Unrecognized metamorphic complexities can produce erroneous interpretations when using equilibrium thermodynamics and isotope geochronology. Universally employed methods for determining pressure-temperature conditions during regional metamorphism are based on the assumption of chemical equilibrium, and geochronology in metamorphic rocks can suffer from cryptic redistribution of isotopes. In this research, the scales of disequilibrium in regionally metamorphosed rocks and the effects of garnet resorption on Lu-Hf garnet ages were examined through numerical simulations of these processes. Concerning scales of disequilibrium, thirteen porphyroblastic datasets, previously measured using X-ray computed tomography, were examined by numerically simulating diffusion-controlled nucleation and growth of garnet while tracking chemical potential gradients to determine reaction affinity Ar (-[Delta]rG). Maximum nucleation rates are 10⁻¹³̇⁶-10⁻⁹̇⁸ nuclei cm⁻³ s⁻¹, interfacial energies are 0.004-0.14 J m⁻² assuming shape factors of 0.1-1.0, and Al intergranular diffusion (QD = 140 kJ/mol⁻¹) is 10⁻¹⁴̇⁴-10⁻¹¹̇¹ m² s⁻¹ at 600 °C. Limitations in determining crystallization kinetics arise from difficulties in constraining rock-specific properties (e.g., porosity and Al solubility). Ar at the time and location of nucleation is 0.4-5.9 kJ/mol⁻¹ of 12-oxygen garnet ([Delta]T = 4.0-62.0 °C) for the earliest nuclei, and 5.3-29.0 kJ/mol⁻¹ ([Delta]T = 50-125 °C) for nucleation at maximum Ar. The results demonstrate potential for delayed nucleation and metastability that can generate spurious interpretations. The timing of metamorphic events is also critical for understanding geologic history. In the Makhavinekh Lake Pluton aureole, Labrador, garnet resorption caused redistribution of Lu and loss of Hf from consumed rims, creating spuriously young ages. Garnet-ilmenite Lu-Hf geochronology using bulk separates yields apparent ages that young toward the contact from 1876 ± 21 Ma (4025 m) to 1396 ± 8 Ma (450 m). Toward the contact, garnet crystals are progressively more resorbed. Numerical modeling was used to test retention of Lu and loss of Hf during resorption as the dominant control on age. More resorption and Lu retention produce younger apparent ages (false ages). Application of the model to the aureole yields model ages from 1850 Ma to 1374 Ma, younging toward the contact. Thus, Lu-Hf geochronology applied to resorbed garnets requires careful examination of Lu zoning. / text

Ce travail de thèse présente des analyses isotopiques Lu-Hf par MC-ICP-MS combinées de zircons ignés et de roches totales d'une importante collection de granitoïdes archéens appartenant à la suite des Tonalite-Trondhjémite-Granodiorite (TTG) afin d'apporter un regard nouveau sur la croissance de la croûte continentale et tout particulièrement dans le début de l'histoire de la Terre. Nos données indiquent un bon accord général entre les zircons ignés, mesurés par ablation-laser et par solution, avec leurs roche-hôtes. Nous démontrons que le rapport Lu/Hf intégré dans le temps de la source mantellique des TTG est près de la valeur chondritique et n'a pas significativement changée au cours des 4 derniers milliards d'années. Par conséquent, les continents se sont formés à partir d'un matériel primitif non fractionné extrait du manteau profond par l'intermédiaire de panaches qui après fusion partielle ont laissés un résidu appauvri dans le manteau supérieur. Les cristaux de zircon extraits des TTG ont des compositions isotopiques en Hf cohérentes au sein d'une même population alors que le système U-Pb, dans les mêmes grains, est souvent perturbé résultant ainsi en l'obtention de valeurs d'εHf initial erronées. Ce problème est endémique aux cristaux de zircon détritiques archéens et en accord avec des résultats expérimentaux sur la mobilité préférentielle de l'Hf en fonction de celle de l'U et du Pb au sein du zircon. Nous suggérons que ce problème biaise l'enregistrement détritique archéen en faveur de valeurs d'εHf initial négatives qui contrastent avec les valeurs obtenues pour les TTG mais peuvent être expliquées par l'utilisation d'âges 207Pb/206Pb non-magmatiques. Si l'on considère les cristaux de zircon de Jack Hills au vu de ces résultats, la source des continents serait restée inchangée depuis 4,3 Ga.

O Granito Chasqueiro aflora como campos de matacões e lajeados que em planta formam um corpo alongado segundo N50o E com área de aproximadamente 400 km2 localizada no sul da porção oriental do Escudo Sul-Rio-Grandense. Constitui-se de monzo a sienogranito, leucocrático de cor cinza-claro e textura porfirítica com megacristais de K-feldspatos em matriz equigranular, hipidiomórfica grossa, composta por quartzo, K-feldspato, plagioclásio, biotita, hornblenda, opacos (magnetita, hematita) e acessórios (zircão, titanita, apatita e alanita). Os megacristais atingem proporções modais entre 30 a 60 % e variam entre 4 e 8 cm que junto com os minerais máficos da matriz evidenciam uma foliação de fluxo magmático subvertical bem desenvolvida que transaciona lateralmente para uma foliação tectônica nos bordos do granito próximo as zonas de cisalhamento onde ocorrem extensas faixas marcadas por intensa deformação dúctil e geração de protomilonitos. O granito apresenta enclaves máficos microgranulares de composição diorítica apresentando diferentes formas e tamanhos. Geoquimicamente é caracterizado por um magmatismo subalcalino do tipo cálcio-alcalino alto potássio, metaluminoso a levemente peraluminoso, com assinatura característica de granitos gerados em ambiente póscolisional. Processos de fusão crustal, mistura de magmas e cristalização fracionada são sugeridos para a sua evolução. Análises geocronológicas obtidas pelo método UPb (LA-ICPMS) e geoquímica isotópica de Lu-Hf (LA-ICPMS) em zircões do granito indicaram, respectivamente, idade de cristalização 574 ± 3 Ma e valores negativos para εHf sugerindo assim uma relação do granito com o evento deformacional D2 e fontes magmáticas dominantemente crustais com participação de componente mantélico subordinado. / Chaqueiro Granite emerges as boulders fields and slabs that in plant form an elongated body at N50o E with an area of approximately 400 km2 located at the southernmost portion of the eastern Sul-Rio-Grandense Shield, RS. It consists of monzo the syenogranite, light gray and leucocratic porphyritic texture with megacrystals K-feldspar in a coarse equigranular hypidiomorphic matrix, composed of quartz, K-feldspar, plagioclase, biotite, hornblende, opaque minerals and accessories. The modal megacrystals reach proportions between 30 and 60 % and range from 4 and 8 cm together with mafic minerals of the matrix showing a subvertical magmatic foliation and a tectonic foliation prominent in the borders marked by intense ductile deformation and protomylonite generation. Another important aspect of the Chasqueiro Granite is the presence of microgranular mafic enclaves of dioritic composition ubiquitous in the granite, having different shapes and sizes. Geochemically the granite is characterized as a slightly expanded acid sequence formed by a sub-alkaline magmatism of calc-alkaline type with high potassium, metaluminous to lightly peraluminous, with characteristic signature of granites generated in post-collisional tectonic setting. Geochronological analyzes obtained by the U-Pb method (LA-ICPMS) and isotope geochemistry of Lu-Hf (LA-ICPMS) in zircons presenting, respectively, crystallization age 574 ± 3 Ma and negative εHf which suggest a granite relationship with deformational event D2 and supporting a magmatic crustal sources with subordinate mantle component.

O Granito Chasqueiro aflora como campos de matacões e lajeados que em planta formam um corpo alongado segundo N50o E com área de aproximadamente 400 km2 localizada no sul da porção oriental do Escudo Sul-Rio-Grandense. Constitui-se de monzo a sienogranito, leucocrático de cor cinza-claro e textura porfirítica com megacristais de K-feldspatos em matriz equigranular, hipidiomórfica grossa, composta por quartzo, K-feldspato, plagioclásio, biotita, hornblenda, opacos (magnetita, hematita) e acessórios (zircão, titanita, apatita e alanita). Os megacristais atingem proporções modais entre 30 a 60 % e variam entre 4 e 8 cm que junto com os minerais máficos da matriz evidenciam uma foliação de fluxo magmático subvertical bem desenvolvida que transaciona lateralmente para uma foliação tectônica nos bordos do granito próximo as zonas de cisalhamento onde ocorrem extensas faixas marcadas por intensa deformação dúctil e geração de protomilonitos. O granito apresenta enclaves máficos microgranulares de composição diorítica apresentando diferentes formas e tamanhos. Geoquimicamente é caracterizado por um magmatismo subalcalino do tipo cálcio-alcalino alto potássio, metaluminoso a levemente peraluminoso, com assinatura característica de granitos gerados em ambiente póscolisional. Processos de fusão crustal, mistura de magmas e cristalização fracionada são sugeridos para a sua evolução. Análises geocronológicas obtidas pelo método UPb (LA-ICPMS) e geoquímica isotópica de Lu-Hf (LA-ICPMS) em zircões do granito indicaram, respectivamente, idade de cristalização 574 ± 3 Ma e valores negativos para εHf sugerindo assim uma relação do granito com o evento deformacional D2 e fontes magmáticas dominantemente crustais com participação de componente mantélico subordinado. / Chaqueiro Granite emerges as boulders fields and slabs that in plant form an elongated body at N50o E with an area of approximately 400 km2 located at the southernmost portion of the eastern Sul-Rio-Grandense Shield, RS. It consists of monzo the syenogranite, light gray and leucocratic porphyritic texture with megacrystals K-feldspar in a coarse equigranular hypidiomorphic matrix, composed of quartz, K-feldspar, plagioclase, biotite, hornblende, opaque minerals and accessories. The modal megacrystals reach proportions between 30 and 60 % and range from 4 and 8 cm together with mafic minerals of the matrix showing a subvertical magmatic foliation and a tectonic foliation prominent in the borders marked by intense ductile deformation and protomylonite generation. Another important aspect of the Chasqueiro Granite is the presence of microgranular mafic enclaves of dioritic composition ubiquitous in the granite, having different shapes and sizes. Geochemically the granite is characterized as a slightly expanded acid sequence formed by a sub-alkaline magmatism of calc-alkaline type with high potassium, metaluminous to lightly peraluminous, with characteristic signature of granites generated in post-collisional tectonic setting. Geochronological analyzes obtained by the U-Pb method (LA-ICPMS) and isotope geochemistry of Lu-Hf (LA-ICPMS) in zircons presenting, respectively, crystallization age 574 ± 3 Ma and negative εHf which suggest a granite relationship with deformational event D2 and supporting a magmatic crustal sources with subordinate mantle component.

O Granito Chasqueiro aflora como campos de matacões e lajeados que em planta formam um corpo alongado segundo N50o E com área de aproximadamente 400 km2 localizada no sul da porção oriental do Escudo Sul-Rio-Grandense. Constitui-se de monzo a sienogranito, leucocrático de cor cinza-claro e textura porfirítica com megacristais de K-feldspatos em matriz equigranular, hipidiomórfica grossa, composta por quartzo, K-feldspato, plagioclásio, biotita, hornblenda, opacos (magnetita, hematita) e acessórios (zircão, titanita, apatita e alanita). Os megacristais atingem proporções modais entre 30 a 60 % e variam entre 4 e 8 cm que junto com os minerais máficos da matriz evidenciam uma foliação de fluxo magmático subvertical bem desenvolvida que transaciona lateralmente para uma foliação tectônica nos bordos do granito próximo as zonas de cisalhamento onde ocorrem extensas faixas marcadas por intensa deformação dúctil e geração de protomilonitos. O granito apresenta enclaves máficos microgranulares de composição diorítica apresentando diferentes formas e tamanhos. Geoquimicamente é caracterizado por um magmatismo subalcalino do tipo cálcio-alcalino alto potássio, metaluminoso a levemente peraluminoso, com assinatura característica de granitos gerados em ambiente póscolisional. Processos de fusão crustal, mistura de magmas e cristalização fracionada são sugeridos para a sua evolução. Análises geocronológicas obtidas pelo método UPb (LA-ICPMS) e geoquímica isotópica de Lu-Hf (LA-ICPMS) em zircões do granito indicaram, respectivamente, idade de cristalização 574 ± 3 Ma e valores negativos para εHf sugerindo assim uma relação do granito com o evento deformacional D2 e fontes magmáticas dominantemente crustais com participação de componente mantélico subordinado. / Chaqueiro Granite emerges as boulders fields and slabs that in plant form an elongated body at N50o E with an area of approximately 400 km2 located at the southernmost portion of the eastern Sul-Rio-Grandense Shield, RS. It consists of monzo the syenogranite, light gray and leucocratic porphyritic texture with megacrystals K-feldspar in a coarse equigranular hypidiomorphic matrix, composed of quartz, K-feldspar, plagioclase, biotite, hornblende, opaque minerals and accessories. The modal megacrystals reach proportions between 30 and 60 % and range from 4 and 8 cm together with mafic minerals of the matrix showing a subvertical magmatic foliation and a tectonic foliation prominent in the borders marked by intense ductile deformation and protomylonite generation. Another important aspect of the Chasqueiro Granite is the presence of microgranular mafic enclaves of dioritic composition ubiquitous in the granite, having different shapes and sizes. Geochemically the granite is characterized as a slightly expanded acid sequence formed by a sub-alkaline magmatism of calc-alkaline type with high potassium, metaluminous to lightly peraluminous, with characteristic signature of granites generated in post-collisional tectonic setting. Geochronological analyzes obtained by the U-Pb method (LA-ICPMS) and isotope geochemistry of Lu-Hf (LA-ICPMS) in zircons presenting, respectively, crystallization age 574 ± 3 Ma and negative εHf which suggest a granite relationship with deformational event D2 and supporting a magmatic crustal sources with subordinate mantle component.

A Faixa Araçuaí, localizada na porção setentrional da Província Mantiqueira, pode ser dividida em três domínios estruturais os quais estão envolvidos em um sistema de empurrões com vergência tanto oeste quanto para leste. A porção ocidental corresponde ao Domínio Milonítico constituido por gnaisses miloníticos de alta temperatura ~750ºC, o Domínio Central é caracterizado por intenso magmatismo tonalítico, granodiorítico e granítico de idade aproximada de 580 Ma e o setor oriental, denominado de Domínio Anatético, formado pelo Leucogranito Carlos Chagas (CC), um granito tipo S de idades compreendidas entre 572 ± 4 Ma a 597 ± 3 Ma. O Domínio Central, formado pelas Suítes Galiléia e Aimorés, são constituídas respectivamente pelos tonalitos São Vitor, e Galiléia e pelo Granito Caladão e o Charnockito Padre Paraíso. A Suíte Aimorés e a borda oeste do Leucogranito Carlos Chagas, constituem-se no foco desta dissertação, a qual teve por meta um estudo estrutural, baseado em Anisotropia de Suscetibilidade Magnética (ASM) e datações através dos métodos U/Pb em zircões e monazitas e Lu/Hf em zircões. Petrograficamente o Granito Caladão tem como característica uma textura porfirítica, com matriz de granulação grossa, composta por quartzo, feldspato, hornblenda e biotita, com cristais de feldspatos de 2 a 5 centímetros. O Charnockito Padre Paraíso é um hiperstênio granito, de cor esverdeada, de matriz de granulação grossa composta de quartzo, feldspato, hiperstênio, biotita e hornblenda, com cristais de feldspato de até 6 centímetros. O Leucogranito Carlos Chagas possui granulação media a grossa e apresenta em sua constituição, quartzo, feldspato, biotita sillimanita, cordierita e granada. Um granito tipo S. Os resultados da análise estrutural através da ASM apresentaram orientações variáveis da foliação magnética em setores distintos dos corpos magmáticos, compatível com a orientação espacial do plúton, indicando assim sua colocação, porém a orientações das lineações magnéticas sugerem uma direção predominantemente NNE-SSW, aventando um fluxo magmático nessa direção. Investigações sobre a mineralogia magnética através de curvas termomagnéticas evidenciaram ocorrências de óxidos de ferro, magnetita e hematita, tanto no Granito Caladão como no Charnockito Padre Paraíso. Os baixos valores de suscetibilidade magnética, da ordem de 10-4 a 10-5 SI sugerem que a ASM, para esses corpos ígneos, é controlada essencialmente pelos minerais paramagnéticos. Os elipsoides de ASM são dominantemente oblatos, caracterizando uma forte deformação por achatamento, apenas localmente foram identificados elipsoides prolato. As análises isotópicas forneceram idades de 500.7 ± 1.5 Ma a 512.1 ± 1.5 Ma (zircão) e 445.0 ± 9.5 Ma (monazita) para o Granito Caladão e de 498 ± 2.4 Ma a 502.7 ± 1.9 Ma (zircão) para o Charnockito Padre Paraíso. Idades obtidas como sendo mais antigas para o Granito Caladão e o Charnockito Padre Paraíso, respectivamente de 556.8 ± 3.7 Ma (zircão) e 576.0 ± 2.2 Ma (zircão) foram interpretadas como zircões herdados das rochas encaixantes quando do emplacement dos plutons. A idade de 570.1 ± 1.7 Ma para o CC na porção norte é compatível com as idades obtidas na literatura, entretanto na porção sul, as idades obtidas são da ordem de 510.8 ± 1.7 Ma e 520.5 ± 2.5 Ma para o CC, indicando pulsos magmáticos diacronicos. As determinações Lu/Hf revelaram valores de ?Hf negativos para todos os plutons estudados, mostrando que são provenientes de retrabalhamento crustal, de uma crosta arqueana e paleoproterozoica. / The Araçuaí Orogen corresponds the northern part of the Mantiqueira Province, which can be divided into three different structural domains. These areas are involved in thrust systems towards the west and east. The western part corresponds to the Mylonites Domain, constituted by high temperature mylonitic gneisses, the Central Domain is characterized by a huge tonalitic, granodioritic and granitic magmatism dated around 580 Ma, and, the eastern area, described as Anatexis Domain where the Carlos Chagas Leucogranite (CC) is the predominant lithology. The Galiléia Suite constituting by the St. Vitor and Galiléia tonalites, Aimorés Suites, by the Caladão Granite and the Padre Paraíso Charnockite, all theses suites belong to the Central Domain. The Aimorés Suite and the western border of the Carlos Chagas Leucogranite are the focus of this Master thesis, which the goals are a structural study based on Anisotropy of Magnetic Susceptibility (AMS) and a geochronological analysis using U/Pb in zircon and monazite and Lu/Hf in zircon methodologies. The petrographic analysis shows the Caladão Granite as porphyritic granite, with a thick granulation matrix composed of quartz, feldspar, hornblende and biotite. The feldspar crystals can reach 2 to 5 centimeters in size. The Padre Paraíso Charnockite is hypersthene granite; greenish-colored matrix with a coarse granulation composed of quartz, feldspar, hypersthene, biotite and hornblende, the feldspar crystals size can be bigger than 5 centimeters. The Carlos Chagas Leucogranite has medium to coarse granulation that is constituted by quartz, feldspar, biotite, sillimanite, cordierite and garnet, the mineralogy typical of type S granite. Structural analysis using the AMS showed variable magnetic foliation orientations in distinct sectors of the magmatic bodies, compatible with the spatial trend of the pluton, your emplacement, but the orientations of the magnetic lines suggest a predominantly NNE-SSW direction, suggesting a magmatic flow in this direction. Investigations on magnetic mineralogy through thermomagnetic curves showed evidence of iron magnetite and hematite oxides in both the Caladão Granite and the Padre Paraíso Charnockite. The low values of magnetic susceptibility, on the order of 10-4 to 10-5 SI, suggest that paramagnetic minerals essentially control the ASM for these igneous bodies. The AMS ellipsoids are predominantly oblate, characterizing a strong flattening deformation; only locally prolate ellipsoids have been identified. Isotopic analyzes performed at Caladão Granite provided ages ranging from 500.7 ± 1.5 Ma to 512.1 ± 1.5 Ma (zircon) and 445.0 ± 9.5 Ma (monazite), and zircon ages from 498 ± 2.4 Ma to 502.7 ± 1.9 Ma obtained in the Padre Paraíso Charnockite. Older zircon ages determined in the Caladão Granite and Padre Paraíso Charnockite are, respectively, 556.8 ± 3.7 Ma and 576.0 ± 2.2Ma, whose ages were interpreted as inherited zircons that were captured from the host rocks during the plutons emplacement. In the northern sector of the studied area, the CC age of 570.1 ± 1.7 Ma is compatible with the ages that were obtained in the literature, ranging from 572 ± 4 Ma to 597 ± 3 Ma, however in the south of the area some surprisingly younger ages (510.8 ± 1.7 Ma and 520.5 ± 2.5 Ma) in the CC, suggesting diachronic magmatic pulses. The Lu/Hf determinations revealed negative ?Hf values for all studied plutons, showing that they are derived from crustal reworking, from an Archaean and Paleoproterozoic crust. The most Hf model age are 2,0 Ga, however there are some Archean ages ranging from 3.0 to 3.8 Ga. The presence of highly negative values of -20 and -30 for the Caladão Granite are interpreted as largely crustal-derived melts.

El estudio geológico llevado a cabo en la zona central del Macizo Nordpatagónico, mas precisamente en las áreas ubicadas al Norte y Oeste de la Localidad de Los Menucos, permitió reconocer tres momentos en la evolución geológica de esta región durante el Mesozoico. Un primer momento ligado al Triásico Temprano a Medio, el segundo ligado al Triásico Tardío y el tercero vinculado con el Jurásico Temprano. El desarrollo durante el Triásico Temprano a Medio se vincula con la cuenca del Grupo Los Menucos. Comprende un magmatismo de tipo transicional a post-orogénico asociado al colapso de la Orogenia Gondwánica, hace 252 Ma, desarrollado en angularidad sobre el Complejo La Esperanza. Los trabajos realizados llevan a proponer un nuevo esquema estratigráfico, sosteniendo el grado de Grupo Los Menucos constituido por tres formaciones: Formación Puesto Tscherig, Formación Puesto Vera y Formación Sierra Colorada. La primera se divide en Miembro Cerro La Laja, comprendiendo depósitos laharicos en estadios sin- e intereruptivos y sobre este el Miembro Barrancas Grandes compuesto exclusivamente por un depósito ignimbrítico de composición dacítica y datado en 252 Ma. La Formación Vera, se dispone en forma erosiva sobre la anterior y comprende dos miembros; el inferior, Miembro Aguada de la Mula corresponde a depósitos clásticos fluviales que se cubren en forma neta por depósitos de lluvia de cenizas del Miembro El Pilquín. La tercera, Formación Sierra Colorada, comprende tres depósitos ignimbriticos de alto grado y composición riolítica a dacítica, datados entre 251 y 248 Ma. El magmatismo del Triásico Tardío fue datado en 211 Ma en la zona occidental de la localidad de Los Menucos. Si bien las relaciones estratigráficas con respecto al Grupo Los Menucos no pudieron ser resueltas, si queda establecido que este magmatismo esta genéticamente desvinculado del anterior. Durante el Jurásico Temprano, en la zona Norte del área estudiada comienza el relleno del Graben del Cerro Piche. En esta depresión tectónica, limitada por fallas subparalelas con dirección E-O, se reconocieron dos etapas de relleno. Un primer relleno volcánico compuesto por lavas y domos que yacen en discordancia sobre el Grupo Los Menucos, y un segundo estadio representado por una secuencia sedimentaria de 500 m de espesor. Este segundo evento fue datado en 185 Ma y yace en discordancia sobre facies plutónicas del Complejo La Esperanza, ignimbritas del Grupo Los Menucos y también sobre las lavas del primer relleno volcánico. Los depósitos volcánicos y sedimentarios limitados a la depresión tectónica son agrupados en esta tesis bajo el nombre de Formación Cerro Piche. Los estudios de isótopos de Lu-Hf llevados a cabo en granos de circon permitieron reconocer tres eventos – EI, EII, EIII – relacionados a la evolución crustal del Macizo Nordpatagónico. El primer evento EI fue subdividido en dos ciclos menores, C1 y C2. El C1 ligado al Pérmico Tardío indica la generación de magmas derivados de una corteza antigua mesoproterozoica, vinculado al engrosamiento de la corteza. El segundo ciclo C2, asociado al Triasico Temprano a Medio, también indica que la generación de magmas estuvo ligado a un proceso de fusión cortical, pero en este caso de edad paleo- a mesoproterozoica. Esta etapa se asocia a un incipiente adelgazamiento cortical en el que la fusión estuvo asociada a proceso de delaminación o remoción convectiva. El segundo evento EII tuvo lugar en el Triásico Superior, en el que lo valores isotópicos de ƐHf cada vez menos negativos sugieren la fusión cortical pero vinculados con participación de magma mantélico. El tercer evento EIII está ligado al Jurásico, los valores de ƐHf positivos y negativos implican la participación efectiva de magmas juveniles en diferentes grados de interacción con la corteza. Tanto el C2 del E1, como EII y EIII implican un progresivo adelgazamiento de la corteza y un paulatino ascenso de magmas juveniles mantelicos. / he geological study carried out in the central part of the North Patagonian Massif, precisely in the North and West portion of Los Menucos town, led to recognize three stages in the geological evolution of this region during the Mesozoic. A first event linked to the Early to Middle Triassic, the second related to the Late Triassic, and the third linked to the Early Jurassic. The geological evolution during the Early to Middle Triassic is linked to the Los Menucos Group. It comprises a transitional to post-orogenic magmatism associated with the collapse of the Gondwana Orogeny, 252 Ma ago, and developed in angularity above the La Esperanza Complex. The stratigraphic works lead to propose a new stratigraphic scheme, supporting the Los Menucos Group, that is composed by three minor units: La Resistencia Formation, Vera Formation and Sierra Colorada Formation. The first is divided into El Molinero Member, comprising laharic deposits in syn- and intereptuion stages, and over this the Don Carlucho Member composed exclusively of an ignimbritic deposit of dacitic composition and dated in 252 Ma. The second, Vera Formation, overlies Don Carlucho Memeber in erosive relation and comprises two members; the lower, Aguada de la Mula Member, corresponds to fluvial clastic deposits that are covered by ash fall-out deposits assigned to El Pilquín Member. The third, Sierra Colorada Formation, comprises three ignimbritic deposits of high grade and rhyolitic to dacitic composition, dated between 251 and 248 Ma. Late Triassic magmatism was dated at 211 Ma in the western area of the town of Los Menucos. Although the stratigraphic relationships with respect to the Los Menucos Group could not be resolved, it is established that this magmatism is genetically disconnected from the previous. During the Early Jurassic period, started the infilling of the Graben del Cerro Piche, located on the northern area of the studied area. This tectonic depression is limited by two subparallel faults with E-O direction, and comprises two stages on it evolution. A first volcanic infilling composed of lavas and domes that lies in unconformity over the Los Menucos Group, and a second filling stage comprised of a 500 m thick sedimentary sequence. This second event was dated at 185 Ma and lies in angularity over plutonic facies of the La Esperanza Complex, ignimbrites of the Los Menucos Group and also over the lavas of the first volcanic filling. The studies of Lu-Hf isotopes carried out in circón crystals allowed to recognize three events - EI, EII, EIII - related to the crustal evolution of the North Patagonian Massif. The first EI event was subdivided into two minor cycles, C1 and C2. The C1 linked to the Late Permian indicates the generation of magmas derived from an ancient Mesoproterozoic crust, linked to the thickening of the crust. The second cycle C2, associated with the Early to Middle Triassic, also indicates that the generation of magmas was linked to a paleo- to mesoproterozoic crust. This stage is associated with an incipient crustal thinning in which the fusion was associated with delamination or convective removal. The second EII event is linked to the Upper Triassic, in which less negative isotopic ƐHf values suggest a crust derived magma but linked with a mantelic input. The third EIII event is linked to the Jurassic, the positive and negative ƐHf values imply the effective participation of juvenile magmas in different degrees of crustal contamination. Both the C2 of the E1, as EII and EIII imply a progressive thinning of the crust and a gradual rise of juvenile mantle derived magmas.

Le travail de thèse reporté dans ce manuscrit se focalise sur la reconnaissance ainsi que l'expression des processus de différenciation crustale à l'Archéen. Cet éon représente à lui tout seul 1/3 des temps géologiques, et se caractérise notamment par des lithologies diagnostiques, ainsi que des contextes géodynamiques complexes. La majorité des études sont portées sur l’investigation des phases alumineuses qui permettent de contraindre précisément les événements métamorphiques au-cours d’une géodynamique d’épaississement crustal. Toutefois, ces phases alumineuses représentent rarement plus de 10% des terrains archéens, alors qu’ils sont faits à plus de 75% de gneiss orthodérivés. L'étude qui suit est une caractérisation du complexe de gneiss gris composite de la marge Nord du craton archéen du Kaapvaal en Afrique du Sud. Les résultats produits durant cette investigation ont amené à plusieurs conclusions importantes au regard de la géodynamique archéenne. L'étude isotopique U-Pb/Lu-Hf sur zircon couplée à des analyses pétro-métamorphiques montre que la construction d’un complexe de gneiss gris composite correspond à une géodynamique prolongée dans le temps, accomplie au-travers de processus de différenciations crustales internes à la Zone accrétée, 1.e. le bloc crustal évolue en système thermodynamiquement fermé. Les complexes de gneiss gris ne sont que modérément étudiés toutefois, les informations contenues dans ces lithologies apparaissent complémentaires avec celles obtenues par les études métamorphiques sur les lithologies alumineuses. Il est donc nécessaire d'approfondir ce type d’investigations afin de mieux contraindre les modèles géodynamiques archéens / The PhD work presented in this manuscript focuses on the recognition and the manifestation of Archean crustal differentiation processes. The Archean eon which represents 1/3 of the geological record is featured by both lithologies unrecognized in younger eons and cryptic geodynamics. Most of investigations concentrate on the characterisation of aluminium-rich lithologies that allow an accurate determination of the pressure-temperature evolution underwent by crustal materials during crustal thickening geodynamics. However, aluminium-rich lithologies - mainly represented by metasediments - account for only 10% on average of Archean terranes whereas orthoderived gneisses - which also testify for crustal differentiation processes - form around 75% of these terranes. The following contribution depicts an Archean composite grey gneiss complex located at the northern edge of the Kaapvaal craton is South Africa. Results carried out during this PhD study have major consequences on Archean geodynamics. The zircon U-Pb/Lu-Hf isotope Investigation coupled with strong petro-metamorphic observations show that composite grey gneiss complexes may be built over a protracted time span, achieved through self-refinement of crustal materials, i.e. the crustal block evolved in a thermodynamically closed system. Grey gneiss compiexes are only moderately investigated even though information enclosed in these lithologies is complementary with those from aluminium-rich rocks. Therefore, deeper investigations of these geological objects must be a central scope in order to improve the knowledge of the Archean eon and appears necessary for the building of even more realistic geotectonic models

The Scandinavian Caledonides are defined by long transported thrust sheets emplaced in a nappe stratigraphic succession onto the Paleozoic Baltica platform, as a result of the collision between the paleo-continents Baltica and Laurentia. This Palaeozoic collisional orogen is nowadays exposed at mid-crustal levels, thus provides an excellent ground for in situ studies of mountain building processes. The complex nappe stack is subdivided into the Lower, Middle, Upper and Uppermost allochthons. The tectonostratigraphic highest unit in the Middle Allochthon is the Seve Nappe Complex (SNC), itself segmented into Lower, Middle and Upper Seve nappes, which all experienced different metamorphic evolution. The SNC is known for high pressure (HP) and ultrahigh pressure (UHP) subduction related rocks and the target for the Collisional Orogeny in the Scandinavian Caledonides (COSC-1) scientific drilling programme. The drilling resulted in a continuous c. 2.4 km long drill core through the Lower Seve Nappe, drilled in the eastern slope of Åreskutan Mt in west-central Jämtland. Above the COSC-1 profile lies the high grade Middle Seve Nappe (i.e. Åreskutan Nappe), which experienced UHP verified by the presence of microdiamonds in kyanite bearing gneisses. Recently, microdiamonds have also been discovered in gneisses (described here) further north close to Saxnäs in southern Västerbotten.     The metamorphic history of the Lower Seve Nappe is reconstructed based on material from the COSC-1 drill core, which also enables evaluation of the tectonometamorphic relationship to the overlying high grade Middle Seve Nappe. The Lower Seve Nappe comprise calc-silicates, calcareous gneisses and mylonitic micaschists and two tectonometamorphic events are recognized, prograde metamorphism (M1-D1) and retrograde thrust related metamorphism (M2-D2). Pressure and temperature (PT) conditions of the Lower Seve Nappe is constrained by state-of-the-art Quartz-in-Garnet (QuiG) barometry based on the shift in Raman band position of quartz inclusions in garnet, and Titanium-in-Quartz (TitaniQ) thermometry (satellite masters project). Supplementary conventional barometry based on phengite composition is applied where the use of QuiG is limited. The PT conditions of the M1-D1 is constrained to ~ 8-13 kbar, 525-695 o C and the M2-D2 event ~7-10 kbar, 450-550 o C. Conclusively, the Lower Seve Nappe was metamorphosed in upper greenschist-amphibolite to lower eclogite facies conditions at depths around 40-60 km and later suffered from greenschist overprint during thrusting. Lu-Hf garnet geochronology confirm that the overlying high-grade Åreskutan Nappe experienced UHP conditions around 450 Ma at depths around 120 km. Likewise, Ar-Ar dating implies peak conditions of the Lower Seve around 460-450 Ma. Moreover, their respective lower shear zones were active at the same time, c. 424 Ma. Conclusively, they were juxtaposed in their current tectonostratigraphic positions in a subduction channel in the early Silurian as a result of exhumation. Additionally, the microdiamond bearing kyanite-garnet gneisses from Saxnäs indeed show similarities to the Åreskutan gneisses, which strongly implies that the UHPM in this unit of the Scandinavian Caledonides is of regional character. / De Skandinaviska Kaledoniderna har bildats genom en kollision mellan de två kontinentalplattorna Baltika och Laurentia då Japetushavet stängdes omkring 400 miljoner år sedan. Till följd av de starkt komprimerande krafterna transporterades stora flak (skollor) av havsbottenberggrund och kontinentalskorpa hundratals kilometer upp på Baltikakontinenten. Skollorna är överskjutna på varandra omlott och benämns som undre, mellersta, övre och översta skollberggrunderna och återfinns idag i vår fjällkedja. Innan kollisionen med Laurentia krockade Baltika med en vulkanisk öbåge, vilket resulterade i att delar av Baltika pressades ner så pass djupt att bland annat diamanter bildades till följd av det ultrahöga trycket. Bevis för omvandling under extremt tryck finns i den så kallade Seveskollan som utgör en del av den mellersta skollberggrunden. Seveskollan är ett komplex av tre olika enheter, som utsatts för olika grad av metamorfos till följd av tryck och temperatur. Till följd av väder och vind under miljontals år så är fjällkedjan idag nederoderad och därav väl exponerad. Det gör att de Skandinaviska Kaledoniderna är en av världens bästa platser att studera och förstå bergskedjebildade processer. Av den anledningen borrade djupborrningsprojektet COSC-1 en cirka 2.4 km långt kärnborrhål genom den lägst belägna enheten i Seve komplexet (lägre Seveskollan) strax nedanför Åreskutan i Jämtlandsfjällen. Över COSC-1 profilen ligger den berggrund som tillhör den mellersta Seveskollan, även kallad Åreskutanskollan. Åreskutanskollan är en del av Baltika som utsattes för ultrahöga tryck, och i kyanitförande gnejser har diamanter inneslutna i det motståndskraftiga mineralet granat påträffats. Nyligen, längre norrut i Saxnäs (södra Västerbotten) har ytterligare diamantförande gnejser påträffats i den mellersta Seveskollan, som karaktäriseras i den här studien.      Material från COSC-1 borrkärnan har använts för att bestämma under vilka tryck och temperatur bergarterna i den lägre Seveskollan har metmorfoserats, för att förstå den tektoniska och metamorfa utvecklingen och även relationen till den överliggande högmetamorfa Åreskutanskollan. Trycket har bestämts genom den relativt oprövade metoden QuiG -barometri. Små kristaller av kvarts inneslutna i granat har analyserats med Raman spektroskopi och de fysikaliska parametrarna av kvarts och granat kan direkt översättas till tryck. Temperatur har erhållits genom det temperaturkänsliga ämnet titan i kvartsinneslutningarna. Resultatet visar att den lägre Seveskollan har genomgått minst två metamorfa faser genom tektonisk påverkan. Den första fasen varierar från övre grönskiffer-amfibolit till lägre eklogitfacies under tryck och temperatur av ca 8-13 kbar, 525-695 o C. Den andra fasen är associerad med överskjutning och skjuvning, vilket orsakade retrograd metamorfos i grönskifferfacies under lägre tryck och temperatur (ca 7-10 kbar, 450-550 o C). Datering baserat på radioaktivt sönderfall av lutetium till hafnium i granat fastställer att Åreskutanskollan utsattes för ultrahögt tryck för omkring 450 miljoner år sedan, samtidigt som lägre Seveskollan nådde metamorft klimax. Resultaten visar även att lägre och mellersta Seveskollorna skjuvades samtidigt, omkring 424 miljoner år sedan. Det betyder att de erhöll sina nuvarande tektonostratigrafiska positioner på stort djup innan överskjutningen på Baltika. Detaljerad petrografi påvisar att de diamantförande kyanit-och granatförande gnejserna från Saxnäs visar påtagliga likheter med Åreskutanskollans högtrycksgnejser. Det tyder på att berggrunden i Saxnäs kan kopplas samman med Åreskutanskollan och att ultrahögtrycksmetamorfos av den mellersta Seveskollan omfattar ett större område än vad som tidigare antagits.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Earth’s oldest preserved granitoid crust dates back to the Paleoarchean and consists predominantly of sodic tonalite-trondhjemite-granodiorite (TTG) granitoids that arose through the partial melting of hydrated metabasalts. In contrast, granites (sensu stricto) typically postdate the TTG and appear late in the plutonic record of the old cratons. However, the existence of Hadean zircons with mineral inclusion suites that are consistent with crystallization from peraluminous granitic magmas indicates that granitic rocks formed part of the earliest felsic crust; although we have direct evidence, this earliest felsic crust is not preserved. In this PhD I present an unusual variety of markedly CaO-poor, K2O-rich, rutile-bearing, peraluminous granite and rhyolite that are located in the basal conglomerate of the Moodies Group (South Africa). These rocks challenge the common view of the Archean craton evolution as they were produced concurrently with TTG magmas during three magmatic cycles in the Barberton Greenstone Belt (BGB) and were later emplaced, as clasts, in a younger conglomerate. The study of mineral inclusions located in the zircons present within the granites and rhyolites, shows that alkali feldspar inclusions are abundant relative to plagioclase inclusions and demonstrates that the main characteristics of these granites, i.e. they are K-rich and Ca-poor, are a magmatic signature. The oxygen isotope signature of these zircon grains reveals that the zircons have preserved the δ18O value of the magma from which the granites originated and that the source of the granites had a magmatic oxygen isotope value close to the one of the regional coeval TTG. Further study of the zircons shows that their Lu-Hf isotopic system reflects the crustal signature of the magma into which they grew. Sm-Nd study of the granites and rhyolites whole rock indicates that the minimum age of the source’s protolith of the granites and rhyolites is close to 3.9 billion years, which is in agreement with the zircons’ Lu-Hf signature. Additionally I show in this thesis that the peraluminous character of the granites and rhyolites, along with their high Sr and low Ca content associated to their Eu/ Eu* ~ 1 is a consequence of phengite melting in a metagreywacke source at pressures in excess of plagioclase stability. My work therefore illustrates that K-rich, Ca-poor peraluminous granites were generated in the Paleo and Meso Archean, alongside with the sodic TTG, through partial melting of sediments at high pressures. Not only has this process demonstrated the ability of the early Earth to recycle relatively young material since 3.9 billions years ago, but it has also contributed to each episode of continental crustal growth through the Paleoarchean to Mesoarchean in the BGB, despite leaving no plutonic record at the typical mid-crustal level of exposure that the TTG plutons around the belt represent. / AFRIKAANSE OPSOMMING: Die aarde se oudste bewaarde granitoïed kors dateer terug na die Paleo Argeïkum en bestaan hoofsaaklik uit natrium-ryke tonaliet-trondhjemiet-granodioriet (TTG) granitoïede wat ontstaan het deur die gedeeltelike smelting van gehidreerde metabasalte. In teenstelling hiermee is graniete (sensu stricto) tipies jonger as die TTG’s en verskyn laat in die plutoniese rekord van die ou kratons. Die bestaan van Hadeaanse zirkone met mineraal insluitsels wat ooreenstem met die kristallisasie van peralumineuse granietiese magma dui egter daarop dat granietiese gesteentes deel gevorm het van die vroegste felsiese kors. Alhoewel daar direkte getuienis is hiervoor het hierdie vroegste felsiese kors nie behoue gebly nie. In hierdie dissertasie toon ek ‘n ongewone verskeidenheid van merkbaar CaO-arm, K2O-ryk, rutiel-draende, peralumineuse graniet en rioliet wat in die basale konglomeraat van die Moodies Groep (Suid-Afrika) voorkom. Hierdie gesteentes daag die algemene siening van Argeïkum kraton evolusie uit omdat hulle gelyktydig met TTG magma geproduseer is tydens drie TTG magmatiese siklusse in die Baberton-groensteenstrook en later ingeplaas is as klaste in ‘n jonger konglomeraat. Die studie op minerale insluitsels in zirkone binne die graniete en rioliete toon dat alkaliveldspaat insluitsels volop is relatief tot plagioklaas insluitsels. Dit toon ook dat die hoof eienskap van hierdie graniete, hulle K-ryke en Ca-arme samestelling, ‘n onderskeidende magmatiese kenmerk is. Die suurstof-isotoop samestelling van hierdie zirkoon minerale onthul dat die zirkone die δ18O waarde van die magma waaruit die graniet gevorm is behou het en dat die bronnemateriaal van die graniete ‘n magmatiese suurstofisotoop waarde gehad het nader aan dié van die plaaslike sinchroniese TTG waardes. Verdere studie van die zirkone dui daarop dat hul Lu-HF isotoopstelsel die aardkorseienskappe weerspieël van die oorspronklike magma waarin hulle gegroei het. Sm-Nd studie van die graniete en rioliete heelgesteente dui daarop dat die minimum ouderdom van die protoliet van graniete en rioliete ongeveer 3,9 biljoen jaar is, wat ooreenstem met die zirkone se Lu-HF eienskappe. Daarbenewens het hierdie dissertasie bewys dat die peralumineuse karakter van die graniete en rioliete, tesame met hulle hoë Sr- en lae Ca-inhoud geassosieer tot hul Eu/Eu * ~ 1, ‘n gevolg is van “phengite” smelting in’ n metagrouwak bron by drukking hoër as plagioklaas stabiliteit. Hierdie studie illustreer dus dat K-ryke, Ca-arme peralumineuse graniete gegenereer is in die Paleo en Meso Argeïkum, saam met die natrium-ryke TTG’s, deur middel van parsiële smelting van sedimente teen ‘n hoë druk. Hierdie proses het nie slegs getoon dat die vroeë aarde sedert 3,9 biljoen jaar gelede die vermoë gehad het om relatief jong materiaal te herwin nie; dit het ook bygedra tot elke episode van kontinentale korsgroei deur die Paleo en Meso Argeïkum in die Barberton groensteenstrook, ten spyte daarvan dat geen plutoniese rekord gelaat is teen die tipiese mid-kors vlak van blootstelling wat die TTG plutone in die strook verteenwoordig nie. / RESUMÉ: La croûte de granitoïdes de la Terre Primitive la plus ancienne qui ait été préservée remonte au Paleoarchéen et se compose principalement de granitoïdes sodiques tonalite-trondhjémite-granodiorite (TTG) qui se sont formés par la fusion partielle de métabasaltes hydratés. En revanche, les granites (stricto sensu) sont en général postérieurs aux TTG et apparaissent tardivement dans les cratons anciens. Cependant, l’existence de zircons Hadéens préservant des suites d’inclusions minérales qui sont compatibles avec la cristallisation à partir d’un magma granitique peralumineu, indique que les roches granitiques faisaient aussi partie de la croûte felsique de la Terre Primitibe; même si nous n’avons pas de preuves directes et que cette dernière n’ait pas été conservée. Dans cette thèse, je présente une variété inhabituelle de granites et rhyolites peralumineux qui sont marquée par une forte teneur en K2O et une faible teneur en CaO et qui possèdent du rutile. Ces roches sont situées dans le conglomérat basal du Groupe du Moodies (Afrique du Sud). Elles défient la vision commune que l’on a de l’évolution des cratons Archéens puisqu’elles ont été produites en même temps que des magmas TTG, pendant trois cycles magmatiques qui ont affecté la ceinture de roches vertes de Barberton (CRVB). Ces roches ont été par la suite mises en place, comme galets, dans un conglomérat plus jeune. L’étude des inclusions minérales localisées dans des zircons présents dans les granites et les rhyolites qui font le sujet de cette étude, montre que les inclusions de feldspaths alcalins sont plus abondantes que les inclusions de plagioclases et démontre que les principales caractéristiques de ces granites, c’est à dire qu’ils sont riches en K et pauvres en Ca, sont une signature magmatique. La signature isotopique de l’oxygène de ces zircons révèle que ceux-ci ont conservé la valeurdu δ18O du magma à partir duquel les granites se sont formés. De plus ceci montre que la valeur du δ18O de la source des granites était proche de celle de TTG contemporains. La poursuite de l’étude des zircons montre que leur système isotopique Lu-Hf reflète la signature crustale du magma dans lequel ils ont cru. L’étude Sm-Nd des granites et rhyolites indique que l’âge minimum du protolithe de leur source est de près de 3,9 milliards d’années, ce qui est en accord avec la signature Lu-Hf des zircons. De plus, je montre dans cette thèse que le caractère peralumineux des granites et des rhyolites, avec leurs forte teneur an Sr et basse teneur en Ca associé à leur Eu / Eu * ~ 1, est une conséquence de la fusion partielle de phengite dans une source métagrauwacke à des pressions supérieures a celle de la stabilité du plagioclase. Mon travail montre donc que des granites peralumineux riche en K et pauvre en Ca ont été générés durant le Paléo et Méso-Archéen, aux côtés des TTG sodiques, par la fusion partielle de sédiments, à haute pression. Non seulement ce processus a démontré la capacité de la Terre Primitive à recycler du matériel relativement jeune et ce, dès 3,9 milliards d’années; mais il a également contribué à chaque épisode de croissance crustale à travers le Paleo- et Méso-Archéen dans la CRVB, malgré l’absence de pluton mis en place profondeur à des profondeurs identiques à celles des TTG.