A series of crustal-scale shear zones demarcates the northern and eastern margins of the North Caribou greenstone belt (NCGB), proximal to a Mesoarchean terrane boundary in the core of the western Superior Province of Canada. The dominant deformation produced a pervasive steeply dipping fabric that trends broadly parallel to the doubly arcuate shape of the belt and was responsible for tight folding the banded iron formation host to Goldcorp’s prolific gold deposit at Musselwhite mine. The shear zones in the North Caribou greenstone belt are of particular interest because of their ability to channel hydrothermal fluids with the potential to bear ore and cause alteration of the middle to shallow crust. Shear zones are commonly reactivated during subsequent tectonism, but exhibit a consistent and dominant dextral shear sense across the belt; fabric-forming micas and chlorite are generally Mg-rich. Although garnets samples from within the shear zones are dominantly almandine, they possess variable geochemical trends (HREEs of >2 orders of magnitude) and can be syn-, intra-, or post-tectonic in origin. In situ geochronological analysis of zircon (U-Pb) and monazite (total-Pb) in high strain rocks in and around the NCGB, interpreted in light of in situ geochemical analysis of garnet and fabric-forming micas and chlorite, reveals four relatively discrete events that span 400 million years. Metamorphism of the mid-crust was coeval with magmatism during docking of the Island Lake domain at c. 2.86 Ga and subsequent terrane accretion at the north and south margins of the North Caribou Superterrane from c. 2.75 to 2.71 Ga. Transpressive shear at c. 2.60 to 2.56 Ga and late re-activation of shear zones at c. 2.44 Ga produced a steeply-dipping pervasive fabric, and channeled fluids for late crystallization of garnet and monazite recorded in the Markop Lake deformation zone. These observations implicate a horizontal tectonic model similar to the modern eastern Pacific plate margin. Further, this study highlights the caution that should be exercised when using traditional rock forming metamorphic minerals (mica, chlorite, garnet) when attempting to vector into zones of hydrothermal alteration within midcrustal rocks.

The Laurentine Shore is the Imperial Roman palaeo-shoreline preserved up to 1km inland of the southern, distal edge of the Tiber Delta coastline of Lazio, western Central Italy. The progradation of the delta is recorded on the site as a series of shore-parallel relict dune ridges. High-status villas developed along the roman period coastline, with a service village (Vicus Augustanus), and other infrastructure such as roads, aqueduct, piscinae and several baths (thermae), these structures have been examined using a multi-scale geoarchaeological approach. A sea level reconstruction based on multi-proxy palaeo-environmental analysis of a silt/peat sedimentary transition from the base of a Roman piscina suggests that the sea level at ca. 2400 ± 40 BP was around 1.25 ± 0.2 m below modern sea level. This analysis provides further context for assessing the development of the site during the late Holocene in relation to the progradation of the Tiber delta and for the important Imperial Roman period occupation of the Laurentine Shore and other important sites such as Portus and Ostia Antica in the central part of the Tiber delta. At several key periods in the late Holocene, the palaeo-shoreline has been reconstructed using a geochronological framework of optical luminescence dates and geomorphological survey of the Tiber Delta dune ridge record. In particular, during the Imperial Roman period, ca. 2000 BP) it has been shown that the Laurentine Shore was settled during a period of significant Tiber delta shoreline progradation. Two-major building phases at the Vicus Augustanus occur within this progradation phase. By the abandonment of the site in the 5th century AD, the shoreline was around 70 m seaward of the shoreline during the 1st building phase of the Vicus. This rate of shoreline change could be noticeable by the population over decadal timescales and may have driven the alteration of coastal building and property plots during the 500 year lifetime of the settlement. A combined methodology incorporating sedimentology, geochemistry and petrological analysis of diagenetically altered sediments found that early vadose diagenesis may have a deleterious effect upon luminescence dating dosimetry, inducing age underestimation, especially of reddened dune sands. Petrological analysis has also shown that a lack of anomalous fading in luminescence behaviour observed in K-feldspars may be due to a lack of complex microstructure in the mineral grains driven by the metamorphic, Alpine origin of these minerals. An assessment of the geoarchaeological approach used in this thesis shows that a scale-driven context provides a useful structure for examining the various processes and factors affecting the geomorphological and sedimentological records improving confidence in the examination of the archaeological record.

Subsurface data derived from ~388 ft of drill core from Martin County (TX) were used to understand the depositional setting of the Wolfcamp-D, a petroleum producing interval in the Midland Basin. Elemental geochemistry collected via x-ray fluorescence revealed a highly variable depositional history marked by the deposition of diverse siliciclastic and carbonate lithofacies. Integration of multiple datasets resulted in the interpretation of nine lithofacies, whose deposition appears cyclical. Correlations between molybdenum and total organic carbon indicate slow recharge of bottom waters and anoxic/euxinicconditions within the basin. The presence of phosphatic nodules coinciding with siliceous black mudrocks suggested high levels of primary productivity driven by upwelling. High-frequency sea level variability, driven by far-field glaciation and regional paleoclimate, were key controls on both the chemostratigraphy and lithofacies. Along-strike variability is seen throughout the basin due to paleobathymetry, proximity and connections to paleochannels, and localized structures. Rhenium-osmium (Re/Os) geochronology was conducted on siliceous mudrocks with high total organic carbon. A depositional age of 300 ± 18 Ma was obtained, partially confirming previous correlations to shelf biostratigraphic data. Scatter in the Re/Os data is likely due to mixing in the basin or non-hydrogenous Os incorporated into the analysis due to the method of preparation.

In this thesis, the response of uranium minerals and poorly crystalline phases to changes in geochemical conditions through geological time has been assessed in order to understand the mobility of natural uranium in the fracture network of a proposed site for a spent nuclear fuel repository in Forsmark, Sweden. Identification and characterization of solid phase uranium have been performed through electron microprobe analysis and optical petrography (Article I). The identified uraninite, haiweeite, and uranophane crystals have been dated using U-Pb and Pb-Pb isotope ratios obtained from secondary ion mass spectrometry and laser ablation-inductively coupled plasma-mass spectrometry (Article II). The mobility of uranium in current Forsmark groundwaters and fracture system has been modelled using the PHREEQC geochemical program and Ra and Rn isotope systematics (Article IV). The rate of submarine groundwater discharge (SGD) from the Forsmark coast to Öregrundsgrepen has also been modelled using Ra isotopes (Article V). Results from these studies support a geologically early (~1200 Ma) oxidation of U(IV) to U(VI). It is further suggested that the old U(VI) minerals present in the bedrock are soluble at the pe values and alkalinities observed in the Forsmark groundwaters. At pe &lt; −4.6 and alkalinity &lt; 60 mg/L, U(VI) can be reduced to U(IV) and deposited in the fracture network. Although a non-negligible rate of SGD has been observed, this cannot be attributed to the discharge of deep (&gt;200 m.b.s.l.) Forsmark groundwaters on the basis of current data. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: In press. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Field observations of the Greater Himalayan Sequence in Eastern Nepal demonstrate a ductile, highly strained package of metamorphic rocks that show extensive evidence of crustal anatexis throughout. These can be distinguished from the Lesser Himalayan sequence below by a distinct reduction in metamorphic grade, an inverted metamorphic sequence and a high strain zone corresponding to the Main Central Thrust. Metamorphic studies are combined with geochronology to demonstrate a protracted period of crustal melting followed by rapid decompression from 18.7 Ma to 15.6 Ma. A metamorphic decompression rate is quantified at c.2mm/yr during this period. This is interpreted to represent exhumation of the Greater Himalayan Sequence by a process of ductile, channelised flow from the mid-crust beneath Tibet. Below a prominent band of kyanite gneiss, previously used to locate the Main Central Thrust, but here mapped within the Greater Himalayan Sequence, partial melting is still exhibited. Here monazites are dated at 10.6 Ma. In the Lesser Himalaya below, allanites record a similar 10.1 Ma event. This implies that following channel flow during the mid-Miocene, the channel widened in the lower-Miocene to incorporate a greater structural thickness. Following these two periods of exhumation and ductile extrusion, separated in time and space, Fission Track studies indicate that much slower, erosion driven exhumation proceeded, at <1 mm/yr. This rate increases slightly in the Pliocene, most likely in response to Northern Hemisphere glaciation; no difference in exhumation is seen across the Greater Himalayan Sequence with respect to the different, earlier, phases of ductile channel flow related exhumation. These results demonstrate the episodic nature of channel flow in the Himalaya and reconcile arguments about the position of the MCT in Eastern Nepal.

In this thesis, I use multiple techniques to investigate the active faulting and deformation of the Altay Mountains, Western Mongolia. The Altay are an intracontinental transpressional mountain range, which are deforming in the far-field of the India-Asia collision. An anastomosing network of dextral faults strikes NNW-SSE, and accommodates NE-SW oriented shortening by rotating anticlockwise about vertical axes. I begin by characterising the Altay faults, and add to what is already known about their surface expression with new observations of active faulting and three previously undescribed ancient earthquake ruptures. I use ¹⁰Be cosmogenic dating and uranium-series dating on pedogenic carbonate to estimate the average Quaternary rate of slip for two of the major fault zones in the Altay. The slip rate on the Ölgiy fault is constrained to 0.3-2.1 mm/yr^-1. Results from the Hovd fault are ambiguous, demonstrating the complications encountered with application of Quaternary dating techniques. I measure palaeomagnetic directions from Cretaceous to Pliocene-aged sediments in the eastern Altay to constrain the degree of anticlockwise rotation. Results from thermal demagnetisation of specimens indicate that the eastern Altay has not undergone significant rotation, in contrast with previous studies from the Siberian Altay that reveal almost 40 degrees of anticlockwise rotation. This suggests that the eastern-most Altay fault is too young to have experienced significant rotation, or is kinematically different from the Siberian Altay. I apply apatite fission track (AFT) dating and track length modeling to the central Altay. Results from AFT dating show rapid cooling in the late Cretaceous due to the distal assembly of Central Asia, suggesting that there was pre-existing topography at the start of the Late Cenozoic phase of deformation, the timing of which is constrained to have initiated at least 20 Myr ago. My work demonstrates that combining results from techniques that cover a variety of time scales quantifies the evolution of active faulting and deformation in the region.

L'évolution sédimentaire des milieux lagunaires est un phénomène complexe faisant intervenir à la fois des processus intenses sur le court terme (crues, tempêtes) et des processus plus lents sur le long terme (variations du niveau marin moyen, changements climatiques). Si les mécanismes généraux de ces phénomènes sont bien connus, leur variabilité spatiale et temporelle les rends difficiles à estimer au niveau local. La grande diversité des milieux lagunaires et l'influence des actions anthropiques rendent plus hasardeuse encore cette estimation. Dans cette étude, je me suis intéressé au cas du système lagunaire méditerranéen des « étangs Palavasiens, étang de l'Or, canal du Rhône à Sète » situé dans le Golfe du Lion (Sud de la France). L'utilisation d'une approche pluridisciplinaire a permis d'évaluer la dynamique sédimentaire sur des échelles de temps multiples. Sur les deux derniers siècles, le comblement du système lagunaire a pu être estimé à la vitesse moyenne de 1,3 mm.an-1 à travers l'utilisation conjointe de données géographiques historiques et d'analyses géochronologiques (210Pb, 137Cs). Une perte de surface imputable pour moitié aux aménagements anthropiques est également mise en avant au cours du XXème siècle. Une campagne de mesures haute fréquence de la dynamique hydro-sédimentaire a été menée à court-terme (2 ans). Elle a permis de déterminer l'influence des conditions de forçages physiques sur les processus internes (érosion, remise en suspension, dépôt). Les seuils caractéristiques tels que la tension critique d'érosion ont pu être estimés et reliés aux conditions météorologiques. Le bilan net sur les stations suivies durant cette période montre une perte de sédiment. Ce bilan opposé aux estimations historiques sur les mêmes secteurs est probablement en lien avec les conditions d'apports réduites durant la période investiguée. L'adaptation d'un modèle numérique sur la zone d'étude a été entreprise afin de préciser cette dynamique sur une plus large échelle spatiale et temporelle. / The sedimentary evolution of coastal lagoons is a complex phenomenon involving both short term extreme processes (floods, storms) and long term processes (mean sea level variations, climate change). If general mechanisms of these phenomena are well known, their spatial and temporal variability makes them difficult to assess at the local scale. The diversity of lagoonal environments and human influence makes this even more risky. I have focussed this study on the case of a Mediterranean lagoon system : “Palavasian lagoons, Or lagoon, and Rhône-Sète waterway” which is located in the Gulf of Lion (South of France). A multidisciplinary approach was used to assess sediment dynamics on multiple time scales. An average filling rate of 1.3 mm.year-1 over the two last centuries was assessed using a both historical maps and geochronology (210Pb, 137Cs). An area loss due for half to anthropogenic impacts was also highlighted in the twentieth century. A short term (2 years) and high frequency monitoring of in situ hydro-sedimentary dynamics was performed to determine the influence of physical forcing over internal processes (erosion, resuspension, deposition). The main characteristics thresholds were estimated and related to weather conditions. The observed net balance during this monitoring shows a loss of sediment. This assessment, opposite of historical trends, is probably related to the conditions of reduced river contribution. The implementation of a numerical model is going on in order to explain the dynamics on a larger spatial and temporal scales.

Sur Mars, la datation par comptage de densité de cratères est actuellement la seule méthode utilisée pour dater les surfaces planétaires. Cependant, sur Mars, elle n’a pas encore été corrigé et complété par des datations absolues. Ce travail consiste à développer un prototype démontrant le potentiel d’une nouvelle approche expérimentale basée sur la méthode K-Ar pour dater les roches martiennes in situ. L’objectif à terme est de proposer une solution instrumentale de datation absolue pour un futur rover d’exploration.Un laser Nd :YAG quadruplé pour tirer à 266 nm ablate un échantillon basaltique mis sous vide secondaire. L’observation du plasma par « Laser Induced Breakdown Spectroscopy » apporte des informations sur la concentration en K et sur la nature chimique et minéralogique de la cible. Puisque l’ablation est faite par un laser UV et sous vide secondaire, l’ablation est reproductible par minéralogie. La reconnaissance stoechiométrique permet donc d’estimer la masse vaporisée. Après purification des gaz libérés, un spectromètre de masse quadripolaire détermine la quantité d’argon.L’ensemble de ces mesures pourvoit un âge avec une incertitude théorique de 13% dans les meilleures conditions.Les calibrations du dispositif expérimental ont apporté de nombreuses informations sur des effets sur les spectres LIBS provoqués par l’ablation sous vide secondaire. L’augmentation de la pression e tla variation de géométrie du cratère d’ablation ont des effets opposés sur les pics des éléments.Nous avons aussi démontré que l’instrument était capable de mesurer l’âge de la mésostase de roche basaltique et qu’il offre des perspectives intéressantes sur certaines phases minérales comme la biotite. / Crater counting is the only method used on Mars to give relative geochronological information but it never had been fitted and corrected by absolute geochronology. This work is about the development of a new prototype demonstrating the ability of a protocol using in situ K-Ar dating. The goal is to propose a solution of an absolute geochronology for the next explorations rovers. A quadrupled Nd:YAG laser at 266 nm ablates a basaltic sample under high vacuum. The light collection by a spectrometer (Laser Induced Breakdown Spectroscopy) gives the rate of potassium and the chemical or the mineralogy of the target. Thanks to the specificities of the ablation in highvacuum and with a UV laser, the ablated mass has a good reproducibility per mineralogy. Thus, theLIBS identification gives an estimation of the ablated mass. After the purification of the released gas,a quadrupole mass spectrometer determines the quantity of argon. All these measures give an age with a theoretical uncertainty of 13% in the best conditions.The calibration of the experiment had given new information about the effects on LIBS spectrarelated to the ablation under high vacuum. The rise of the pressure and the variation of geometry of the pit have opposite effects on the elements peaks. We also demonstrated that the instrument was capable of measuring the age of the groundmass of basalt and has some interesting perspectives on some mineral phases such as biotite.

Lors de cette étude, 47 nouveaux âges ont été obtenus par la technique Cassignol-Gillot, complétant à 128 âges le nombre de données disponibles sur l'île de Basse-Terre. La très bonne reproductibilité des âges obtenus dans cette étude, et la cohérence de ces derniers sur l'ensemble des massifs, appuie l'utilisation de la méthode K-Ar pour la datation des laves des Petites Antilles. Les données géochronologiques ont été associés à des analyses géochimiques et géomorphologiques dans le but de contraindre l'évolution spatio-temporelle du volcanisme de Basse-Terre, mais également d'apporter de nouvelles contraintes sur les taux de construction et d'érosion en contexte tropical.Le volcanisme récent de Basse-Terre, i.e. inférieur à 1 Ma, se concentre dans la moitié sud de l'île. Composée de trois massifs volcaniques (Piton de Bouillante, Sud Chaîne Axiale et le Complexe Volcanique de Grande-Découverte), son activité a débuté au nord-ouest par la mise en place du Piton de Bouillante entre 906 ± 13 et 712 ± 12 ka, avec un taux de construction de 0.7 ± 0.2 km3/kyr. Les nouvelles données obtenues lors de cette étude montrent qu'aucun effondrement de flanc majeur n'a affecté cet édifice. L'activité volcanique a ensuite rapidement migrée vers le sud-est pour former entre 681 ± 12 et 509 ± 10 ka les volcans de Moustique, Matéliane, Capesterre et Icaque, qui constitue le massif Sud Chaine Axiale. La contemporanéité des âges obtenus sur l'ensemble des édifices, et le taux de construction calculé à 0.5 km 3/kyr, appuient la mise en place du sud de la Chaine Axiale par un unique massif volcanique, contredisant les hypothèses d'effondrement de flanc précédemment proposées. L'homogénéité géochimique observée sur l'ensemble du massif supporte l'hypothèse d'un seul édifice. Entre 500 et 450 ka, le flanc ouest du massif Sud Chaîne Axial a été affecté par un slump actuellement matérialisé par le volcan d'Icaque. La dépression formée a permis la mise en place du volcan du Sans-Toucher entre 451 ± 13 et 412 ± 8 ka. Entre 400 et 200 ka, très peu d'activité effusive a pu être mise en évidence. Depuis 200 ka, l'activité volcanique se concentre dans le sud de l'île, avec la mise en place du Complexe Volcanique de la Grande-Découverte, par une succession de phases de construction et de destruction. La dernière activité volcanique a permis la construction du dôme actuel de La Soufrière. Les investigations géomorphologiques nous ont également permis de contraindre les taux d'érosion ayant affecté l'île de Basse-Terre. Ainsi, le Piton de Bouillant subit une érosion de 1 250 ± 700 t/km'/an depuis 700 ka. Pour les volcans du Sans-Toucher, et des Monts-Caraïbes, nous avons obtenus un taux d'érosion similaire, respectivement de 940 ± 380 et 610± 550 t/km2/an. Malgré une localisation et une morphologie initiale différentes, la similarité des taux d'érosion obtenus pour les volcans de Basse-Terre met en évidence l'absence d'un effet barrière sur l'érosion à long terme, pourtant majeur à plus courte échelle de temps. / In this study, forty-seven new ages have been obtained by the Cassignol-Gillot technique, increasing to 128, the geochronological database available for the Basse-Terre Island. The very good reproducibility of the ages obtained in this study, added to a strickly consistency observed between the volcanic edifices, support the use of the K-Ar method in the dating of the Lesser Antilles lavas. This new geochronological dataset has been combined with geochemical and geomorphological analyses in order to constrain the volcanic history of Southern Basse-Terre Island as well as to compute construction and erosion rates.Southern part of Basse-Terre hosts the recent volcanic activity since the last 1 Myr. Composed by three volcanic massifs (Piton de Bouillante, Southern Axial Chain and the Grande-Découverte Volcanic Complex), its activity has begun in the northwest part by the construction of the Piton de Bouillante between 906 ± 13 and 712 ± 12 ka, with a construction rate of 0.7 ± 0.2 km3/kyr. Our new data show that no major flank collapse have affected this volcano. Then, volcanic activity has migrated to the southeast, constructing between 681 ± 12 and 509 ± 10 ka the Southern Axial Chain massif, composed by Moustique, Matéliane, Capesterre and Icaque volcanoes. The contemporaneity of the ages for the whole massif together with the construction rate computed at 0.5 km3/kyr suggest the formation of the southern Axial Chain by a unique volcanic edifice, which did not experienced major flank collapses as previously proposed. The geochemical homogeneity observed throughout the massif supports this single volcano hypothesis. Between 500 and 450 ka, a slump has affected the western part of the Southern Axial Chain and forming the Icaque volcano. The resulting depression has allowed the construction of the Sans-Toucher volcano from 451 ± 13 to 412 ± 8 ka. After the construction of the Sans-Toucher volcano, only few evidences for an effusive activity occurring between 400 and 200 ka can be found. Since 200 ka, volcanic activity is present in the southern part with the construction of the Grande-Découverte Volcanic complex (GDVC), alternating constructive and destructive phase. The last volcanic activity formed the 1530 AD La Soufrière dome. Geomorphological investigations have also allowed us to constrain the erosion rates having affected Basse-Terre Island. Thus, Piton de Bouillante volcano have suffered of an erosion rate of 1,250 ± 700 t/km²/yr since 700 ka. We have obtained for the Sans-Toucher and Monts-Caraïbes volcanoes similar rates of 940 ± 380 and 610 ± 550 t/km²/yr, respectively. Despite a different location and different initial morphology, the similarity erosion rates observed for each massif suggest that the barrier effect does not significantly affect the long-term erosion budget while it plays a major role at much shorter time-scale.

A zona de cisalhamento Patos consiste em uma mega-estrutura transcorrente E-W que deformou rochas pré-cambrianas durante a orogênese brasiliana. As relações entre fusão parcial e deformação, os mecanismos de deformação envolvidos na nucleação da estrutura e a evolução termocronológica da milonitização foram investigados por meio de trabalhos de campo e técnicas multidisciplinares tais como a anisotropia de suscetibilidade magnética (ASM), geocronologia (U-Pb SHRIMP) e orientações preferenciais cristalográficas medidas através de difração de elétrons retroespalhados (EBSD). O domo de Santa Luzia, situado na conexão da zona de cisalhamento com a Faixa Seridó, caracteriza-se pela trama magnética levemente oblíqua à elongação NE do corpo. Idades U-Pb obtidas na borda recristalizada de zircões do migmatito forneceram idades de 575 ± 3.4 Ma. Trama magnética e idade semelhantes foram encontradas no granito Acari, sugerindo a contemporaneidade entre o alojamento dos magmas e a deformação cisalhante. No anatexito Espinho Branco, geometrias complexas observadas em campo não são reproduzidas na trama de ASM, a qual concorda com a cinemática da zona de cisalhamento Patos. Entretanto, sítios com suscetibilidades baixas (< 0.5 mSI) exibem dispersões na trama magnética, as quais contrastam com orientações cristalográficas de biotita e dados de campo. Contudo, a anisotropia de remanência anisterética mantém-se coerente com o campo de deformação a que foi submetido o anatexito, sugerindo que a dispersão das direções principais de ASM relaciona-se à fases hidrotermais tardias que desorganizam a trama magnética. Ortognaisses miloníticos situados na borda norte da zona de cisalhamento são marcados por migração de bordas dos grãos, fraturamento intracristalino e mirmequitização periférica. As tramas de eixos [0001] de quartzo exibem máximos em Y nos milonitos de alto-grau, sugerindo ativação do sistema de deslizamento prismático-a. As microestruturas gradam para o estado magmático no contato com o anatexito, sendo comuns tramas randômicas de eixo-c de quartzo. Zircões extraídos de leucossomas fornecem uma idade de 566 ± 5 Ma, atribuídos à cristalização do magma. A margem sul da estrutura exibe uma progressiva redução do tamanho dos grãos e geração de milonitos finos a ultramilonitos sem a presença de fusão parcial. Zircões extraídos de um augen granítico forneceram uma idade de intercepto inferior de 545 ± 14 Ma, atribuída ao metamorfismo. Os milonitos da borda sul registram tramas de eixo-c de quartzo com máximos entre Z e Y, sugerindo ativação dos sistemas romboédrico- e basal-a. Nos feldspatos, os principais sistemas de deslizamento são (010)[001] e (010)[100] em todos os litotipos, com exceção do sistema (100)[010], observado na transição entre migmatitos e os milonitos de baixo grau. Estimativas de temperatura por meio do método TitaniQ registram temperaturas médias de ~ 490ºC nos milonitos da borda sul. O conjunto de resultados permite concluir que: i) a ASM reflete os incrementos finais da deformação regional que afetou os migmatitos, ii) a fusão parcial associada ao cisalhamento dextral do Patos ocorreu em c. 565 Ma, enquanto a milonitização de médio a baixo grau, datada em 545 Ma, caracteriza o retrabalhamento metamórfico ocasionado pela localização da deformação em regime dúctil-rúptil; iii) este retrabalhamento é correlacionável a outras zonas de cisalhamento da Província Borborema, constituindo um evento de caráter regional possivelmente relacionado às colisões tardias na margem oeste do Gondwana e, iv) a zona de cisalhamento Patos foi formada após a colisão dos crátons Oeste Africano e Congo-São Francisco ao escudo da Borborema, acomodando deslocamentos transcorrentes a partir de descontinuidades crustais formadas em estágio pré-colisional. / The Patos shear zone is an E-W transcurrent structure that deformed Precambrian rocks from the Borborema Province during the Neoproterozoic. The relationships between partial melting and deformation, the nucleation of the shear zone and the thermochronological evolution of mylonites were investigated by means of detailed field work coupled with Anisotropy of Magnetic Susceptibility (AMS), U-Pb SHRIMP geochronology and crystallographic fabrics measured through electron backscatter diffraction (EBSD). In the Santa Luzia dome, located within the Seridó Belt, the magnetic lineations are slightly oblique to the dome NE elongation. Zircon recrystallized rims yield U-Pb ages of 575 ± 3.4 Ma. These data are consistent with ages and magnetic fabrics found in the Acari granite, suggesting that magma emplacement and shearing were coeval in the Seridó belt. In the Espinho Branco anatexite, emplaced within the mylonites of the Patos shear zone, complex field leucosome geometries are not reproduced in the magnetic fabric, which is consistent with the kinematics of the shear zone. However, low susceptibilities (< 0.5 mSI) display a scattering of magnetic orientations and do not correlate with biotite lattice fabrics and field foliations. Nevertheless, anisotropy of anhystheretic remanence fabrics remain parallel to the external strain field, suggesting that AMS dispersions may be related to late percolation of hydrothermal fluids. Mylonitic orthogneisses from the northern border of the Patos shear zone are marked by grain boundary migration, intracrystalline fracturing and myrmekitization at the periphery of grains. Quartz [0001] lattice fabrics form maxima mainly on Y, suggesting activation of prism-a slip systems. Towards the contact with migmatites, the microstructures progressively change from solid-state to magmatic, characterized by widespread interstitial quartz and random orientations of quartz c-axis fabrics. Zircons from the leucosomes yield an age of 566 ± 5 Ma, which is attributed to magma crystallization. The southern border of the Patos shear zone is marked by progressive grain size reduction and formation of fine-grained mylonites to ultramylonites without traces of partial melting. An age of 545 ± 14 Ma, obtained in zircons from an ultramylonitic augen granite, constrains the timing of the low-grade metamorphism. These Southern mylonites show quartz [0001] fabrics with maxima spreading between Z and Y, suggesting activation of prism and basal slip systems. In feldspars, the main activated slip systems are (010)[001] and (010)[100] in all rock types, except for the (100)[010] slip system, observed in the transition from migmatites to low-grade mylonites. TitaniQ temperature estimates record mean temperatures of ~ 490ºC for the southern mylonites. These data allows us to conclude that: i) AMS reflects the final strain increments recorded in migmatites during regional deformation, ii) partial melting and dextral shearing in the Patos shear zone occurred at ~ 565 Ma, while low-grade mylonitisation dated at 545 Ma defines a late reworking at ductile-brittle conditions, iii) this reworking event is observed in other areas of the Borborema Province, defining a regional event possibly associated with late collisions in the western margin of Gondwana, iv) the Patos shear zone was nucleated after the collision between the Congo-São Francisco and West-African Cratons, through accommodation of strike-slip displacements localized in crustal discontinuities previously formed in an early pre-collisional stage.