O anfibolito Cafelândia faz parte da Sequência Serra da Malacacheta, Complexo Barro Alto, GO. Por ser rocha com bandamento composicional bem definido, o anfibolito tem sido interpretado como produto de metamorfismo de gabro acamadado. Entretando, uma das feições que esse bandamento composicional apresenta é a presença de veios de leucossoma paralelos à foliação da rocha. O contato transicional entre o anfibolito e alguns dos veios de leucossoma indicam que os veios foram formados por fusão in situ. O objetivo do presente trabalho é investigar o processo de fusão que afetou a rocha, utilizando descrições macroscópicas, microscópicas e análises químicas de minerais em diversos contextos texturais. O bandamento composicional é definido pela variação na proporção modal de hornblenda, plagioclásio, titanita, clinopiroxênio, granada e quartzo. Veios de leucossoma com porfiroblastos de hornblenda, concordantes ou discordantes da foliação são observados reforçando o bandamento. No topo estrutural do anfibolito ocorrem camadas com mais de 70% de hornblenda e outras dominadas por clinopiroxênio e granada. Ortopiroxênio é raro e não é possível ter certeza se os grãos presentes são reliquiares do protolito ígneo ou se são metamórficos. As camadas ricas em granada e clinopiroxênio não ultrapassam espessuras maiores que 5 a 10 cm. Na porção basal do anfibolito a proporção de hornblenda é menor e a proporção de clinopiroxênio e granada maior, ocorrendo ortopiroxênio em alguns afloramentos. Os porfiroblastos de hornblenda do leucossoma são substituídos por clinopiroxênio e rara granada. Diferenças sutis nas composições dos grãos de hornblenda e clinopiroxênio do anfibolito Cafelândia e do leucossoma ocorrem, mas são mascaradas pela influência da composição da banda na composição dos minerais. De modo geral, a hornblenda no leucossoma é mais rica em Si e Mg do que os grãos da matriz, enquanto o clinopiroxênio do leucossoma é mais rico em Al. Micro-exsoluções no clinopiroxênio do leucossoma também impedem a comparação da sua composição real com os grãos da matriz da rocha. Cálculos termobarométricos foram feitos em amostras do topo e da base estrutural do anfibolito utilizando o termômetro granada-clinopiroxênio e o barômetro granada-clinopiroxênio-plagioclásio-quartzo, além do programa THERMOCALC. A termobarometria convencional fornece valores P-T menores para temperatura e similares de pressão aqueles calculados com o THERMOCALC e não são muito diferentes dos que já foram calculados previamente, com valores para o topo de 870 ºC e 10,9 kbar e para a base de 881 ºC e 9,8 kbar. Se quartzo não é usado nos cálculos P-T, acréscimo de 2 a 3 kbar ocorre nos resultados. Os dados P-T calculados são compatíveis ou algo inferiores aos resultados experimentais de fusão de rochas máficas contendo hornblenda, produção de líquido tonalítico e resíduo contendo clinopiroxênio e granada. A presença de hornblenda dentro do leucossoma do topo da unidade pode estar associada com influxo de H2O no sistema durante a fusão, diferente do que ocorre na base do corpo. É possível que o líquido que se encontrava na porção basal esvai em direção as porções superiores do anfibolito, reidratando a rocha e formando porfiroblastos de hornblenda dentro do leucossoma do topo. Uma conclusão importante tirada aqui é que o protolito do anfibolito Cafelândia pode ser o anfibolito da base da sequência Juscelândia, sobreposta, e que o bandamento composicional foi gerado por metamorfismo, fusão e segregação/perda do liquido e não por metamorfismo de gabro acamadado. / The Cafelândia amphibolite is part of the Serra da Malacacheta sequence, Barro Alto Complex, GO. As it is a rock with well-defined compositional banding, the amphibolite has been interpreted as a product of metamorphism of layered gabbro. However, a feature that reinforces the banding is the presence of leucosome veins, which are mainly parallel to the rock foliation. The transitional contact between amphibolite and some of the veins of leucosome indicate that the veins were formed by in situ melting. The purpose of this study is to investigate the melting process that affected the rock using macroscopic and microscopic descriptions, as well as chemical analysis of minerals in various textural contexts. The compositional banding is defined by variation in modal proportion of hornblende, plagioclase, titanite, clinopyroxene, garnet and quartz. Veins of leucosome with porphyroblasts of hornblende, concordant or discordant to foliation are observed, reinforcing the banding. At the structural top, layers of amphibolite occur with more than 70% of hornblende and others are dominated by clinopyroxene and garnet. Orthopyroxene is rare and its metamorphic origin cannot be assured, being possible that these grains are relicts of the igneous protolith. The garnet and clinopyroxene rich layers do not exceeding thicknesses greater than 5 to 10 cm. In the basal portion hornblende proportion is much smaller, but clinopyroxene and garnet are larger. Orthopyroxene occurs in some outcrops. The porphyroblasts of hornblende from the leucosome are replaced by clinopyroxene and rare garnet. Subtle differences in the composition of the of hornblende and clinopyroxene grains in the Cafelândia amphibolite and leucosome occur, but are masked by the influence of the bulk composition of each band in the composition of minerals. In general, the hornblende in the leucosome is richer in Si and Mg than the matrix grains, whereas the leucosome clinopyroxene is richer in Al. Micro-exsolutions in clinopyroxene in the leucosome also hampers the comparison of its \"real\" composition with the grains of the rock matrix. Thermobarometric calculations were done on samples from the structural top and bottom of amphibolite, using the garnet-clinopyroxene thermometer and garnetclinopyroxene- plagioclase-quartz barometer, besides the THERMOCALC. The conventional thermobarometry provides lower P-T values for temperature and similar pressure to those calculated with the THERMOCALC, and results are not very different from those that have been previously calculated. Results for the top are 870 ºC and 10.9 kbar and for the basis 881 ºC and 9.8 kbar. If quartz is not used in the P-T calculations, raise of 2 to 3 kbar occurs in the results. The calculated P-T data are compatible or something lower than the results of experiments for melting of hornblende-bearing mafic rocks with production tonalitic liquid and clinopyroxene and garnet residue. The hornblende-bearing leucosome of the top of the unit may be associated with influx of H2O in the system during melting, unlike what occurs at the base of the body. It is also possible that the liquid formed in basal portion oozes toward the upper portions of amphibolite, rehydrating it to form the hornblende porphyroblasts within the leucosome. An important conclusion drawn here is that the protolith of amphibolite Cafelândia can be bottom amphibolite of the Juscelândia sequence, which overly the Cafelândia amphibolite, and that the banding was generated by metamorphism, melting and segregation / loss of melt and not by metamorphism of layered gabbro.

O anfibolito Cafelândia faz parte da Sequência Serra da Malacacheta, Complexo Barro Alto, GO. Por ser rocha com bandamento composicional bem definido, o anfibolito tem sido interpretado como produto de metamorfismo de gabro acamadado. Entretando, uma das feições que esse bandamento composicional apresenta é a presença de veios de leucossoma paralelos à foliação da rocha. O contato transicional entre o anfibolito e alguns dos veios de leucossoma indicam que os veios foram formados por fusão in situ. O objetivo do presente trabalho é investigar o processo de fusão que afetou a rocha, utilizando descrições macroscópicas, microscópicas e análises químicas de minerais em diversos contextos texturais. O bandamento composicional é definido pela variação na proporção modal de hornblenda, plagioclásio, titanita, clinopiroxênio, granada e quartzo. Veios de leucossoma com porfiroblastos de hornblenda, concordantes ou discordantes da foliação são observados reforçando o bandamento. No topo estrutural do anfibolito ocorrem camadas com mais de 70% de hornblenda e outras dominadas por clinopiroxênio e granada. Ortopiroxênio é raro e não é possível ter certeza se os grãos presentes são reliquiares do protolito ígneo ou se são metamórficos. As camadas ricas em granada e clinopiroxênio não ultrapassam espessuras maiores que 5 a 10 cm. Na porção basal do anfibolito a proporção de hornblenda é menor e a proporção de clinopiroxênio e granada maior, ocorrendo ortopiroxênio em alguns afloramentos. Os porfiroblastos de hornblenda do leucossoma são substituídos por clinopiroxênio e rara granada. Diferenças sutis nas composições dos grãos de hornblenda e clinopiroxênio do anfibolito Cafelândia e do leucossoma ocorrem, mas são mascaradas pela influência da composição da banda na composição dos minerais. De modo geral, a hornblenda no leucossoma é mais rica em Si e Mg do que os grãos da matriz, enquanto o clinopiroxênio do leucossoma é mais rico em Al. Micro-exsoluções no clinopiroxênio do leucossoma também impedem a comparação da sua composição real com os grãos da matriz da rocha. Cálculos termobarométricos foram feitos em amostras do topo e da base estrutural do anfibolito utilizando o termômetro granada-clinopiroxênio e o barômetro granada-clinopiroxênio-plagioclásio-quartzo, além do programa THERMOCALC. A termobarometria convencional fornece valores P-T menores para temperatura e similares de pressão aqueles calculados com o THERMOCALC e não são muito diferentes dos que já foram calculados previamente, com valores para o topo de 870 ºC e 10,9 kbar e para a base de 881 ºC e 9,8 kbar. Se quartzo não é usado nos cálculos P-T, acréscimo de 2 a 3 kbar ocorre nos resultados. Os dados P-T calculados são compatíveis ou algo inferiores aos resultados experimentais de fusão de rochas máficas contendo hornblenda, produção de líquido tonalítico e resíduo contendo clinopiroxênio e granada. A presença de hornblenda dentro do leucossoma do topo da unidade pode estar associada com influxo de H2O no sistema durante a fusão, diferente do que ocorre na base do corpo. É possível que o líquido que se encontrava na porção basal esvai em direção as porções superiores do anfibolito, reidratando a rocha e formando porfiroblastos de hornblenda dentro do leucossoma do topo. Uma conclusão importante tirada aqui é que o protolito do anfibolito Cafelândia pode ser o anfibolito da base da sequência Juscelândia, sobreposta, e que o bandamento composicional foi gerado por metamorfismo, fusão e segregação/perda do liquido e não por metamorfismo de gabro acamadado. / The Cafelândia amphibolite is part of the Serra da Malacacheta sequence, Barro Alto Complex, GO. As it is a rock with well-defined compositional banding, the amphibolite has been interpreted as a product of metamorphism of layered gabbro. However, a feature that reinforces the banding is the presence of leucosome veins, which are mainly parallel to the rock foliation. The transitional contact between amphibolite and some of the veins of leucosome indicate that the veins were formed by in situ melting. The purpose of this study is to investigate the melting process that affected the rock using macroscopic and microscopic descriptions, as well as chemical analysis of minerals in various textural contexts. The compositional banding is defined by variation in modal proportion of hornblende, plagioclase, titanite, clinopyroxene, garnet and quartz. Veins of leucosome with porphyroblasts of hornblende, concordant or discordant to foliation are observed, reinforcing the banding. At the structural top, layers of amphibolite occur with more than 70% of hornblende and others are dominated by clinopyroxene and garnet. Orthopyroxene is rare and its metamorphic origin cannot be assured, being possible that these grains are relicts of the igneous protolith. The garnet and clinopyroxene rich layers do not exceeding thicknesses greater than 5 to 10 cm. In the basal portion hornblende proportion is much smaller, but clinopyroxene and garnet are larger. Orthopyroxene occurs in some outcrops. The porphyroblasts of hornblende from the leucosome are replaced by clinopyroxene and rare garnet. Subtle differences in the composition of the of hornblende and clinopyroxene grains in the Cafelândia amphibolite and leucosome occur, but are masked by the influence of the bulk composition of each band in the composition of minerals. In general, the hornblende in the leucosome is richer in Si and Mg than the matrix grains, whereas the leucosome clinopyroxene is richer in Al. Micro-exsolutions in clinopyroxene in the leucosome also hampers the comparison of its \"real\" composition with the grains of the rock matrix. Thermobarometric calculations were done on samples from the structural top and bottom of amphibolite, using the garnet-clinopyroxene thermometer and garnetclinopyroxene- plagioclase-quartz barometer, besides the THERMOCALC. The conventional thermobarometry provides lower P-T values for temperature and similar pressure to those calculated with the THERMOCALC, and results are not very different from those that have been previously calculated. Results for the top are 870 ºC and 10.9 kbar and for the basis 881 ºC and 9.8 kbar. If quartz is not used in the P-T calculations, raise of 2 to 3 kbar occurs in the results. The calculated P-T data are compatible or something lower than the results of experiments for melting of hornblende-bearing mafic rocks with production tonalitic liquid and clinopyroxene and garnet residue. The hornblende-bearing leucosome of the top of the unit may be associated with influx of H2O in the system during melting, unlike what occurs at the base of the body. It is also possible that the liquid formed in basal portion oozes toward the upper portions of amphibolite, rehydrating it to form the hornblende porphyroblasts within the leucosome. An important conclusion drawn here is that the protolith of amphibolite Cafelândia can be bottom amphibolite of the Juscelândia sequence, which overly the Cafelândia amphibolite, and that the banding was generated by metamorphism, melting and segregation / loss of melt and not by metamorphism of layered gabbro.

Fiordland is located southwest of South Island of New Zealand. The field area of this thesis is in northern Fiordland, at the boundary of pristine arc rocks (Median Tectonic Zone) and a belt of Paleozoic paragneisses and orthogneisses of variable age that represent the metamorphosed paleo-Pacific Gondwana margin.

Fiordland is located southwest of South Island of New Zealand. The field area of this thesis is in northern Fiordland, at the boundary of pristine arc rocks (Median Tectonic Zone) and a belt of Paleozoic paragneisses and orthogneisses of variable age that represent the metamorphosed paleo-Pacific Gondwana margin.

Thesis (PhD (Earth Sciences))--University of Stellenbosch, 2009. / Fluid-present partial melting has generally been regarded a poor candidate for effecting crustal differentiation. In this study I report on anatectic metasediments from the Pan-African Damara Belt in Namibia that have undergone fluid-present biotite melting at a relatively low temperature, yet appear to have lost a significant volume of melt. In situ anatectic features have been identified on the basis of the existence of new generations of cordierite and/or garnet produced as the solid products of incongruent anatexis within or adjacent to leucosomes, that most commonly occur as lens shaped pods at a high angle to the lineation and formed during extension in a direction parallel to the long axis of the orogeny. Within these sites biotite underwent incongruent melting via the reaction Bt + Qtz + Pl + H2O = Melt + Grt + Crd. Cordierite nucleated on preexisting crystals within the bounding gneiss; garnet nucleated within the fracture sites (leucosomes) and typically occurs as individual, large (50 to 120 mm in diameter) poikiloblastic crystals. Thermobarometry applied to the anatectic assemblage yields low-temperature, granulitefacies peak conditions of 750 °C, 0.5 GPa. This temperature is approximately 100 °C lower than the accepted conditions for the onset of fluid-absent biotite melting. This, coupled to the focussing of anatexis on extensional fractures, suggests that anatexis occurred through waterpresent biotite incongruent melting. In order to better understand this process, both fluid-absent and water present partial melting experiments were conducted within the temperature interval 700 to 900 °C at 0.7 GPa. In the fluid-absent experiments, biotite incongruent melting started between 800 and 850 °C to produce melt coexisting with peritectic garnet and cordierite. In contrast, in water-saturated experiments, biotite melted via the reaction Bt + Pl + Q + H2O = Grt + Crd + Melt, between 700 and 750 °C, to produce melt, cordierite and garnet in the proportions 73:24:3.

Thesis (DSc)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: This study is an investigation of the anatectic history of high-grade paragneisses from the Ancient Gneiss Complex (AGC) in Swaziland. The work involved an integrated field, metamorphic, geochemical, geochronological and structural study of metasedimentary granulites from three separate, but spatially related areas of outcrop in south-central Swaziland, which were subjected to multiple high-grade partial melting events throughout the Meso- to Neoarchaean. The project has aimed to constrain the age(s) and conditions of metamorphism, so as to contribute to the understanding of geodynamic processes in the Barberton and AGC granite-greenstone terranes, as well as to investigate certain physical and chemical aspects of anatexis in the migmatites. The metamorphic record retained in these rocks, constrained by phase equilibria modelling as well as zircon and monazite SHRIMP and LA-ICP-MS geochronology, informs on the state of the mid- to lower-crust of the southeastern Kaapvaal Craton during key events associated with early lithosphere assembly and crustal differentiation. It also suggests that the region is comprised of more than one high-grade terrane. Two of the areas investigated experienced high-temperature metamorphism at ca. 3.23-3.21 Ga, in addition to a major 830-875º C, 6.5-7.6 kbar anatectic event at ca. 3.11-3.07 Ga. Intermediate and younger high-temperature events are recorded at ca. 3.18 Ga, ca. 3.16 Ga and 2.99 Ga. The timing of these metamorphic events coincided with the amalgamation of the eastern domain of the proto-Craton via subduction and accretion of micro-continental fragments at ca. 3.23 Ga, including the Barberton Greenstone Belt (BGB) and AGC terranes, as well as discrete episodes of crustal differentiation and potassic granitic magmatism between ca. 3.23 and 3.10 Ga. The third area investigated holds no record of Mesoarchaean metamorphism, but instead experienced a 830- 855 ºC, 4.4-6.4 kbar partial melting episode at ca. 2.73 Ga. This broadly coincided with the formation of a large continental flood basalt province, the ca. 2.71 Ga Ventersdorp LIP, and widespread intracratonic granitic magmatism on the Craton towards the end of the Neoarchaean. An explanation for the contrast in metamorphic record in the two terranes may be that the 2.71 Ga granulites represent a much younger sedimentary succession, and that granulites from the older terrane were left too restitic, after substantial partial melting during the Mesoarchaean, to record subsequent high-grade events. Finally, this study documents the details of S-type granitic magma production and extraction from a typical metapelitic source. Using the 2.73 Ga granulites from the AGC as a natural field laboratory, a case is made for the selective entrainment of peritectic garnet to the magma as a mechanism for generating relatively mafic, peraluminous S-type granite compositions. The work demonstrates the evolution of entrained peritectic garnet in such magmas, and is in strong support of a ‘peritectic phase entrainment’ process by which relatively mafic granite magmas are produced from melts which, in theory, should be highly leucocratic. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die anatektiese geskiedenis van hoëgraadse metasedimentêre gneise uit die Ancient Gneiss Complex (AGC) in Swaziland. Die werk behels 'n geïntegreerde veld, metamorfiese, geochemiese, geochronologiese en strukturele studie van metasedimentêre granuliete van drie afsonderlike, maar ruimtelik verwante gebiede in suid-sentraal Swaziland, wat aan verskeie hoëgraadse anatektiese gebeure onderworpe was gedurende die Meso-tot Neoargeïese tydsperiode. Die studie is daarop gemik om die ouderdomme en die kondisies van metamorfose vas te stel, om sodoende by te dra tot die begrip van die geodinamiese prosesse in die Barberton en AGC granietgroensteen terrein, asook om sekere fisiese en chemiese aspekte van die anatektiese proses te ondersoek. Die metamorfe rekord, bepaal deur mineraal ewewigsmodellering sowel as sirkoon en monasiet SHRIMP en LA-ICP-MS geochronologie, belig die toestand van die middel-tot laer-kors van die suidoostelike Kaapvaal Kraton tydens vroeë litosfeer samesmelting en differensiasie. Dit stel ook voor dat die streek uit meer as een hoëgraadse terrein bestaan. Twee van die gebiede het hoë-temperatuur metamorfose by 3.23-3.21 Ga ervaar, asook 'n hoof 830-875 ° C, 6.5-7.6 kbar anatektiese gebeurtenis by 3.11-3.07 Ga. Intermediêre en jonger hoë-temperatuur gebeure was ook by 3.18 Ga, 3.16 Ga en 2.99 Ga geregistreer. Die metamorfose van die gebied stem ooreen met die samesmelting van die oos Kaapvaal Kraton domein deur subduksie en aanwas van mikro-kontinente by 3.23 Ga, insluitend die Barberton en AGC terreine, asook diskrete episodes van kors differensiasie en kalium-ryke graniet magmatisme tussen 3.23 en 3.10 Ga. Die derde gebied hou geen rekord van Mesoargeïkum metamorfose nie. In plaas daarvan het dit 'n 830-855 ° C, 4.4-6.4 kbar anatektiese episode by 2.73 Ga ervaar, wat ooreenstem met die vorming van 'n groot kontinentale vloedbasalt provinsie, die 2.71 Ga Ventersdorp Supergroep, en wydverspreide intrakratoniese graniet magmatisme teen die einde van die Neoargeïkum. 'n Moontlike verduideliking vir die kontras in metamorfe rekord in die twee terreine mag wees dat die 2.71 Ga granuliete 'n jonger sedimentêre afsetting verteenwoordig, en dat granuliete van die ouer terrein te restieties gelaat was na aansienlike anateksis in die Mesoargeïkum, om daaropvolgende hoëgraadse gebeure te registreer. Ten slotte, hierdie studie dokumenteer die besonderhede van S-tipe graniet magma produksie en ontginning van 'n tipiese metasedimentêre bron. Die 2.73 Ga granuliete word gebruik as 'n natuurlike veld laboratorium om die selektiewe optel-en-meevoering van peritektiese granaat tot die magma te ondersoek. Die werk toon die evolusie van peritektiese granate in sulke magmas aan, en ondersteun lewering van relatiewe mafiese graniet magmas deur 'n ‘peritektiese fase optel-en-meevoerings’ proses.

A Nappe Lima Duarte está situada no sudeste do Orógeno Brasília. É constituída por paragnaisses migmatíticos com granada, sillimanita, biotita e muscovita, e ortoquartzitos grossos, com intercalações esparsas de gnaisses calciossilicáticos e de anfibolitos. O Complexo Mantiqueira, infraestrutura alóctone da nappe, ocorre na forma de lascas tectonicamente imbricadas na mesma. É constituído por ortognaisses migmatíticos e polimetamórficos, tipo TTG, com intercalações de rochas metabásicas granulíticas, na forma de enclaves máficos alongados e boudins, geralmente concordantes com a foliação principal. Também ocorrem rochas charnockíticas aparentemente intrusivas nos ortognaisses Mantiqueira, com rochas metabásicas associadas. A associação mineral observada nos paragnaisses (Grt + Bt + Sil + Pl + Rt +Ilm + Qtz ± Ms ± Kfs ± Ky) é relacionada a um metamorfismo progressivo de fácies anfibolito superior, caracterizado por reações de quebra de muscovita e geração de feldspato potássico. As condições de pico bárico obtidas no THERMOCALC para a associação com cianita são de 10 ± 0.6 kbar, a 807 ± 25ºC. O pico térmico de 827 ± 44ºC a 8.2 ± 1.8 kbar, no limite da curva de quebra da dumortierita, foi obtido no THERMOCALC com a associação mineral envolvendo sillimanita. As rochas metabásicas inseridas nos ortognaisses do Complexo Mantiqueira e rochas charnockíticas associadas apresentam a associação Grt-Cpx-Pl-Qtz±Opx+Hbl, que é diagnóstica do fácies granulito de alta pressão. São caracterizadas pela presença de texturas coroníticas progressivas de Grt-Cpx-Pl-Qtz nos contatos entre Opx, Pl e/ou opacos, aparentemente de origem ígnea, que marca a passagem do campo dos granulitos de pressão intermediária para o campo dos granulitos de alta pressão. As condições de pico registradas nos veios constituídos por Grt-Cpx-Pl nos metagabronoritos é de 831.8ºC, a 10 kbar. O granada granulito registra o pico metamórfico a 890 ± 41ºC, a 9.26 ± 1.93 kbar. Cálculos realizados no TWEEQU forneceram condições de equilíbrio de 801ºC, a 9.6 kbar para a associação de fácies granulito. As condições de pico bárico nas rochas charnockíticas são de 14.36 ± 1.9 kbar, a 680ºC, enquanto que as temperaturas máximas registradas são de 885.17ºC, a 10 kbar. Cálculos realizados no THERMOCALC forneceram temperatura de 771 ± 166ºC, a 11.8 ± 2.4 kbar. As rochas metabásicas relacionadas ao Complexo Mantiqueira apresentam baixas concentrações de elementos LILE, possivelmente devido ao empobrecimento destes elementos durante o metamorfismo através de perdas por reações de desidratação. Os dados geoquímicos apontam fontes do tipo E-MORB para grande parte das rochas metabásicas, embora sempre com enriquecimento em ETR maior, o que é sugestivo de fontes enriquecidas. O Grt-cpx anfibolito simplectítico apresenta assinaturas geoquímicas distintas, com enriquecimento maior em elementos LILE e ETRL, o que sugere uma origem a partir de fontes OIB. Os padrões de ETR e diagramas de variação multi-elementares de elementos traço sugerem que as rochas charnockíticas têm fontes relacionadas à ambientes de arco vulcânico. Os paragnaisses, em fácies anfibolito superior a granulito, registram uma trajetória inicial horária, descompressiva ao campo da sillimanita. É distinta da trajetória inicial anti-horária exibida pelas rochas metabásicas e charnockíticas, que registram nas coronas de Grt-Cpx-Pl o metamorfismo progressivo de fácies granulito de alta pressão. Sugere-se que esse relativo aumento de pressão tenha sido condicionado pela colocação dos metassedimentos da Nappe Lima Duarte sobre as rochas do Complexo Mantiqueira, porém no mesmo campo de temperatura. Assim, o avanço da nappe metassedimentar pode ter sido responsável pelo soterramento das rochas metabásicas e charnockíticas relacionadas com o Complexo Mantiqueira, o que justifica a pressão mais elevada nestes litotipos. A etapa de exumação foi compartilhada por ambas, o que é evidenciado nas semelhanças de condições metamórficas durante a trajetória de resfriamento quase isobárico, porém com os litotipos do Complexo Mantiqueira em nível crustal mais profundo. / The Lima Duarte Nappe is located in southeastern Brasília Orogen and is composed by migmatitic paragneisses presenting garnet, sillimanite, biotite and muscovite, and coarse-grained orthoquartzites, with few amphibolite and calc-silicate interlayers. The Mantiqueira Complex occurs as tectonic imbricated lenses in the Lima Duarte Nappe, resembling an allochthon structure. It comprises TTG-type migmatitic and polymetamorphic orthogneisses, presenting granulitic metabasic interlayers, as mafic bands and lenses, as well as boudins, which are often concordant with the main foliation. Charnockitic rocks are apparently intrusive in the Mantiqueira orthogneisses, with associated metabasic rocks. The mineral assemblage observed in paragneisses (Grt + Bt + Sil + Pl + Rt + Ilm + Qtz ± Ms ± Kfs ± Ky) is related to an upper amphibolite facies progressive metamorphism characterized by muscovite breakdown reactions producing potassic feldspar. The peak baric conditions obtained in the THERMOCALC processing software for the assemblage involving kyanite are 10 ± 0.6 kbar and 807 ± 25ºC. The thermal peak of 827 ± 44ºC and 8.2 ± 1.8 kbar obtained in THERMOCALC for the assemblage envolving sillimanite, is placed in the boundary of breakdown curve for dumortierite. The metabasic rocks interlayered in Mantiqueira Complex orthogneisses show the Grt-Cpx-Pl-Qtz±Opx+Hbl assemblage, indicating high pressure granulite facies. They are characterized by the presence of Grt-Cpx-Pl progressive coronitic textures between Opx, Pl and/or opaques boundaries, apparently with an igneous origin, which marks the transitions from intermediate pressure granulites field to high pressure granulite field. The peak conditions recorded in Grt-Cpx-Pl veins in metagabbronorites is 831.8ºC, and 10 kbar. The garnet granulite records the metamorphic peak at 890 ± 41ºC, and 9.26 ± 1.93 kbar. Thermobarometric calculations performed at TWEEQU revealed equilibrium conditions at 801ºC, and 9.6 kbar based on granulite facies mineral assemblage. The peak baric conditions achieved by the charnockitic rocks are 14.36 ± 1.9 kbar, and 680ºC, while maximum temperatures recorded are 885.17ºC, and 10 kbar. Thermobarometric calculations performed at THERMOCALC revealed temperatures of 771 ± 166ºC, and 11.8 ± 2.4 kbar. The metabasic rocks related to Mantiqueira Complex show low concentrations of LILE elements, possibly due to the depletion of these elements during metamorphism in dehydrating reactions. Geochemical data point out to E-MORB type sources for the great majority of metabasic rocks, even though with an REE enrichment, suggesting more enriched sources. The symplectitic Grt-Cpx amphibolite show distinct geochemical signatures, characterized by a greater enrichment in LILE and light-REE elements, suggesting an OIB source for their origin. REE patterns and trace element spidergrams suggest that charnockitic rocks sources are related to a volcanic arc tectonic setting. Paragneisses, in upper amphibolite to granulite facies, recorded an initial clockwise path, decompressing to the sillimanite field. It differs from initial counterclockwise path exhibited by the metabasic and charnockitic rocks, which preserves the progressive high pressure granulite facies metamorphism in Grt-Cpx-Pl coronae. This pressure increase is probally related to the metassediments of the Lima Duarte Nappe, that thrusted over the Mantiqueira Complex rocks, although in the same temperature field. The buried character of metabasic and charnockitic rocks may be caused by the thrust of the metassedimentary nappe, justifying the higher pressure found in these lithotypes. The exhumation phase was shared by both of them, which is confirmed in the metamorphic similarities conditions, as they cooled out together in a near isobaric path, although the Mantiqueira Complex lithotypes were in a deeper crustal level.

A Nappe Lima Duarte está situada no sudeste do Orógeno Brasília. É constituída por paragnaisses migmatíticos com granada, sillimanita, biotita e muscovita, e ortoquartzitos grossos, com intercalações esparsas de gnaisses calciossilicáticos e de anfibolitos. O Complexo Mantiqueira, infraestrutura alóctone da nappe, ocorre na forma de lascas tectonicamente imbricadas na mesma. É constituído por ortognaisses migmatíticos e polimetamórficos, tipo TTG, com intercalações de rochas metabásicas granulíticas, na forma de enclaves máficos alongados e boudins, geralmente concordantes com a foliação principal. Também ocorrem rochas charnockíticas aparentemente intrusivas nos ortognaisses Mantiqueira, com rochas metabásicas associadas. A associação mineral observada nos paragnaisses (Grt + Bt + Sil + Pl + Rt +Ilm + Qtz ± Ms ± Kfs ± Ky) é relacionada a um metamorfismo progressivo de fácies anfibolito superior, caracterizado por reações de quebra de muscovita e geração de feldspato potássico. As condições de pico bárico obtidas no THERMOCALC para a associação com cianita são de 10 ± 0.6 kbar, a 807 ± 25ºC. O pico térmico de 827 ± 44ºC a 8.2 ± 1.8 kbar, no limite da curva de quebra da dumortierita, foi obtido no THERMOCALC com a associação mineral envolvendo sillimanita. As rochas metabásicas inseridas nos ortognaisses do Complexo Mantiqueira e rochas charnockíticas associadas apresentam a associação Grt-Cpx-Pl-Qtz±Opx+Hbl, que é diagnóstica do fácies granulito de alta pressão. São caracterizadas pela presença de texturas coroníticas progressivas de Grt-Cpx-Pl-Qtz nos contatos entre Opx, Pl e/ou opacos, aparentemente de origem ígnea, que marca a passagem do campo dos granulitos de pressão intermediária para o campo dos granulitos de alta pressão. As condições de pico registradas nos veios constituídos por Grt-Cpx-Pl nos metagabronoritos é de 831.8ºC, a 10 kbar. O granada granulito registra o pico metamórfico a 890 ± 41ºC, a 9.26 ± 1.93 kbar. Cálculos realizados no TWEEQU forneceram condições de equilíbrio de 801ºC, a 9.6 kbar para a associação de fácies granulito. As condições de pico bárico nas rochas charnockíticas são de 14.36 ± 1.9 kbar, a 680ºC, enquanto que as temperaturas máximas registradas são de 885.17ºC, a 10 kbar. Cálculos realizados no THERMOCALC forneceram temperatura de 771 ± 166ºC, a 11.8 ± 2.4 kbar. As rochas metabásicas relacionadas ao Complexo Mantiqueira apresentam baixas concentrações de elementos LILE, possivelmente devido ao empobrecimento destes elementos durante o metamorfismo através de perdas por reações de desidratação. Os dados geoquímicos apontam fontes do tipo E-MORB para grande parte das rochas metabásicas, embora sempre com enriquecimento em ETR maior, o que é sugestivo de fontes enriquecidas. O Grt-cpx anfibolito simplectítico apresenta assinaturas geoquímicas distintas, com enriquecimento maior em elementos LILE e ETRL, o que sugere uma origem a partir de fontes OIB. Os padrões de ETR e diagramas de variação multi-elementares de elementos traço sugerem que as rochas charnockíticas têm fontes relacionadas à ambientes de arco vulcânico. Os paragnaisses, em fácies anfibolito superior a granulito, registram uma trajetória inicial horária, descompressiva ao campo da sillimanita. É distinta da trajetória inicial anti-horária exibida pelas rochas metabásicas e charnockíticas, que registram nas coronas de Grt-Cpx-Pl o metamorfismo progressivo de fácies granulito de alta pressão. Sugere-se que esse relativo aumento de pressão tenha sido condicionado pela colocação dos metassedimentos da Nappe Lima Duarte sobre as rochas do Complexo Mantiqueira, porém no mesmo campo de temperatura. Assim, o avanço da nappe metassedimentar pode ter sido responsável pelo soterramento das rochas metabásicas e charnockíticas relacionadas com o Complexo Mantiqueira, o que justifica a pressão mais elevada nestes litotipos. A etapa de exumação foi compartilhada por ambas, o que é evidenciado nas semelhanças de condições metamórficas durante a trajetória de resfriamento quase isobárico, porém com os litotipos do Complexo Mantiqueira em nível crustal mais profundo. / The Lima Duarte Nappe is located in southeastern Brasília Orogen and is composed by migmatitic paragneisses presenting garnet, sillimanite, biotite and muscovite, and coarse-grained orthoquartzites, with few amphibolite and calc-silicate interlayers. The Mantiqueira Complex occurs as tectonic imbricated lenses in the Lima Duarte Nappe, resembling an allochthon structure. It comprises TTG-type migmatitic and polymetamorphic orthogneisses, presenting granulitic metabasic interlayers, as mafic bands and lenses, as well as boudins, which are often concordant with the main foliation. Charnockitic rocks are apparently intrusive in the Mantiqueira orthogneisses, with associated metabasic rocks. The mineral assemblage observed in paragneisses (Grt + Bt + Sil + Pl + Rt + Ilm + Qtz ± Ms ± Kfs ± Ky) is related to an upper amphibolite facies progressive metamorphism characterized by muscovite breakdown reactions producing potassic feldspar. The peak baric conditions obtained in the THERMOCALC processing software for the assemblage involving kyanite are 10 ± 0.6 kbar and 807 ± 25ºC. The thermal peak of 827 ± 44ºC and 8.2 ± 1.8 kbar obtained in THERMOCALC for the assemblage envolving sillimanite, is placed in the boundary of breakdown curve for dumortierite. The metabasic rocks interlayered in Mantiqueira Complex orthogneisses show the Grt-Cpx-Pl-Qtz±Opx+Hbl assemblage, indicating high pressure granulite facies. They are characterized by the presence of Grt-Cpx-Pl progressive coronitic textures between Opx, Pl and/or opaques boundaries, apparently with an igneous origin, which marks the transitions from intermediate pressure granulites field to high pressure granulite field. The peak conditions recorded in Grt-Cpx-Pl veins in metagabbronorites is 831.8ºC, and 10 kbar. The garnet granulite records the metamorphic peak at 890 ± 41ºC, and 9.26 ± 1.93 kbar. Thermobarometric calculations performed at TWEEQU revealed equilibrium conditions at 801ºC, and 9.6 kbar based on granulite facies mineral assemblage. The peak baric conditions achieved by the charnockitic rocks are 14.36 ± 1.9 kbar, and 680ºC, while maximum temperatures recorded are 885.17ºC, and 10 kbar. Thermobarometric calculations performed at THERMOCALC revealed temperatures of 771 ± 166ºC, and 11.8 ± 2.4 kbar. The metabasic rocks related to Mantiqueira Complex show low concentrations of LILE elements, possibly due to the depletion of these elements during metamorphism in dehydrating reactions. Geochemical data point out to E-MORB type sources for the great majority of metabasic rocks, even though with an REE enrichment, suggesting more enriched sources. The symplectitic Grt-Cpx amphibolite show distinct geochemical signatures, characterized by a greater enrichment in LILE and light-REE elements, suggesting an OIB source for their origin. REE patterns and trace element spidergrams suggest that charnockitic rocks sources are related to a volcanic arc tectonic setting. Paragneisses, in upper amphibolite to granulite facies, recorded an initial clockwise path, decompressing to the sillimanite field. It differs from initial counterclockwise path exhibited by the metabasic and charnockitic rocks, which preserves the progressive high pressure granulite facies metamorphism in Grt-Cpx-Pl coronae. This pressure increase is probally related to the metassediments of the Lima Duarte Nappe, that thrusted over the Mantiqueira Complex rocks, although in the same temperature field. The buried character of metabasic and charnockitic rocks may be caused by the thrust of the metassedimentary nappe, justifying the higher pressure found in these lithotypes. The exhumation phase was shared by both of them, which is confirmed in the metamorphic similarities conditions, as they cooled out together in a near isobaric path, although the Mantiqueira Complex lithotypes were in a deeper crustal level.

<p> The Whitestone Anorthosite is a relatively small anorthosite body (160 km2 ) located within the Parry Sound structural domain, Western Grenville Province, Ontario. Both the anorthosite and the surrounding gneisses have been affected by a granulite grade metamorphic event which predates the Grenville Orogeny. The outer margin of the anorthosite body has been strongly deformed and recrystallized and is characterized by a pervasive metasomatic alteration consisting of garnet, scapolite, hornblende, apatite, biotite, sphene, carbonate and opaques. The country rock gneisses exhibit a corresponding discontinuous, and highly variable, reaction aureole. Pre-existing mafic gneisses are particularily affected, being characterized by the breakdown of orthopyroxene and hornblende, an increase in garnet, clinopyroxene, apatite and opaques, and enrichment in Fe, Ti and P. </p> <p> The metasomatic alteration exhibited by the Whitestone Anorthosite is thought to be due to a combination of two processes: 1. Mechanical mixing at the anorthosite/country rock contact during intense deformation (tectonic assimilation), and 2. Widespread absorption of mobile components (predominantly volatiles) from both included material and the surrounding gneisses. </p> <p>The formation of the country rock reaction aureole is a continuous solid state metamorphic process, whereby mobile components are preferentially leached from the rock leaving a mafic restite. Post-deformation cooling of the anorthosite, combined with an increased volatile flux, has imparted a polygonal mosaic texture suggestive of contact metamorphism. The typical garnet-clinopyroxene assemblage exhibited by mafic gneisses within the reaction aureole, is a consequence of the increased Fe/Mg ratio which stabilizes this assemblage at lower P, T conditions. The temperature of final equilibration and recrystallization is estimated to be 750 ± 70 °C, based on clinopyroxene-garnet geotherrnometry. </p> <p> A similar metasomatic interaction, to the one outlined in this thesis, is to be expected at all anorthosite/country rock contacts which have been overprinted by granulite metamorphism. </p> / Thesis / Master of Science (MSc)

Deformation and partial melting have long been recognized to occur together, but differentiating which actually occurred first has remained enigmatic. Prevailing theories suggest that partial melting typically occurs first, and deformation is localized into melt-rich areas because they are rheologically weak. However, evidence from three different areas, suggests the role of strain has been underestimated in localizing partial melting. The Wet Mountains of central Colorado provide evidence for synchronous partial melting and deformation, with each process enhancing the other. Throughout the Wet Mountains, deformation is concentrated in areas where melt producing reactions occurred, and melt appears to be localized along deformation-related features. Melt microstructures present within the Wet Mountains correlate well with crustal-scale plutons and magmatic bodies and provide a proxy for crustal-scale melt flow. Granitic gneisses from the Llano Uplift, central Texas, provide evidence for partial melting occurring within small-scale shear zones and surrounding country rocks, synchronously. In the field, shear zones appear to contain former melt, whereas the country rock does not provide macroscopic evidence for partial melting. However, detailed microstructural investigation of shear zones and country rocks indicates the same density of melt microstructures, in both rock types. Melt microstructures are important for understanding the full melting history of a rock and without detailed structural and petrographic analysis, erroneous conclusions may be reached. Granulite-facies migmatites of the Albany-Fraser Orogen, southwestern Australia, have undergone partial melting, synchronous with three phases of bidirectional extension. Four major groups of leucosomes, including: foliation-parallel, cross-cutting, boudin neck and jumbled channelway leucosomes and late pegmatites were analyzed via whole-rock geochemistry, and there is evidence for fluid-saturated and -undersaturated biotite- and amphibole-dehydration melting. Migmatites from these three locations contain pseudomorphs of melt along subgrain and grain boundaries, areas of high dislocation density, in quartz and plagioclase. For these rocks that involve multicomponent systems, the primary cause for preferential melting in high strain locations is enhanced diffusion rates along the subgrain boundary because of pipe diffusion or water associated with dislocations. / text