Araguaia, Paraguay and Brasília belts) with records of ancient oceanic lithosphere that mark suture zones resulting of the convergence and collision of three cratonic blocks (Amazonian, São Francisco and Paranapanema). The Araguaia belt, north-branch of the TTP, presents the major and best preserved ophiolite complexes in a mélange terrane, extending for over 500 km in the north-south direction. The ophiolitic fragments correspond to decametric to kilometric slices (e. g., Quatipuru and Serra do Tapa complexes), composed of serpentinized and/or metamorphosed mantle peridotites and crustal mafic rocks, the last represented by basaltic pillow lavas or sills. Besides this, the mantle peridotites host a suite of scattered narrow ultramafic and mafic dikes and sills, and nodular chromitite pods. Oceanic sedimentary sequences related to a basin floor and lower to upper-slope turbidites are associated with the ophiolitic slices, being both metamorphosed under anquimetamorphic to greenschist facies conditions, structurally conformable and with tectonic vergence to west, towards the Amazonian Craton. The age of 757± 49 Ma (Sm-Nd whole-rock isochron) for the ophiolite remnants in the Araguaia belt, along with geochronological data for the tectonic evolution of this orogen (e. g. last granitic intrusion from 530 to 510 Ma) render comparisons with other Neoproterozoic orogens in South America, such as the Brasília belt in Brazil and the Eastern Pampean Ranges (Argentine), suggesting a common evolution during the Neoproterozoic–Early Cambrian assembly of West Gondwana. Moreover, the metallogenic potential of the Araguaia belt, characterized by sulfide polymetallic mineralisations (Cu, Pb and Zn), chromium and lateritic nickel deposits could be suggested and investigated in other branches of the Tocantins Tectonic Province or in its counterparts in South America.