>Magister Scientiae - MSc / The thesis provides a study into the main structural features of the Namaqua Region and their relation to the intrusion of the Keimoes Suite. This was achieved by producing a digitized map of the Namaqua Region structural framework using a LandSAT image and MOVE software for remote sensing. The structural framework showed an array of shear zones and fault systems which trend in a NW-SE direction. The validation of the sense of movement, location and orientation of the shear zones was done by field mapping. The general orientation of all shear zones was NW-SE. The sense of movement along the Neusspruit, Boven Rugzeer and Trooilapspan shear zones was found to be dextral strike slip movement and the Cnydas shear zone had a sinistral strike slip movement. The location of the shear zones were determined by analyzing the deviation in general foliation trend which was visualized using Rose Diagrams. The field data and the remote sensing were found to agree with the transpressive environment of the Namaqua Region. The oblique collision of the Namaqua-Natal crustal block with the Kaapvaal Craton during the orogenic event at ~1.2 Ga created a compressionalgeotectonic setting which allowed for the intrusion of the early to late syn-tectonic Keimoes Suite granites. The lateral escape of the Namaqua-Natal crustal block took place along the western margin of the Kaapvaal Craton. This was brought on by prolonged compression which resulted in the formation of a releasing bend in the Namaqua Region. This releasing bend produced the negative flower structure with dextral shear zones which facilitated the intrusion of the post-tectonic Keimoes Suite granites.

The geomorphic expression, sedimentation, and near-field deformation of a fault system may be characterized to obtain an understanding of its kinematic evolution and potential seismic hazards. The dynamics and deformation history of the Eastern California shear zone (ECSZ), a wide and complex network of right-lateral strike-slip faults, is not well understood, despite hosting three large (>Mw 7.0) earthquake ruptures in recent decades. The low-net slip faults of the ECSZ (each with <10 km) offer a unique opportunity to assess strain distribution in a developing, kinematically immature strike-slip system. To do so, I conducted field-based investigations of these faults within the Mojave Block of the ECSZ. First, I investigated the morphology, structure, and controls of restraining bend growth along the numerous faults of the ECSZ via field mapping and numerical deformational modeling. I found that the ECSZ restraining bends are small (kilometer-scale), exhibit high-angle, doubly fault-bound geometries with positive flower structures, and have self-similar morphologies characterized by a "whaleback" longitudinal profile and an arrowhead shape in map view. Gradual changes in form with increasing restraining bend size suggest a common growth mechanism influenced more by the kinematics of local fault geometries than by the fault's obliquity to plate motion. Modeling results indicate that concentrated shear strain at single transpressional bends facilitates the development of new secondary faults with cumulative strain as a mechanism to accommodate horizontal shortening via uplift between the faults. The ECSZ restraining bends contribute minimally to regional contractional strain due to their small size, steep fault angles, and shallow crustal penetration (< 5 km), which also suggests that they are unlikely to obstruct large earthquake ruptures. Second, I conducted a spatiotemporal slip rate analysis of the Calico fault with new mapping and geochronology of offset alluvial fans from North Hidalgo Mountain. From this work I obtain several findings. 1) The slip rate along North Hidalgo Mountain ranges from 1.5-2.1 mm/yr in the Holocene and 0.8-2.0 mm/yr in the late Pleistocene. 2) The similarity in slip rates between North Hidalgo Mountain and the Rodman Mountains suggests that this 38 km stretch is a kinematically coherent fault segment with a relatively steady slip rate of 1.7 +0.4/-0.3 mm/yr over the past 60 ka. Faster rates reported from Newberry Springs suggest either a significant increase in slip rate from the Rodman Mountains to Newberry Springs or temporal variations in slip rate. 3) The new rates support previous work which showed the central section of the Calico fault has the highest slip rate in the Mojave Block. However, it does not resolve the discrepancy between ECSZ geodetic and geologic slip rates, implying that transient changes in slip rate, or the contribution of off-fault deformation or other structures may be required. Additionally, the lack of geological slip rate data might contribute to this discrepancy if significant spatial and temporal variations exist on other ECSZ faults. / Doctor of Philosophy / The topography and geology within a fault system may be studied to understand tectonic plate motion over time and assess earthquake hazards. The Eastern California shear zone is a complex network of strike-slip faults within the Mojave Desert, which has hosted three large earthquakes (>Mw 7.0) in recent decades. Despite this significant seismic activity, the mechanisms of motion across the numerous faults in the Eastern California shear zone remain poorly understood. The individual faults have accumulated relatively little strike-slip motion since their inception (less than 10 kilometers), offering a unique opportunity to investigate the early-stage kinematics and seismic hazards of a strike-slip fault system. To do so, I conducted field-based investigations of the faults within the Eastern California shear zone. First, I investigated the early evolution and controls of compressional strike-slip fault bends in the Eastern California shear zone. From mapping and numerical modeling, I characterized the shape, structure, and uplift of numerous small compressional bends dispersed across the faults. From these efforts, I found that uplifted crust in the fault bends exhibit self-similar forms with shallow crustal depths (<5 km). Small changes in the shape of these structures occur with increasing size indicating a predictable pattern of growth with increasing cumulative slip that appears to be partially controlled by local fault conditions. Numerical modeling of simple compressional fault bends indicate that shear strain concentrates at bend corners, which may facilitate the growth of a new fault that more efficiently accommodates contraction in the bend via uplift of the crust between the two faults. The compressional strike-slip fault bends in the Eastern California shear zone are too small to significantly impact regional contractional strain and are therefore also unlikely to impede large earthquake ruptures. Second, I studied the slip rate (or rate at which the fault moves) of the Calico fault via new mapping and age data of displaced alluvial fans. I found that 1) the Calico fault at North Hidalgo Mountain slips at a rate of 0.8-2.0 mm/yr since ~70,000 years ago. 2) The slip rates from North Hidalgo Mountain and the Rodman Mountains are similar, indicating that the 38 kilometers between them behaves consistently, with a steady rate of ~1.7 mm/yr over the last ~60,000 years. However, faster slip rates reported at Newberry Springs suggest either a significant increase in slip rate from the Rodman Mountains to Newberry Springs or that it varies over time. 3) These findings confirm that the central Calico fault has the fastest slip rate in the Mojave Block but does not reconcile regional differences between rates from geodetic and geological measurements. The difference between the slip rates measured by geodetic methods and those from geological studies in the Eastern California shear zone suggests that there could be temporary changes in slip rates or that deformation might be occurring in areas away from the main fault. Also, the lack of geological slip rate data might contribute to this discrepancy if significant spatial and temporal variations exist on other Eastern California shear zone faults.

Discrete (mm- to m-scale) mylonitic shear zones in the northeastern Harquahala metamorphic core complex, Arizona, show evidence of fluid-mineral interactions catalyzing deformation and metamorphism. Many contain a deformed central epidote vein with adjacent bleached haloes and flanking paired shear zones that indicate significant fluid-rock interaction during deformation. An integration of structural and geochemical methods was employed to understand timing, metamorphic conditions, and physiochemical processes responsible for producing the discrete shear zones. Field and microstructural evidence suggest the zones initiated on antecedent fractures. Electron backscatter diffraction (EBSD) analyses show a significant coaxial contribution to the shear, and quartz deformation predominately by prism <a> slip, along with some rhomb <a> slip, suggesting amphibolite-facies conditions during shearing. Fourier Transform Infrared spectroscopy analyses of quartz reveal higher water contents within shear zones than within country rocks, indicating fluid infiltration synchronous with shearing. Stable isotope analyses of quartz and feldspar from mylonites are consistent with an igneous or metamorphic fluid origin. Microstructural observations suggest that the zone morphology with epidote veins, bleached haloes, and flanking discrete paired shear zones was developed predominantly from reaction softening mechanisms. The increase in deformation from bleached rock to flanking shear zones is marked by progressive modal increases in biotite and myrmekite, and modal decreases in K-feldspar, and locally epidote and titanite. Myrmekitic textures recrystallized readily and resulted in progressively greater grain size reduction of feldspar, which aided in the progressive alignment and linkage of the biotite grains, which together concentrated the deformation in bands. Volume reduction resulting from some of the metamorphic reactions may have led to a positive feedback cycle among fluid infiltration, metamorphism and deformation. U-Pb isotope analyses of syn-metamorphic titanite yield an age of ~70 Ma, suggesting the shear zones formed during cooling of the Late Cretaceous (75.5±1.3 Ma) Brown’s Canyon pluton, consistent with their top-to-the-southwest sense of shear, rather than during top-to-the-northeast directed Miocene metamorphic core complex exhumation. Petrography, EBSD analyses, and U-Pb dating of titanite from other (non-discrete) mylonites in the area imply most formed synchronously with the discrete shear zone mylonites. Only rare, scattered mylonites show features consistent with metamorphic core complex exhumation. / text

La présente étude porte sur les caractéristiques structurales de la zone de cisaillement de Kandi dans la région Savalou-Dassa au Centre-Bénin et ses relations avec le magmatisme spatialement associé. Elle vise à comprendre l’évolution tardi- à post-collision de la chaîne panafricaine des Dahoméyides. Les études structurales, pétrologiques et géochronologiques indiquent que la zone de cisaillement de Kandi au Centre-Bénin correspond à un décrochement ductile dextre, large d’au moins 50 Km, et dans laquelle l’évolution de la déformation jusqu’à plus basse température a entraîné l’apparition des bandes de tectonites d’épaisseur kilométrique. Le décrochement ductile de Kandi a fonctionné dans la chaîne des Dahoméyides à partir de c. 606 Ma et il a affecté des granulites d’âge paléoprotérozoïque et des gneiss, migmatites et granitoïdes néoprotérozoïques. Les magmatites spatialement associés à la zone de cisaillement de Kandi sont anté- et syn-décrochements ductiles. Le magmatisme anté-décrochement ductile est sub-alcalin et comporte une composante crustale et une composante mantellique appauvrie. Le magmatisme sub-alcalin s’est poursuivi au cours du décrochement ductile et cette période se caractérise par un cogénétisme plutonisme-volcanisme. De même, on observe une transition de magmas sub-alcalins-alcalins, qui traduit un changement de sources mantelliques-manteau appauvri manteau enrichi. Nous montrons également que le bassin volcano-sédimentaire de Idaho-Mahou est ouvert par le jeu de décrochements. Les volcanites du bassin, présentant des analogies de composition chimique et de chronologie de mise en place avec le pluton syn-cisaillement de Fita, indiquent que ce bassin est syn-orogénique, intramontagneux. La présence de magmas d’origine mantellique remontant dans la zone de cisaillement implique l’ampleur lithosphérique de la zone de cisaillement de Kandi. La synthèse des données indique que le fonctionnement du décrochement ductile de Kandi est contemporain de l’édifice de nappes et chevauchements dans les unités externes des Dahoméyides et démontre ainsi une partition de la déformation à l’échelle de la chaîne pendant la période post-collision. Elle indique également que le fonctionnement du décrochement ductile de Kandi à l’Ouest de la chaîne des Dahoméyides est synchrone de la période d’activité des zones de cisaillement à l’Est de la chaîne et du Hoggar et du Brésil / The present study focuses on the structural characteristics of the Kandi shear zone (KSZ) and the time and space relationships between deformation and magmatic events in the central region of Bénin. This tectonic structure is a segment of a lithospheric-scale shear zone that extends from the Hoggar massif (Algeria) to the Atlantic Coast in Bénin and continues down to western Brazil. The present work aims at better understanding the late to post-collision geodynamic evolution of the pan African Dahomeyide fold beltIn summary, this study reveals that the Kandi shear zone in the Central-Bénin is a large (more than 50 km width) dextral transcurrent shear zone, where the latest increments of deformation occur as more localized (kilometric-scale width) shear bands at low temperature. The KSZ activity started at c. 610 Ma and affected the rock basement, including Paleoproterozoic granulites and Neoproterozoic gneisses, migmatites and granitoids. The granitoids intrusions that are spatially associated to the KSZ display ante- to syn-shearing structural features. The earliest intrusion, ante-tectonic Dassa has sub-alkaline affinity deriving from crustal and depleted mantle magmas. This sub-alkaline series carry on during the transcurrent shearing with the Gobada, Tré, Tchetti intrusions. The latest magmatic event of Fita intrusion suggests the transition from sub-alkaline to alkaline magmas, probably reflecting mantle source evolution, from depleted to enriched mantle. We also showed that the Idaho-Mahou volcano-sedimentary basin opened during the transcurrent shearing and the volcanic mafic and felsic rocks are probably related to the successive sub-alkaline to alkaline intrusions. The occurrence of mantle-derived magmas in the shear zone confirms the lithospheric scale of the Kandi shear zone. According to the available radiometric data from the Dahomeyides fold belt, the Kandi shear zone activity seems to contemporaneous with the nappes stacking and thrusting stages in the external orogenic zone (Atacora and western Benin plain) orogen-scale. It also indicates that the KSZ was coeval with the major shear zones from the easternmost region of the Dahomeyides fold belt (NE Nigeria), of the Hoggar and Braziliano belts.

The rheology and strength of the lower crust play a key role in lithosphere dynamics, influencing the orogenic cycle and how plate tectonics work. Despite their geological importance, the processes that cause weakening of the lower crust and strain localization are still poorly understood. Through microstructural analysis of naturally deformed samples, this PhD aims to investigate how weakening and strain localization occurs in the mafic continental lower crust. Mafic granulites are analysed from two unrelated continental lower crustal shear zones which share comparable mineralogical assemblages and high-grade deformation conditions (T > 700 °C and P > 6 Kbar): the Seiland Igneous Province in northern Norway (case-study 1) and the Finero mafic complex in the Italian Southern Alps (case-study 2). Case-study 1 investigates a metagabbroic dyke embedded in a lower crustal metasedimentary shear zone undergoing partial melting. Shearing of the dyke was accompanied by infiltration of felsic melt from the adjacent partially molten metapelites. Findings of case-study 1 show that weakening of dry and strong mafic rocks can result from melt infiltration from nearby partially molten metasediments. The infiltrated melt triggers melt-rock reactions and nucleation of a fine-grained (< 10 µm average grain size) polyphase matrix. This fine-grained mixture deforms by diffusion creep, causing significant rheological weakening. Case-study 2 investigates a lower crustal shear zone in a compositionally-layered mafic complex made of amphibole-rich and amphibole-poor metagabbros. Findings of case-study 2 show that during prograde metamorphism (T > 800 °C), the presence of amphibole undergoing dehydration melting reactions is key to weakening and strain localization. Dehydration of amphibole generates fine-grained symplectic intergrowths of pyroxene + plagioclase. These reaction products form an interconnected network of fine-grained (< 20 µm average grain size) polyphase material that deforms by diffusion creep, causing strain partitioning and localization in amphibole-rich layers. Those layers without amphibole fail to produce an interconnected network of fine grained material. In this layers, plagioclase deforms by dislocation creep, and pyroxene by microfracturing and neocrystallization. Overall, this PhD research highlights that weakening and strain localization in the mafic lower crust is governed by high-T mineral and chemical reactions that drastically reduce grain size and trigger diffusion creep.

O período pós-colisional Neoproterozoico no sul do Brasil é marcado por intensa atividade tectônica transcorrente. Neste contexto, a Zona de Cisalhamento Quitéria Serra do Erval, uma das inúmeras estruturas que compõe o Cinturão de Cisalhamento Sul-brasileiro, controlou o aporte, a ascensão e o posicionamento de diversos granitoides, dentre eles, os Granitoides Arroio Divisa, intrusivos no Complexo Arroio dos Ratos. Os Granitoides Arroio Divisa compreendem uma associação de rochas predominantemente granodioríticas, com termos dioríticos e tonalíticos ocorrendo em menor expressão. Apresentam textura heterogranular média a grossa e são sempre foliadas. Ao longo da intrusão, são distinguidas zonas de mais alta e mais baixa deformação, distribuídas de forma heterogênea, o que é evidenciado pelo grau de desenvolvimento e morfologia das estruturas planares e lineares. Nas zonas de mais baixa deformação, concentradas nas porções centrais do corpo granítico, predominam as estruturas magmáticas e a componente deformacional é menos intensa, enquanto que em direção à borda norte da intrusão, a morfologia destas estruturas progride por aumento na intensidade da deformação, com a geração de foliação milonítica bem desenvolvida A evolução estrutural dos Granitoides Arroio Divisa é marcada por estruturas tardi-magmáticas que avançam progressivamente para estruturas subsolidus, e subsequentemente para estruturas de mais baixa temperatura, evidenciando a cristalização com concomitante história deformacional sob condições de temperatura decrescente. Feições microestruturais de alta temperatura incluem o desenvolvimento do padrão tabuleiro de xadrez em cristais de quartzo, e a geração de subgrãos grandes em cristais de K-feldspato e plagioclásio, compatíveis com temperaturas da fácies anfibolito superior e com a temperatura solidus de composições graníticas. As feições microestruturais de baixa temperatura consistem na recristalização dos cristais de quartzo por bulging, neoformação de grãos finos ao redor dos cristais de feldspato, e desenvolvimento de pertitas em chamas nos K-feldspato, compatíveis com temperaturas da fácies xistos verdes, bem abaixo da solidus. Enquanto as microestruturas de alta deformação estariam associadas aos estágios iniciais da cristalização e resfriamento do magma, as de mais baixa estariam relacionadas aos estágios pós-cristalização, quando rocha e encaixante alcançam equilíbrio térmico. / The Neoproterozoic post-collisional period in southern Brazil is marked by intense transcurrent tectonic activity. In this context, the Serra do Erval Quitéria Shear Zone, one of the several structures that compose the South Brazilian Shear Belt, controlled the input, ascent and emplacement of several granitoids, among them the Arroio Divisa Granitoids, intrusive in the Complex Arroio dos Ratos. The Arroio Divisa Granitoids consist an association of predominantly granodioritic rocks, with dioritic and tonalitic terms occurring in lesser expression. They presented medium to thick heterogranular texture and are always foliated. Along the intrusion, zones of higher and lower deformation are distinguished, distributed in a heterogeneous way, which is evidenced by the degree of development and morphology of the planar and linear structures. In the lower deformation zones, which are concentrated in the central portion of the granitic body, the magmatic structures prevail and the deformation component is less intense, whereas towards the north margin of the intrusion the morphology of these structures progresses by increase in the intensity of the deformation, with the generation of well-developed milonitic foliation The structural evolution of the Arroio Divisa Granitoids is marked by progressively advance of the late-magmatic to subsolidus structures, and subsequently to structures of lower temperature, evidencing the crystallization with concomitant deformational history under conditions of decreasing temperature. High-temperature microstructural features include the development of the chessboard pattern in quartz crystals, and the generation of large subgrains in K-feldspar and plagioclase crystals, compatible with temperatures of amphibolite high-grade facies and with the solidus temperature of granite compositions. The low temperature microstructural features consist of recrystallization of the quartz crystals by bulging, neoformation of fine grains around the feldspar crystals, and development of flaming pertite in the K-feldspar, compatible with temperatures of the greenschist facies, well below the solidus. While the high deformation microstructures would be associated to the initial stages of crystallization and cooling of the magma, the one of lower deformation would be associated to the post crystallization stages, when rock and host rock reach thermal balance.

Les riches gisements filoniens aurifères de Tirek-Amesmessa, situés dans le Sud algérien, sont liés au fonctionnement d'un cisaillement décrochant majeur, (Zone de Cisaillement Est Ouzzalienne, ZCEO) tardi-panafricain ( 540Ma), dont le compartiment ouest est constitué par l'unité granulitique d'In Ouzzal, d'âge archéen, métamorphisée au cours du cycle éburnéen (2Ga) L'étude pétro-structurale régionale, celle des inclusions fluides (microthermomètrie, analyse par sonde Raman), des isotopes stables (C,O,H) et du plomb des galènes, permettent de découper l'histoire des gisements en trois cycles: Cycle 1 : Une longue période de fonctionnement ductile de la ZCEO, accompagnée de l'intrusion de roches basiques syncinématiques, se termine par une altération hydrothermale complexe (bérisites) localisée dans des couloirs de déformation et suivie de la mise en place de filons de quartz. La déformation ductile, évoluant vers le fragile en fin de cycle se focalise de façon croissante dans les quartz. La future zone minéralisée agit comme une structure drainant un type assez constant de fluides à température décroissante (500 à 300°C) et à profondeur assez stable (18 à 15km): fluides aqueux "métamorphiques" contenant une composante carbonique mantélique en relation avec les intrusions basiques syncinématiques. Le cycle Il : correspond à la maturation tectonique du quartz: microfracturation en plusieurs stades au cours de la remontée vers la surface jusque vers 4-5km. Des fluides de type saumures relaient les précédents. Le cycle III : voit la minéralisation aurosulfurée (sphalérite puis galène-or) se déposer en utilisant la microperméabilité créée précédemment. Le dépôt de l'or résulte d'un mélange de fluides (dont des saumures) qui traversent l'unité granulitique selon des circuits de profondeur différente, dans le contexte d'un hydrothermalisme activé par de grandes intrusions acides tardi-tectoniques. La nature des fluides impliqués, les isotopes du plomb des galènes, les teneurs en or des protolithes granulitiques d'In Ouzzal impliquent que ces derniers constituent les roches mères de l'or.

O período pós-colisional Neoproterozoico no sul do Brasil é marcado por intensa atividade tectônica transcorrente. Neste contexto, a Zona de Cisalhamento Quitéria Serra do Erval, uma das inúmeras estruturas que compõe o Cinturão de Cisalhamento Sul-brasileiro, controlou o aporte, a ascensão e o posicionamento de diversos granitoides, dentre eles, os Granitoides Arroio Divisa, intrusivos no Complexo Arroio dos Ratos. Os Granitoides Arroio Divisa compreendem uma associação de rochas predominantemente granodioríticas, com termos dioríticos e tonalíticos ocorrendo em menor expressão. Apresentam textura heterogranular média a grossa e são sempre foliadas. Ao longo da intrusão, são distinguidas zonas de mais alta e mais baixa deformação, distribuídas de forma heterogênea, o que é evidenciado pelo grau de desenvolvimento e morfologia das estruturas planares e lineares. Nas zonas de mais baixa deformação, concentradas nas porções centrais do corpo granítico, predominam as estruturas magmáticas e a componente deformacional é menos intensa, enquanto que em direção à borda norte da intrusão, a morfologia destas estruturas progride por aumento na intensidade da deformação, com a geração de foliação milonítica bem desenvolvida A evolução estrutural dos Granitoides Arroio Divisa é marcada por estruturas tardi-magmáticas que avançam progressivamente para estruturas subsolidus, e subsequentemente para estruturas de mais baixa temperatura, evidenciando a cristalização com concomitante história deformacional sob condições de temperatura decrescente. Feições microestruturais de alta temperatura incluem o desenvolvimento do padrão tabuleiro de xadrez em cristais de quartzo, e a geração de subgrãos grandes em cristais de K-feldspato e plagioclásio, compatíveis com temperaturas da fácies anfibolito superior e com a temperatura solidus de composições graníticas. As feições microestruturais de baixa temperatura consistem na recristalização dos cristais de quartzo por bulging, neoformação de grãos finos ao redor dos cristais de feldspato, e desenvolvimento de pertitas em chamas nos K-feldspato, compatíveis com temperaturas da fácies xistos verdes, bem abaixo da solidus. Enquanto as microestruturas de alta deformação estariam associadas aos estágios iniciais da cristalização e resfriamento do magma, as de mais baixa estariam relacionadas aos estágios pós-cristalização, quando rocha e encaixante alcançam equilíbrio térmico. / The Neoproterozoic post-collisional period in southern Brazil is marked by intense transcurrent tectonic activity. In this context, the Serra do Erval Quitéria Shear Zone, one of the several structures that compose the South Brazilian Shear Belt, controlled the input, ascent and emplacement of several granitoids, among them the Arroio Divisa Granitoids, intrusive in the Complex Arroio dos Ratos. The Arroio Divisa Granitoids consist an association of predominantly granodioritic rocks, with dioritic and tonalitic terms occurring in lesser expression. They presented medium to thick heterogranular texture and are always foliated. Along the intrusion, zones of higher and lower deformation are distinguished, distributed in a heterogeneous way, which is evidenced by the degree of development and morphology of the planar and linear structures. In the lower deformation zones, which are concentrated in the central portion of the granitic body, the magmatic structures prevail and the deformation component is less intense, whereas towards the north margin of the intrusion the morphology of these structures progresses by increase in the intensity of the deformation, with the generation of well-developed milonitic foliation The structural evolution of the Arroio Divisa Granitoids is marked by progressively advance of the late-magmatic to subsolidus structures, and subsequently to structures of lower temperature, evidencing the crystallization with concomitant deformational history under conditions of decreasing temperature. High-temperature microstructural features include the development of the chessboard pattern in quartz crystals, and the generation of large subgrains in K-feldspar and plagioclase crystals, compatible with temperatures of amphibolite high-grade facies and with the solidus temperature of granite compositions. The low temperature microstructural features consist of recrystallization of the quartz crystals by bulging, neoformation of fine grains around the feldspar crystals, and development of flaming pertite in the K-feldspar, compatible with temperatures of the greenschist facies, well below the solidus. While the high deformation microstructures would be associated to the initial stages of crystallization and cooling of the magma, the one of lower deformation would be associated to the post crystallization stages, when rock and host rock reach thermal balance.

O período pós-colisional Neoproterozoico no sul do Brasil é marcado por intensa atividade tectônica transcorrente. Neste contexto, a Zona de Cisalhamento Quitéria Serra do Erval, uma das inúmeras estruturas que compõe o Cinturão de Cisalhamento Sul-brasileiro, controlou o aporte, a ascensão e o posicionamento de diversos granitoides, dentre eles, os Granitoides Arroio Divisa, intrusivos no Complexo Arroio dos Ratos. Os Granitoides Arroio Divisa compreendem uma associação de rochas predominantemente granodioríticas, com termos dioríticos e tonalíticos ocorrendo em menor expressão. Apresentam textura heterogranular média a grossa e são sempre foliadas. Ao longo da intrusão, são distinguidas zonas de mais alta e mais baixa deformação, distribuídas de forma heterogênea, o que é evidenciado pelo grau de desenvolvimento e morfologia das estruturas planares e lineares. Nas zonas de mais baixa deformação, concentradas nas porções centrais do corpo granítico, predominam as estruturas magmáticas e a componente deformacional é menos intensa, enquanto que em direção à borda norte da intrusão, a morfologia destas estruturas progride por aumento na intensidade da deformação, com a geração de foliação milonítica bem desenvolvida A evolução estrutural dos Granitoides Arroio Divisa é marcada por estruturas tardi-magmáticas que avançam progressivamente para estruturas subsolidus, e subsequentemente para estruturas de mais baixa temperatura, evidenciando a cristalização com concomitante história deformacional sob condições de temperatura decrescente. Feições microestruturais de alta temperatura incluem o desenvolvimento do padrão tabuleiro de xadrez em cristais de quartzo, e a geração de subgrãos grandes em cristais de K-feldspato e plagioclásio, compatíveis com temperaturas da fácies anfibolito superior e com a temperatura solidus de composições graníticas. As feições microestruturais de baixa temperatura consistem na recristalização dos cristais de quartzo por bulging, neoformação de grãos finos ao redor dos cristais de feldspato, e desenvolvimento de pertitas em chamas nos K-feldspato, compatíveis com temperaturas da fácies xistos verdes, bem abaixo da solidus. Enquanto as microestruturas de alta deformação estariam associadas aos estágios iniciais da cristalização e resfriamento do magma, as de mais baixa estariam relacionadas aos estágios pós-cristalização, quando rocha e encaixante alcançam equilíbrio térmico. / The Neoproterozoic post-collisional period in southern Brazil is marked by intense transcurrent tectonic activity. In this context, the Serra do Erval Quitéria Shear Zone, one of the several structures that compose the South Brazilian Shear Belt, controlled the input, ascent and emplacement of several granitoids, among them the Arroio Divisa Granitoids, intrusive in the Complex Arroio dos Ratos. The Arroio Divisa Granitoids consist an association of predominantly granodioritic rocks, with dioritic and tonalitic terms occurring in lesser expression. They presented medium to thick heterogranular texture and are always foliated. Along the intrusion, zones of higher and lower deformation are distinguished, distributed in a heterogeneous way, which is evidenced by the degree of development and morphology of the planar and linear structures. In the lower deformation zones, which are concentrated in the central portion of the granitic body, the magmatic structures prevail and the deformation component is less intense, whereas towards the north margin of the intrusion the morphology of these structures progresses by increase in the intensity of the deformation, with the generation of well-developed milonitic foliation The structural evolution of the Arroio Divisa Granitoids is marked by progressively advance of the late-magmatic to subsolidus structures, and subsequently to structures of lower temperature, evidencing the crystallization with concomitant deformational history under conditions of decreasing temperature. High-temperature microstructural features include the development of the chessboard pattern in quartz crystals, and the generation of large subgrains in K-feldspar and plagioclase crystals, compatible with temperatures of amphibolite high-grade facies and with the solidus temperature of granite compositions. The low temperature microstructural features consist of recrystallization of the quartz crystals by bulging, neoformation of fine grains around the feldspar crystals, and development of flaming pertite in the K-feldspar, compatible with temperatures of the greenschist facies, well below the solidus. While the high deformation microstructures would be associated to the initial stages of crystallization and cooling of the magma, the one of lower deformation would be associated to the post crystallization stages, when rock and host rock reach thermal balance.

Upper part of the orogenic crust (superstructure) significantly differs from the lower part of the crust (infrastructure) by structural and metamorphic record. This fundamental observation is explained by interruption of the mutual evolution due to mechanical decoupling of the hot and ductile infrastructure from the cold and brittle superstructure at certain stages of the orogenic evolution. The superstructure-infrastructure transition zone is a rheologically predisposed domain of sharp deformation and metamorphic gradients with polyphase structural record. Understanding of the deformation partitioning in such a rheologically complex setting is a key aspect in linking of the individual deformation stages between upper and lower crust. The transition zone between unmetamorphosed early-Variscan superstructure (Teplá-Barrandian Domain) and late Variscan high- grade infrastructure (Saxothuringian Domain) crops out at the western margin of the Teplá- Barrandian Domain in the Bohemian Massif. This area is a continuous mid- to lower-crustal section with early-Variscan structural and metamorphic record, which is superposed onto pre-Variscan episode. This thesis aims to decipher individual deformation events, to evaluate their manifes- tations at different crustal levels and to bring new and unifying...