This thesis is a study of some of the processes which operate at mid crustal levels (10- 20km) during the emplacement of granitoid magmas, with particular reference to the process of in-situ expansion and the association between magma emplacement and orogen evolution. A number of plutons were studied to assess this the Ardara pluton from Donegal, NW Ireland, together with the Atibaia, Morro Azul, Imbiricu and Itapeti plutons from the Rio Paraiba do Sul shear belt (RPSSB), Sao Paulo state, SE Brazil. The emplacement of the Ardara pluton has been the subject of studies by many authors since the 1950's. It has been interpreted as a diapir ascending along a thrust, a granite balloon which forcefully created more than 60% of its space and, most recently, as a set of nested diapirs which forcefully created only 30% of their own space. Field mapping together with the determination of finite strain within the pluton, shortening estimates, shear sense determinations, petrographic deformation fabrics and computer modelling indicates that: i) the pluton displays a concentrically increasing finite strain and it expanded in-situ from a central 'injection point', having possibly ascended along a shear zone-related conduit; ii) the country rocks partitioned intense strains into the 500m closest to the pluton, a deformation feature which is shown to be consistent with a power-law wallrock theology; Hi) earlier granite pulses and the country rock were 'shouldered aside' to the east and west, expansion of the pluton, which was preferentially in a northwards direction; iv) that the intrusion related shortening preserved within the wallrocks was approximately equivalent to the strain preserved within pluton and the space requirements for the pluton are essentially met by preserved forceful emplacement-related strains; and v) if the pluton magma is considered as having ascended through dyke-like conduits emplacement could occur in a minimum of ~4000yrs, whereas magma ascent as a Hot Stokes diapir would require hundreds of thousands to millions of years for complete emplacement. Finally, the Ardara pluton does not conform to any of the established criteria for diapir-like ascent of a magma body and the data demonstrate it to be a testable example of a pluton which expanded entirely in-situ. The Rio Paraiba do Sul shear belt (RPSSB) is a dextral transpressional segment of the Late Precambrian Brasiliano-Pan African orogenic belt. The studied plutons were emplaced in the latter stages of this orogen in close spatial association with one of the many northeast-southwest trending, sub-vertical, continental-scale shear zones. All the granites show a similar emplacement and deformation history despite their different petrographic features and isotopic ages. This history consists of an early shallowly dipping, low angle fabric, in the country rocks, associated with crustal thickening, the later development of dominantly dextral sub-vertical shear zones, followed by the emplacement of the studied plutons and finally overprinting by a pervasive dextral plane strain and late-stage discrete mylonitic shears. Field examination demonstrates that: i) each of the plutons preserves an internally homogeneous emplacement-related finite strain, weak magmatic fabric, magma sheets and weakly deformed wallrocks; ii) magmatic shear sense determinations and wallrock deformation fabrics indicate that, during emplacement, the RPSSB was extending (at least at the emplacement level) in an east-west direction creating sinistral dilatational pull-aparts along the major shear zones, into which granitic magma was preferentially emplaced; and Hi) within this generally extensional context there was a component of long axis perpendicular in-situ forceful expansion, this created no more than 20% of the width of any one granite. Applying a simple pull-apart extension model suggests that pluton emplacement was associated with approximately 40% regional extension sub-parallel to the former orogenic convergence direction. This emplacement, as a result of sheeting through dyke-like conduits, requires thousands of years, rather than the millions of years required for ascent and emplacement of a Hot Stokes diapir. Interpreting these results suggests that the intruded granitoids are associated with a mid-crustal component of orogen perpendicular extension I collapse during the latter stages of the Brasiliano orogeny. Such extension I collapse could have been initiated by: a cessation in continental convergence or; by the delamination of a thickened thermal boundary layer, a process which has been suggested to be the driving force behind orogenic collapse in younger orogenic belts. These examples demonstrate that: i) 'forceful' balloon-like emplacement of granitic magma can occur; ii) there are very close inter-relationships between granite emplacement and orogenic dynamics; and Hi) that 'space' for granitoid magma can be created by a combination of forceful and dilatational and fault-related mechanisms.

Theory and experiment show that the rate and geographic distribution of erosion control the rate and pattern of deformation in collisional mountain belts. Enhanced erosion reduces the mass of material that must be moved up and over ramps and uplifted in large folds. In order to test this and related ideas in a natural example, we have compared modeled rainfall to measured thrust sheet displacement, geometry, and internal deformation in the Appalachian fold and thrust belt. We use mean annual precipitation from a global climate model (GCM) as a proxy for rate of erosion. Deformation measurements were made on a portfolio of regional cross sections from Alabama to New England. During the Carboniferous Allegheny orogeny the Southern Appalachians moved from -30 ° to 0° latitude whereas the Central and Northern Appalachians lay between -15° and 5° latitude. Mean annual precipitation determined from the GENESIS 2 GCM (Grossman, per. comm.) varied from tropical to arid conditions as the collision both moved north and grew in breadth and height. The Southern Appalachians, which experienced more net rainfall than other regions, generally show more displacement, deeper present day exhumation, and shallower ramps than regions to the north. The vicinity of the Pine Mountain thrust sheet in the Southern Appalachians experienced the most displacement (~1.5X the Central Appalachian average) and bulk shortening (~1.6X the Central Appalachians) and produced the most eroded material (~1.5X the Central Appalachians). The latitude of the Pine Mountain thrust sheet in the Southern Appalachians received ~20% more rainfall than the Central Appalachians. Although the number of regional detachments and lithologies change from Southern to Central and Northern Appalachians, the change in rainfall both regionally at any one time and as the collision progressed may explain part of the change in structural style from south to north.

The Himalaya-Tibetan orogen has become the paradigm for continental collision and is central to deciphering continental tectonics. Neogene extension in the orogen is not predicted by plate tectonic theory, and its significance is widely debated. In the Himalaya, north-south extension is restricted to the Southern Tibetan Detachment System (STDS), which juxtaposes the High Himalayan Crystalline Series (HHCS) against the Tibetan Sedimentary Series (TSS). ⁴⁰Ar-³⁹Ar ages from HHCS and TSS of the Garhwal Himalaya indicate that STDS movement initiated between 17.3 ± 0.4 to 24.3 ± 1.6 Ma (2σ), synchronous with Main Central Thrust (MCT) movement. One-dimensional thermal modelling suggests that the STDS is a reactivated thrust, implying a fundamental change in Himalayan tectonics in the early Miocene. The onset of east-west extension in southern Tibet is constrained by north-south trending shoshonitic dykes to be 13.3 ± 0.8-18.3 ± 2.7 Ma. Trace-element modelling indicates that the shoshonitic dykes and associated lavas in southern and northern Tibet were derived by ≤2% melting of enriched sub-continental lithospheric mantle (SCLM) at 65-85km. The northern and southern shoshonites have distinctive isotopic (εNd_(i), north, -5.5 to-10.3; south -8.8 to - 18.1) and major element signatures that relate to distinct SCLM sources corresponding to the tectonically accreted terranes of the plateau. The trace-element compositions of these sources, determined by inverse modelling, suggest subduction-related metasomatism. ⁴⁰Ar- ³⁹Ar dating of xenocrystic phlogopites indicates metasomatism of the southern SCLM occurred at 62±2 Ma, synchronous with collision. These data link Neogene extension to a thermally perturbed lithosphere. SCLM thinning following slab detachment explains magmatism, extension and uplift in southern Tibet. Episodic convective removal of the SCLM is proposed for northern Tibet. In view of these models, initiation of extension at 18.3±1.6 Ma in southern Tibet places a minimum constraint on plateau uplift. This overlaps with STDS and MCT movement, implying that changes in Himalayan tectonics are controlled by plateau uplift.

Over the last two decades, gold occurrences in the Palaeoproterozoic Pine Creek Orogen (PCO) have been cited as type-examples of high-temperature contact-metamorphic or thermal-aureole deposits associated with granitoid magmatism. Furthermore, spatial relationships between these gold occurrences and the granitoids have led to inclusion of these deposits in the intrusion-related gold deposit group. Research on the characteristics, distribution and timing of these gold deposits tests these classifications and supports an alternative interpretation. The deposits display many similarities to well-described ‘turbidite-hosted’ orogenic gold deposits described from several Palaeozoic orogens. As in most ‘turbidite-hosted’ orogenic deposits, the gold mineralisation is dominantly epigenetic, sediment-hosted (typically greywacke and siltstone) and fold-controlled. Most gold is hosted by concordant or discordant veins, with limited alteration halos in host rocks, except where they occur in silicate-facies BIF or other Fe-rich rocks. The domal culminations of major doubly-plunging anticlines, and/or fold-limb thrust-faults, are important structural controls at the camp- and deposit-scales. Many deposits are sited in parts of the lithostratigraphy where there is significant competency and/or chemical contrast between units or sequences. In particular, the complex interdigitated stratigraphy of euxinic and transitional high-energy sedimentary rocks of the c.1900-1880Ma South Alligator Group is important for the localisation of gold deposits. The distribution of deposits is influenced further by the location and shape of granitoids and their associated contact-metamorphic aureole. Approximately 90% of gold deposits lie within the ∼2.5km wide contact-aureole, and most of these are concentrated in, and just beyond, the biotite-albite-epidote zone (0.5-1.0km from granitoid), with few deposits located in the inner hornblende-hornfels zone. At the deposit scale, gold is commonly associated with arsenopyrite-loellengite and pyrite, native-Bi and Bi-bearing minerals, and is confined to a variety of extensional quartz-sulphide ± carbonate veins. Such veins formed typically at 180-320°?C and ∼1kbar from low- to moderate salinity, two-phase aqueous fluids. Isotopic studies of the deposits are equivocal in terms of the source of hydrothermal fluid. Most δD and δ18O values fall within the range defined for contact-metamorphic and magmatic fluids, and sulphur isotopes indicate that the fluids are within the range of most regional sources. Significantly, lead isotope ratios show that the goldbearing fluid does not have a felsic magmatic-source signature, but instead suggest a homogenous regional-scale lead source. Excluding a few outliers, the relative uniformity of deposit characteristics, including host rocks, structural style, alteration, sulphide paragenesis and fluid P-T-X conditions, suggests that most deposits represent a continuum of broadly coeval mineralisation that formed under similar geological conditions

Orogene Prozesse in kontinentalen Kollisionszonen werden in zwei- und dreidimensionalen numerischen Modellen auf Basis der Finite-Elemente Methode (FEM) untersucht. Dabei stehen die Verteilung der Deformation innerhalb der Modellkruste, die korrespondierenden Spannungsfelder und die aus Temperaturfelddaten und Partikelpfaden abgeleitete metamorphe Entwicklung von Krustengesteinen im Vordergrund. Die Studie gliedert sich in einen methodischen Teil, umfangreiche Parameterstudien und spezielle Anwendungen auf fossile und rezente Orogene. Kontinentale Kollisionszonen sind - insbesondere in den tieferen Krustenstockwerken – durch hohe Beträge penetrativer Deformation gekennzeichnet. Im methodischen Teil der Arbeit wird eine Technik vorgestellt, mit deren Hilfe Verformungen des beobachteten Umfangs mit dem auf rein LAGRANGEscher Formulierung basierenden kommerziellen FE-Programmpaket ANSYS® modelliert werden können. Die speziell für Fragestellungen orogener Krustendynamik entwickelten Programmpakete OROTRACK bzw. OROTRACK3D umfassen Neuvernetzungs- und Ergebnisverwaltungsalgorithmen, die eine Modellierung von Konvergenzbeträgen bis zu mehreren hundert Kilometern erlauben. Zusätzlich können mittels einer Schnittstelle zu Oberflächenmodellen die Folgen exogener Prozesse auf die orogene Dynamik berücksichtigt werden. Weitere Charakteristika der Modellierungstechnik sind eine vollständige thermomechanische Kopplung, die Anwendung differenzierter Materialeigenschaften für verschiedene Krustenstockwerke sowie die Möglichkeit, die Deformation - den lokal herrschenden Druck- und Temperaturbedingungen entsprechend - entweder durch spröde oder duktile Materialgesetze zu approximieren. Die zur Beschreibung eines Kollisionsszenarios aufgebrachten Randbedingungen basieren auf den Grundlagen eines Mantelsubduktionsmodells (Willett et al. 1993). In 2D-Modellen wird ebene Verformung in einem Schnitt durch die kontinentale Kruste zweier kollidierender Platten modelliert, die basal einer vom lithosphärischen Mantel aufgeprägten Verschiebung unterliegen. Wird der lithosphärische Mantel der linken Platte an einem Punkt S unter die rechte Platte subduziert, ergibt sich für den linken Modellteil eine horizontale Verschiebung der Modellbasis nach rechts, während im rechten Modellteil keine Verschiebung der Modellbasis erlaubt ist. Im Bereich des Punktes S kommt es zu einer Diskontinuität der basalen Geschwindigkeit und somit zu maximaler Deformation. In publizierten Kollisionsmodellen, die auf ähnlichen Ansätzen beruhen, wird häufig rein sprödes Materialverhalten angenommen oder der duktile Anteil der Kruste durch geringe Krustentemperaturen klein und hochviskos gehalten. Unter diesen Bedingungen kann eng auf das Orogenzentrum lokalisierte Deformation mit einem typischerweise bivergenten Strukturmuster abgebildet werden (Willett et al. 1993 u.a.). Demgegenüber beweist eine erste Reihe zweidimensionaler Parameterstudien eine starke Abhängigkeit des beobachteten Deformationsmusters von den herrschenden Krustentemperaturen und der Konvergenzrate. Bei höheren Krustentemperaturen bildet sich demnach ein Entkopplungshorizont an der Krustenbasis, der für die oberen Krustenstockwerke eine verbreiterte und diffuse Deformationszone bedingt und die erzielte Krustenverdickung limitiert. Über die Verformungsratenabhängigkeit des duktilen Materialverhaltens und den unterschiedlichen Grad thermischer Reequilibrierung innerhalb der verdickten Kruste haben Variationen der Konvergenzrate ähnliche Auswirkungen auf das orogene Deformationsmuster. Verbesserte Modelle mit Neuvernetzungstechnik werden in Parameterstudien getestet, die den Einfluss unterschiedlicher Temperatur-Viskositätsfunktionen auf die Lokalisierung der Deformation und die resultierende synkonvergente Exhumierung metamorpher Gesteine quantifizieren. Ein rheologisches Verhalten, das eine effiziente mechanische Kopplung innerhalb des Krustenprofils gewährleistet, ist demzufolge nicht nur Voraussetzung für lokalisierte Krustenverdickung, sondern auch für rasche Exhumierung von Unterkrustengesteinen durch ein Zusammenspiel von Erosion und isostatischer Hebung. Die Modelle zeigen weiter, dass maximale Exhumierungsbeträge bei rheologisch vergleichsweise festem Verhalten der Unterkruste erzielt werden. Im Einzelnen kann die Variabilität der Versenkungs- und Exhumierungsgeschichte von Materialpunkten im Modellschnitt aus synthetischen PT-Pfaden ersehen werden. Der Wirkungskomplex um Krustentemperaturen, orogene Deformationslokalisierung und synkonvergente Exhumierung ist für die Kollisionsphase der variscischen Orogenese in Mitteleuropa von besonderer Bedeutung. Hochtemperaturmetamorphose und weitverbreitete granitoide Intrusionstätigkeit sind hier Ausdruck hoher Krustentemperaturen; dennoch sind an den Grenzen der klassischen tektonometamorphen Einheiten - im Bereich von Schwarzwald und Vogesen sowie der Mitteldeutschen Kristallinschwelle (MDKS) - eng lokalisierte Teilorogene mit bivergentem Strukturmuster sowie eine rasche synkonvergente Exhumierung amphibolitfazieller Gesteine dokumentiert. Ein solches Nebeneinander ist aus Sicht der Parameterstudien nur durch eine vergleichsweise hochviskose Unterkrustenrheologie zu erklären. In einer Fallstudie zur MDKS kommen in neueren experimentellen Arbeiten bestimmte Kriechparameter (Mackwell et al. 1998) zur Anwendung, mit denen ein derartiges Materialverhalten simuliert werden kann. Der in den reflexionsseismischen Profilen DEKORP 2N und 2S dokumentierte großmaßstäbliche Strukturbau im Bereich des rhenohercynischen Falten- und Überschiebungsgürtels, der MDKS und des saxothuringischen Beckens, sowie die an heute exhumierten Gesteine bestimmten metamorphen Maximalbedingungen können auf dieser Grundlage numerisch reproduziert werden. Eine Erweiterung der Modellierungstechnik auf dreidimensionale FE-Modelle dient der Berücksichtigung orogenparalleler Deformation, die im Randbereich von Kollisionszonen in effektivem Materialtransport resultieren kann; diese Prozesse sind u.a. als „tectonic escape“ (Burke & Sengör 1986) oder „lateral extrusion“ (Ratschbacher et al. 1991b) beschrieben worden. Unter der Annahme orthogonaler Konvergenz wird im 3D-Modell der Mantelsubduktionsansatz der 2D-Modelle zunächst in orogenparalleler Richtung extrudiert (Randbereich des Kollisionsorogens). Im angrenzenden, hinteren Teil des Modells (laterales Vorland des Kollisionsorogens) ist die Modellbasis dagegen keiner Verschiebung oder Fixierung unterworfen. Die Modellränder unterliegen hier einer sogenannten „no-tilt“-Bedingung, die eine differentielle Horizontalverschiebung initial übereinanderliegender Knoten verbietet. In einer Reihe von Parameterstudien werden das kinematische Muster, die räumliche Verteilung der Deformation und die zeitlichen Variationen des oberflächlichen Spannungsfelds untersucht, die sich bei modifizierten Randbedingungen ergeben. Laterale Extrusion ist demnach im Randbereich von Kollisionsorogenen trotz unterschiedlichster Modellszenarien stets präsent. Da die Lateralbewegungen zeitgleich mit der Kollision einsetzen und im Laufe der weiteren konvergenten Krustenverkürzung nur wenig beschleunigt werden, ist der von horizontalen Kräften ausgelöste „tectonic escape“ der dominierende Prozess, während gravitativ induzierte Bewegungen nur eine sekundäre Rolle spielen. Rigide Modellränder in Teilen des lateralen Vorlands modifizieren sowohl Umfang als auch Verteilung der Horizontalbewegungen, ihre Auswirkungen auf das Orogen selbst sind dagegen vergleichsweise gering. Variationen der Krustentemperaturen, der Konvergenzrate und der Unterkrustenrheologie beeinflussen dagegen sowohl die orogene Deformation als auch die des lateralen Vorlands. Unter der Annahme einer festen, isotropen Kopplung zwischen der Krustenbasis und dem bewegten lithosphärischen Mantel werden Extrusionsraten simuliert, die 30% der Konvergenzrate nicht überschreiten. Bis zu 70% können dagegen erreicht werden, wenn eine orogenparallele Beweglichkeit der Modellbasis gestattet wird. Die überragende Bedeutung dieser basalen Randbedingung erlaubt eine Interpretation des miozänen lateralen Extrusionsereignisses in den Ostalpen (z.B. Ratschbacher et al. 1991a). Wenn im Bereich der heutigen Ostalpen zu Beginn der lateralen Extrusion noch kein orogene Topographie bestand (Frisch et al. 1998), fand laterale Extrusion zeitgleich mit bedeutender Krustenverdickung statt; dies spricht für eine Dominanz des von horizontalen Kräften induzierten Prozesses „tectonic escape“ über gravitatives Kollabieren. In jedem Fall legt das in etwa ausgeglichene Verhältnis zwischen Plattenkonvergenz und lateraler Extrusion die Existenz eines basalen Entkopplungshorizonts nahe. Andere Faktoren, die zur Erklärung des Extrusionsereignisses herangezogen werden, z.B. die Indentation der Südalpen oder ein extensives Regime im Bereich des Pannonischen Beckens, können das Deformationsmuster beeinflusst haben, die beobachteten Verschiebungsbeträge sind damit jedoch aus Sicht der Modellstudien nicht plausibel zu machen. Aufgrund ihres großen Maßstabs lassen sich die Verhältnisse bei der Kollision Indiens mit der Eurasischen Platte bislang nur phänomenologisch mit den Modellergebnissen vergleichen. Eine skalierte Fallstudie bleibt somit eine Herausforderung für zukünftige FE-Modelle. / Orogenic processes in continental collision zones are studied by means of two- and three-dimensional numerical models based on the finite-element method (FEM). Special emphasis is laid on the crustal strain distribution, the corresponding stress field, and the metamorphic evolution of crustal rocks which can be determined by analyzing particle paths and temperature field data. The study comprises the description of a new modelling approach based on commercial software, extensive parameter studies and implications for fossil and recent orogens. The methodical part of the work focuses on the task to handle large penetrative deformation observed during orogenies using the commercial FE software package ANSYS® which is based on an updated Lagrangian formulation. Limitations inherited by this approach are overcome by using a remeshing technique. The software package OROTRACK and OROTRACK3D is developed to model orogenic deformation and comprises remeshing, mapping and tracking algorithms. Combined with ANSYS® they are capable of describing total plate convergence up to amounts of several hundreds of kilometers. A surface model inteface allows taking into consideration the effect of erosion on collisional mechanics. Additionally, the models presented in this study are characterized by full thermomechanical coupling, specific material properties describing different crustal layers, and the capability to switch between brittle and ductile material laws depending on current stress and temperature conditions. 2d models represent a vertical section cutting the continental crust of two colliding plates at an orientation perpendicular to the evolving orogen. Based on the mantle subduction approach (Willett et al. 1993) the lithospheric mantle which is not a part of the model itself exerts a basal velocity boundary condition on the crustal scale model. Assuming an asymmetric subduction of the lithospheric mantle of the left plate beneath the right plate’s mantle taper occurring at a point S, the basal FE nodes of the left model half are moved by a horizontal displacement whereas the right part basal nodes are fixed horizontally. The discontinuity of the basal boundary condition at S typically results in a local high strain area. Published modelling studies with similar boundary conditions frequently are based on the assumption of purely brittle deformation (analog models) or keep the ductile domain small and highly-viscous by low crustal temperatures. Under these conditions, orogenic deformation is highly localized and typically shows a bivergent pattern rooting in S and forming the boundary of a central pop-up structure. In contrast, a number of model runs performed without applying the remeshing option demonstrates that raised crustal temperatures result in a decoupling layer at the base of the crust, a widened and indistinct zone of mid to upper crustal deformation, and, subsequently, in only small amounts of crustal thickening. Variations of convergence rates show a similar effect on strain localization which is caused by the strain rate dependence of power law creep and variable degrees of thermal reequilibration in the thickened domain. Improved models with remeshing technique are evaluated during parameter variations quantifying the influence of different temperature-viscosity functions on strain localization and the resulting syncollisional exhumation of metamorphic rocks. It is shown that a rheological behaviour which promotes efficient mechanical coupling all over the crustal profile is a requirement not only for localized crustal thickening but also for rapid exhumation of lower crustal rocks by an interaction of isostatic forces and surface erosion. Exhumation becomes most powerful when a relatively low-viscous upper crust is combined with a relatively stiff lower crust. In detail, systematic variations of the burial and exhumation history of different marker points along the model section can be illustrated by synthetic PTt data. The correlation between crustal temperatures, orogenic strain localization and syncollisional exhumation is of great importance for the late collisional events in the Variscan orogeny in Central Europe. There, high temperature/ low pressure metamorphism and widespread granitoid intrusions document high crustal temperatures. On the other hand, localized bivergent orogenic structures mark the boundaries between the tectonometamorphic units at the region of Schwarzwald and Vosges as well as the Mid German Crystalline Rise (Mitteldeutsche Kristallinschwelle, MDKS). Strain localization and synconvergent exhumation of amphibolite grade metamorphic rocks in these areas can be only explained by assuming a lower crustal rheology much stiffer than previously estimated. Creep parameters determined in recent laboratory studies (Mackwell et al. 1998) are capable of supporting rheologies of that kind and are applied in a case study focusing on the MDKS. Under these assumptions, metamorphic peak pressures and temperatures from the Rhenohercynian fold and thrust belt, the MDKS itself, and the Saxothuringian basin as well as the main structural pattern derived from the reflection seismic profiles DEKORP 2N and 2S are well reproduced by the numerical model. An expansion of the modelling technique to 3d FE models aims at taking orogen-parallel deformation into consideration which can result in prominent transport of rocks towards the lateral foreland areas of collisional belts; these processes have been described as tectonic escape (Burke & Sengör 1986) or lateral extrusion (Ratschbacher et al. 1991b). Given the assumption of orthogonal convergence, the 2d mantle subduction model is extruded in orogen-parallel direction to build a three-dimensional crustal block (marginal area of the collision zone). In the adjacent rear part of the model (lateral foreland of the collison zone), basal nodes are no longer object of the velocity boundary condition or fixation, respectively. The model margins obey a no-tilt-requirement preventing differential horizontal displacements of nodes initially on top of each other. Depending on the geodynamic scenario characterizing the marginal area, further boundary conditions like plate boundary forces or rigid buttresses can be defined. A set of model runs is used to gain quantitative insight into the effect of different parameters and boundary conditions on the resulting kinematic pattern, the spatial distribution of strain as well as temporal variations of the surface stress field. According to the modelling results, lateral extrusion is a common process in the marginal area of orogenic belts since it is present in all modelled scenarios. As lateral motions start contemporaneously with the onset of collision and are only slightly accelerated during further convergence, tectonic escape driven by horizontal forces seems to be a more powerful process than gravitational spreading. Rigid model margins surrounding parts of the lateral foreland modify the amount as well as the distribution of horizontal motions but their effect on the orogen itself is rather small. Variations in crustal temperatures, convergence rates, and lower crustal rheology effect both orogenic and lateral foreland deformation. Assuming an isotropic coupling mechanism between the crust and the lithospheric mantle, extrusion rates no higher than 30% of the current convergence rate can be modelled. As much as 70% are reached when the model base is allowed to move laterally. The significance of this basal boundary condition allows to interpret the Miocene lateral extrusion event in the Eastern Alps (z.B. Ratschbacher et al. 1991a). If there was no mountaineous topography in the Eastern Alps area before the onset of lateral movements (Frisch et al. 1998), the lateral extrusion was contemporaneous with prominent crustal thickening and should be induced rather by tectonic escape than by gravitational collapse. In each case, the almost 1:1 ratio of convergence vs. lateral extrusion implies the existence of a basal decoupling horizon. Other proposed causes like the indentation of the Southern Alps or an extensive regime in the Pannonian basin could have modified the resulting structural pattern but fail to explain the dimension of lateral motions by a factor of 2. Due to the large scale of the Indian-Eurasian collision, modelling results can only be compared phenomenologically with tectonic escape in Eastern Asia. A scaled case study therefore remains a great challenge for future FE modelling.

The first documented carbonatites in Manitoba occur as dykes and pods up to 15 meters in length and several meters in width at Eden Lake hosted in a post-orogenic syenitic complex within the Trans-Hudson Orogen. The carbonatites consist dominantly of calcite with lesser clinopyroxene, feldspar, apatite and titanite. Primary and xenocrystic clinopyroxene have distinct compositions, whereas xenocrystic feldspar has well-developed plagioclase and alanite rims. The whole-rock major- and trace-element composition of the carbonatite is consistent with global averages for calcio-carbonatites. Stable-isotope compositions of calcite indicate an igneous origin; the low δ13C ratios may reflect the influence of subducted sedimentary carbonate. A zircon age of 1815±8 Ma corresponds with the time of emplacement, whereas younger titanite ages reflect local thermal history. Although field relations suggest a genetic link to the host syenites, whole-rock geochemical data is incompatible with immiscibility or crystal fractionation models, suggesting a discrete mantle source for the carbonatite.

To understand the fluid temperature and pressure during the Ouachita orogeny, we used isotopic analysis of syntectonic veins and adjacent host material, quartz-calcite oxygen isotope thermometry and fluid inclusion analysis. The veins were at or near isotopic equilibrium with their host rocks; neither the host nor veins has been isotopically reset. The average isotopic variation in (delta18)O between vein and host is 2.4 plus/minus 1.7% and 0.7 plus/minus 1.7% for quartz and calcite, respectively. The temperature of vein formation from quartz-calcite oxygen isotope thermometry is about 210-430 degrees C. Although this is a large range, the temperature does not vary systematically in the exposed Ordovician through Mississippian rocks. The lack of isotopic difference between host and vein suggests that the host oxygen determined that of the veins. This in turn suggests that the fluid in the rocks did not change regionally. The vitrinite reflectance/temperature of the host rocks increases with restored stratigraphic depth more than that calculated with the quartz-calcite thermometer in veins. Fluid inclusion analysis in vein quartz constrains homogenization temperatures to be from 106-285 degrees C. Isochores from fluid inclusion analyses were constrained using quartz-calcite thermometry and vitrinite reflectance temperatures to calculate vein formation pressures of 0.3?4.7 kbars. These pressures correspond to vein formation depths up to 19 km, assuming an unduplicated stratigraphic section. Using burial curves and a reasonable range of geothermal gradients, vein formation ages are between 300 to 315 Ma, i.e., Early to Middle Pennsylvanian.

The first documented carbonatites in Manitoba occur as dykes and pods up to 15 meters in length and several meters in width at Eden Lake hosted in a post-orogenic syenitic complex within the Trans-Hudson Orogen. The carbonatites consist dominantly of calcite with lesser clinopyroxene, feldspar, apatite and titanite. Primary and xenocrystic clinopyroxene have distinct compositions, whereas xenocrystic feldspar has well-developed plagioclase and alanite rims. The whole-rock major- and trace-element composition of the carbonatite is consistent with global averages for calcio-carbonatites. Stable-isotope compositions of calcite indicate an igneous origin; the low δ13C ratios may reflect the influence of subducted sedimentary carbonate. A zircon age of 1815±8 Ma corresponds with the time of emplacement, whereas younger titanite ages reflect local thermal history. Although field relations suggest a genetic link to the host syenites, whole-rock geochemical data is incompatible with immiscibility or crystal fractionation models, suggesting a discrete mantle source for the carbonatite.

Univ., Diss., 2008--Frankfurt (Main). / Zsfassung in engl. und dt. Sprache.

Neoproterozoic-Early Cambrian continental rifting related to the breakup of the supercontinent Rodinia framed the continental margin of eastern Laurentia and the departing cratons around the opening Iapetus Ocean. The result of continental extension was the production of a zig-zag set of promontories and embayments on the eastern Laurentian margin defined by northeast-trending rift segments offset by northwesttrending transform faults. The St. Lawrence promontory defines the Laurentian margin in western Newfoundland. There, Neoproterozoic-Carboniferous clastic, volcanic, and carbonate successions record protracted continental rifting and passive-margin thermal subsidence followed by destruction of the margin during the early, middle, and late Paleozoic Appalachian orogenic cycles. Palinspastic restoration of deformed Paleozoic strata by a set of balanced cross sections resolves the structure, stratigraphy, and timing of Paleozoic tectonic events on the St. Lawrence promontory. Synrift and post-rift subsidence profiles, as well as abrupt along-strike variations in the age, thickness, facies, and the palinspastically restored extent of synrift and post-rift stratigraphy, indicate the St. Lawrence promontory was founded upon a low-angle detachment rift system. Upperplate margins, lower-plate margins, and transform faults that bound zones of oppositely dipping low-angle detachments are recognized along specific segments of the promontory. A detailed U-Pb and Lu-Hf isotopic detrital zircon study elucidates the identity of specific cratons conjugate to the St. Lawrence promontory in the pre-rift configuration of Rodinia. Approximately 510 zircons from 9 samples collected from basement and overlying Early Cambrian synrift rocks in Newfoundland were analyzed by LA-ICP-MS for U-Pb ages and Hf isotopic ratios. Synrift samples yielded ages ranging from 3605 Ma to 544 Ma with maximum age frequencies of 1000-1200 Ma (Grenville), 1350-1450 Ma (Pinware), and 2650-2800 Ma (Superior), while two basement samples yielded U-Pb ages of 1044 Ma and 1495 Ma. 177Hf/176Hf isotopic ratios of ca.1000 Ma, 1200 Ma, and 1400- 1600 Ma zircons from Newfoundland basement and synrift rocks are a close match to reported 177Hf/176Hf ratios for Baltican zircons of the same vintage, suggesting that Baltica was conjugate to the St. Lawrence promontory.