A review of the tectonic evolution of the Sunsas belt, SW Amazonian Craton

The Sunsas-Aguapei province (1.20-0.95 Ga), SW Amazonian Craton, is a key area to study the heterogeneous effects of collisional events with Laurentia, which shows evidence of the Grenvillian and Sunsas orogens. The Sunsas orogen, characterized by an allochthonous collisional-type belt (1.11-1.00 Ga), is the youngest and southwestern most of the events recorded along the cratonic fringe. Its evolution occurred after a period of long quiescence and erosion of the already cratonized provinces (>1.30 Ga), that led to sedimentation of the Sunsas and Vibosi groups in a passive margin setting. The passive margin stage was roughly contemporary with intraplate tectonics that produced the Nova Brasilandia proto-oceanic basin (<1.21 Ga), the reactivation of the Ji-Parana shear zone network (1.18-1.12 Ga) and a system of aborted rifts that evolved to the Huanchaca-Aguapei basin (1.17-1.15 Ga). The Sunsas belt is comprised by the metamorphosed Sunsas and Vibosi sequences, the Rincon del Tigre mafic-ultramafic sill and granitic intrusive suites. The latter rocks yield epsilon(Nd(t)) signatures (-0.5 to -4.5) and geochemistry (S,1, A-types) suggesting their origin associated with a continental arc setting. The Sunsas belt evolution is marked by ""tectonic fronts"" with sinistral offsets that was active from c. 1.08 to 1.05 Ga, along the southern edge of the Paragua microcontinent where K/Ar ages (1.27-1.34 Ga) and the Huanchaca-Aguapei flat-lying cover attest to the earliest tectonic stability at the time of the orogen. The Sunsas dynamics is coeval with inboard crustal shortening, transpression and magmatism in the Nova Brasilandia belt (1.13-1.00 Ga). Conversely, the Aguapei aulacogen (0.96-0.91 Ga) and nearby shear zones (0.93-0.91 Ga) are the late tectonic offshoots over the cratonic margin. The post-tectonic to anorogenic stages took place after ca. 1.00 Ga, evidenced by the occurrences of intra-plate A-type granites, pegmatites, mafic dikes and sills, as well as of graben basins. Integrated interpretation of the available data related to the Sunsas orogen supports the idea that the main nucleus of Rodinia incorporated the terrains forming the SW corner of Amazonia and most of the Grenvillian margin, as a result of two independent collisional events, as indicated in the Amazon region by the Ji-Parana shear zone event and the Sunsas belt, respectively. (C) 2009 Elsevier Ltd. All rights reserved.

Metamorphic P-T evolution of granulites in the central Ribeira Fold Belt, SE Brazil

Pseudosections, geothermobarometric estimates and careful petrographic observations of gneissic migmatites and granulites from Neoproterozoic central Ribeira Fold Belt (SE Brazil) were performed in order to quantify the metamorphic P-T conditions during prograde and retrograde evolution of the Brasiliano Orogeny. Results establish a prograde metamorphic trajectory from amphibolite facies conditions to metamorphic peak (T = 850 +/- 50 A degrees C; P = 8 +/- 1 kbar) that promoted widespread dehydrationmelting of 30 to 40% of the gneisses and high-grade granitization. After the metamorphic peak, migmatites evolved with cooling and decompression to T a parts per thousand 500 A degrees C and P a parts per thousand 5 kbar coupled with aH2O increase, replacing the high-grade paragenesis plagioclase-quartz-K-feldspar-garnet by quartz-biotite-sillimanite-(muscovite). Cordierite absence, microtextural observations and P-T results constrain the migmatite metamorphic evolution in the pseudosections as a clockwise P-T path with retrograde cooling and decompression. High-temperature conditions further dehydrated the lower crust with biotite and amphibole-dehydration melting and granulite formation coupled with 10% melt generation. Granulites can thus be envisaged as middle to lower crust dehydrated restites. Granulites were slowly (nearly isobarically) cooled, followed by late exhumation/retrograde rapid decompression and cooling, reflecting a two step P-T path. This retrograde evolution, coupled with water influx, chemically reequilibrated the rocks from granulite to amphibolite/greenschist facies, promoting the replacement of the plagioclase-quartz-garnet-hypersthene peak assemblage by quartz-biotite- K-feldspar symplectites.

GEOCHEMISTRY AND U-PB ZIRCON AGE OF THE INTERNAL OSSA-MORENA ZONE OPHIOLITE SEQUENCES: A REMNANT OF RHEIC OCEAN IN SW IBERIA

The Early Paleozoic geodynamic evolution in SW Iberia is believed to have been dominated by the opening of the Rheic Ocean. The Rheic Ocean is generally accepted to have resulted from the drift of peri-Gondwanan terranes such as Avalonia from the northern margin of Gondwana during Late Cambrian-Early Ordovician times. The closure of the Rheic Ocean was the final result of a continent-continent collision between Gondwana and Laurussia that produced the Variscan orogen. The Ossa-Morena Zone is a peri-Gondwana terrane, which preserves spread fragments of ophiolites - the Internal Ossa-Morena Zones Ophiolite Sequences (IOMZOS). The final patchwork of the IOMZOS shows a complete oceanic lithospheric sequence with geochemical characteristics similar to the ocean-floor basalts, without any orogenic fingerprint and/or crustal contamination. The IOMZOS were obducted and imbricated with high pressure lithologies. Based on structural, petrological and whole-rock geochemical data, the authors argue that the IOMZOS represent fragments of the oceanic lithosphere from the Rheic Ocean. Zircon SHRIMP U-Pb geochronological data on metagabbros point to an age of ca. 480 Ma for IOMZOS, providing evidence of a well-developed ocean in SW Iberia during this period, reinforcing the interpretation of the Rheic Ocean as a wide ocean among the peri-Gondwanan terranes during Early Ordovician times.

Conflicting structural and geochronological data from the Ibituruna quartz-syenite (SE Brazil): Effect of protracted ""hot"" orogeny and slow cooling rate?

The Ibituruna quartz-syenite was emplaced as a sill in the Ribeira-Aracuai Neoproterozoic belt (Southeastern Brazil) during the last stages of the Gondwana supercontinent amalgamation. We have measured the Anisotropy of Magnetic Susceptibility (AMS) in samples from the Ibituruna sill to unravel its magnetic fabric that is regarded as a proxy for its magmatic fabric. A large magnetic anisotropy, dominantly due to magnetite, and a consistent magnetic fabric have been determined over the entire Ibituruna massif. The magmatic foliation and lineation are strikingly parallel to the solid-state mylonitic foliation and lineation measured in the country-rock. Altogether, these observations suggest that the Ibituruna sill was emplaced during the high temperature (similar to 750 degrees C) regional deformation and was deformed before full solidification coherently with its country-rock. Unexpectedly, geochronological data suggest a rather different conclusion. LA-ICP-MS and SHRIMP ages of zircons from the Ibituruna quartz-syenite are in the range 530-535 Ma and LA-ICP-MS ages of zircons and monazites from synkinematic leucocratic veins in the country-rocks suggest a crystallization at similar to 570-580 Ma, i.e., an HT deformation >35My older than the emplacement of the Ibituruna quartz-syenite. Conclusions from the structural and the geochronological studies are therefore conflicting. A possible explanation arises from (40)Ar-(39)Ar thermochronology. We have dated amphiboles from the quartz-syenite, and amphiboles and biotites from the country-rock. Together with the ages of monazites and zircons in the country-rock, (40)Ar-(39)Ar mineral ages suggest a very low cooling rate: <3 degrees C/My between 570 and similar to 500 Ma and similar to 5 degrees C/My between 500 and 460 Ma. Assuming a protracted regional deformation consistent over tens of My, under such stable thermal conditions the fabric and microstructure of deformed rocks may remain almost unchanged even if they underwent and recorded strain pulses separated by long periods of time. This may be a characteristic of slow cooling ""hot orogens"" that rocks deformed at significantly different periods during the orogeny, but under roughly unchanged temperature conditions, may display almost indiscernible microstructure and fabric. (C) 2009 Elsevier B.V. All rights reserved.

Mineralogical and microthermometric studies and structural aspects of imperial topaz mineralization in Antonio Pereira, Ouro Preto District (Minas Gerais) - Brazil

The occurrences of imperial topaz in the Antonio Pereira mine, Ouro Preto, Minas Gerais, are associated with the metamorphic carbonate rocks of the Minas Supergroup. The crystals have densities varying from 3.46 to 3.58. The parameters of the unitary cells obtained were: 4.658 to 4.663 angstrom (ao), 8.823 to 8.832 angstrom (b(o)), 8.382 to 8.389 angstrom (c(o)), and 344.65 to 345.46 angstrom 3 (V). The refraction indices presented the following variations: 1.622 to 1.630 (nX), 1.624 to 1.632 (nY), 1.633 to 1.640 (nZ), and 0.008 to 0.011 (B). These properties are coherent with the low fluorine contents obtained (16,48%/17,05wt%). Infrared spectroscopy and microthermometry showed that the fluid inclusions, which represent the mineralizing fluids, are formed by H(2)O (with Ca(2+), Mg(2+) and Na(+)), and CO(2) +/- CH(4). The minimal trapping T-P conditions of 290/320 degrees C and 2,349/2,497bar were obtained for the primary fluid inclusions. The pseudo-secondary fluid inclusions were trapped at conditions of lower temperatures and variable pressures, during the deformation process under local alternating states of stress. The microthermometric studies, the structural analysis and the fluorine contents suggest that the mineralized veins were formed from hydrothermal fluids originated during the Brasiliano tectono-metamorphic event.

Dating coeval mafic magmatism and ultrahigh temperature metamorphism in the Anapolis-Itaucu Complex, Central Brazil

Dating granulites has always been of great interest because they represent one of the most extreme settings of an orogen. Owing to the resilience of zircon, even in such severe environments, the link between P-T conditions and geological time is possible. However, a challenge to geochronologists is to define whether the growth of new zircon is related to pre- or post-P-T peak conditions and which processes might affect the (re) crystallization. In this context, the Anapolis-Itaucu Complex, a high-grade complex in central Brazil with ultrahigh temperature (UHT) granulites, may provide valuable information within this topic. The Anapolis-Itaucu Complex (AIC) includes ortho- and paragranulites, locally presenting UHT mineral assemblages, with igneous zircon ages varying between 760 and 650 Ma and metamorphic overgrowths dated at around 650-640 Ma. Also common in the Anapolis-Itaucu Complex are layered mafic-ultramafic complexes metamorphosed under high-grade conditions. This article presents the first geological and geochronological constraints of three of these layered complexes within the AIC, the Damolandia, Taquaral and Goianira-Trindade complexes. U-Pb (LA-MC-ICPMS, SHRIMP and ID-TIMS) zircon analyses reveal a spread of concordant ages spanning within an age interval of similar to 80 Ma with an ""upper"" intercept age of similar to 670 Ma. Under cathodoluminescence imaging, these crystals show partially preserved primary sector zoning, as well as internal textures typical of alteration during high-grade metamorphism, such as inward-moving boundaries. Zircon grains reveal homogeneous initial (176)Hf/(177)Hf values in distinct crystal-scale domains in all samples. Moreover. Hf isotopic ratios show correlation neither with U-Pb ages nor with Th/U ratios, suggesting that zircon grains crystallized during a single growth event. It is suggested, therefore, that the observed spread of concordant U-Pb ages may be related to a memory effect due to coupled dissolution-reprecipitation process during high grade metamorphism. Therefore, understanding the emplacement and metamorphism of this voluminous mafic magmatism is crucial as it may represent an additional heat source for the development of the ultrahigh temperature paragenesis recorded in the paragranulites. (C) 2010 Elsevier B.V. All rights reserved.

The basement of the Punta del Este Terrane (Uruguay): an African Mesoproterozoic fragment at the eastern border of the South American Rio de La Plata craton

The Punta del Este Terrane (eastern Uruguay) lies in a complex Neoproterozoic (Brasiliano/Pan-African) orogenic zone considered to contain a suture between South American terranes to the west of Major Gercino-Sierra Ballena Suture Zone and eastern African affinities terranes. Zircon cores from Punta del Este Terrane basement orthogneisses have U-Pb ages of ca. 1,000 Ma, which indicate an lineage with the Namaqua Belt in Southwestern Africa. U-Pb zircon ages also provide the following information on the Punta del Este terrane: the orthogneisses containing the ca. 1,000 Ma inheritance formed at ca. 750 Ma; in contrast to the related terranes now in Africa, reworking of the Punta del Este Terrane during Brasiliano/Pan-African orogenesis was very intense, reaching granulite facies at ca. 640 Ma. The termination of the Brasiliano/Pan-African orogeny is marked by formation of acid volcanic and volcanoclastic rocks at ca. 570 Ma (Sierra de Aguirre Formation), formation of late sedimentary basins (San Carlos Formation) and then intrusion at ca. 535 Ma of post-tectonic granitoids (Santa Teresa and Jos, Ignacio batholiths). The Punta del Este Terrane and unrelated western terranes represented by the Dom Feliciano Belt and the Rio de La Plata Craton were in their present positions by ca. 535 Ma.

THE RIO APA CRATON IN MATO GROSSO DO SUL (BRAZIL) AND NORTHERN PARAGUAY: GEOCHRONOLOGICAL EVOLUTION, CORRELATIONS AND TECTONIC IMPLICATIONS FOR RODINIA AND GONDWANA

The Rio Apa cratonic fragment crops out in Mato Grosso do Sul State of Brazil and in northeastern Paraguay. It comprises Paleo-Mesoproterozoic medium grade metamorphic rocks, intruded by granitic rocks, and is covered by the Neoproterozoic deposits of the Corumbi and Itapocurni Groups. Eastward it is bound by the southern portion of the Paraguay belt. In this work, more than 100 isotopic determinations, including U-Pb SHRIMP zircon ages, Rb-Sr and Sm-Nd whole-rock determinations, as well as K-Ar and Ar-Ar mineral ages, were reassessed in order to obtain a complete picture of its regional geological history. The tectonic evolution of the Rio Apa Craton starts with the formation of a series of magmatic arc complexes. The oldest U-Pb SHRIMP zircon age comes from a banded gneiss collected in the northern part of the region, with an age of 1950 +/- 23 Ma. The large granitic intrusion of the Alumiador Batholith yielded a U-Pb zircon age of 1839 +/- 33 Ma, and from the southeastern part of the area two orthogneisses gave zircon U-Pb ages of 1774 +/- 26 Ma and 1721 +/- 25 Ma. These may be coeval with the Alto Terere metamorphic rocks of the northeastern corner, intruded in their turn by the Baia das Garcas granitic rocks, one of them yielding a zircon U-Pb age of 1754 +/- 49 Ma. The original magmatic protoliths of these rocks involved some crustal component, as indicated by the Sm-Nd TDm model ages, between 1.9 and 2.5 Ga. Regional Sr isotopic homogenization, associated with tectonic deformation and medium-grade metamorphism occurred at approximately 1670 Ma, as suggested by Rb-Sr whole rock reference isochrons. Finally, at 1300 Ma ago, the Ar work indicates that the Rio Apa Craton was affected by widespread regional heating, when the temperature probably exceeded 350 degrees C. Geographic distribution, age and isotopic signature of the fithotectonic units suggest the existence of a major suture separating two different tectonic domains, juxtaposed at about 1670 Ma. From that time on, the unified Rio Apa continental block behaved as one coherent and stable tectonic unit. It correlates well with the SW corner of the Amazonian Craton, where the medium-grade rocks of the Juruena-Rio Negro tectonic province, with ages between 1600 and 1780 Ma, were reworked at about 1300 Ma. Looking at the largest scale, the Rio Apa Craton is probably attached to the larger Amazonian Craton, and the actual configuration of southwestern South America is possibly due to a complex arrangement of allochthonous blocks such as the Arequipa, Antofalla and Pampia, with different sizes, that may have originated as disrupted parts of either Laurentia or Amazonia, and were trapped during later collisions of these continental masses.

The position of the Amazonian Craton in supercontinents

This paper examines the extensive regions of Proterozoic accretionary belts that either formed most of the Amazonian Craton, or are marginal to its southeastern border. Their overall geodynamic significance is considered taking into account the paleogeographic reconstruction of Columbia, Rodinia and Gondwana. Amazonia would be part of Columbia together With Laurentia, North China and Baltica, forming a continuous, continental landmass linked by the Paleo- to Mesoproterozoic mobile belts that constitute large portions of it. The Rodinia supercontinent was formed in the Mesoproterozoic by the agglutination of the existing cratonic fragments, such as Laurentia and Amazonia, during contemporary continental collisions worldwide. The available paleomagnetic data suggest that Laurentia and Amazonia remained attached until at least 600 Ma. Since all other cratonic units Surrounding Laurentia have already rifted away by that time, the separation between Amazonia and Laurentia marks the final break-up of Rodinia with the opening of the lapetus ocean. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Precambrian geotectonic units of the Rio de La Plata craton

The main Precambrian tectonic units of Uruguay include the Piedra Alta tectonostratigraphic terrane (PATT) and Nico Perez tectonostratigraphic terrane (NPTT), separated by the Sarandi del Yi high-strain zone. Both terranes are well exposed in the Rio de La Plata craton (RPC). Although these tectonic units are geographically small, they record a wide span of geologic time. Therefore improved geological knowledge of this area provides a fuller understanding of the evolution of the core of South America. The PATT is constituted by low-to medium-grade metamorphic belts (ca. 2.1 Ga); its petrotectonic associations such as metavolcanic units, conglomerates, banded iron formations, and turbiditic deposits suggest a back-arc or a trench-basin setting. Also in the PATT, a late to post-orogenic, arc-related layered mafic complex (2.3-1.9 Ga), followed by A-type granites (2.08 Ga), and finally a taphrogenic mafic dike swarm (1.78 Ga) occur. The less thoroughly studied NPTT consists of Palaeoproterozoic high-grade metamorphic sequences (ca. 2.2 Ga), mylonites and postorogenic and rapakivi granites (1.75 Ga). The Brasiliano-Pan African orogeny affected this terrane. Neoproterozoic cover occurs in both tectonostratigraphic terranes, but is more developed in the NPTT. Over the past 15 years, new isotopic studies have improved our recognition of different tectonic events and associated processes, such as reactivation of shear zones and fluids circulation. Transamazonian and Statherian tectonic events were recognized in the RPC. Based on magmatism, deformation, basin development and metamorphism, we propose a scheme for the Precambrian tectonic evolution of Uruguay, which is summarized in the first Palaeoproterozoic tectonic map of the Rio de La Plata craton.

U-Pb zircon and (40)Ar-(39)Ar K-feldspar dating of syn-sedimentary volcanism of the Neoproterozoic Marica Formation: constraining the age of foreland basin inception and inversion in the Camaqua Basin of southern Brazil

New U-Pb zircon and (40)Ar-(39)Ar K-feldspar data are presented for syn-sedimentary volcanogenic rocks from the Neoproterozoic Marica Formation, located in the southern Brazilian shield. Seven (of nine) U-Pb sensitive high-resolution ion microprobe analyses of zircons from pyroclastic cobbles yield an age of 630.2 +/- 3.4 Ma (2 sigma), interpreted as the age of syn-sedimentary volcanism, and thus of the deposition itself. This result indicates that the Marica Formation was deposited during the main collisional phase (640-620 Ma) of the Brasiliano II orogenic system, probably as a forebulge or back-bulge, craton-derived foreland succession. Thus, this unit is possibly correlative of younger portions of the Porongos, Brusque, Passo Feio, Abapa (Itaiacoca) and Lavalleja (Fuente del Puma) metamorphic complexes. Well-defined, step-heating (40)Ar-(39)Ar K-feldspar plateau ages obtained from volcanogenic beds and pyroclastic cobbles of the lower and upper successions of the Marica Formation yielded 507.3 +/- 1.8 Ma and 506.7 +/- 1.4 Ma (2 sigma), respectively. These data are interpreted to reflect total isotopic resetting during deep burial and thermal effects related to magmatic events. Late Middle Cambrian cooling below ca. 200 degrees C, probably related to uplift, is tentatively associated with intraplate effects of the Rio Doce and/or Pampean orogenies (Brasiliano III system). In the southern Brazilian shield, these intraplate stresses are possibly related to the dominantly extensional opening of a rift or a pull-apart basin, where sedimentary rocks of the Camaqua Group (Santa Barbara and Guaritas Formations) accumulated.

Lu-Hf and U-Pb age determination of Capivarita Anorthosite in the Dom Feliciano Belt, Brazil

The Capivarita Anorthosite, formed in an intraplate environment and later metamorphosed under amphibolites fades conditions, is exposed in the Dom Feliciano Belt as part of the Brasiliano magmatic arc and occurs as a roof-pedant in, or is even intruded by, 0.6 Ga post-collisional granites. In this work, magmatic and metamorphic minerals were dated using the LA-MC-ICP-MS in situ method. U-Pb magmatic and metamorphic zircon dating yielded an age of 1573 +/- 21 Ma and of 606 +/- 6 Ma, respectively, whereas the igneous titanite dating yielded an age of 1530 +/- 33 Ma and the metamorphic ages were 651 +/- 9 Ma and 601 +/- 5 Ma. The Lu-Hf model ages showed two clusters from 1.81 to 2.03 Ga (calf from +2.21 to +6.42) and 2.55-2.62 Ga (epsilon epsilon Hf from -4.59 to -5.64). This intraplate magmatism can be connected to a very important episode of continental accretion in an extensional setting from the fragmentation of the supercontinent during the Early Mesoproterozoic. (C) 2011 Elsevier B.V. All rights reserved.

Aplicação de sensoriamento remoto orbital no mapeamento de unidades vulcano-sedimentar no Platô da Ramada, Vila Nova do Sul, RS

Os produtos de sensoriamento remoto gerados pelos novos sensores orbitais, aliados ao desenvolvimento de sistemas computacionais e de técnicas de processamento de imagens possibilitam a manipulação numérica das imagens, visando o realce de informações de interesse para a interpretação visual ou automática. O uso dessas técnicas traz boas perspectivas no mapeamento geológico básico, pois possibilita uma visão sinóptica de amplas áreas e a integração de dados litológicos e estruturais de várias fontes. Este trabalho selecionou as imagens do sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) devido as características de suas resoluções espectral e espacial, como as mais promissoras para identificação dos diferentes litotipos da área do Platô da Ramada, em especial as unidades vulcânicas e hipabissais relacionadas e sedimentares subjacentes. O Platô da Ramada, região de Vila Nova do Sul (RS) constitui uma feição geomorfológica de destaque na área, facilmente identificável nas imagens orbitais, sendo formado por uma seqüência vulcânica caracterizada por depósitos efusivos e piroclásticos, de composição dominantemente ácida. Representa uma fração significativa do magmatismo alcalino sódico neoproterozóico no Escudo Sul-rio-grandense e marca um dos ciclos vulcânicos do período pós-colisional do Ciclo Brasiliano Este estudo testou e avaliou diversos processamentos das imagens multiespectrais para diferenciação litológica, a identificação de alvos e a definição de morfoestruturas da área do Platô da Ramada. A integração de dados geológicos existentes com os produtos obtidos neste estudo possibilitou novas informações anexadas ao mapa geológico utilizado como verdade terrestre. O processamento utilizando a técnica de Transformação por Componentes Principais Seletivas proporcionou os melhores resultados realçando diferenças espectrais existentes entre as rochas vulcânicas e hipabissais e as rochas sedimentares. A partir dessa técnica, selecionou-se as imagens CP2 dos pares das bandas 4-5 (R), 3-4 (G) e 8-9 (B) na geração de uma composição colorida. Esta imagem permitiu a diferenciação espectral entre as rochas vulcânicas do Platô da Ramada e as rochas sedimentares do Grupo Maricá, bem como a individualização, no Grupo Maricá, de duas subunidades, levando-se em conta a densidade de intrusões de diques riolíticos ao norte da área. Identificou-se, ainda, um corpo diorítico com forma elíptica na borda SW do Platô da Ramada, não registrado anteriormente.

Memórias da prisão: literatura e liberdade m estudo sobre Graciliano Ramos e Antonio Gramsci

La tese avvicina le Memorie dal carcere, di Graciliano Ramos e i Quaderni dal carcere di Antonio Gramsci, in una prospettiva in cui essi erano uniti per lo stesso ideale politico della prima metá del XX secolo e rappresentavano la resistenza intellettuale di fronte alla repressione. Entrambi furono vittime dell autoritarismo dei poteri fascisti e registrarono il periodo di prigione in differenti forme memorialistiche. Questi scrittori sono uniti anche per il contesto nazionale molto simile per la differenza economica tra le regioni. Condividono, inoltre, anche il concetto di arte e la certezza che l alienzazione dell intelligenza può essere superata solamente attraverso la ricostruzione delle basi nazionali per mezzo della conoscenza, dell educazione e della cultura. Si vuole mostrare come i concetti di Gramsci sono presenti non solo nella convinzione politica di Graciliano, ma in tutto il suo stile letterario memorialístico. Il lavoro, ancora, paragona le Memorie del carcere con due testi memorialistici di prigione in Italia, che sono Le mie prigioni, di Silvio Pellico, e Se questo è un uomo, di Primo Levi, per dimostrare che la proposta della letteratura gramsciana è molto più vicina allo scrittore brasiliano che ai due suoi conazionali.

Condicionamento estrutural das zonasa de cisalhamento da região de Forquilha, domínio Ceará Central: uma abordagem integrada de sensoriamento remoto e geologia estrutural

The studied region, named Forquilha and localized in northwestern Central Ceará domain (northern portion of Borborema Province), presents a lithostratigraphic framework constituted by paleoproterozoic metaplutonics, metasedimentary sequences and neoproterozoic granitoids. The metasedimentary rocks of Ceará group occupy most part of the area. This group is subdivided in two distinct units: Canindé and Independência. Canindé unit is represented basically by biotite paragneisses and muscovite paragneisses, with minor metabasic rocks (amphibolite lens). Independência sequence is composed by garnetiferous paragneisses, sillimanite-garnet-quartz-muscovite schists and quartz-muscovite schists, pure or muscovite quartzites and rare marbles. At least three ductile deformation events were recognized in both units of Ceará group, named D1, D2 and D3. The former one is interpreted as related to a low angle tangential tectonics which mass transport is southward. D2 event is marked by the development of close/isoclinal folds with a N-S oriented axis. Refolding patterns generated by F1 and F2 superposition are found in several places. The latest event (D3) corresponds to a transcurrent tectonics, which led to development of mega-folds and several shear zones, under a transpressional regime. The mapped shear zones are Humberto Monte (ZCHM), Poço Cercado (ZCPC) and Forquilha (ZCF). Digital image processing of enhanced Landsat 7-ETM+ satellite images, combined with field data, demonstrate that these penetrative structures are associated with positive and negative geomorphologic patterns, distributed in linear and curvilinear arrangements with tonal banding, corresponding to the ductile fabric and to crests. Diverse color composites were tested and RGB-531 and RGB-752 provided the best results for lineament analysis of the most prominent shear zones. Spatial filtering techniques (3x3 and 5x5 filters) were also used and the application of Prewitt filters generated the best products. The integrated analysis of morphological and textural aspects from filtered images, variation of tonalities related to the distribution of geologic units in color composites and the superposition over a digital elevation model, contributed to a characterization of the structural framework of the study area. Kinematic compatibility of ZCHM, ZCPC, ZCF shear zones, as well as Sobral-Pedro II (ZCSPII) shear zone, situated to the west of the study area, was one of the goal of this work. Two of these shear zones (ZCHM, ZCPC) display sinistral movements, while the others (ZCSPII, ZCF) exhibit dextral kinematics. 40Ar/39Ar ages obtained in this thesis for ZCSPII and ZCPC, associated with other 40Ar/39Ar data of adjacent areas, indicate that all these shear zones are related to Brasiliano orogeny. The trend of the structures, the opposite shear senses and the similar metamorphic conditions are fitted in a model based on the development of conjugate shear zones in an unconfined transpression area. A WNW-ESE bulk shortening direction is infered. The geometry and kinematic of the studied structures suggest that shortening was largely accommodated by lateral extrusion, with only minor amounts of vertical stretch