This thesis investigates a sequence of 17 cycles of coarse-grained syn-rift delta progradation in the Loreto basin, Baja California Sur. The Loreto basin is a Pliocene half-graben bounded by the 30 km long easterly dipping extensional Loreto fault, with 1.5 km throw. The Loreto basin uniquely provides a temporally constrained setting that couples preserved alluvial architecture with marine depositional geometries that enables these controls to be distinguished. The depositional architecture of each cycle is reconstructed by correlating 61 close-spaced (20 m to 320 m), detailed (1:5000) sections. Of the 17 progradational cycles, the lower 11 are particularly well exposed. Temporal constraints achieved through the dating of two sequence bounding tuff horizons, give an average duration for a single cycle of delta progradation to be 14±8.6 kyr., with most cycles being <10 kyr. This duration is too short to be explained by Pliocene eustatic variations (41 kyr). A consistency in measured palaeocurrents towards the NNE suggests that lobe switching was not a significant factor in controlling delta architecture. A facies framework is established that recognises both shoal-water and Gilbert-type delta deposition in the basin. The facies framework, coupled with reconstructed depositional architectures reveals that 7 of the 11 lower cycles, and at least one upper cycle (12) exhibit a palaeoseaward transition from shoal-water to Gilbert-type deltas. This nucleation of clinoforms with initially oblique, but increasingly sigmoidal geometries is characterised by a down-transport development of forests, which increase in height from 4 m to >26 m as they are traced basinward. Each cycle is capped by a shell bed that records drowning of the delta top. The geometry, and specifically the nucleation of clinoforms in single cycles of progradation requires a continued basinward increase in bathymetry. In one case this increase can be attributed to the topography of an underlying delta cycle. However for most of the cycles the increase in bathymetry can only be achieved if the rate of tectonically-controlled accommodation creation accelerates during their deposition.

This thesis investigates a critical part of the Tethyan orogenic system in northern Greece and, based on new stratigraphic, structural, sedimentological and geochemical data, a new tectonic model for the area is proposed. The main unit investigated is the Païkon Massif which is situated centrally within the Vardar/Axios zone of the Internal Hellenides, which is part of the Alpine-Himalayan belt. The area is bounded to the west and east by ophiolitic units of the Almopias (western Vardar/Axios) and Peonias (eastern Vardar/Axios) subzones, respectively. During the break-up of the northern margin of Gondwana in the Permo-Triassic, the Païkon Massif formed the western margin of the Serbo-Macedonian continental unit, where a deep-water mixed carbonate-clastic slope succession (the Gandatch Formation) accumulated. At this time the Serbo-Macedonian zone was bordered to the west by the Triassic-Jurassic Almopias Ocean. Inferred onset of eastward subduction of the Almopias Ocean beneath the western margin of Serbo-Macedonia (Middle Jurassic) led to the eruption of Island Arc Tholeiites, which are basic to intermediate in composition at their base and become progressively more acidic upwards. A relatively wide Almopias Ocean is envisaged. Back-arc spreading is believed to have generated the Guevgueli back-arc basin (Peonias subzone) in the late-Middle to Late Jurassic, separating the Païkon Massif from its parent continent, leaving a remnant arc in its wake (the Chortiatis Group of the Circum-Rhodope zone). Continued subduction culminated in collision of the Pelagonian continental unit with the southern margin of Eurasia. Regional contractional (Eohellenic) deformation ensued and emplaced the Guevgueli Ophiolite westward onto the Païkon Massif. Deep burial of the Païkon Massif at this time is recorded by blueschist to upper greenschist facies mineral assemblages and pervasive ductile folding and fabric development.

This thesis has used patterns of ground deformation since Roman times to develop new models of the magmatic system beneath Campi Flegrei, an active caldera to the west of Naples in Southern Italy. New data have been obtained from historical and archaeological records, as well as from reanalyses of measurements obtained during the volcano-seismic crises of 1968-72 and 1982-84. The results show that deformation has occurred against a background rate of caldera subsidence of about 17 mm yr1. This subsidence has been interrupted by extended episodes of net uplift in 540-800, 1430-1538 and since 1968, which produced maximum uplifts of approximately 15, 17 and (to date) 3 m. New modelling of the post-1968 deformation, which was concentrated between 1968-72 and 1982-84, suggests that each uplift was driven by the emplacement of radiaUy-symmetric sills at depths of 2.5-2.75 km, near the contact between basement rock and overlying volcanic deposits. The sills have radii between 1.56 and 2.75 km and volumes of 0.02 km3. Heating of aquifers produced temporary additional uplifts of some 0.2-0.5 m, but these decayed following the outflow of water. Extrapolation of the results suggests that each of the preceding episodes of extended uplift involved the intrusion of about 10 sills. Such behaviour is consistent with the sills having been fed from a reservoir of tens of km3 at a depth of about 15 km, near the base of the upper elastic crust. This reservoir has itself been supplied from a source about ten times larger and at a depth of about 30 km. During the post-1968 crises, the deformation due to sill emplacement was supplemented by an additional WNW-ESE horizontal extension at a strain rate of about 2.7 x 10_ 5 yr1. The additional deformation is consistent with the elastic upper crust being dragged apart during visco-elastic relaxation of the lower crust, with an inferred viscosity of 6 x 1018 Pa s. The preferred direction of relaxation may reflect different rates of regional NE-SW extension to the north and south of Campi Flegrei. If the current unrest follows previous extended episodes, uplift may continue for another 80-90 years and produce a further net uplift of some 12-14 m. The 21st Century is thus expected to represent a period of elevated volcano-seismic hazard in Campi Flegrei.

Southern South Africa provides a unique setting to study the extension of a pre-existing compressional belt (negative structural inversion) because of the juxtaposition of excellent levels of pre-rift exposure, enabling basement structures to be determined, and high quality 2D seismic data, allowing the detailed temporal and spatial controls on rift system evolution to be established. Through the construction of five regional transects, orientated perpendicular to the Permian-Triassic Cape Fold Belt (CFB), an intimate link between compression and the subsequent Mesozoic extension can be established. A comparison between the CFB and other orogens suggests that it is atypical and it is proposed that the north of the foldbelt is controlled by low angle listric faults, while the centre and south are dominated by high angle planar faults. These faults have been reactivated during the subsequent extension. This model is supported by depth converted seismic sections that reveal listric normal faults that detach at a shallow crustal level in the north, while the south is dominated by a limited number of large, planar crustal scale normal faults. Comparison with both contractional and extensional reactivation (structural inversion and negative inversion respectively) models and examples supports the model. The high quality of the available 2D seismic data arrays have enabled a sequence level seismic stratigraphic framework to be established for the three offshore basins (Pletmos, Gamtoos, and Algoa). The integration of the three basins has revealed a generally uniform evolution that differs from previous studies. In particular, the formation of complex deformation features, previously considered to be of a compressional origin, are re-examined in light of detailed basin modelling. The dimension and evolution of the South African system are atypical when compared to other basins. The lengths of faults are at least 150 km with approximately 12 km of throw on the basin-bounding faults, which are significantly larger than most rift settings. There is also no evidence of along trend segmentation of the faults and extreme localisation of stress occurring from an early stage in the rift history. The results provide a critical test for existing models, which adequately account for normal fault evolution in homogeneous crust, to a region with a significant pre-existing, compressional fabric.

The Baer-Bassit area of NW Syria exemplifies the evolution of Neotethys at the W end of the "ophiolitic crescent". The stratigraphy of the Baer-Bassit area is divisible into four main units. 1) At the base, there is a relatively autochthonous Mesozoic Arabian carbonate platform (1500-1800 m thick), of Mid Jurassic-Early Cretaceous age. This is exposed only in the north, as the mountainous Jebel Aqraa massif. Shallow-marine limestones are overlain by Cenomanian-Lower Maastrichtian pelagic carbonates. 2) The Mesozoic carbonate platform is overthrust by deformed Mesozoic rocks of continental margin and oceanic affinities. There is a structurally lower unit of highly deformed volcanic-sedimentary lithologies, ca. 450m thick (Baer-Bassit Melange). Deep-sea sediments and alkaline volcanics of Late Triassic age mark the opening of Neotethys in the Eastern Mediterranean region. Middle Jurassic-Lower Cretaceous volcanics of alkaline composition are interbedded with ribbon radiolarites. Successions continue upwards into Early Cretaceous channalized sandy limestone. Late Cretaceous (Cenomanian) limestone debris flows, calciturbidites and pelagic muds, related to sediment instability along the Arabian passive margin to the south. 3) Structurally above is a complete, but thrust deformed, Upper Cretaceous ophiolitic suite of supra-subduction zone-type, based on geochemical characteristics, that includes plutonics, sheeted dykes and volcanics, the latter similar to the upper pillow lavas of the Troodos ophiolite, Cyprus. Locally, the uppermost extrusives are overlain by Fe-Mn sediments, comparable with the hydrothermal umbers of the Troodos ophiolite, Cyprus. The plutonics are structurally underlain by a well developed metamorphic sole, 200-300m thick, for which the protoliths were mainly alkaline extrusives and associated sediments similar to those within the melange beneath. The entire assemblage of passive margin and ophiolitic units was emplaced onto the Arabian margin in middle Maastrichtian time.

Analysis of newly acquired and existing 2-D seismic data from the Rockall Plateau to the Faroe Shelf, has demonstrated that the NE Atlantic Margin is the site of significant active deformation. Seismic data have revealed the presence of numerous compression-related deformation. Seismic data have revealed the presence of numerous compression-related Cenozoic folds, such as the Alpin, Ymir Ridge and Wyville Thomson Ridge anticlines. The presence, timing and nature of these structures have provided new insights into the controls and effects of contractional deformation in the region. Gravity models support the presence of low-density sediments in the core of folds. This is consistent with folds developed due to the inversion of sedimentary basins. The spatial extent of the deformation could thus reflect the differing underlying basin morphologies. The mapping and dating of angular and erosional unconformities that define the folding suggest that the growth of these compressional features occurred in five main phases – Thanetian, late Ypresian, late Lutetian, Late Eocene (C30) and Early Oligocene, each of which appear to have been driven by regional events affecting the NE Atlantic Margin. The late Ypresian, Late Eocene (C30) and Early Oligocene events correlate with the timings of hot-spot influenced ridge-push based on the ages of V-shaped ridges. The late Lutetian event is tentatively also ascribed to hot-spot influenced ridge-push. Mohr-Coulomb circle plots, however, reveal that the forces exerted by hot-spot influenced ridge- push appear to be insufficient to result in the reactivation of faults in the underlying Mesozoic basins. Alpine and Pyrenean Orogenies may have, thus, produced the additional force needed for the inversion of these basins. The Thanetian phase, just prior to Atlantic Ocean spreading, would suggest compression due to depth-dependent stretching and uplift.

The Polis graben system in west Cyprus consists of two neotectonic extensional basins. The Polis graben is of Late Miocene age, bounded to both sides by major NNW-SSE trending normal faults. Around 7% extension occurred perpendicular to the fault trend. The Pegia half-graben, to the west of the Polis graben, is of latest Pliocene to earliest Pleistocene age and is bounded by WNW-ESE striking normal faults. Approximately 10% extension occurred perpendicular to these faults. In both graben normal faults are seen on three scales; extensional joints are also common. Faults of all scales bound generally internally undeformed fault blocks which are tilted perpendicular to the graben trend, normally back-rotated on synthetic faults and forward rotated on antithetic faults. In the Polis graben, transfer zones accommodate changes in the structural style and timing of faults along the length of the graben. The location of faults within the Polis graben system may be partly controlled by the underlying basement structure. Extensional structures in the Polis gaben are comparable with extensional features in other basins. The sedimentary sequence in west Cyprus reflects the structural development of the two extensional basins. Early to mid-Miocene pre-rift, Late Miocene syn-rift and Pliocene post-rift sequences are recognized in the Polis graben. The first depositional features related to neotectonic structures are seen at the Oligo-Miocene boundary. Erosion of the Palaeogene Lefkara Formation on the margins of the area was followed by deposition of Lower Miocene reef limestones (the Terra Member), whilst basinal chalk deposition (the Miocene Pakhna Formation) continued in the centre of the area. This is thought to reflect relative uplift of west Cyprus and development of a broad basin in the Early Miocene. Hemipelagic carbonates of the Pakhna Formation were deposited throughout the basin by mid-Miocene times. In the Late Miocene, shallowing of the basin occurred and early syn-rift reef limestones of the Koronia Member accumulated on the flanks of a narrow basin. Rapid eustatic fall in the Messinian led to emergence and erosion of the northern part of the graben, and of the area of the Pegia half-graben. The southern basin was the site of syn-rift evaporite deposition (the Kalavasos Formation). In the north, conglomerates and breccias derived from active fault scarps were locally deposited.

No description available.

The Meso-Hellenic Trough (MHT) is an elongate NW-SE trending intermontane basin that developed during the Mid-Tertiary within the Hellenide fold-and-thrust belt. It formed in the late Eocene behind the deformation-front as the locus of thrusting migrated towards the foreland in the south-west. This followed collision between the Apulian and Pelagonian micro-plates and final closure of the Pindos Ocean basin (a strand of the Neotethys). The MHT basin-fill is of U. Eocene-M. Miocene age, was predominantly marine in nature and can be sub-divided into the Basin-margin and Meso-Hellenic Groups, which are separated by a basin-wide angular unconformity. The Basin-margin Group (Upper Eocene) is only preserved in small outcrops around the basin margin and the Meso-Hellenic Group (Oligocene-Middle Miocene) forms the majority of the basin-fill. The Basin-margin Group was deposited on the sub-Pelagonian thrust-sheets and is of identical age to the youngest Pindos foreland basin sediments exposed beneath the same thrust-sheets. However, large-scale folds which deform the basal thrust demonstrably do not deform the overlying Meso-Hellenic Group. The Basin-margin Group can therefore be shown to have been deposited on the thrust sheets as they overthrust the Pinodos foreland basin. Coarse ophiolitic breccia up to 600 m thick characterises the south-western margin of the Krania sub-basin (a depocentre of the Basin-margin Group) and is interpreted as having been deposited at the base of an active (?reverse) fault-scarp. In addition, there is evidence that strike-slip faults were active along the northern and southern margins of the sub-basin. Although these structures may have controlled subsidence locally, the overall setting of the Basin-margin Group is interpreted as that of a piggy-back basin, formed above the south-westward propagating thrust stack. The palaeobathymetry of the basin increased during the late Eocene, as marked by the change from shallow-marine limestone, fan delta and lagonal facies to deeper-water turbidite facies. During this period, sedimentation was tectonically controlled, for example where basement uplift along reverse faults to the north of the Krania sub-basin shed limestone-dominated mass-flow deposits southwards in Priabonian times. Further compressional folding and high-angle faulting, interpreted to have resulted from overthrusting of the Olympos seamount/micro-plate, deformed the Basin-margin Group at the end of the Eocene and eventually led to its sub-aerial erosion.

The interaction between the Mid Atlantic Ridge and Iceland plume produced an uninterrupted sequence of tholeiite lava flows between NW Iceland and the Snaefellsnes Peninsula from 15 Ma until 5.2 Ma, when the spreading centre relocated to its present position on the Reykjanes Peninsula. Widespread glaciation, at the end of the Tertiary (3.3 Ma), eroded the lava flows in the extinct spreading centre. Renewed volcanism along the peninsula, during the glacial period, resulted in a sequence of off-axis, Quaternary flows that rest unconformably on the Tertiary rift-axis tholeiites. Basalt samples collected from the Snaefellsnes Peninsula, in the region of the extinct central volcano, Setberg, were used to determine both the length-scale of mantle heterogeneity beneath the peninsula and the time-scale during which the distinct domains of heterogeneity were sampled. In the Setberg region the basalt composition changed with time from tholeiitic in the Tertiary, through transitional, to mildly alkaline by 0.7 Ma. The change in major-element composition is coupled with an increase in LREE/HREE, a progressive increase in the ratios of highly to moderately incompatible trace elements (e.g. Ce/Y, Nb/Zr), increasing ⁸⁷Sr/⁸⁶Sr, and decreasing ¹⁴⁵Nd/¹⁴⁴Nd. The Pb-isotope ratios of the Quaternary basalts are generally more radiogenic than those of the Tertiary flows, but these younger basalts display a larger spread of Pb-isotope ratios. The oxygen-isotope ratios of the basalts from the Setberg region (Sigmarsson <i>et al.</i>, 1992; Hardarson, 1993) suggest that the geochemical signatures of the basalts are representative of the mantle source from which they were derived. The increasing fractionation of the REE and the change in major-element composition suggests that progressively deeper parts of the melt column were sampled following the cessation of spreading along the rift. The increasing values of the ratios Nb/Zr, Nb/Y, Zr/Y, and Ce/Y, after the cessation of spreading, and the positive correlations between these ratios indicate that the Quaternary basalts were produced by lower degrees of partial melting.