It is hotly debated about the final closural time and position of the Paleo-Asian Ocean. Some geologists advocated the "Solonker" suture marks the final closural zone in Permian, whereas others insist in middle Paleozoic. Our three study areas, the Hongqi, the Ondor Sum and the Mandula is essential and important to solve those controversies. The litho-tectonic units recognized in the Hongqi-Ondor Sum area include the Hongqi-Ondor Sum mélange belt, the Bainaimiao arc belt, North China Craton and post-orogenic unconformably sedimentary rocks. The Hongqi-Ondor Sum mélange belt experienced two phase ductile deformation and one phase ductile-brittle deformation. D1 is responsible for the regional greenschist foliation S1, elongated mineral lineation L1, and intrafolial fold F1. The kinematic criteria indicates a top-to-the-NW shearing sense. D2 is characterized by various sized of unsymmetrical folds with nearly NE axis corresponding to the NW thrust shearing. D3 formed the regional framework in the Hongqi and the Ondor Sum areas. The Mandula area contains olistostrome sediments, turbiditic sediments and volcano-sedimentary rocks. Detrital zircon grains in sedimentary samples argue the Mandula study area received the southern Bainaimiao arc materials and coeval Permian volcanic erupting materials nearby. The sediments and volcanic rocks in Mandula area subject a nearly NW-SE or N-S compressional shortening. The geological data support that an Early Paleozoic subduction and collsioan, Late Palezoic rifting and rift closure model. The so called "Solonker" ophiolitic fragments indeed are olistostrome. Typical ophiolite components are not observed in the Mandula area.

Thesis (PhD)--Macquarie University, Division of Environmental & Life Sciences, Department of Earth and Planetary Sciences, 2005. / Bibliography: leaves 202-224. / Introduction -- Geological setting of the New England Fold Belt -- Regional geophysical investigation -- Data acquisition and reduction -- Modelling and interpretation of magnetic data over the Peel Fault -- Modelling and interpretation of magnetic data over the Mooki Fault -- Gravity modelling of the Tamworth Belt and Gunnedah Basin -- Interpretation and discussion -- Conclusions. / This thesis presents new magnetic and gravity data for the Southern New England Fold Belt (SNEFB) and the Gunnedah Basin that adjoins to the west along the Mooki Fault in New South Wales. The SNEFB consists of the Tamworth Belt and Tablelands Complex that are separated by the Peel Fault. The Tablelands Complex to the east of the Peel Fault represents an accretionary wedge, and the Tamworth Belt to the west corresponds to the forearc basin. A total of five east-north-east trending gravity profiles with around 450 readings were conducted across the Tamworth Belt and Gunnedah Basin. Seven ground magnetic traverses of a total length of 60 km were surveyed across the bounding faults of the Tamworth belt, of which five were across the Peel Fault and two were across the Mooki Fault. The gravity data shows two distinct large positive anomalies, one over the Tamworth Belt, known as the Namoi Gravity High and another within the Gunnedah Basin, known as the Meandarra Gravity Ridge. All gravity profiles show similarity to each other. The magnetic data displays one distinct anomaly associated with the Peel Fault and an anomaly immediately east of the Mooki Fault. These new potential field data are used to better constrain the orientation of the Peel and Mooki Faults as well as the subsurface geometry of the Tamworth Belt and Gunnedah Basin, integrating with the published seismic data, geologic observations and new physical properties data. --Magnetic anomalies produced by the serpentinite associated with the Peel Fault were used to determine the orientation of the Peel fault. Five ground magnetic traverses were modelled to get the subsurface geometry of the serpentinite body. Modelling results of the magnetic anomalies across the Peel Fault indicate that the serpentinite body can be mostly modelled as subvertical to steeply eastward dipping tabular bodies with a minimum depth extent of 1-3 km, although the modelling does not constrain the vertical extent. This is consistent with the modelling of the magnetic traverses extracted from aeromagnetic data. Sensitivity analysis of a tabular magnetic body reveals that a minimum susceptibility of 4000x10⁻⁶cgs is needed to generate the observed high amplitude anomalies of around 2000 nT, which is consistent with the susceptibility measurements of serpentinite samples along the Peel Fault ranging from 2000 to 9000 x 10⁻⁶ cgs. Rock magnetic study indicates that the serpentinite retains a strong remanence at some locations. This remanence is a viscous remanent magnetisation (VRM) which is parallel to the present Earth's magnetic field, and explains the large anomaly amplitude over the Peel fault at these locations. The remanence of serpentinite at other localities is not consistent enough to contribute to the observed magnetic anomalies. A much greater depth extent of the Peel Fault was inferred from gravity models. It is proposed that the serpentinite along the Peel Fault was emplaced as a slice of oceanic floor that has been accreted to the front of the arc, or as diapirs rising off the serpentinised part of the mantle wedge above the supra subduction zone. / Magnetic anomalies immediately east of the Mooki Fault once suggested to be produced by a dyke-like body emplaced along the fault were modelled along two ground magnetic traverses and three extracted aeromagnetic lines. Modelling results indicate that the anomalies can be modelled as an east-dipping overturned western limb of an anticline formed as a result of a fault-propagation fold with a shallow thrust step-up angle from the décollement. Interpretation of aeromagnetic data and modelling of the magnetic traverses indicate that the anomalies along the Mooki Fault are produced by the susceptibility contrast between the high magnetic Late Carboniferous Currabubula Formation and/or Early Permian volcanic rocks of the Tamworth Belt and the less magnetic Late Permian-Triassic Sydney-Gunnedah Basin rocks. Gravity modelling indicates that the Mooki Fault has a shallow dip ( ̃25°) to the east. Modelling of the five gravity profiles shows that the Tamworth Belt is thrust westward over the Sydney-Gunnedah Basin for 15-30 km. --The Meandarra Gravity Ridge within the Gunnedah Basin was modelled as a high density volcanic rock unit with a density contrast of 0.25 tm⁻³, compared to the rocks of the Lachlan Fold Belt in all profiles. The volcanic rock unit has a steep western margin and a gently dipping eastern margin with a thickness ranging from 4.5-6 km, and has been generally agreed to have formed within an extensional basin. --The Tamworth Belt, being mainly the product of volcanism of mafic character and thus has high density units, together with the high density Woolomin Association, which is composed chiefly of chert/jasper, basalt, dolerite and metabasalt, produces the Namoi Gravity High. Gravity modelling results indicate that the anomaly over the Tamworth Belt can be modelled as either a configuration where the Tablelands Complex extends westward underthrusting the Tamworth Belt, or a configuration where the Tablelands Complex has been thrust over the Tamworth Belt. When the gravity profiles were modelled with the first configuration, the Peel Fault with a depth extent of around 1 km can only be modelled for the Manilla and Quirindi profiles, modelling of the rest of the gravity profiles indicates that the Tablelands Complex underthrust beneath the Tamworth belt at a much deeper location. / Mode of access: World Wide Web. / xi, 242 leaves ill., maps

[Formulae and special characters can only be approximated here. Please see the pdf version of the abstract for an accurate reproduction.] The formation of world-class Archean orogenic gold deposits in the Eastern Goldfields Province of Western Australia was the result of a critical combination of physical and chemical processes that modified a single and widespread ore-fluid along fluid pathways and at the sites of gold deposition. Increased gold endowment in these deposits is associated with efficient regional-scale fluid focusing mechanisms and the influence of multiple ore-depositional processes at the deposit-scale. Measurement of the complexity of geologic features, as displayed in high-quality geologic maps of uniform data density, can be used to highlight areas that influence regional-scale hydrothermal fluid flow. Useful measurements of geological complexity include fractal dimensions of map patterns, density and orientation of faults and lithologic contacts, and proportions of rock types. Fractal dimensions of map patterns of lithologic contacts and faults highlight complexity gradients. Steep complexity gradients, between domains of high and low fractal dimensions within a greenstone belt, correspond to district-scale regions that have the potential to focus the flow of large volumes of hydrothermal fluid, which is critical for the formation of significant orogenic gold mineralization. Steep complexity gradients commonly occur in greenstone belts where thick sedimentary units overly more complex patterns of lithologic contacts, associated with mafic intrusive and mafic volcanic units. The sedimentary units in these areas potentially acted as seals to the hydrothermal Mineral Systems, which resulted in fluid-pressure gradients and increased fluid flow. The largest gold deposits in the Kalgoorlie Terrane and the Laverton Tectonic Zone occur at steep complexity gradients adjacent to thick sedimentary units, indicating the significance of these structural settings to gold endowment. Complexity gradients, as displayed in surface map patterns, are an indication of three-dimensional connectivity along fluid pathways, between fluid source areas and deposit locations. Systematic changes in the orientation of crustal-scale shear zones are also significant and measurable map features. The largest gold deposits along the Bardoc Tectonic Zone and Boulder-Lefroy Shear Zone, in the Eastern Goldfields Province, occur where there are counter-clockwise changes in shear zone orientation, compared to the average orientation of the shear zone along its entire length. Sinistral movement along these shear zones resulted in the formation of district-scale dilational jogs and focused hydrothermal fluid-flow at the Golden Mile, New Celebration and Victory-Defiance deposits. Faults and lithologic contacts are the dominant fluid pathways in orogenic gold Mineral Systems, and measurements of the density of faults and contacts are also a method of quantifying the complexity of geologic map patterns on high-quality maps. Significantly higher densities of pathways in areas surrounding larger gold deposits are measurable within 20- and 5-kilometer search radii around them. Large variations in the sulfur isotopic composition of ore-related pyrites in orogenic gold deposits in the Eastern Goldfields Province are the result of different golddepositional mechanisms and the in-situ oxidation of a primary ore fluid in specific structural settings. Phase separation and wall-rock carbonation are potentially the most common mechanisms of ore-fluid oxidation and gold precipitation. The influence of multiple gold-depositional mechanisms increases the potential for significant ore-fluid oxidation, and more importantly, provides an effective means of increasing gold endowment. This explains the occurrence of negative δ34S values in ore-related pyrites in some world-class orogenic gold deposits. Sulfur isotopic compositions alone cannot uniquely define potential gold endowment. However, in combination with structural, hydrothermal alteration and fluid inclusion studies that also seek to identify multiple ore-forming processes, they can be a useful indicator. The structural setting of a deposit is also a potentially important factor controlling ore-fluid oxidation and the distribution of δ34S values in ore-related pyrites. At Victory-Defiance, the occurrence of negative δ34S(py) values in gently-dipping dilational structures, compared to more positive δ34S(py) values in steeply-dipping compressional structures, is potentially associated with different gold-depositional mechanisms that developed as a result of fluid-pressure fluctuations during different stages of the fault-valve cycle. During the pre-failure stage, when fluids are discharging from faults, fluid-rock interaction is the dominant gold-depositional mechanism. Phase separation and back-mixing of modified ore-fluid components are dominant during and immediately after faulting. Under appropriate conditions, any, or all, of these three mechanisms can oxidize orogenic gold fluids and cause gold deposition. The influence of multiple gold-depositional mechanisms during fault-valve cycles at dilational jogs, where fluid pressure fluctuations are interpreted to be most severe, can potentially explain both the large gold endowment of the giant to world-class Golden Mile, New Celebration and Victory-Defiance deposits along the Boulder-Lefroy Shear Zone, and the presence of gold-related pyrites with negative δ34S values in these deposits. This study highlights the interplay that exists between physical and chemical processes in orogenic gold Mineral Systems, during the transport of ore fluids in pathways from original fluid reservoirs to deposit sites. Potentially, a single and widespread orogenic ore-fluid could become oxidized, and lead to the formation of ore-related sulfides with variable sulfur isotopic compositions, depending on the nature and orientation of major fluid pathways, the nature of wall-rocks through which it circulates, and the precise ore-depositional processes that develop during fault-valve cycles.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The granitic stocks of Canhoba (≈6,0 km2), Gravatá (≈3,5 km2) and Lagoa do Mato (≈5,0 km2) occur intrusive in the metasediments of the northeastern part of the Macururé Domain in the Sergipano Orogenic System. These stocks exhibit rounded shapes include angular xenoliths of metasediments and in the contacts regions have abundant dykes and granitic pegmatites. The granites have well-developed tectonic foliation marked by the alignment of muscovite and quartz crystals. Leucocratic granitic compositions are dominate and exist granodioritic types, with muscovite and biotite. The petrographic and mineraloquímicos studies revealed that the dominant mafic mineral is biotite, the plagioclase is albite and oligoclase, has muscovite and titanite, opaque minerals, epidote, zircon and F-apatite are accessory minerals. The biotite crystals have 0.4 <Fe / (Fe + Mg) <0.7, the most ferrous being those of the Canhoba and Gravatá stocks. Based on the FeO content, MgO, Al2O3 the biotite crystals indicate that these granites have peraluminous affinities (Canhoba and Gravatá) and calc-alkaline (Lagoa do Mato). Temperatures obtained with biotite are too low to reflect igneous conditions and should indicate metamorphic conditions. The geochemical data confirm that rhese granites have subalkaline affinity, and are peraluminous and metaluminous and calc-alkaline high potassium. The Stock Lagoa do Mato belongs to the group of magnesia granites while the others (Canhoba and Gravatá) are ferrous. The early crystallization of zircon in the magma was calculated as between 772 and 811 oC which is reasonable for rhyolite magmas. In multielement diagrams it is clear that there valleys pronounced in Nb, Ta and Ti associated with the strong fractionation of LREE reflect orogenic affinity of the rocks of the studied stocks. In these diagrams tectonic granites position in volcanic arc environment. These data support the current hypothesis that granites occurring in Macururé Domain are orogenic. / Os stocks graníticos de Canhoba (≈6,0 km2), Gravatá (≈3,5 km2) e Lagoa do Mato (≈5,0 km2) ocorrem intrusivos na parte nordeste dos metassedimentos do Domínio Macururé no Sistema Orogênico Sergipano. Esses stocks exibem formas arredondadas, incluem xenólitos angulares de metassedimentos e nas regiões dos contatos apresentam abundantes diques e pegmatitos graníticos. Os granitos apresentam foliação tectônica bem desenvolvida marcada pelo alinhamento de cristais de muscovita e quartzo. Dominam composições graníticas leucocráticas existindo também tipos granodioríticos, com muscovita e biotita. Os estudos petrográfico e mineraloquímicos revelaram que o mineral máfico dominante é a biotita, os plagioclásios são albita e oligoclásio, e tem-se ainda muscovita e titanita, minerais opacos, epídoto, zircão e F-apatita são os minerais acessórios. Os cristais de biotita têm 0,4<Fe/(Fe+Mg)<0,7, sendo as mais ferrosas aquelas dos stocks Canhoba e Gravata. Com base nos conteúdos de FeO, MgO, Al2O3 os cristais de biotita indicam que esses granitos apresentam afinidades peraluminosas (Canhoba e Gravatá) e cálcioalcalina (Lagoa do Mato). As temperaturas obtidas com a biotita são muito baixas para refletirem condições ígneas, devendo indicar condições metamórficas. Os dados geoquímicos confirmaram a afinidade subalcalinas, peraluminosa a metaluminosa e cálcio-alcalina de alto potássio desses granitos. O Stock Lagoa do Mato pertence ao grupo dos granitos magnesianos enquanto dos demais (Canhoba e Gravatá) são ferrosos. A cristalização precoce do zircão no magma foi calculada como entre 772 e 811 oC o que é razoável para magmas riolíticos. Em diagramas multielementares observam-se vales pronunciados em Nb, Ta e Ti, fato este que associado ao forte fracionamento dos ETRLeves, refletem a afinidade orogênica das rochas dos stocks estudados. Em diagramas geotectônicos esses granitos posicionam-se em ambiente de arco vulcânico. Estes dados reforçam a hipótese corrente que os granitos que ocorrem no Domínio Macururé sejam orogênicos.

Cette étude a visé à contraindre les processus tectoniques, magmatiques et métamorphiques actifs dans la croûte moyenne, du Permien à l’exhumation des roches pendant les riftings mésozoïques, en se focalisant sur un gabbro permien dans les nappes austroalpines (Italie du nord, sud-est de la Suisse). L’évolution du gabbro de Sondalo, mis en place dans l’unité de Campo, est examinée en combinant géologie structurale, pétrologie magmatique et métamorphique, et géochronologie. Les résultats de cette étude (1) apportent des contraintes sur les relations thermiques et mécaniques entre le pluton et l’encaissant pendant sa mise en place dans la croûte moyenne, (2) décrivent les mécanismes d’ascension de magmas mafiques au travers de la croûte continentale et (3) documentent l’exhumation et le refroidissement de l’unité de Campo et de l’unité sus-jacente de Grosina pendant la formation de la marge riftée adriatique. / This study aims to unravel tectonic, magmatic and metamorphic processes active at midcrustal levels from the Permian to the exhumation of the rocks during the Mesozoic riftings by focusing on a Permian gabbro in the Austroalpine nappes (N–Italy, SE–Switzerland). The evolution of the Sondalo gabbro, emplaced in the Campo unit, is examined by combining structural geology, magmatic and metamorphic petrology, and geochronology. The results of this study bring constrains on (1) the thermal and mechanical relationship between the pluton and the host rock during its emplacement in the middle crust, (2) the mechanisms of mafic magmas ascent through the continental crust and (3) the exhumation and cooling history of the Campo unit and the overlying Grosina unit during the formation of the Adriatic rifted margin.

Cette thèse visait à mieux définir les méthodes de ciblage et apporter des éléments de réponse sur la genèse des gisements d’or de type orogénique en périphérie des grands couloirs de déformation archéens. Cette thèse est présentée sous forme de trois articles. Le premier article traite de la distribution mathématique des gisements aurifères de type orogénique le long des grands couloirs de déformation. Une approche permettant de d’établir que la localisation des gisements se situant le long de structure de premier ordre n’est pas indépendante de la localisation de ses voisins a été développée. Cette approche permet de donner des éléments de réponse sur la formation de ces gisements et de générer des probabilités de découvertes à l’échelle régionale. La deuxième partie de cette présente une méthode l’évaluation du potentiel minéral sous couverture sédimentaire en 3D. Les teneurs aurifères compilées dans le secteur ont permis d’évaluer et de quantifier les relations spatiales existantes entre certaines entités géologiques et les emplacements minéralisés afin de cibler les endroits à haut potentiel. Enfin, les travaux présentés dans le dernier chapitre visent à délimiter les zones possédant une perméabilité structurale accrue lors de l’épisode de déformation contemporain à la mise en place de gisements aurifères de type orogénique. Une modélisation géomécanique 3D qui tient compte des propriétés physiques des roches a été effectuée sur un segment de faille choisi en utilisant un code d’élément fini. La déformation s’effectue en attribuant sur chaque discontinuité structurale des vecteurs ou des champs de déplacement en fonction des observations de terrain / This thesis had the objective to define targeting methods adapted to orogenic gold deposits hosted in greenstone belts and to better understand the formation mechanism of these deposits. The work accomplished is presented in three distinct articles. The first article aimed to determine if a mathematical relation can characterize the spatial distribution of orogenic gold deposits along a crustal scale fault zone within or if the localization of a deposit is independent of the position of each other. A uniform law was fitted between the frequency and the curvilinear inter-distance between successive orogenic gold occurrences along the CLLF for distances ranging from 315 to 5600 m. This approach gave insights on the formation mechanism and allowed the generation of a probability map for undiscovered deposits at a regional scale. The second chapter of this thesis focuses on a sector of the Cadillac Larder Lake Fault that was considered as having a high potential for discovery using the methodology presented in the last chapter. Compiled assays allowed the evaluation of the spatial association of certain geological features with orogenic gold mineralizations to allow targeting high potential areas. Finally, the work presented in the last chapter aimed at identifying dilatant zones during the deformation that is contemporaneous to the orogenic gold deposit formation. A 3D geomechanical modelling which takes rock properties into account was performed on a chosen segment of a fault zone using a finite element code. The deformation was induced using displacement vectors or fields interpreted from field data

Le TOC des sédiments du système Gange-Brahmapoutre croît linéairement avec la proportion de phylosilicates et de particules fines. La proportion de Corg fossile est ~ 20 % dans les MES et > 50 % dans les sédiments de fond. Plus de 50 % du Corg dérivé de l'Himalaya est oxydé et remplacé lors du transport dans la plaine du Gange. La charge en Corg est similaire dans les sédiments du Cône et dans les sédiments de rivière. L'abondance et le d13C des biomarqueurs indique que le Corg est dominé par les apports terrigènes. Par conséquent, l'efficacité d'enfouissement du Corg terrigène est proche de 100 %. Dans le système himalayen, nous estimons les flux d'enfouissement de Corg récent et fossile à respectivement 3.1±0.3 × 1011 mol/an et 0.9±0.4 × 1011 mol/an. L'enfouissement de Corg représente donc ~ 80 % de la consommation de CO2 engendrée par l'érosion de l'Himalaya. De manière générale, les orogènes actifs se caractérisent probablement par un enfouissement efficace de Corg / In the Ganga-Brahmaputra system, TOC linearly increases with the relative proportion of philosilicates and fine grain minerals. The proportion of fossil Corg in the suspended and bed sediments is respectively ~ 20 % and > 50 % of the TOC. During the Gangetic floodplain transit, more than 50 % of recent Corg derived from the Himalaya is oxidised and is replaced by Corg derived from the floodplain. The Corg loadings of river and recent Bengal Fan sediments are comparable. Biomarker abundance and ð13C show that Corg is dominated by terrestrial inputs. Consequently, the terrestrial Corg burial efficiency must be around 100 %. In the Himalayan basin, we estimate the burial fluxes or recent and fossil Corg to be respectively 3.1±0.3 × 1011 mol/yr and 0.9±0.4 × 1011 mol/yr. Corg burial therefore account for ~ 80 % of atmospheric CO2 consumption generated by Himalayan erosion. Efficient burial of Corg is likely a characteristic of high physical erosion typical of active orogenic systems

La zone de déformation compressive des Brooks Range et des British-Barn située entre l’Alaska (Etats-Unis) et la région du Nord Yukon (Canada), en position arrière-arc, se développe dans un contexte cinématique et géodynamique depuis longtemps débattu. L’histoire tectonique du bloc continental Arctique d’Alaska, situé dans l’avant-pays de Brooks Range, est diversement interprétée dans les reconstructions de l’ouverture du bassin canadien. La chaîne de Brooks se développe à partir du Crétacé inférieur et sa mise en place se poursuit au Cénozoïque. Mieux contraindre son histoire d’exhumation, en relation avec le raccourcissement est essentiel dans cette région arctique où la cinématique des plaques, associée à l’ouverture du bassin canadien au Nord, fait l'objet de nombreux modèles géodynamiques controversés. La relation avec la subduction active Pacifique au Sud et les grands décrochements en arrière de la subduction fait de cette chaîne, en position arrière arc, une zone-clef pour affiner les reconstructions géodynamiques régionales et notre compréhension des processus orogéniques. Si le lien n'est pas établi entre la déformation mise en jeu dans cette subduction au Mésozoïque et la déformation dans la chaîne de Books, ce lien est en revanche assez bien documenté à l'heure actuelle. Il est donc légitime d'appréhender les événements sud-alaskans dans l'étude de cette chaîne de Brooks. La croissance de la chaîne au Cénozoïque est également mal comprise. Or, il s’agit d’un exemple quasi-unique de chaîne en milieu arctique active durant le Cénozoïque et qui a donc potentiellement enregistré des bouleversements climatiques majeurs, en l'occurrence depuis l‘optimum climatique à la transition Paléocène-Eocène, le refroidissement Oligocène jusqu’à la mise en place de glaciers et de la calotte nord-américaine au Quaternaire. Cet orogène est donc clef pour étudier voire quantifier l'impact du climat sur la construction topographique nord-alaskane. Ce travail a combiné une étude thermochronométrique basse-température multidatation (FT, (U-Th)/He) dans les massifs granitiques et dans les sédiments, qui ont fait l'objet de modélisation thermo-cinématiques via Pecube, dans le but de contraindre la construction orogénique depuis 100 Ma jusqu’à l’actuel. En parallèle, une approche structurale de terrain (Nord Yukon et Brooks Range) et l'analyse de données de subsurface ont été menées. Les données thermochronologiques, couplées à des analyses thermométriques RSCM et de la modélisation thermique soulignent la mise en place de reliefs au Crétacé supérieur avec une exhumation modérée (0.2 km/Ma) qui se poursuit jusqu'à la fin de l'Eocène, où les taux d'exhumation dans les chaînes de Brooks et British-Barn sont clairemement orogéniques (1.25-1.29km/Ma), et associés à la migration de la déformation vers les bassins adjacents. Ce travail souligne une migration de la déformation du SO vers le NE. Dans les deux segments de la chaîne un événement d'exhumation distinct est identifié à l'Oligocène : celui-ci est clairement associé dans la partie interne de la chaîne de Brooks à la mise en place hors-séquence d'un duplex crustal ; et associé à la migration de la déformation compressive en mer au large de la chaîne de British-Barn. Si le calendrier tectonique est semblable dans ces deux zones d'étude, il existe une différence majeure dans le style de déformation entre ces deux régions. Le front de déformation semble beaucoup plus éloigné de la chaîne et les failles beaucoup plus espacées dans la partie canadienne, éloignement et espacement probablement liés à l’épaisseur de sédiments syn-sédimentaires présents dans le bassin... / The kinematics and geodynamics associated with the compressional deformation in the Brooks Range and British-Barn Mountains, respectively in Alaska (USA) and North Yukon (Canada), in a back-arc setting has long been debated. In particular, the tectonic history of the Arctic Alaska continental block located in the foreland of the Brooks Range has been diversely interpreted in the plate reconstructions proposed for the Canadian basin. The Brooks Range mountain chain develops from the Lower Cretaceous to the Cenozoic. Constraining its exhumational history and its link with shortening evolution is essential in this arctic area where plate tectonics, associated to the Canadian basin opening in the North, has led to controversial geodynamic models. Tectonic coupling with the active Pacific subduction in the south as well as major seismogenic strike-slip faulting make this orogen a key area where to refine the regional plate reconstructions and understanding of orogenic processes. The Cenozoic evolution of the Brooks Mountains is poorly understood although it is a nearly unique example of arctic orogen, which have potentially recorded major climate changes like Paleocene-Eocene Thermal Maximum, the Oligocene cooling and Quaternary glaciations. This orogen is a key to study and quantify the climate impact on the north-alaskan topographic growth. This study combined low-temperature thermochronometry (FT, U-Th/He) on granitic and sedimentary rocks, which were thermo-kinematically modeled using Pecube in order to define the orogenic evolution of this arctic region since 100 Ma. In parallel, a field-based structural study (North Yukon and Brooks Range) was combined with the analysis of subsurface data. Thermochronological data, coupled to thermometric RSCM analyses and thermal modeling first define a slow exhumation period (0.2 km/Ma) from Upper Cretaceous up to the Eocene. With the Eocene, exhumation rates drastically increased to reach 1.25-1.29km/Ma as the deformation also migrates from SW toward NE. In both alaskan and canadian parts of mountains ranges a clear Oligocene exhumational event is identified. This event is linked to out-of-sequence crustal duplexing in the internal part of the range in the Brooks Range, contemporaneous with the propagation of deformation offshore, along British and Barn Mountains...

Le massif du Mayo Kebbi au sud-ouest du Tchad est localisé entre le craton du Congo au Sud, le craton Ouest Africain à l'Ouest et le Métacraton du Sahara à l'Est. Formé au cours de l'orogenèse panafricaine, entre 800 et 570 Ma, il est constitué de deux ceintures de roches vertes (Zalbi et Goueygoudoum), trois complexes magmatiques (Chutes Gauthiot, Léré et Figuil) et des intrusions post-tectoniques distingués sur la base de leurs caractères structuraux, pétrologiques, géochimiques et géochronologiques. L'évolution géodynamique de ce massif comprend les phases suivantes:Phase 1: Mise en place d'un complexe mafique et intermédiaire (CMI) dont la métadiorite de Boloro datée à 748 ± 4 Ma (U-Pb sur zircon). Cette métadiorite, riche en terres rares, se caractérise par LaN/YbN ~ 12, Sr/Y > 32, teneurs en LILE, Cr, Ni élevées et des anomalies négatives en Nb-Ta. Ces caractéristiques sont attribuées à la fusion partielle de la plaque océanique plongeante et interaction des magmas produits avec le coin mantellique au cours de leur ascension.Phase 2: Mise en place des métagabbros et métabasaltes (700 ± 10 Ma: U-Pb sur zircon) de la série métavolcano-sédimentaire de Zalbi. Ces roches sont caractérisées par un découplage LILE/HFSE, des anomalies négatives en Nb-Ta et des rapports LaN/YbN indiquant un fractionnement faible à modéré des terres rares. En particulier, leurs caractères géochimiques sont similaires à ceux des bassins arrière-arcs modernes. La signature isotopique en Sr et Nd de ces roches exclut toute contamination par une croûte continentale ancienne au moment de leur mise en place. CMI et série métavolcano-sédimentaires, regroupés dans le cadre des ceintures de roches vertes, représentent ainsi une accrétion juvénile en contextes d'arc insulaire/bassin arrière-arc.Phase 3: La métadiorite quartzique syntectonique du complexe magmatique des chutes Gauthiot (665 ± 1 Ma: âge U-Pb sur zircon, Penaye et al., 2006) correspond à la mise en place de magmas contemporains d'une première collision, qui implique le massif du Mayo Kebbi et le bloc rigide de l'Adamaoua-Yadé à l'Est. Cet évènement marque le début de la fermeture du bassin arrière-arc de Zalbi et d'un épaississement crustal.Phase 4 : L'épaississement est responsable de la différentiation intracrustale par fusion partielle des roches accrétées au cours des phases précédentes à la base de l'arc. Pendant cette phase se mettent en place des magmas tonalitiques, dont la tonalite à hornblende-biotite de Guegou (complexe magmatique de Léré) datée à 647 ± 5 Ma (U-Pb sur zircon). Les magmas produits ont des caractères de magmas TTG et laissent un résidu à grenat à la base de la croûte continentale.Phase 5: La tonalite syntectonique du complexe magmatique de Figuil, datée à 618 ± 6 Ma (U-Pb sur zircon), se distingue par eNd initial = -3 et 87Sr/86Sr initial = 0,7073. Les signatures isotopiques de cette tonalite démontrent l'implication dans le magmatisme d'une croûte Pré-Néoprotérozoïque. Elle est contemporaine d'une deuxième collision qui fait intervenir le massif du Mayo Kebbi et le domaine Occidental de la Ceinture Orogénique d'Afrique Centrale.Phase 6: La mise en place du granite de type A de Zabili à 567 ± 10 Ma (âge U-Pb sur zircon) est associée aux dernières manifestations magmatiques du cycle orogénique panafricain (intrusions post-tectoniques). Les caractères géochimiques (appauvrissement extrême en Sr, Eu, Ca, Mg, Ni) et isotopiques (eNd initial = +3 à +7) de ce granite indiquent une origine par cristallisation fractionnée à partir de magmas d'origine mantellique et contamination de ceux-ci au cours de leur mise en place dans la croûte supérieure par une composante crustale ancienne / The Mayo Kebbi massif (south-western Chad) is located between the Congo craton, the West African craton and the Saharan Metacraton. It consists of two greenstone belts (Zalbi and Goueygoudoum), three magmatic complexes (Gauthiot falls, Lere, Figuil) and post-tectonic intrusions distinguished on the basis of their structural, petrological, geochemical and geochronological characteristics. The geodynamic evolution of this massif includes the following phases:Phase 1: Emplacement of a Mafic to Intermediate Plutonic (MIP) complex. Boloro metadiorite, which belongs to this complex, is dated at 748 ± 4 Ma (U-Pb zircon age). This metadiorite is enriched in REE and characterized by LaN/YbN ~ 12, Sr/Y > 32, high LILE, Cr and Ni contents but negative anomalies in Nb-Ta. These features are attributed to partial melting of the slab followed by interaction of the produced magmas with the mantle wedge during their ascent.Phase 2: Emplacement of metagabbros and metabasalts (700 ± 10 Ma: U-Pb zircon age) of the Zalbi metavolcanic-sedimentary group. These rocks are characterized by a decoupling of LILE and HFSE, negative Nb-Ta anomalies, weak to moderate LREE fractionation relative to HREE. In particular, their geochemical characteristics are similar to modern back-arc basins. The isotopic compositions of Sr and Nd of these rocks preclude contamination by old continental crust of the related magmas during their emplacement. Accordingly, the MIP complex and the Zalbi metavolcanic-sedimentary group are associated to juvenile accretion in an island arc/back-arc basin tectonic setting.Phase 3: The syntectonic quartz metadiorite of Gauthiot Falls magmatic complex (665 ± 1 Ma: U-Pb zircon age, Penaye et al., 2006) is emplaced during a first collision event, which involves the Mayo Kebbi massif and the Adamaoua-Yade domain to the east. This event marks the beginning of the closure of the Zalbi back-arc basin and crustal thickening.Phase 4: The thickening is responsible of intra-crustal differentiation by partial melting of rocks accreted during the previous phases at the base of the arc. During this phase, several tonalitic intrusions are emplaced, including hornblende-biotite tonalites of Gauthiot Falls and Guegou tonalite (Lere magmatic complex). The latter is dated at 647 ± 5 Ma (U-Pb zircon age). The produced magmas have typical features of TTG magmas, leaving a garnet bearing residue at the base of the continental crust.Phase 5: The syntectonic tonalite of Figuil magmatic complex dated at 618 ± 6 Ma (U-Pb zircon age), is characterized by initial ?Nd = -3 and initial 87Sr/86Sr = 0.7073 attesting for the involvement of pre-Neoproterozoic crust on its origin. It marks a second collision event between the Mayo Kebbi massif and the Western domain of the Central African Orogenic Belt to the west.Phase 6: The Zabili A-type granite emplaced at 567 ± 10 Ma (U-Pb zircon age) and is related to the last magmatic events of the Pan-African orogenic cycle (post-tectonic intrusions). The geochemical (low Sr, Eu, Ca, Mg, Ni) and isotopic compositions (initial ?Nd = +3 à +7) of this granite point to an origin involving extreme fractionation of mantle-derived magmas which interacted with an old crustal component during their emplacement in the upper continental crust

La chaîne de collision d'âge néoprotérozoïque de Jiangnan, orientée NE-SW, marque la limite entre les blocs duYangtze et de Cathaysia. Son évolution tectonique reste encore débattue. Une des questions les plus controversées est l'âge de la collision entre les deux blocs. Afin d'acquérir une meilleure compréhension de ce problème, nous avons collecté des échantillons dans les couches sédimentaires situées au-dessus et au-dessous de la discordance dans le but de comparer les spectres d'âge des zircons détritiques et aussi de les confronter à ceux décrits dans les séries néoprotérozoïques des régions du Yangtze, Jiangnan et Cathaysia. En outre, nous nous sommes intéressés aux plutons granitiques d'âge néoproterozoïque de Sanfang et Yuanbaoshan, de type-S, situés dans la partie occidentale de la chaîne de Jiangnan afin de tracer l'évolution tectonique de la région depuis 830 Ma par la mise en œuvre de méthodes pluridisciplinaires : géologie structurale, géochronologie U-Pb, AMS, modélisation gravimétrique et thermochronologie Argon.Notre étude montre les résultats suivants : (i) La chaîne de Jiangnan s'est formée par la collision des blocs de Yangtze et Cathaysia entre ca. 865 and 830 Ma ; (ii) Les intrusions granitiques de 830 Ma se sont mises en place dans des formations encaissantes du groupe Sibao plissées et faillées. Les plutons ont été construits par accumulation latérale E-W de filons N-S, avec un écoulement horizontal du magma du sud vers le nord ; (iii). Un cisaillement ductile du haut vers l'Ouest a été reconnu dans la partie supérieure des plutons. Des âges Ar/Ar vers 420 Ma obtenus sur plusieurs grains de muscovite et biotite déformés impliquent que le cisaillement ductile peut être : a) formé pendant l'orogenèse du Paléozoïque inférieur de Chine du Sud, ou b) pendant la mise en place des plutons au Néoprotérozoïque dans une croûte chaude, sous la température de fermeture du chronomètre argon, puis lors de l'orogenèse du Paléozoïque inférieur, ce domaine crustal de Chine du Sud est passé au-dessous de 350°C; (iv) Durant la période 420-240 Ma, la région de Sanfang-Yuanbaoshana connu un refroidissement lent qui pourrait correspondre au ré-équilibrage isostatique de la croûte. / The Jiangnan Orogenic Belt is a NE-SW trending Neoproterozoic collisional suture, marking the boundary between the Yangtze Block and the Cathaysia Block. Its tectonic evolution is still debated. One of the most controversial questions is the timing of the collision between the Yangtze and Cathaysia blocks. In order to have a better understanding of this problem, we have collected the sedimentary rocks from the strata both overlying and underlying the Neoproterozoic unconformities to compare the detrital zircon age spectra between them, as well as to compare the detrital zircon spectra of Neoproterozoic sequences among the Yangtze, Jiangnan and Cathaysia regions. Moreover, we paid attention to the Neoproterozoic S-type granite plutons located in the western Jiangnan region in order to trace the crustal evolution in the Sanfang-Yuanbaoshan area since 830 Ma by multidisciplinary methods, including structural geology, geochronology, AMS, gravity modelling and Argon isotopic dating.Our study shows that : (i) The Jiangnan Orogenic Belt was built up due to the assembly of the Yangtze and Cathaysia blocks between ca. 865 and 830 Ma ; (ii) The 830 Ma granitic magma intruded into the pre-existing folds and faults in the Sibao group, the tongue-and/orsill-shaped plutonswere constructed by anE-W lateral accumulation of N-S oriented dykeswith adominantly northward horizontal magma flow from south to north ; (iii)A top-to-the-W ductile shearband has been identified on the top of plutons, (iv) the coherent mica Ar-Ar age of ca. 420 Ma, obtained from the deformed muscovite, implies that this shearing may be formed either a)during the Early Paleozoicorogeny, or b) during the Neoproterozoic plutons emplacement, then the plutons were exhumed by the Paleozoic orogeny ; (iv) During the 420-240 Ma period, the Sanfang-Yuanbaoshan area has experienced a slow cool ingrate, which may correspond to the isostatic re-equilibration of the crust.