Abrupt lateral changes in thrust geometry occur in many mountain-building fold-thrust belts. Whilst many works have dealt with palinspastic reconstructions and transport-directionparallel balanced cross-sections, far fewer show a full three-dimensional architecture, or examine how lateral variations in thrust architecture can be linked via cross-strike discontinuities or transverse zones. Systematic alignments of lateral structures are suggested to be related to kinematic responses to irregularities generated across pre-existing, sometimes reactivated, sub-décollement basement faults, pre-thrusting cover strata deformation above basement faults, development of duplex structures / antiformal stacks, and / or along-strike variations in mechanical stratigraphy. New cross-strike discontinuity / transverse zone identification methodologies developed within this research incorporating thrust ramp-flat alignment analyses and branch-point, cutoff point and fault-tip point analyses, together with a variety of previously utilised identification techniques, allow spatial alignments of lateral structures to be determined. New methodologies help to better characterise the pre-thrust template and assess that template’s capacity to control subsequent lateral thrust geometries on a variety of scales during allochthon formation within two contrasting fold-thrust belts, the linear Moine Thrust Belt and the oroclinal Cantabrian Thrust Belt. Within the Kinlochewe region of the Moine Thrust Belt, a distinct compartmentalisation is identified across the Loch Maree Fault (LMF). A thrust dominated region of overturned Torridonian / Lewisian, overlying a right-way-up Cambrian succession can be clearly identified on the northern wall of the LMF, compared to a fold-and-thrust dominated section on the southern wall. Compartmentalisation is suggested to be a response to a step in basement that generated a transport-parallel lateral ramp or sidewall during thrusting. A series of potential cross-strike discontinuities / transverse zones are identified within the Cantabrian Thrust Belt. Structural disparities are suggested to have developed as a result of along-strike variations in stratigraphical thickness and regional transport during a multiphase oroclinal development.

This thesis reports on over 27 sills and 213 associated vents. The sills and vents were investigated using 3D seismic data, in a ~1000 km2 area, offshore Norway between the Møre and Vøring Basins (the Edvarda survey). A wide range of sill geometries are observed which are interpreted to be the result of five different processes acting on the sills. Three of these processes relate to how the host deforms. If sill intrusion causes deformation of the seafloor, creating folds, or the sills interact with folds created by neighbouring sills, sills are found to cross bedding (transgress) abruptly. Alternatively, if deformation is interpreted to be local, then continuously increasing Young’s Modulus with depth is interpreted to result in sills which transgress continuously upwards, akin to smooth ‘bowls’. At shallow depths the host is interpreted to fluidise, leading to limited transgression or in some cases multiple bowls. The seismic amplitude responses of shallow sills include flow related features such as channels and lobes. The other two processes interpreted to affect sill propagation stem from structures in the host: abrupt changes in lithology and pre-existing faults. Multiple sills are found to terminate, and in some cases form, at sand rich units in the otherwise mudstone dominated host. Additionally, some sills are interpreted to have intruded into a host with pre-existing polygonal faults, which led to angular sill geometries. Vents are found to occur directly above sills, often along the margins of sills, but in some cases over sill interiors, especially where the sills are locally shallower. Additionally, a cluster of 98, relatively small vents occur above the shallowest sill. Differential compaction and slumping are found to affect some larger vent morphologies. Overall, vent size is found to closely follow a power-law such that smaller vents are significantly more numerous than larger vents.

The origin of high elevation topography at so-called “passive” continental margins and their interior hinterlands has been an outstanding question in geoscience for decades. An important step towards answering this question is to improve our understanding of the response of the landscape to deformation of the lithosphere over different length scales. During continental rifting, elevated rift flanks may develop as a result of lateral extension of the lithosphere combined with vertical movements of the lithosphere driven by isostasy or convection of buoyant mantle flow. However, mechanisms capable of maintaining rift-related topography over geological timescales or driving post-rift rejuvenation of margin topography remain largely speculative and are strongly dependent on theoretical models. By constraining the timing and magnitude of major erosional events that have occurred across a particular margin using suitable empirical data we can begin to unravel the geomorphic development of the margin and identify the forces driving surface uplift. Apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) thermochronometry has the unique ability to deliver these constraints by providing information on the cooling of rocks through temperatures of c. 120 – 40°C as they are exhumed from depth (c. 4 – 6 km) by erosion of overlying rock. Along the western continental margin of South Africa recent insights from thermochronology, structural geology and geomorphology has revealed that the margin may have experienced a more complex post-rift tectonic history than is to be expected for a “passive” margin. In this study, AFT and AHe analysis was performed on samples collected across the high relief escarpment zone along the continental margin (Namaqualand Highlands) and across the continental interior plateau (Bushmanland Plateau) to determine the post-break up cooling history of the continental margin. Sampling was undertaken from a structural perspective by sampling individual fault blocks within the heavily faulted Namaqualand Highlands and by collecting a profile of samples, from the interior plateau, that crosses major structural features at the boundary of the Kaapvaal craton. The approach for AHe analysis was to obtain multiple single grain age measurements (up to 20 grains per sample) for selected samples in order to investigate and exploit the primary causes of natural dispersion of AHe single grain ages and the influence of this dispersion on thermal history modelling. AFT and AHe data from 56 outcrop samples are jointly inverted using a Bayesian transdimensional approach incorporating the compositional influence on fission track annealing and radiation damage enhanced He retention. Two major discrete cooling episodes are recorded in thermal history models at c. 150 – 130 Ma and 110 – 90 Ma, respectively. These cooling episodes are broadly coeval with periods of enhanced deposition in the offshore Orange Basin and are therefore linked to discrete periods of enhanced continental erosion. The first phase of erosion is believed to involve the progressive destruction of syn-rift topography which prevailed across the developing continental margin and inland to the SW boundary of the Kaapvaal craton. The second phase of erosion is proposed to have been induced by regional uplift of southern Africa coupled with localised reactivation of basement structures at the continental margin and craton boundary. A vertical thickness of at least c. 3 – 5 km of material was eroded across the continental margin during the Cretaceous with only minor erosion (typically < 0.5km) occurring during the Cenozoic. There is now considerable support from the low temperature thermochronology record that km-scale denudation has occurred regionally across South Africa during the Mid-Late Cretaceous, long after the end of continental rifting in the South Atlantic. Data from this study reveals a more localised structural component to this regional event and more complexity in the spatial and temporal distribution of denudation during this period. The mechanisms driving this denudation are still uncertain but it is proposed here that regional dynamic uplift of South Africa has occurred due to the presence of an underlying upwelling of buoyant mantle, while in-plane horizontal stresses have triggered reactivation of basement structures. It now seems appropriate to revise the classification of the southwest African continental margin as being “passive” in a tectonic sense and consider the implications this has for our understanding of global plate tectonics.

Reservoirs of South Brae Oilfield comprise a 1540m sequence of Upper Jurassic submarine fan sandstones and conglomerates. The diagentic history of the reservoir between 3684 and 4202m was studied using petrographic, geochemical, fluid inclusion thermometry and isotope techniques in core samples from 5 wells. This enabled interpretation of the processes involved in the supply of ions for authigenic mineral growth and allowed the paragenetic sequence and associated porefluid movements to be related to the burial and tectonic history. The earliest diagenetic phase was calcite cementation, which formed concretionary bodies 0.8-4m diameter during shallow burial. These concretions were precipitated from a meteoric fluid 18O= -7%0 SMOW), which flushed through the reservoir during shallow burial, displacing the depositional marine porefluid and causing aggressive dissolution of detrital shell debris, plagioclase (supplying Ca) and K-feldspar. Oxygen isotope values record precipitation at temperatures between 15o and 70oC at depths of 0.3 to 2.3 km. 13C and 87Sr/86Sr ratios record increasing thermal decarboxylation and silicate disolution. No significant diagenetic clays are present, so Al has been lost to the system. This was followed by quartz cementation. Oxygen isotope and fluid inclusion data suggest that the greatest volume of quartz was precipiated at temperatures between 70o and 110o (2.3 to 3.7km), from a layered porewater. Our model suggests that warm, isotopically modified, compaction-driven, basinal waters (18O= + 4 %0 ) overlay cooler meteoric derived waters (18O= -4%0 ). Cementation occurred from 55 to 20Ma and may be related to periods of overpressure release. Silica was supplied locally by presssure solution and possibly from mudrocks. A late dissolution event has enhanced porosity by up to 8%, due to dissolution of diagenetic calcite and K-feldspar, particularly in the upper reservoir zones. This seocndary porosity formation was probably due to the movement of basinal fluids, compacted from the interdigitating Kimmeridge Clay and drained out of the basin laterally through the reservoir. Subsequently, minor amounts of illite, kaolinite, calcite, dolomite and pyrite have further reduced the porosity of South Brae to 3-19%. The oilwater contact has no poroperm effect. From 2Ma, the reservoir sealed and became overpressured by 900psi halting fluid movement through the oilfield, and permitting final hydrocarbon accumulation to occur.

Seafloor spreading at mid-ocean ridges is accommodated by a combination of magmatic accretion and tectonic stretching of the lithosphere. Recent investigations of mid-ocean ridges show evidence for large-offset normal faults or detachments that accommodate a significant portion of the plate separation. Once thought of as rarities along the global spreading system, detachment faults are now considered to play an integral role in seafloor spreading at slow- and ultra-slow-spreading ridges. Estimates of the proportion and extent of tectonic spreading however vary widely; some authors suggest as much as 50% of the Mid Atlantic Ridge is underlain by active detachment faults. The lack of consensus is in part a consequence of the difficulty in documenting the extent of tectonic stretching and detachment faulting, especially from surface morphology alone. On the modern seafloor tectonic activity may potentially be greatly under-estimated if lava flows blanket and obscure the faulting below. This thesis addresses the question of whether and how such ‘hidden tectonics’ may be accommodated beneath the seafloor by means of a field-based study of the Troodos ophiolite, Cyprus, which is believed to be a slow-spreading ridge analogue. My interdisciplinary approach utilises structural mapping, palaeomagnetism and geochemistry to investigate the spreading structure and mechanism of accretion of the Troodos upper crust. I document significant extensional faulting and rotation within the crust above a detachment fault at the level of the sheeted dyke complex, yet show that the lavas at the surface are sub-horizontal and unaffected by the deformation beneath. Unconformities in the lava section demonstrate progressively greater rotations deeper in the extrusive pile, controlled by tectonic stretching and tilting of the underlying dykes, rather than rotation by loading and/or subsidence within the lava pile as previously proposed. Ponding of late, primitive, low viscosity lava flows against normal faults on the seafloor thickens the extrusive sequence substantially and obscures the faulting below. The study shows that syn-tectonic volcanism is an effective mechanism for filling active half-grabens at slow-spreading ridges. Tens of percent tectonic stretching at depth may be completely masked at the surface by syn-tectonic lava extrusion. Such ‘hidden tectonics’ may be far more common at modern mid-ocean ridges than commonly supposed.

The West Orkney Basin is situated in a frontier hydrocarbon region of the United Kingdom Continental Shelf. This study presents a reappraisal of the tectono-stratigraphic development and petroleum potential of the basin, and is based on a recent compilation and partial reprocessing of all the available 2D reflection seismic for the area. Evidence for the presence of Devonian lacustrine source-rocks in the basin is demonstrated by the recognition of a syn-rift sequence overlying basement, which comprises two packages of contrasting seismic facies characteristics, which are correlateable to onshore Devonian source-rock and reservoir facies. The syn-rift sequence is truncated at unconformity; that is related to Late Carboniferous inversion of the Great Glen-Walls Boundary Fault system. A second major phase of rifting within the basin, with formation of new faults and reactivation of pre-existing Devonian faults, is interpreted to have initiated in the Late Permian and dwindled into the Early Jurassic. Subsequent extensive exhumation events occurred in the Mid-Jurassic to Early Cretaceous and Cenozoic, with removal of about 2.5 km of Upper Triassic to Lower Jurassic sediments and perhaps 0.5 to 1 km of Upper Cretaceous rocks. Timing of hydrocarbon generation from Devonian source-rocks was modelled using Genesis 1D basin-modelling software from Zetaware, and the results from this indicate that it most probable that the majority of hydrocarbon generation in the basin preceded the end of the second phase of rifting in the basin (Late Permian to Early Jurassic). Therefore, the major risks with play-concepts based on a Devonian source-rock are considered to be seal integrity during multiple and prolonged uplift events.

On September 12 2007, an Mw 8.4 earthquake occurred within the southern section of the Mentawai segment of the Sumatra subduction zone, where the subduction thrust had previously ruptured in 1833 and 1797. Following the 2007 rupture, a temporary local network was installed in the Mentawai region between December 2007 and October 2008 to record the aftershocks. Additionally, a second network was installed in central Sumatra between April 2008 and February 2009. In this study the data obtained from the Mentawai network were used to determine 2D and 3D Vp and Vp/Vs models, first motion polarity focal mechanisms and accurate hypocentre locations. In addition to this, shear wave splitting (SWS) measurements from both networks were used to determine the type, amount and location of anisotropy. This has enabled us to obtain a detailed image of the structure of the subduction zone, ascertain the down-dip limit of the seismogenic zone and determine the deformation occurring. The forearc islands are characterized by a low Vp (4.5-5.8 km/s) and a high Vp/Vs ratio (>2.0), suggesting that they consist of fluid-saturated sediments. The down-going slab is clearly distinguished by a dipping region of high Vp (8.0 km/s), which can be traced to ~50 km depth, with an increased Vp/Vs ratio (1.75 to 1.90) beneath the forearc islands and the western side of the forearc basin, suggesting hydrated oceanic crust. Beneath the slab, a ~150 km thick layer of sub-slab anisotropy has developed due to the oceanic asthenosphere being entrained by the subducting slab. Two clusters of seismic activity are found within the ~25-30 km thick overriding crust. The location of the first cluster confirms that the Mentawai Fault is active and may accommodate backthrust movement, while the second cluster suggests a backthrust may be present on the eastern side of the forearc basin. Local SWS measurements suggest that in the overriding plate, adjacent to the Sumatran Fault, a layer of anisotropy has formed from fault-parallel aligned fractures and minerals. Beneath the forearc, a shallow continental Moho of < 30 km depth can be inferred. Within the mantle wedge there is no widespread serpentinization; only localized serpentinization is present at the toe. Beneath the backarc, 2D corner flow is occurring in the continental asthenosphere. The co-seismic slip of the 2007 events, as well as the aftershock distribution, suggests that the down-dip limit to rupture propagation is beneath the slab-Moho intersection at ~50 km depth. Consequently, as the Mw 7.7 Mentawai earthquake on 25 October 2010 showed that the updip limit of the seismogenic zone is at the trench, a potential 200 km wide rupture could take place.

The aim of this thesis was (i) to develop analytical methodologies and a workflow to identify the ocean-continent transition (OCT) and to locate the continent-ocean crustal and lithosphere boundaries (COCB and COLB) at continental rifted margins and (ii) to apply these methodologies and workflow to six cross-sections of the Northeast Brazilian rifted margin. The six cross-sections were taken from the margin segments Almada-Jequitinhonha, Jacuípe, Sergipe, Alagoas and Pernambuco and were constructed using seismic reflection sections from the borders of sedimentary basins to the oceanic crust. The OCT of the Northeast Brazilian rifted margin is complex due to variable extrusive and intrusive magmatism and antithetic tectonics. COCB locations interpreted on seismic reflection data have been tested with those determined using the analytical methodologies and workflow developed in this study. The workflow comprises: 1) the determination of sediment-corrected basement depth profiles, 2) the analysis of the residual depth anomalies of the oceanic crust and its extrapolation into the rifted margin, 3) the gravity inversion of the Moho with crustal thinning determination and 4) the inversion of lithosphere thinning using subsidence analysis. The calibration of the gravity inversion through the fit of the residual depth anomaly in unequivocal oceanic crust is a new approach to determine the reference Moho depth in areas without seismic refraction data. The Almada-Jequitinhonha OCT corresponds to a region of antithetic faulting and low free-air gravity anomaly. The Jacuípe OCT corresponds to a region of development of normal magmatic addition, expressed in the seismic sections as seaward-dipping reflectors, and has a relatively high free-air gravity anomaly. Although the Jacuípe margin represents a narrow rift, this margin seems to be wider and offshore syn-rift sediments are either not imaged or have been eroded. The Sergipe margin is interpreted as being magma-poor during rifting and evolved to slightly magma rich in the early post-rift. The OCT corresponds to a region of continental crust thinner than the adjacent oceanic crust, with antithetic faulting and a stable free-air gravity anomaly. The Alagoas margin is interpreted as being magma-poor during rifting and evolved to normal magmatic addition in the early post-rift, while the Pernambuco margin is interpreted as being slightly magma-rich. The OCT of both margins corresponds to a region of synthetic and antithetic faulting with a low free-air gravity anomaly. The predicted COCB and COLB locations for each cross-section tend to be similar to each other. Only minor differences between the crustal and lithosphere thinning profiles have been observed. The rifted margin width, measured along the cross-sections, does not vary significantly in the South between Almada-Jequitinhonha and Sergipe North, ranging from 110 to 130 km. While, in the North between Alagoas and Pernambuco it is wider, around 170 km. The Northeastern Brazil margin varies from magma-poor in the Almada-Jequitinhonha region to slightly magma-rich in Sergipe and Pernambuco, both probably affected by the Santa Helena Hot Spot. The workflow developed here can be considered successful in locating the COCB and COLB positions and in identifying the OCT in the cross-sections across the Northeast Brazil margin and can be applied to other rifted margins without seismic refraction data.

Internal waves in the ocean are the principal generators of mixing in the abyssal ocean and regions of rough topography. The present research work diagnoses the influence of internal wave activity over the Continental slope in the Gulf of Cadiz. Mediterranean Outflow (MOW) and North Atlantic Central Water (NACW) are the main baroclinic flows over the study region and diapycnal mixing acts in each layer. Semi-diurnal internal tides and a continuous MOW flow are observed on the slope. The MOW flow is persistent reaching >0.40 ms-1, but varies in strength with the tides. The Internal wave field in the Gulf of Cadiz can play an important role affecting the MOW signal over the continental slope; MOW can be displaced by the internal tide. Internal waves are generated by tides and MOW flow interacting with the bottom, the two most energetic sources locally. Also MOW bottom stress provides strong diapycnal mixing, providing well-mixed conditions in the MOW. Internal tides can transfer energy on the slope and can cause turbulence. A critical slope characteristic for semidiurnal internal waves occurs over the continental slope with local background stratification where MOW travels as an undercurrent. Diapycnal mixing is found to be enhanced inside the MOW with a diapycnal diffusivity O(7x10-4 m2s-1), and at the MOW-NACW interfaces, reaching O(2x10-4 m2s-1) for the upper interface and O(5x10-4 m2s-1) for the lower interface. Fine-structure methods are used to estimate mixing using CTD measurements; however most of the records came from temperature profiles (XBTs) and an alternative approach to diagnose the strain uses temperature profiles with inferred salinity (using temperature-salinity relations from the CTDs). Applying the strain method using temperature with inferred salinity profiles provides a plausible approximation of the strain spectrum and the mixing estimates, with uncertainties similar to those diagnosed using CTD measurements. Mixing estimates are also diagnosed using a large scale box model, where a salinity budget is applied to study gain and loss over the Gulf of Cadiz. Box model results confirm that salinity is diapycnally transferred from the MOW layers into the neighbouring NACW layers. The advective and diffusive transfers of salt along the layer are much larger than the diapycnal transfer. The inferred diffusivities from the box model are broadly in accord with the estimates from strain.

Subduction margins, as in the case of south-central Chile, are active seismotectonic environments and locus of the world largest earthquakes. In this thesis, two segments of the south-central Chilean subduction margin are studied: (A) the southernmost portion, at the termination of the Nazca-South America convergence (~46ºS), and (B) the segment located between 34º-38ºS, where the Mw 8.8 Maule Earthquake took place in 2010. Analysis of data from a local seismic network deployed in 2004-2005 in area A, indicates low levels of background seismicity with magnitudes ranging 0-3.4 Ml. The seismicity corresponds to shallow crustal events, mostly occurring within the upper 10 km. A third of the seismicity is associated to volcanic activity present in the area, while scarce seismicity is associated with a large strike-slip fault, the Liquiñe-Ofqui Fault System (LOFS), that intersects the region along the arc in a N-S-trend. In 2007, this region was affected by a seismic sequence with a peak of activity associated with a Mw 6.2 earthquake in April that year. A local seismic network was deployed after this main event in order to study its sequence of aftershocks, which provided a unique opportunity to characterise seismotectonically this area that usually lacks intermediate magnitude seismicity, including the calculation of a new local velocity model, accurate aftershock locations and computation of focal mechanisms. The results show P-wave velocities of ~5 km/s for the upper 5 km in accordance with the geology of the area, and low S-wave velocities for the upper 3 km of crust due to rock fracturing and the presence of fluids. An average Vp/Vs ratio of 1.76 was calculated for the region. The alignment of most of the aftershocks within the LOFS plus obtained focal mechanisms, indicate that this sequence had tectonic origin related to the re-activation of the LOFS. Further, a maximum seismogenic depth of about 15 km was determined for the entire region. Regarding area B, affected by a large megathrust earthquake in 2010, the study of moment tensor solutions for the sequence of aftershocks provided new insight into the distribution of postseismic activity relative to co-seismic slip and the release of seismic afterslip. Thrust aftershocks dominate the postseismic activity, but also normal faulting was detected in the outer-rise area and in the overriding plate near the coastline. The largest seismically released afterslip is located between the two main patches of co-seismic slip. Large aftershocks (M>4) occur along the megathrust interface, in zones of intermediate co-seismic slip associated to stress introduced on dislocation tips with high co-seismic slip contrast. On the other hand, smaller events (M<4) tend to occur in areas of large co-seismic slip, and might indicate a more diffuse distribution within the damage zone of the megathrust plane. It is likely that these smaller events are associated to secondary processes (fluid release, re-activation of secondary structures). Although belonging to the same subduction margin, the seismotectonics and earthquake patterns of the two areas investigated here show different underlying tectonic regimes. For the northern area, locus of the 2010 Mw 8.8 Chile earthquake, inter-plate thrust seismicity is dominant both in term of quantity of events and moment release. Conversely, the southern area presents only shallow intra-plate crustal seismicity mainly occurring in the arc, where Quaternary volcanism and the LOFS are present.