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THE ARCHEAN BLOCKS Each aforementioned segment is well discriminated by Sm-Nd model ages as well as the distribution in the ΕNd x ΕSr diagram, supporting their distinct origin and evolution. In the Gavião Block two groups of TTG rocks constituted the early continental crust. The first (3.4-3.2 Ga) has been considered, as originated from the melting of tholeíitic basalts. The second (3.2-3.1 Ga.), had similar origin but with some crustal contamination. Greenstone belts have been formed in intra-cratonic basins of the early TTG crust. The granitic/granodioritic/migmatitic crust with ages of 2.8-2.7Ga is interpreted as products of partial melting of the TTG during the closing of these basins. The Itabuna-Salvador-Curaçá Belt is composed by at least three tonalite/trondhjemites groups with 2.7-2.6Ga.
These rocks are interpreted as resulting of the tholeiitic oceanic crust melting. Reequilibrated in the granulite facies, also include charnockite bodies and stripes of intercalated metasediments and ocean-floor/back-arc gabbros and basalts, originated from mantle sources. Monzonites with shoshonitic affinity and with age about 2.0 Ga, also occur. The island-arcs, back-arc basins and subduction zones were the predominant environments during the construction of this Belt. The Jequié Block is characterized by migmatites with supracrustal inclusions (3.0-2.8Ga) and granodioritic¡Vgranitic intrusions (2.8-2.7Ga). The oldest component is mainly constituted of granitic rocks that form the basement of the rift-type intracratonic basins, where basalts and andesitic basalts, cherts, banded iron formation, graphitites and kinzigites were accumulated. The youngest component is constituted of multiple intrusions of granodiorites and granites of high to low Ti. In the Serrinha Block occurs orthogneisses and migmatites (2.9 Ga) with grabbroic enclaves that represent the basement of Paleoproterozoic greenstone belts, described ahead.
THE PALEOPROTEROZOIC COLLISION During the Paleoproterozoic (c.a.2.3-2.0Ga), these four crustal segments collided in the NW-SE sense resulting in the formation of an important mountain belt. The evidences of this collision are found not only through the structural elements, but also studying the pre-and syntectonic Paleoproterozoic rocks that are present in the above mentioned crustal segments. In the Gavi∼o Block it was identified the Jacobina Group (foreland basin). In the Itabuna-Salvador-Curaçá Belt, the lithologie are tonalites and trondhjemites, with zircons dated approximately 2.1G. In the Serrinha Block occurs the Greenstone Belts Rio Itapicuru and Capim (2.2-2.1 Ga). The Paleoproterozoic hight grade metamorphism possesses average pressures of 7kbar and temperatures of about 850°, with its peak occuring at about 2.0Ga. Along the Itabuna-Salvador-Curaçá Belt this metamorphism reached the granulite grade. PTt diagrams show a trajectory of the metamorphism of the clock-wise type, confirming the collision context.
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