No description available.

The Irumide belt is an elongate crustal province characterised by Mesoproterozoic tectonism and magmatism that stretches over a distance of approximately 900 kilometers from central Zambia to the Zambia-Tanzania border and northern Malawi. It is bounded to the northwest by largely undeformed Palaeoproterozoic basement lithologies of the Bangweulu block and is truncated to the northeast by Mesoproterozoic and Neoproterozoic transcurrent shear zones within reactivated parts of the Palaeoproterozoic Ubendian belt. To the southeast and south, Irumide lithologies were reworked within the Neoproterozoic Lufilian and Zambezi belts, and to the east by the East African Orogen. Lithologies in the Irumide belt comprise a Palaeo- to Mesoproterozoic complex of gneisses and granitoids and a supracrustal succession of quartzites and pelites. A three-fold subdivision was accepted prior to this study; (1) Palaeoproterozoic granites and gneisses forming the Irumide basement, (2) a supracrustal succession of quartzites and metapelites called the Muva Supergroup, (3) various deformed and undeformed granitoids intruding both the Palaeoproterozoic basement and Muva Supergroup and considered to be pre-Irumide (1.4 Ga) and syn-, late- to post-Irumide (1.1-0.95 Ga). The age of Irumide tectonism itself was poorly constrained between 1.4 and 1.0 Ga. The basement units comprise the Mkushi Gneiss in the southwest and the Luwalizi Granite, Mwambwa River and Mulungwizi Gneisses in the northeast. These units have been correlated with the Palaeoproterozoic Bangweulu block and Ubendian belt in the past. These basement units are structurally and in places unconformably overlain by a metasedimentary succession of quartzites and metapelites, which in the southwest has been called the Kanona Group, and in the northeast the Manshya River Group. / Both sequences have been correlated with similar quartzite-pelite successions on the Bangweulu block, termed the Mporokoso Group, and, together with a second cycle reworked unit on the Bangweulu block called the Kasama Formation, were collectively grouped into the Muva Supergroup. Both basement and supracrustals have been deformed, metamorphosed and intruded by a host of granitoids which, based on structural fabrics, were subdivided into pre-, syn-, late- and post-tectonic suites with respect to Irumide tectonism. Due to the lack of reliable geochronological constraints, this subdivision had remained untested until now. All units in the Irumide belt have been strongly affected by compressional tectonics, resulting in northwest-directed thrusting onto the Bangweulu block basement and extensive crustal shortening. Minor southeast-verging structures form part of locally developed backthrusts within an overall northwest-vergent tectonic regime. At least parts of the Irumide basement were affected by Irumide tectonism, but large-scale thrusting was mainly accommodated along a basal decollement at the basement-cover interface. Extensive shortening is exemplified by tight- to isoclinal folding within the supracrustal sequence, ranging from upright to recumbent. Thrusts developed where shortening could not be accommodated by tight folding, which produced tectonic duplication within the metasedimentary pile, making formation-to-formation correlations across the belt tenuous at best. Irumide tectonism has been reported to affect the base of the Mporokoso Group on the Bangweulu block, where folding along the Luongo shear zone occurred contemporaneously with thermal resetting of biotite dated at ~1.0 Ga (K-Ar dates). Metamorphic parageneses record low- to medium-pressure/medium- to high-temperature conditions. / Metamorphic grades range from greenschist facies in the northwestern foreland, to upper amphibolite facies in the southeast, with local granulites. Peak Irumide metamorphism, recorded in metamorphic zircon rim overgrowths, has been dated in this study at 1.02 Ga. Metamorphism to the southeast, across the younger Karoo grabens, had previously been constrained at 1.05 Ga, indicating an across strike diachronous development of metamorphism for the Irumide belt. The lithological units identified and dated as part of this study in the Irumide belt include: (1) limited Neoarchaean rocks emplaced at 2.73 Ga and representing the oldest rocks in the Bangweulu block; (2) ca. 2.05-1.85 Ga volcano-plutonic complexes and gneisses representing the most important components in the Bangweulu block; (3) an extensive quartzite-metapelite succession with minor carbonate forming the Mporokoso, Kanona and Manshya River groups, and deposited at ca. 1.8 Ga; (4) granitoids emplaced between 1.65-1.55 Ga; (5) deposition of the Kasama Formation between 1.43 and 1.05 Ga (second-cycle reworking of the Mporokoso Group); (6) voluminous syn- to post-kinematic Irumide granitoids emplaced between 1.05-0.95 Ga. In addition, a minor suite of 1.36-1.33 Ga anorogenic plutons (nepheline syenite and biotite granite) have been identified in the far northeastern Irumide belt, but were not included in this study. Whole-rock geochemical data for magmatic rocks in northern Zambia, predominantly from within the Irumide belt, indicate uniform crust-dominated patterns. Overall high REE contents and trace element characteristics indicate the significant participation of older crust in the generation of all magmatic suites. / The data are insufficient to conclusively demonstrate that this crustal melting was associated with either intra-plate, volcanic arc or post-collisional/extensional collapse. A limited number of Sm/Nd isotopic data for the entire range of magmatic suites corroborate the highly reworked nature of parent magmas, with all samples characterised by strongly negative åNd(T) values and TDM model ages between 2.2 and 3.2 Ga. The geochronological data presented in this thesis show that the Irumide belt includes a Palaeoproterozoic basement complex comprising units as old as 2.73 Ga, but mostly made up of granitic gneisses ranging in age between 2.05 and 1.93 Ga, while granitic and volcanic units of the Bangweulu block to the northwest were dated at 1.87-1.86 Ga. Detrital zircon age data from quartzites and zircon crystallisation ages of interlayered tuffs within the Muva Supergroup indicate a depositional age of between 1.88 and 1.85 Ga, with local derivation from locally recognised basement units, although similarly aged rocks of the Tanzania craton to the northeast are also a possible source. The detrital record of the Muva Supergroup shows that the various components of the Bangweulu block, including 2.73, 2.05-1.93 and 1.87-1.86 Ga units, were assembled by the time of deposition of the Muva Supergroup at around 1.8 Ga. Both the basement units and the Muva Supergroup were intruded by a previously unknown magmatic suite of biotite granites between 1.65-1.55 Ga, the first record of such a magmatic event in central Africa. The new data presented in this thesis allow a critical assessment of previously proposed regional correlations between Mesoproterozoic teranes in central and southern Africa. / Significant temporal differences between the Irumide belt and the Kibaran belt, Choma-Kalomo block and Namaqua-Natal belts had previously not been detected due to the poor quality, low resolution or limited size of isotopic data sets. The new data set produced in this study indicates a distinct and separate tectono-magmatic history for each of these terranes, therefore precluding previously suggested correlations. In particular, the presumed southeastward continuation of the Irumide belt across the Neoproterozoic Zambezi belt into the Choma-Kalomo block is precluded by the data presented in this thesis. This new geochronological framework allows for significant spatial separation of the Kalahari and Congo cratons prior to the Neoproterozoic closure of the Damara-Lufilian-Zambezi ocean, and is therefore in support of palaeogeographic models of Rodinia which either place the Congo and Kalahari cratons as distinct and separate fragments within the supercontinent, or show one or both of the two cratons not to form part of it. Currently, available data are not able to determine the tectonic setting or the palaeogeographic location of the Irumide belt, and as a result it is unclear whether it developed within Rodinia as a collisional orogen, at its margin as an accretionary orogen, or was not associated with Rodinia at all.

No description available.

Os Granitóides Arroio Divisa (GAD), localizados na região de Quitéria, porção leste do Escudo Sul-rio-grandense, constituem um corpo alongado de direção NE-SW, com apro-ximadamente 30 km de extensão e 1 a 6 km de largura. Ao norte, são intrusivos em metatona-litos, metagranodioritos e gnaisses tonalíticos a dioríticos do Complexo Arroio dos Ratos, de idade paleoproterozóica, e ao sul são intrudidos por granitos e riolitos neoproterozóicos. Os GAD são predominantemente granodioritos e granitos foliados, de textura equigranular média a grossa, contendo anfibólio e biotita, além de titanita, zircão e apatita como minerais acessó-rios. Rochas dioríticas a tonalíticas ocorrem na forma de enclaves microgranulares, emulsões e diques sinplutônicos, de contatos interdigitados e interlobados, característicos de mistura heterogênea de magmas. Nas proximidades dos termos dioríticos observa-se um aumento no teor de máficos dos granitóides. É também comum a ocorrência de xenólitos centimétricos a decamétricos de gnaisses e metatonalitos do Complexo Arroio dos Ratos e hornblenda-biotita granodiorito correlacionado ao Granodiorito Cruzeiro do Sul. Nas proximidades das zonas de mistura e de xenólitos maiores, observa-se nos GAD o desenvolvimento de textura heterogra-nular a porfirítica em zonas de espessura métrica. A foliação magmática é marcada pela orien-tação dimensional de plagioclásio e biotita. Paralela à mesma, é frequente a ocorrência de foliação milonítica de intensidade variável, com movimento transcorrente sinistral. Estas es-truturas, de direção E-W e mergulho acentuado, sofrem inflexão para NE-SW em sua porção leste, causada pela atuação de uma zona de cataclase regional que favoreceu o posicionamen-to das intrusões graníticas tardias. Os GAD e rochas máficas associadas possuem característi-cas geoquímicas indicativas de afinidade toleítica médio a alto-K, incluindo também magmas produzidos por fusão crustal de gnaisses com granada, que além de gerar corpos graníticos, contaminou os magmas parentais dioríticos. A integração das interpretações estratigráficas, tectônicas e geoquímicas indica que este magmatismo constitui manifestação precoce do magmatismo pós-colisional neoproterozóico do sul do Brasil. / The ArroioDivisaGranitoids (ADG), situated in the Quitéria region, eastern Sul-rio-grandense Shield, conform an elongate, NE-SW oriented body about 30 km long and 1 to 6 km wide. They are intrusive in Paleoproterozoic metatonalites, metagranodiorites, and tonalit-ic to dioritic gneisses at the northern border, whilst in the south they are intruded by Neopro-terozoic granites and rhyolites. The ADG rocks are predominantly foliated granodiorites to granites, with medium- to coarse-grained equigranular textures, containing amphibole and biotite. Titanite, zircon, and apatite are accessory minerals. Dioritic to tonalitic rocks occur as mafic microgranular enclaves, emulsions, and synplutonic dikes, with interpenetrated and sinuous contacts, as usual for magma mingling products. Near the diorites, the mafic contents of the granitoids is increased. Centimeter- to meter-sized xenoliths of gneisses and metato-nalites from the Arroio dos Ratos Complex, and of horblende-biotite granodiorites correlated to the Cruzeiro do Sul Granodiorite are frequently observed. Where mingling and large xeno-liths are abundant, the ADG granodiorites change their texture to heterogranular and porphy-ritic, in meter-wide zones. Magmatic foliation is marked by the shape orientation of plagio-clase and biotite. Parallel to the magmatic foliation, a mylonitic one is developed with varia-ble intensity and sinistral transcurrent movement. The steeply-dipping, ENE-striking struc-tures are rotated towards NE strike at the eastern part of the body, where a regional cataclastic zone has controlled the emplacement of later intrusions. Quartz-mylonites and phylonites are found within the ADG along high-strain, low-temperature zones, sometimes hundred-meters wide. The ADG and associated mafic rocks show geochemical features that indicate their me-dium to high-K tholeiitic affinity, also including crustal magmas produced by partial melting of garnet-bearing gneissic protoliths. These crustal melts yielded granitic liquids that contam-inated the dioritic parental magmas of ADG. The integrated interpretation of stratigraphic, tectonic and geochemical evidences indicates that the ADG and associated mafic rocks have formed during the early period of Neoproterozoic post-collisional magmatism in southern-most Brazil.

Os Granitóides Arroio Divisa (GAD), localizados na região de Quitéria, porção leste do Escudo Sul-rio-grandense, constituem um corpo alongado de direção NE-SW, com apro-ximadamente 30 km de extensão e 1 a 6 km de largura. Ao norte, são intrusivos em metatona-litos, metagranodioritos e gnaisses tonalíticos a dioríticos do Complexo Arroio dos Ratos, de idade paleoproterozóica, e ao sul são intrudidos por granitos e riolitos neoproterozóicos. Os GAD são predominantemente granodioritos e granitos foliados, de textura equigranular média a grossa, contendo anfibólio e biotita, além de titanita, zircão e apatita como minerais acessó-rios. Rochas dioríticas a tonalíticas ocorrem na forma de enclaves microgranulares, emulsões e diques sinplutônicos, de contatos interdigitados e interlobados, característicos de mistura heterogênea de magmas. Nas proximidades dos termos dioríticos observa-se um aumento no teor de máficos dos granitóides. É também comum a ocorrência de xenólitos centimétricos a decamétricos de gnaisses e metatonalitos do Complexo Arroio dos Ratos e hornblenda-biotita granodiorito correlacionado ao Granodiorito Cruzeiro do Sul. Nas proximidades das zonas de mistura e de xenólitos maiores, observa-se nos GAD o desenvolvimento de textura heterogra-nular a porfirítica em zonas de espessura métrica. A foliação magmática é marcada pela orien-tação dimensional de plagioclásio e biotita. Paralela à mesma, é frequente a ocorrência de foliação milonítica de intensidade variável, com movimento transcorrente sinistral. Estas es-truturas, de direção E-W e mergulho acentuado, sofrem inflexão para NE-SW em sua porção leste, causada pela atuação de uma zona de cataclase regional que favoreceu o posicionamen-to das intrusões graníticas tardias. Os GAD e rochas máficas associadas possuem característi-cas geoquímicas indicativas de afinidade toleítica médio a alto-K, incluindo também magmas produzidos por fusão crustal de gnaisses com granada, que além de gerar corpos graníticos, contaminou os magmas parentais dioríticos. A integração das interpretações estratigráficas, tectônicas e geoquímicas indica que este magmatismo constitui manifestação precoce do magmatismo pós-colisional neoproterozóico do sul do Brasil. / The ArroioDivisaGranitoids (ADG), situated in the Quitéria region, eastern Sul-rio-grandense Shield, conform an elongate, NE-SW oriented body about 30 km long and 1 to 6 km wide. They are intrusive in Paleoproterozoic metatonalites, metagranodiorites, and tonalit-ic to dioritic gneisses at the northern border, whilst in the south they are intruded by Neopro-terozoic granites and rhyolites. The ADG rocks are predominantly foliated granodiorites to granites, with medium- to coarse-grained equigranular textures, containing amphibole and biotite. Titanite, zircon, and apatite are accessory minerals. Dioritic to tonalitic rocks occur as mafic microgranular enclaves, emulsions, and synplutonic dikes, with interpenetrated and sinuous contacts, as usual for magma mingling products. Near the diorites, the mafic contents of the granitoids is increased. Centimeter- to meter-sized xenoliths of gneisses and metato-nalites from the Arroio dos Ratos Complex, and of horblende-biotite granodiorites correlated to the Cruzeiro do Sul Granodiorite are frequently observed. Where mingling and large xeno-liths are abundant, the ADG granodiorites change their texture to heterogranular and porphy-ritic, in meter-wide zones. Magmatic foliation is marked by the shape orientation of plagio-clase and biotite. Parallel to the magmatic foliation, a mylonitic one is developed with varia-ble intensity and sinistral transcurrent movement. The steeply-dipping, ENE-striking struc-tures are rotated towards NE strike at the eastern part of the body, where a regional cataclastic zone has controlled the emplacement of later intrusions. Quartz-mylonites and phylonites are found within the ADG along high-strain, low-temperature zones, sometimes hundred-meters wide. The ADG and associated mafic rocks show geochemical features that indicate their me-dium to high-K tholeiitic affinity, also including crustal magmas produced by partial melting of garnet-bearing gneissic protoliths. These crustal melts yielded granitic liquids that contam-inated the dioritic parental magmas of ADG. The integrated interpretation of stratigraphic, tectonic and geochemical evidences indicates that the ADG and associated mafic rocks have formed during the early period of Neoproterozoic post-collisional magmatism in southern-most Brazil.

Os Granitóides Arroio Divisa (GAD), localizados na região de Quitéria, porção leste do Escudo Sul-rio-grandense, constituem um corpo alongado de direção NE-SW, com apro-ximadamente 30 km de extensão e 1 a 6 km de largura. Ao norte, são intrusivos em metatona-litos, metagranodioritos e gnaisses tonalíticos a dioríticos do Complexo Arroio dos Ratos, de idade paleoproterozóica, e ao sul são intrudidos por granitos e riolitos neoproterozóicos. Os GAD são predominantemente granodioritos e granitos foliados, de textura equigranular média a grossa, contendo anfibólio e biotita, além de titanita, zircão e apatita como minerais acessó-rios. Rochas dioríticas a tonalíticas ocorrem na forma de enclaves microgranulares, emulsões e diques sinplutônicos, de contatos interdigitados e interlobados, característicos de mistura heterogênea de magmas. Nas proximidades dos termos dioríticos observa-se um aumento no teor de máficos dos granitóides. É também comum a ocorrência de xenólitos centimétricos a decamétricos de gnaisses e metatonalitos do Complexo Arroio dos Ratos e hornblenda-biotita granodiorito correlacionado ao Granodiorito Cruzeiro do Sul. Nas proximidades das zonas de mistura e de xenólitos maiores, observa-se nos GAD o desenvolvimento de textura heterogra-nular a porfirítica em zonas de espessura métrica. A foliação magmática é marcada pela orien-tação dimensional de plagioclásio e biotita. Paralela à mesma, é frequente a ocorrência de foliação milonítica de intensidade variável, com movimento transcorrente sinistral. Estas es-truturas, de direção E-W e mergulho acentuado, sofrem inflexão para NE-SW em sua porção leste, causada pela atuação de uma zona de cataclase regional que favoreceu o posicionamen-to das intrusões graníticas tardias. Os GAD e rochas máficas associadas possuem característi-cas geoquímicas indicativas de afinidade toleítica médio a alto-K, incluindo também magmas produzidos por fusão crustal de gnaisses com granada, que além de gerar corpos graníticos, contaminou os magmas parentais dioríticos. A integração das interpretações estratigráficas, tectônicas e geoquímicas indica que este magmatismo constitui manifestação precoce do magmatismo pós-colisional neoproterozóico do sul do Brasil. / The ArroioDivisaGranitoids (ADG), situated in the Quitéria region, eastern Sul-rio-grandense Shield, conform an elongate, NE-SW oriented body about 30 km long and 1 to 6 km wide. They are intrusive in Paleoproterozoic metatonalites, metagranodiorites, and tonalit-ic to dioritic gneisses at the northern border, whilst in the south they are intruded by Neopro-terozoic granites and rhyolites. The ADG rocks are predominantly foliated granodiorites to granites, with medium- to coarse-grained equigranular textures, containing amphibole and biotite. Titanite, zircon, and apatite are accessory minerals. Dioritic to tonalitic rocks occur as mafic microgranular enclaves, emulsions, and synplutonic dikes, with interpenetrated and sinuous contacts, as usual for magma mingling products. Near the diorites, the mafic contents of the granitoids is increased. Centimeter- to meter-sized xenoliths of gneisses and metato-nalites from the Arroio dos Ratos Complex, and of horblende-biotite granodiorites correlated to the Cruzeiro do Sul Granodiorite are frequently observed. Where mingling and large xeno-liths are abundant, the ADG granodiorites change their texture to heterogranular and porphy-ritic, in meter-wide zones. Magmatic foliation is marked by the shape orientation of plagio-clase and biotite. Parallel to the magmatic foliation, a mylonitic one is developed with varia-ble intensity and sinistral transcurrent movement. The steeply-dipping, ENE-striking struc-tures are rotated towards NE strike at the eastern part of the body, where a regional cataclastic zone has controlled the emplacement of later intrusions. Quartz-mylonites and phylonites are found within the ADG along high-strain, low-temperature zones, sometimes hundred-meters wide. The ADG and associated mafic rocks show geochemical features that indicate their me-dium to high-K tholeiitic affinity, also including crustal magmas produced by partial melting of garnet-bearing gneissic protoliths. These crustal melts yielded granitic liquids that contam-inated the dioritic parental magmas of ADG. The integrated interpretation of stratigraphic, tectonic and geochemical evidences indicates that the ADG and associated mafic rocks have formed during the early period of Neoproterozoic post-collisional magmatism in southern-most Brazil.

Beypazari Granitoid is a low temperature and shallow-seated batholite intruded the Tepek&ouml / y metamorphic rocks of the Central Sakarya Terrane. Composition of the granitoid varies from granite to diorite. The granitoid is unconformably overlain by Palaeocene and Eocene rock units. Thus the age is probably Late Cretaceous. The Beypazari Granitoid comprises mafic microgranular enclaves. The granitoid mainly consists of quartz, plagioclase, orthoclase and minor amphibole, biotite, chlorite, zircon, sphene, apatite, and opaque minerals. Plagioclase shows sericitation whereas biotite and hornblende, chloritization. Holocrystalline and hypidiomorphic are characteristic textures of the granitoid. Geochemically, the Beypazari Granitoid is calc-alkaline, metaluminous and I-type. REE data indicate that it may have been generated from a source similar to the upper continental crust. The trace element data of the Beypazari Granitoid suggest a volcanic arc tectonic setting. The possible mechanism of Beypazari granitoid is the northdipping subduction of Neo-Tethyan northern branch under Sakarya continent during Late Cretaceous. The Beypazari Granitoid may be related with Galatean volcanic arc granitoids.

A review of the geotectonic settings of granitoids and various tin-tungsten provinces in Europe, Malaysia and southern Africa shows a close spatial and temporal association of mineralisation to S-type ilmenite series granitoids. Granitoids with these affinities are derived from crustal anatexis and are most commonly found in continental collision and different ensialic, intraplate orogenic settings, (e.g. SW England, Malaysia, Namibia) as well as in association with anorogenic magmatism (Nigeria, Brazil, South Africa). Tin-tungsten mineralisation is related to late- to post-tectonic granites, emplaced into areas of substantial tectonic thickening. Crustal anatexis leads to an observable calcalkaline chemical trend, with a source of gabbroic or amphibolite composition through anatexis to; mafic-intermediate enclaves, para-autochthonous anatectic granitoids (tonalite, granodiorite), to intermediate level quartz monzonite, granodiorite, biotite-granite, to late-tectonic highly fractionated muscovite-bearing granites, and high level porphyry intrusions. Mineralisation is spatially related to apical protrusions of the youngest most differentiated granite. Various mineralised environments are recognised, including endogranitic veins, primary disseminations, pegmatites and pipes, and exogranitic stockwork and fissure veins, and replacement bodies. A common factor to all these deposits is the inherent greisen environment, characterised by postmagmatic metasomatic alteration and mineral deposition. Common alteration mineral assemblages include albite, quartz, muscovite, tourmaline, and fluorite ∓ topaz. Ore mineral assemblages commonly display a paragenetic sequence of oxides (cassiterite, wolframite, scheelite), followed by sulphides (molybdenite, pyrite, pyrrhotite, chalcopyrite sphalerite, arsenopyrite/loëllingite, Pb-Bi(Ag) sulphosalts) and then lower temperature carbonates (calcite, siderite, ankerite). Analysis of Pan African orogenic provinces in southern Africa (Damara and Saldanian Provinces) shows there is good potential for applying integrated exploration techniques in search of endo-exogreisen Sn-W systems. Careful analysis and interpretation of granitoid geochemistry (K₂0, Na₂0, FeO/Fe₂0₃, F, B, Sn, W, Mo, Cu, Rb, Sr, Ti, Zr) should aid delineation of Sn-W and Mo-Cu metallogenic provinces in these regions. Magnetic susceptibility determinations should also aid distinction of S-type ilmenite series (less than 1 x lO⁻⁴emu/g ) from I-type magnetite series (more than 1 x lO⁻⁴emu/g ) granitoids

The Cardigan pluton, located in the southern half of New Hampshire, is a strongly peraluminous, S-type granite which is granodioritic in composition. It is inferred to have been emplaced rapidly, thrust up along west-verging nappes during the Acadian orogeny. Distinctive pods, consisting of 50 to 70 percent modal garnet, are found throughout the pluton in assemblages of garnet + sillimanite + biotite + plagioclase + quartz. These garnetite rocks present an intriguing case for restite. Textural features of the garnetite rocks, such as fibrolitic sillimanite mats and flat, unzoned major and trace-element garnet grain profiles, provide evidence for biotite dehydration melting with single-stage garnet growth from the reaction: bio + plag + qtz + kspar = gar + sill + liq. Temperatures calculated using garnet-biotite (GB) thermometry and garnet-aluminum silicate-quartz-plagioclase (GASP) barometry yield estimates between 662-714ºC and 3.8 kbars. These low calculated temperatures are most likely the result of biotite compositions which have been altered by retrograde exchange reactions. The dominant source rock for the Cardigan magmas was likely calc-pelitic to greywacke in composition. Major element modeling suggests that ~70% melting of a calc-pelitic metasediment from the Central Maine trough could have generated a granodioritic melt similar to the average granodiorite of the Cardigan pluton. However, most of the Cardigan garnetite rocks appear to have been derived from pelites, as they are too poor in CaO and Na2O. Hence, though the majority of garnetite rocks cannot represent the dominant restite of the source rocks that produced the Cardigan pluton, they do appear to be the melt-depleted residue of an unidentified pelitic source. Comparison of Nd and Sr isotopic data from garnetite and Central Maine trough metasediments permit an interpretation that the Lower Rangeley Formation, from the Central Maine trough, could be the source rock of the Cardigan magmas. However, one feldspar Pb isotopic analysis in the literature (Moench and Allienikoff, 2002) and rare monazite chemical ages near 600 Ma suggest that the Cardigan pluton does not have a Laurentian source (i.e. Lower Rangeley Formation or other Central Maine trough metasediments), whereas an inferred peri-Gondwanan basement source is permissible.

Esta dissertação faz parte de um projeto que tem como objetivo investigar a origem e evolução do magmatismo de arco e pós-colisional do Escudo Sul-rio-grandense (ESRG), caracterizando a partir de estudos geoquímicos, estruturais e petrográficos os Granitóides Sanga do Areal (GSA), localizados na região de Quitéria, porção leste do Escudo Sul-rio-grandense. Estes granitóides consistem de dois corpos principais, alongados na direção NE-SW, com aproximadamente 14 km de extensão e 2 km de largura, e também de diversas intrusões menores, posicionadas, preferencialmente, na porção mediana de alta deformação cisalhante do Complexo Arroio dos Ratos. Estão em contato na porção NW com metatonalitos, metagranodioritos e gnaisses tonalíticos a dioríticos de idade paleoproterozóica do referido complexo e com horblenda-biotita granodioritos da unidade neoproterozóica Granodiorito Cruzeiro do Sul. Na porção SE o contato se dá com tonalitos a dioritos relacionados aos Granitóides Arroio Divisa de idade neoproterozóica. Os GSA são biotita monzogranitos de textura porfirítica em seu termo principal, com cerca de 30% de megacristais de até 5 cm de comprimento de plagioclásio e K-feldspato. A matriz heterogranular média a grossa é composta por quartzo fitado, feldspato parcialmente recristalizado e biotita. Subordinadamente, observam-se corpos de espessura centimétrica a métrica de biotita granodiorito equigranular médio, com fenocristais esparsos de feldspatos alinhados na foliação. Raramente ocorrem enclaves microgranulares máficos. A foliação milonítica é bem marcada pela orientação da biotita, dos megacristais lenticulares e do quartzo fitado e tem direção E-W, com alto ângulo de mergulho para N e para S, contendo lineação de estiramento direcional, com baixo caimento para W a SW. A foliação ígnea primária, concordante a sub-concordante com a foliação milonítica, tem ocorrência restrita e é marcada pela orientação dos megacristais não deformados e das lamelas de biotita. Estruturas S-C, caudas assimétricas em porfiroclastos de feldspatos, biotita fish e fitas assimétricas de quartzo são consistentes e indicam movimento transcorrente sinistral. Os Granitóides Sanga do Areal têm afinidade sub-alcalina médio a alto K, provavelmente toleítica, compatível com ambiente pós-colisional, onde foram deformados e controlados por zonas de cisalhamento transcorrente sub-verticais. Foi obtida uma idade U-Pb em zircão dos granitóides de 626,6±4,9 Ma (MSWD=2.2), coerente com as relações de campo. / This research investigates the evolution of arc to post-collisional magmatism in the Sul-rio-grandense Shield (ESGR), using geochemistry, structural and petrographic studies of the Sanga do Areal Granitoids (GSA). These granitoids are located in the Quitéria region, east of ESRG. The GSA form two main, NE-striking intrusions, and several other small ones, mainly within the shear zone croscutting the central portion of the Arroio dos Ratos Complex. The two main bodies are about 14 km long and 2 km wide. To the northwest, the GSA rocks are in contact with Paleoproterozoic metatonalites, metagranodiorites, tonalitic to dioritic gneisses of the Complex, and Neoproterozoic horblende-biotite granodiorites of the Cruzeiro do Sul unit. To the southeast, they are surrounded by tonalitic to dioritic rocks, related to the Neoproterozoic Arroio da Divisa Granitoids. The GSA rocks are composed mainly of porphyritic biotite monzogranites, with about 30% megacrysts of plagioclase and 5 cm long K-feldspar. The medium to coarse grained heterogranular groundmass is composed of microcrystalline ribbon quartz, partially re-crystallized feldspar and biotite. Medium-grained equigranular granodiorite occurs as centimeter to meter- thick bodies, with sparse feldspar megacrysts aligned on the foliation plane. Microgranular mafic enclaves are rarely observed within the GSA rocks. The mylonitic foliation is well-developed and marked by biotite, oriented lenticular megacrysts, as well as quartz ribbons. It strikes E-W and dips at high angles either N or S. The stretching lineation within the foliation shows shallow plunges, preferentially W-SW. A primary igneous foliation is sometimes observed, and it is concordant or sub-concordant with the mylonitic one, and marked by orientation of igneous megacrysts and biotite lamellae. S-C structures, asymetric tails in feldspar porphyroclasts, biotite fish, and asymetric quartz ribbons indicate transcurrent movement with consistent sinistral shear sense. The Sanga do Areal Granitoids show subalkaline medium- to high-K affinity, probably tholeiitic, and trace element composition consistent with sources related to post-collisional settings, which were deformed and controlled by E-NE and NE sub-vertical transcurrent shear zones. A U-Pb age in zircon grains from Sanga do Areal Granitoids of 626.6 ± 4.6Ma ((MSWD=2.2) was obtained and considered coherent with stratigraphic relations.