This thesis deals to the geology and petrogenesis of the Identidade greenstone belt, located between Xinguara and Rio Maria towns, SE of Pará state. The data of this area permitted the discussion of the tectonic evolution of the gravite greenstone terrain of the Rio Maria region in the context of the Província Mineral de Carajás, SE of the Amazonian craton. The greenstone studied compose a synformal belt in the WNW-ESE direction, corresponding to one metavolcanic pile, formed predominantly by ultramafic schists (UM), basalts (BAS) and gabbros (GB) at the base, and hypabyssal dacitic rocks (DAC - ca. 2.94 Ga, Pb/Pb) at the top. The whole was intruded by metaplutonic rocks of Mesoarchean ages, the older one being quartz diorites, followed successively by granodiorites, trondhjemites / tonalites and leucogranites. The gneissic basement (GN - outcroping toward north and recognized for having an older fabric Sn-1/D1), the greenstone and the metagranitoids were intruded by hypabyssal rhyolitic (ca. 1.60 Ga, Rb/Sr) and basic dykes at the end of the Paleoproterozoic. The greenstone presents igneous structures and textures still recognized, although obliterated near the contacts with the metagranitoids and shear zones. The ultramafics occur as tremolitites, tremolite - talc schists and talc schists; the amphibole is very elongated and thin, commonly in parallel arrays, interpreted as ghosts of spinifex textures. The basalts are massive or pillowed and frequently variolitic. They show different degrees of recrystallization, with some relicts of hyalophitic, pilotaxitic and traquitoid textures. Clinoamphibole (actinolitic hornblende), epidotes and plagioclase (albite - andesine) are the most abundant minerais. The gabbros may be massives to porphyritics (plagioclase phenocrysts), still with some relicts of subophitic and granophyric textures. The dacites are porphyritic, with phenocrysts of quartz and plagioclase (oligoclase), besides hornblende and mafic clots (biotite, chlorite, opaque minerais, epidotes, sphene, apatite) in the less evolved samples. Concerning the metagranitoids, the leucogranites and trondhjemites have chloritized biotite, whereas the granodiorites and some tonalites comprise biotite or biotite + hornblende (also in quartz diorites). The greenstone and the metagranitoids were affected by one event of heterogeneous, ductile deformation, that evolved to mylonitic zones. The structural framework of the area is marked by a planar fabric (Sn//Sm/D2) in the WNW-ESE to E-W direction, with moderate to strong dips in a divergent fan. E-W, WNW-ESE or NW-SE stretching lineations, meso and asymmetric S-C microstructures, mica and clinoamphibole fishes, and rotation of o and i porphyroclasts indicated one megastructure resulting from a binary system with NW-SE shortening direction. The actual geometry of the greenstone would be derived from a dextral transpression, with the greenstone forming a positive flower structure. The transpressional regime favored the grow of transtensional cites and subsequent emplacement of granitic plutons on the NW contact, and extensional crenulation cleavage (Sn+1/D2) on the SW of the greenstone. Strain measurements displayed a ca. 60% shortening, subhorizontal extension of ca. 60 to 500% parallel to the greenstone trend, and vertical extension of ca. 101 to 280%. The strain ellipsoid may be oblate to prolate, with changes in density and rotation of the axis of maximum stretching (X) toward the mylonitic zones. The inversion of the deformation permitted the reconstruction of the original shape of the greenstone, that would be also elongated WNW-ESE, but with lesser eccentricity than today. These data, together with the quartz petrofabric, suggested that the deformation has been accommodated by pure and simple shear mechanisms, the final framework resulting essentially from the later. The last event (D3) are represented by faults and fractures which also affected the felsic and basic dykes. The paragenesis of the main metamorphic event (Mn/M2) is represented by static recrystallization, which modified some textures and almost ali minerais within the greenstone. The minerais formed phases were bluish green amphibole (actinolitic hornblende), epidotes, sphene and quartz in BAS and GB; tremolite, talc and chlorite in UM. The metagranitoids show transformations of plagioclase (saussurite, fine white mica), amphibole (to biotite and/or sphene) and biotite (to chlorite). The coexistence of hornblende + plagioclase (An>17) and/or actinolitic hornblende + chlorite in metabasic rocks shows that this event was of low pressures and temperatures in the transitional field of the greenschist and amphibolite facies. This episode should reflect a regional crustal heating produced by the plutonism at the end of the Mesoarchean, that obliterated the previous associations of ocean floor metamorphism. Slightly coeval to subsequently, it occurred one event of extensive dynamic recrystallization (Mm/M2) in the greenschist facies, specially within shear zones and lithological contacts. In these places, there are evidences of fluid incoming (schistose blastomylonites and abundant quartz veins) and remobilization of chemical elements (Al, Fe, Ca, K, Na, Rb, Sr, Zr). Finally, under lower PT conditions, it occurred a less expressive event related to crenulation cleavages and forming chlorite, epidotes and quartz (Mn+1/M2). The M2 event, as well as the one detected only in GN (M1 under amphibolite facies), was of ductile nature and cleary distinguished from the last one (D3/M3). The later was placed at the end of the Paleoproterozoic, being of hydrothermal character and associated to high crustal structures. The progressive evolution of the M2 metamorphism with its thermal peak predating the deformation suggested a counterclockwise P-T-t path, corresponding to the metamorphic evolution of Phanerozoic marginal basins. Some chemical analysis of the metavolcanic rocks permitted the definition of magmatic series and a discussion of petrogenetical modeling. It was possible to recognize three geochemical series, that is, from the older to the younger, komatiitic (UM), tholeiitic (BAS and GB) and calc-alkaline (DAC). The first one corresponds to peridotitic komatiites with MgO>18 weight % (volatile-free basis), with an enrichment trend in Al, such as in Geluk and Munro, and less calcic than the Barberton one. The light rare earth element patterns are irregular with (La/Sm)N ratios between 0.42 and 4.2 and negative Eu anomalies. The heavy rare earth elements seem less affected by post-eruptive processes, being plate or slightly fractionated (1.0<(Gd/Yb)N<2.3). The quantitative models were of hard execution due to the remobilization of several elements. It was possible estimate cumulates rich in olivine and orthopyroxene. With regarding to tholeiites, the BAS and GB showed very similar geochemical signatures, both being low potassium tholeiites comparable to depleted Archean tholeiites. The rare earth elements are almost plate, with values 10X the chondrite, and slight or no Eu anomaly. Preliminary modeling suggested similar cumulates for BAS and GB, composed essentially by clinopyroxene and plagioclase. The magma sources that originated the komatiites and tholeiites would be a garnet lherzolite. The DAC presented geochemical characteristics of modern and Archean metavolcanics and metaplutonics of trondhjemitic nature. The magmatic differentiation would be achieved by fractionation of plagioclase>quartz>hornblende>K-feldspar, with subordinated amount of biotite, magnetite, sphene, allanite and zircon. The source of the dacitic magma would be a tholeiite metamorphosed to the garnet amphibolite facies and somewhat enriched in light rare earth elements. The geodynamical model proposed admit the existence of a gneissic basement prior to 2.96 Ga. Between 2.96 and 2.90 Ga, the interplay of high geothermal gradients and lithospheric extension was responsible for extensive rifting, forming marginal basin systems, where extruded the komatiitic and tholeiitic rocks. At 2.94(?)-2.90 Ga, the DAC were generated from partia' melting of oceanic crust in subduction zone settings, and evolved by low pressure fractional crystallization. The same mechanisms that generated the DAC are extended also to the calc-alkaline plutonism, this one being responsible for the structural inversion of the greenstone, crustal thickening and final shape of the granite - greenstone terrain (dextral transpression ca. 2.88-2.86 Ga). The region still suffered a late episode (end of Eoarchean, 2.69-2.50 Ga) of (re)heating, registered only in sorne mineral, without any evidente of deformation and/or metamorphism. Finally, it occurred the intrusion of felsic (1.60 Ga, Rb/r) and basic dykes at the end of the Paleoproterozoic. The correlation with the actual understanding of the Província Mineral de Carajás permitted envisage that the Rio Maria granite - greenstone terrain was then configured at the moment of implantation of the Itacaiúnas Supergroup (ca. 2.76 Ga) and alkaline granitic plutonism at the Serra dos Carajás. So the sinistrai transpression that inverted that supergroup would correspond to a newer event, very distinct as regards as the dextral transpression of the Rio Maria region.
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