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.

This thesis focuses on mineralogy, geochemistry, and origin of eight pegmatites and two spatially associated granites of Late Archean and Paleoproterozoic ages located in Marquette and Dickinson Counties, Michigan. Biotite geochemistry reveals that both granites and all pegmatites are peraluminous and have an orogenic signature. However, bulk composition reveals the Humboldt granite is a peraluminous A-type granite and the Bell Creek granite is a peraluminous mix between I-, S-, and A-type granites. The Republic Mine pegmatite appears to be geochemically similar to the Bell Creek granite and Grizzly pegmatite. The Crockley pegmatite is genetically related to the Humboldt granite. The Groveland Mine, Sturgeon River, and Hwy69 pegmatites appear to be a product of the Peavy Pond Complex being contaminated with the Marquette Range Super Group. Contamination and anatexis have made classification of the granites and pegmatites problematic. The Grizzly should be classified as a primitive LCT-type even though this pegmatite lacks characteristic enrichment associated with LCT pegmatites. Mineralogical geochemistry reveals that the Republic Mine is relatively more primitive than other pegmatites and should be classified as a primitive Mixed-type pegmatite. Groveland Mine has mineralogy and geochemistry not normally associated with NYF-type pegmatites and should be classified as Mixed. The Crockley pegmatite should be classified as NYF-type with a primitive LCT overprint. Dolfin, Hwy69, Sturgeon River, and Black River pegmatites should be classified as Rare Element, REE, NYF-type, although the Black River has slight tantalum enrichment expressed in columbite group minerals.

Ce travail imposant concerne : - l'historique des idées sur ce massif - l'étude stratigraphique très détaillée des formations géologiques - une approche du métamorphisme alpin - des données d'interprétation tectonique . "Le pays de Vanoise est un lieu de transition, une charniére privilégiée. En première analyse on y voit la zone du Briançonnais ( ou plutôt son prolongement un peu plus interne) devenir progressivement métamorphique , sous les lambeaux de la nappe des schistes lustrés."

L'évolution du flux de matière, de l'architecture et de la rhéologie d'un prisme d'accrétion orogénique au cours du temps est abordée à l'aide d'une étude géologique multiméthode. Le dôme d'Orlica-Śnieżnik dans les Sudètes est situé au front d'un butoir rigide. La formation de ce dôme est expliquée par l'influx de croûte continentale felsique issue de la marge passive subductée jusqu'à 50-60km de profondeur dans un prisme d'accrétion d'échelle crustale. La racine ainsi formée comprend une croûte inférieure felsique avec quelques lentilles basiques partiellement fondues en profondeur et séparées de la croûte moyenne (metasédiments, metavolcanites) par une couche rigide d'orthogneiss peu déformée. Cette infrastructure rhéologiquement hétérogène résultant du remplissage du prisme est fortement remaniée au front du butoir par des plissements plurikilométriques de longueurs d'onde variables. Ceux-ci permettent des échanges verticaux aboutissant à l'exhumation des différents niveaux crustaux de l'infrastructure. La croissance du dôme par plissement au front du butoir s'achève par le décoiffement de la suprastructure associé à un amincissement ductile localisé et à un remplissage des bassins syn-orogéniques adjacents. Cette étude montre bien la formation et l'évolution conjuguée des différents niveaux crustaux en particulier lors de l'enfouissement le long de la zone de subduction au sein du prisme. Ici, la déformation dans les orthogneiss est très localisée et permet le transport passif de larges portions de roches peu déformées et rigides. Ceci est expliqué par un changement dans le mécanisme de recristallisation des roches quartzo feldspathiques d'un fluage- dislocation intense vers un glissement aux joints de grains. Ce changement est initié par la croissance de phases interstitielles dans les agrégats monominéraux. Ce type d'évolution dans un gradient prograde éclogitique est aussi observé dans les migmatites formant le cœur des anticlinaux proches du butoir. Ils permettent l'adoucissement rhéologique nécessaire au fluage dans le prisme d'accrétion crustal.

La chaine de Belledonne est l'un des massifs cristallins,comme le Mont Blanc, l'Aar-Gothard au Nord-Est, les grandes Rousses , les Ecrins-Pelvoux, l'Argentera-Mercantour au Sud-Est. Ces massifs sont cernés de terrains sédimentaires vis à vis desquels ils jouent le rôle de socle . Ces massifs cristallins externes montrent une évolution très complexe au niveau stratigraphique et structural . Cette présente étude porte sur un petit secteur et contribue à la compréhension de la géologie du massif de Belledonne.

The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded domes with ~2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites exhumed in an Oligocene-Miocene arc-continent collision and subduction zone subject to Late Miocene to Recent continental extension. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, a grid of 1,518 km of 2-D multi-channel seismic (MCS) reflection data and well data is interpreted from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. The offshore study is combined with onshore geologic information to constrain the area's Oligocene to Recent basinal and tectonic evolution. MCS and well data show the Trobriand basin formed as a forearc basin caused by southward Miocene subduction at the Trobriand trench. Late Miocene basin inversion uplifted the southern and northern basin margins. Subduction slowed at ~8 Ma as the margin transitioned to an extensional tectonic environment. Since then, the Trobriand basin has subsided 1-2.5 km as a broad sag basin with few normal faults deforming the basin fill. South of the DEI, the Goodenough rift basin developed after extension began (~8 Ma) as the hanging-wall of the north-dipping Owen-Stanley normal fault bounding the southern margin of the basin. Rapid uplift of the adjacent footwall of the Owen-Stanley fault zone in the Papuan Peninsula accompanied the formation of the Goodenough submarine rift basin. The lack of upper crustal extension accompanying subsidence in the Trobriand and Goodenough basins suggests depth-dependent lithospheric extension from 8-0 Ma has accompanied uplift of the DEI gneiss domes. Structural reconstructions of seismic profiles show 2.3 to 13.4 km of basin extension in the upper crust, while syn-rift basin subsidence values indicate at least 20.7 to 23.6 km of extension occurred in the lower crust since ~8 Ma. Results indicating thinning is preferentially accommodated in the lower crust surrounding the DEI are used to constrain a schematic model of uplift of the DEI domes involving vertical exhumation of buoyant, post-orogenic lower crust, far-field extension from slab rollback, and an inverted two-layer crustal density structure. / text

[pt] A presente pesquisa trata da avaliação da resistência ao arrancamento de grampos em solo residual de gnaisse. Foram realizados ensaios de arrancamento em uma obra de solo grampeado executada em um maciço de solo residual de gnaisse. A resistência ao arrancamento foi avaliada em 4 cotas diferentes ao longo do perfil de escavação. Foram realizados 8 ensaios de arrancamento em grampos de 4m de comprimento. Quatro ensaios foram executados em grampos instrumentados com strain-gages, para avaliar a distribuição das cargas de tração durante os estágios de carregamento. Foram também realizados ensaios de cisalhamento direto no solo e na interface solo/cimento para avaliação das propriedades mecânicas destes materiais. Amostras indeformadas foram coletadas imediatamente à frente dos furos de instalação dos grampos ensaiados garantindo uma maior representatividade dos materiais. Uma relação semi-empírica é proposta para se avaliar a resistência do solo e da interface solo/nata de cimento, obtidos em ensaios de cisalhamento direto no laboratório. Os resultados obtidos nesta pesquisa são comparados com ensaios realizados por outros autores, em encostas de solos residuais de gnaisse e empregados para validação da relação desenvolvida. / [en] The present research presents an evaluation of the pullout resistance of nails in residual gneissic soil. Pullout tests were carried out in 4 different levels of the nailed wall with nails 4m long. Four tests were carried out in strain-gauged nails for evaluating the tension distribuition along the nail. A series of direct shear tests in soil specimens and in the soil/grout interface were also performed for obtaining the mechanical properties of these materials. Undisturbed samples had been collected very close to the pull-out test locations. A semi-empirical relation is proposed for evaluating the pullout resistance of nails, based on the shear strenghth parameters of the soil and of the soil/grout interface from laboratory direct shear tests.

No description available.

[pt] Ao longo das últimas décadas, a cidade do Rio de Janeiro vem sofrendo com vários eventos de queda de blocos de rochas que não podem ser relacionados a quaisquer fatores desencadeantes evidentes, como temporadas de chuva ou eventos sismicos. Assim, outros possíveis fenômenos iniciais ou causas foram avaliados e as variações térmicas naturais parecem ser um dos fatores desencadeantes que contribuem para esses eventos. O mecanismo associado à flutuação diária de temperatura é capaz de gerar deslocamentos irreversíveis, sendo um fator preparatório para as quedas de rochas. Em maciços rochosos fraturados, os blocos de rochas se expandem, empurram outros blocos em sua volta, se contraem, podendo ou não voltar para sua posição de origem, gerando movimentos cíclicos. O proposito principal deste trabalho é estudar o comportamento mecânico e hidráulico de descontinuidades de rochas gnáissicas sob carregamento cíclico cisalhante pré-pico para diferentes tipos de JRC (Joint Roughness Coefficient), variações da tensão normal entre 100 e 1000 kPa e da frequência entre 0,1 e 0,01 Hz, garantindo uma velocidade quase estática, simulando as condições de temperatura no campo. Foi possível verificar que o comportamento dos deslocamentos irreversíveis das amostras ensaiadas foi influenciado pela tensão cisalhante de pré-pico para tensões normais e frequências baixas e para tensões normais altas o deslocamento foi constante e quase estático, diminuindo pouco a resistência ao cisalhamento em 2000 ciclos e gerando níveis de deslocamentos irreversíveis bem mais baixos. / [en] Over the last few decades, the city of Rio de Janeiro has been suffering from several rockfall events that cannot be related to any obvious triggering factors such as rainy seasons or earthquakes. Thus, other possible initial phenomena or causes were evaluated and natural thermal variations seem to be one of the triggering factors that contribute to these events. The mechanism associated with the daily fluctuation of temperature is capable of generating irreversible displacements, being a preparatory factor for rockfalls. In fractured rock mass, rock blocks expand, push other blocks around them, contract, and may or may not return to their original position, generating cyclical movements. The main purpose of this work is to study the mechanical and hydraulic behavior of gneiss rock discontinuities under pre-peak cyclic shear loading for different types of JRC (Joint Roughness Coefficient), normal stress variations between 100 and 1000 kPa and frequency variations between 0.1 and 0.01 Hz, ensuring an almost static speed, simulating the temperature conditions in the field. It was possible to verify that the behavior of the irreversible displacements of the tested samples was influenced by the pre-peak cyclic shear for normal stresses and low frequencies and for high normal stresses the displacement was constant and almost static, decreasing the shear strength in 2000 cycles and generating much lower levels of irreversible displacements.

The Tjeliken Mountain in northern Jämtland, central Scandinavian Caledonides is by most authors considered to belong to the Lower Seve Nappe Complex (SNC). However, recently P-T conditions similar to the Middle Seve have been constrained for the eclogite at the top of the mountain, revitalizing the tectonic debate about Tjeliken. Also the timing of high-pressure metamorphism is debated. Two earlier studies of the eclogite yield ages between 464 Ma and 446 Ma. This study focuses on the garnet-phengite gneiss hosting the eclogite. By construction of P-T conditions and dating the two discrepancies above are investigated. U/Pb zircon dating by secondary ion mass spectrometry technique (SIMS) targeted on metamorphic rims yield a concordia age of 460.2 ± 2.7 Ma corresponding well to earlier c. 463.7 ± 8.9 Ma Sm/Nd dating of the eclogite. The inferred peak mineral assemblage of the gneiss is garnet + phengite + quartz + K-feldspar + titanite ± H2O. Thermodynamic modelling reveal that garnet cores equilibrated within 1.9 - 2.6 GPa and 600 - 700 oC. Fe2+-Mg garnet-phengite thermometry involving garnet rims yields temperatures of c. 650 - 715 oC revealing relatively similar temperatures during growth of garnet core and rim, respectively. Garnet chemistry is characterised by oscillatory zoning with an antithetic pattern of Ca and Fe. The former decreases from core to rim, whereas the latter increases. The opposite trend is observed in epidote-group minerals suggesting exchange between the two minerals during garnet growth. Skeletal textures and atoll textures together with observed chemical pattern may indicate multiple garnet growth episodes. The results of the study points toward similar P-T history of the Tjeliken eclogite and gneiss in favour of the interpretation of considering the whole Tjeliken to belong to the Lower Seve. The obtained U/Pb age support other age constraints in the area suggesting high-pressure metamorphism at c. 460 Ma related to a subduction event affecting the central Scandinavian Caledonides at c. 460 - 450 Ma. / Den skandinaviska fjällkedjan, vetenskapligt benämnd de skandinaviska Kaledoniderna, har bildats på samma sätt som Himalaya och har därför liknande uppbyggnad. Från början tros fjällen ha varit av samma storlek som Himalayas berg. Deras ålder på cirka 400 miljoner år gör dock att miljontals års påverkan från vatten och vind har eroderat ner dem till dagens betydligt lägre fjäll. Den bergsyta vi ser idag utgör därför vad som från början var fjällkedjans kärna. Därför utgör de skandinaviska Kaledoniderna en unik möjlighet att studera en bergskedjas inre, vilket kan ge viktig information om bergkedjebildande processer.Forskning har visat att fjällkedjan bildades då Japetushavet mellan kontinenterna Baltika och Laurentia stängdes. Detta resulterade till slut i en kollision mellan de två kontinenterna där stora flak (skollor) av mellanliggande havsbotten och kontinentalskorpa transporterades hundratals kilometer upp på Baltika. Skollorna utgör idag våra fjäll. Känt är också att innan kontinentalkollisionen så kolliderade Baltika med öar i havet, varvid dess kontinentalkant pressades djupt ner under jordskorpan, ända ner i manteln. Bevis för detta återfinns idag i Sevesskollan ibland annat de jämtländska fjällen i form av högtrycksbergarter. Dessa har bildats under de höga tryck och temperaturer som råder på stora djup i jordens inre. Genom att studera högtrycksbergarter kan man förstå fjällkedjans bildande. Fjället Tjeliken i norra Jämtland är en av de idag kända fyndplatserna av högtrycksbergarter. Dess topp består av bergarten eklogit och dess lägre delar av gnejs, samt kvarts. Tidigare studier av eklogiten visar att den har bildats vid tryck och temperatur på cirka 2.6 GPa och 700 °C, vilket motsvarar att den varit nedpressad cirka 80 km under jordytan. Den exakta tidpunkten då detta skedde har inte kunnat fastställas då olika dateringsmetoder gett olika resultat mellan cirka 464 till 446 miljoner år sedan. I denna studie studeras tryck- och temperaturförhållanden för gnejsen som jämförelse till eklogiten, för att kunna fastställa om de båda bergarterna har genomgått samma bildningsprocesser. En ny datering genomförs också för att bättre kunna fastställa tidpunkten för högtrycksfasen.Datering baserat på radioaktivt sönderfall av uran till bly i mineralet zirkon visar att högtrycksfasen inträffade för cirka 460 miljoner år sedan. Modellering baserat på termodynamiska principer visar att kärnorna i mineralet granat bildades inom tryck- och temperaturområdet 1.9–2.6 GPa och c. 680-700 °C. En komplex kemisk zonering av granaterna indikerar att de möjligen bildades under flera tillväxtfaser, vilka inom ramen för denna studie inte kunnat modelleras, då mer avancerade metoder krävs. Denna studie visar dock att eklogiten och gnejsen sannolikt delar en gemensam tryck- och temperaturhistoria, vilken är relaterad till den djupa nedpressningen av Baltikas kontinentalkant under sen ordovicium. Dateringen stödjer även övriga åldersdateringar i området av högtrycksfasen.