A computational Discrete Element Model (DEM) is developed to investigate the kinematic evolution of erosive and non-erosive doubly vergent wedges, focusing on the implications for the interpretation of field data. Many current field studies focus on attempting to identify a positive correlation between tectonic and surface processes. Techniques and observations include thermochronometry, geobarometry, geomorphology, structural reconstruction and syn-tectonic stratigraphy. In order to further constrain the evolution, analogue and computational modelling is required. Modelling studies include analogue sandbox models and computational Finite Element Models (FEMs). Analogue models generate many emergent structural features, but cover a small range of parameter space and have poor reproducibility. FEMs provide poor structural resolution due to underlying continuum assumptions in their formation, but are effective investigating a wider range of parameter space, boundary conditions and erosive feedbacks. The DEM provides the opportunity to build on the best parts of both techniques, providing structural resolution on the sub-orogen scale. This thesis investigates the possibility that some of the discrepancies in the results may be resolved by basing the interpretation of this data on a DEM computational model that allows the emergence of displacements across discrete structures. In order to achieve this, the thesis develops the DEM, highlighting the importance of formulating appropriate boundary conditions and emergent material properties. The role of particle shape, packing structure and inter-particle force parameterisation is investigated using angle of repose and singly vergent wedge experiments. Particles consisting of clusters of three random sized discs produce results most comparable with sandbox analogues and real accretionary prisms. This thesis provides evidence that the discrepancies in field investigations searching for the erosive-tectonic signal may be masked by these emergent second order tectonic fluctuations.

As displacement is accumulated on a fault surface through time, deformation is generated in the volume surrounding the fault. Previous studies have tended to only look at parts of this entire fault system in isolation. This thesis is a systematic survey of fault zone architecture at millimeter to kilometer scales, which is linked to variations in fault displacement. Structural data and displacement variations have been measured from two isolated normal faults cutting the Jurassic Navajo Sandstone in the Chimney Rock fault array, Utah, USA. Both faults are approximately four kilometres long with maximum displacements of thirty metres. The faults are surrounded by deformation bands and slip-surfaces typical of deformation in high porosity sandstones. Deformation is seen ahead of the fault tip and to either side of the well-developed fault surface. On average, the width of this zone of deformation is twice the displacement on the main slip surface. This implies that while some deformation is generated ahead of the fault tip (a process zone) deformation is then continuously accumulated after a through-going fault surface has developed, intensifying and widening the zone of off-fault deformation. The latter is referred to as a kinematic damage zone. The relationship between off-fault deformation width and displacement is potentially useful for predicting fault zone architecture below seismic resolution. However the exact form of the scaling relationship is not well controlled and is expected to vary in different lithologies. The off-fault deformation consists of an orthorhombic pattern of deformation bands, with a low angle between strike sets. This can be attributed to a small component of along-strike extensional strain (due to variation in displacement along the fault) combined with larger extensions perpendicular to the fault.

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An integrated sedimentological, structural and geochemical study has been used to elucidate the tectono-sedimentary evolution of the Pindos Zone in the NW Peloponnese. The study area is interpreted as part of the Apulian passive margin which was bordered to the east by a small Neotethyan basin, the Pindos Ocean. The Pindos Zone is an elongate north-south trending imbricated terrane consisting of deep-water sedimentary rocks (the Pindos Group) that were deposited in the Pindos Ocean. The sedimentary rocks range in age from the Late Triassic to the Eocene. These sediments were deposited on a volcanic substratum that is sparsely preserved as blocks within melange at the base of Pindos thrust sheets. Cursory analysis suggests that the extrusive igneous rocks exhibit geochemical signatures comparable with island arch tholeite (IAT). However, further geochemical study indicates that parental members of the suites represent transitional within plate basalt (WPB) to mid-ocean ridge basalt (MORB) lava. The recognition of spatial and temporal facies trends within the over lying sedimentary rocks, augmented by laboratory analysis, allows the sedimentary evolution of the passive margin to be documented from rifting to final suturing. Earliest recorded sediments consist of Late Triassic sandstones, derived mainly from a metamorphic source terrane, intercalated with <i>Halobia</i>-bearing limestones. Thereafter, a proximal to distal facies distinction is recognised in the sedimentary sequence. Late Triassic to Liassic facies consist of coarse calcirudites and nodular limestones in the west, while to the east, distal calciturbidite, micrite and chert facies are present. During Aalenian times, sedimentation underwent a fundamental change from calcareous to siliceous deposition, via an argillaceous interval. The Middle and Late Jurassic is dominated by radiolarian-rich, ribbon-bedded, cherts. The passive margin period was interrupted in the Late Jurassic by a short period of localised faulting and volcanic activity.

High temperatures and pressures inhibit frictional sliding, normally restricting the occurrence of earthquakes to depths less than 30 km. However, in subduction zones, earthquakes occur down to depths approaching 700 km. In the literature, the process which enables unstable sliding at great depths is often linked to the occurrence of mineral reactions. In this thesis, both the pressure-temperature conditions of deep seismogenesis and the detailed kinematics of deep earthquake sources are investigated. Two dimensional thermal models are calculated for many subduction zones and are used to predict the spatial loci of various mineral reactions, and also to estimate the temperatures at which earthquakes nucleate. I show that the spatial distribution of seismicity is strongly controlled by temperature but is largely independent of pressure, suggesting that seismogenesis is unrelated to the occurrence of mineral reactions, which are dependent on both pressure and temperature. Moment tensor inversion using the polarities and relative amplitudes of P and its surface reflections, pP and sP, provides high-resolution constraint on the mechanisms of deep earthquakes. Using this technique, analysis of eight earthquakes revealed them all to be compatible with a double couple source (constant volume, simple shear). The most well constrained solution shows explicitly that any reduction in volume accounts for less than 2% of the total seismic moment. Variations in the duration of P and pP are modelled as directivity effects to invert for the geometry of rupture. The inferred rupture velocities vary widely between different events, with a minimum range 1.2 £ <i>V_r</i> £ 4.5 km s^-1, and are independent of pressure, temperature and fault plane orientation. The results described are in agreement with the hypothesis that instability develops as a result of dynamic grain size reduction and / or heating through viscous dissipation in a predominantly plastic deformation regime. This mechanism is consistent with published field observations, of pseudotachylytes in otherwise ductile shear zones, from the deep crust and shallow lithospheric mantle.

Recent parameterisations of melting experiments may be used to predict the volume and composition of magma generated by melting anhydrous peridotite during adiabatic decompression of the asthenosphere (McKenzie & Bickle 1988). Here they are used to predict the character of magmas generated during adiabatic upwclling which accompanies the formation of sedimentary basins. The objective of this thesis is to test the model predictions with observations from the Mesozoic North Sea Basin. At ocean ridges the degree to which the asthenosphere melts is principally governed by its potential temperature (Tp) and the entropy change on melting (AS). The amount of melt produced and its average composition are controlled by the average extent and average depth of melting. The model predicts that in order to generate the normal 7 km of oceanic crust at a mid-ocean ridge, the 'normal' Tf of the asthenosphere must be 1280±40°C; the error results from uncertainty in AS. Predicted average melt compositions agree favourably with compositions of primitive MORB (mid-ocean ridge basalt). Some ridge segments are located above anomalously hot 'plumes' in the mantle. The greater thicknesses and distinctive compositions of the crust in such regions (e.g. Iceland) are consistent with model predictions for Tp's 100 to 300°C greater than normal. The generation of melt from dry peridotite during rifting of the litho-sphere depends critically on the T,, of the asthenosphere, the amount (J3e) of lithospheric thinning, and the initial shape of the geotherm; i.e. the thickness of the mechanical boundary layer (MBL) prior to extension. In most extensional basins the steady state MBL is ~100 km thick. The maximum amount of lithospheric thinning which occurs during extension depends on the partitioning of strain between the crust (ftc) and mantle (/3m) and on whether extension is accommodated by pure shear or simple shear. At normal Tj,'s the amount and average composition of the melt produced during rifting is simply related to the size of the average melt fraction and the average pressure of melting. When a plume accompanies rifting, regional doming over an area 1000 to 2000 km in diameter is expected. High temperatures and rates of plume-flow may lead to the production of large volumes of alkaline magma when there is little or no stretching and flood tholeiites when ft is large. The most important episode of extension in the North Sea took place from the Middle Jurassic (180-170 Ma) to the Early Cretaceous (120-100 Ma) and resulted in the development of a trilete rift system. Associated mag-matic activity occurred shortly after the onset of rifting (ca. 160-150 Ma) and was located principally in the triple-junction area, where an average thickness of 0.5-1.5 km of subaerially erupted alkali basalt comprise the Forties volcanic province. More minor volumes of nephelinites, basanites and ultrapotassic rocks, are observed on the western edge of the Egersund Basin, on the flanks of the Central Graben and in the Netherlands sector of the North Sea. Dates generated by 40Ar/39Ar stepwise degassing of the freshest samples suggest that the igneous activity is contemporaneous throughout the region; i.e. there is no migration of magmatism with time. The North Sea rocks are variably altered and range from mildly to highly alkaline in character. The Forties basalts are chemically similar to OIB (ocean island basalt), but the ultrapotassic rocks found elsewhere in the North Sea have no oceanic equivalents. All of the North Sea rocks lie between MORB and bulk earth in terms of U3Nd/U4Nd (0.51265-0.51285) and 87Sr/86Sr (0.703-0.704). Simple single stage melting calculations suggest that if the source of the Forties parental magmas was a garnet peridotite with a composition betwen that of bulk earth and the inferred source of MORB, then they were produced by very small amounts of melting (< 3%). The extreme fractionation of LILE (large ion lithophile elements) and light REE (rare earth elements) from heavy REE seen in the magmas from other parts of the North Sea is difficult to explain by single-stage melting unless the source is more enriched in LILE and light REE than bulk earth. The stretching factor (ft) in the triple junction region is estimated from thermal subsidence and gravity data to be between 2 and 3; larger than elsewhere in the North Sea. Many of the subsidence curves are abnormal in that they show condensed, or non-existent, syn-rift subsidence, and very rapid thermal subsidence. These effects are not considered to be due to fault block rotations and do not affect the estimates of ft. They may be explained by decoupling of the strain rates in the crust and mantle which results in extreme but localised thinning of the mantle at the start of rifting (ftm > > ftc) but importantly, allows the lithospheric section to be balanced at all times. The stratigraphy and the absence of a hot-spot trail during the Mesozoic is inconsistent with a plume-model for rifting. There was, however, localised uplift along the rift flanks and in the triple junction, which can be explained by the 'decoupled' stretching mechanism. The simplest model for the Forties basalts involves stretching by a factor of between 2 and 3 of a MBL 90 km thick over asthenosphere with a Tp of 1280 to 1320°C. The predicted volume and composition of melt are largely consistent with these observations. A full explanation of the Forties magma compositions does, however, require an input from mantle that is enriched in incompatible elements and volatiles relative to bulk earth. This component in the forties magmas was probably produced in a metasomatised layer at the base of the MBL. Volatile-controlled melting in the MBL was probably also responsible for the ultra alkaline rocks found in less-stretched regions of the North Sea.

The latest Cretaceous and Tertiary saw a significant change in the tectonic regime of northwestern Europe. North Atlantic rifting over the Iceland "hot-spot" to the northwest resulted in the total separation of North America from Europe by the mid-Miocene while to the southeast the closure of the Tethyan Ocean resulted in the Alpine Orogeny which culminated by the Pliocene. Contemporaneous with these events many of the pre-existing Mesozoic basins of northwestern Europe experienced tectonic reactivation characterised by dip-slip inversion, while regional uplift of both basin and massif areas occurred. Seismic reflection profiles and field studies indicate that the Inner Moray Firth experienced tectonic reactivation during the Tertiary, although the precise dating remains uncertain. Extensional reactivation of the pre-existing half graben bounding faults and the formation of new extensional features such as the faults forming the Sinclair Horst was the most common form of reactivation. The Great Glen Fault shows structures indicative of dextral strike-slip motion. This dextral movement combined with sinistral motion of the Helmsdale Fault resulted in the folding seen in the Sutherland Terrace (the area between the two faults) as a result of space problems. Minor inversion folds with their associated shortcut faults can also be found within the basin and attest to a period of compression. Probably the most regionally important structure within the basin is the eastward dipping mid-late Danian unconformity which provides evidence for a period of uplift and erosion in the area prior to the deposition of Cenozoic sediments. Apatite fission track analysis of the Scottish Highlands shows that samples currently at surface experienced elevated palaeotemperatures and consequently must have been uplifted and eroded from their maximum burial-depth.