The intraplate deformation in the Central Indian Ocean Basin is a well known example of a deviation from an axiom of plate tectonics: that of rigid plates with deformation concentrated at plate boundaries. In this thesis a range of geophysical data collected during CHARLES DARWIN Cruise 28, together with several different geodynamic modelling techniques, is used to investigate the structural style of intraplate deformation. The deformation occurs in lithosphere of age 65-90 Ma that formed at a fast spreading-rate (im60 mm yr<SUP>-1</SUP>) at the south-east Indian Ridge. It manifests itself as a diffuse zone of compressional and strike-slip earthquakes, high localised heat-flow, geoid anomalies and tectonic deformation. The tectonic deformation can be considered to be occurring on two spatial scales: the first order is represented by long wavelength (100-300 km), large amplitude (1-2 km) undulations of oceanic basement and overlying sediments; and the second order by unusual high-angle reverse faults with associated folds in the basement cover. The reduction and inversion of disposable sonobuoy data revealed that the velocity-depth structure of the oceanic crust is not unusual. The sediment velocity increases from 1.6-1.7 km s<SUP>-1</SUP> in the near surface to 3.4-3.5 km s<SUP>-1</SUP> immediately above basement with a velocity gradient of 0.75 s<SUP>-1</SUP>. A velocity for the top of the oceanic layer 2 of 4.1 km s<SUP>-1</SUP> was identified as layer 2A. An estimate for the thickness of the crust could not be made from the sonobuoys and other refraction work is contradictory. A study of structural style from single-channel seismic reflection profiles revealed that the reverse fault fabric, which has a strike (090<SUP>0</SUP>-100<SUP>o</SUP>E) perpendicular to that of fracture zones (005<SUP>o</SUP>-010<SUP>o</SUP>E) developed in this area, resulted from the reactivation under compression of two sets of spreading-centre formed normal faults. In the survey area the first and second orders of deformation are discontinuous across fracture zones. A transpressive model is developed for the survey area to explain the discontinuity of the axes of the undulations, other basement trends, and regional seismicity studies. Previously, two hypotheses had been advanced for the formation of the long wavelength undulations: buckling and inverse boudinage of the lithosphere. This study used three modelling techniques to determine the deformation mode, two of which decisively favoured buckling. Physical modelling using the sandbox technique, in which the oceanic lithosphere was modelled with a two layer (brittle/viscous) rheology, suggested that buckling of the entire brittle lithosphere was responsible for the formation of the long wavelength undulations. Two and three-dimensional gravity modelling supports buckling of at least the oceanic crust. However, numerical modelling was unsuccessful in modelling the long wavelength undulations. The transpressive model for the Central Indian Ocean Basin, on which buckling forms within fracture zone compartments, and strike-slip motion occurs both along fracture zones (left-lateral) and along the reactivated ridge-parallel fabric, may be extended eastwards to the Wharton Basin. Compressive forces with anticlockwise rotation are seen as a consequence of a dramatic change in plate boundary activity in the north-eastern Indian Ocean from 7 Ma ago, with subduction occurring faster at the Sunda Trench than continental collision at the Himalayas.

The Lycian Taurides of southwest Anatolia, Turkey, are composed of a series of limestones, peridotites and lithic-rich clastic rocks. Their origin and subsequent tectonic evolution have been the subject of much controversy as the rocks form an integral part of the Tauride belt and provide a well exposed field laboratory for the study of both the opening and closure of Tethys. During this study, field observations of sedimentological, structural and lithological features of the rocks in southwest Anatolia have been combined with geochemical data derived from collected samples, to define a series of thrust- or unconformity-bounded tectonostratigraphic units. These units are: (i) the Lycian Autochthon, encompassing both the unmetamorphosed Lower Jurassic to Miocene rocks to the Bey Daglari Unit in the southeast and Pre-Cambrian to Eocene rocks of the Menderes Metamorphic Massif to the northwest: (ii) the Lycian Thrust Sheets, a series of Carboniferous to Middle Eocene neritic limestones, calci-clastics, turbidites and debris-flow deposits and lithic clastics and volcanics: (iii) the Lycian Mélange, with inclusions of neritic and pelagic limestone, basalts, serpentinite, red and black chert and amphibolite in a highly sheared silt and sandstone matrix: (iv) the Lycian Peridotite Thrust Sheet, a large (-4500km<SUP>2</SUP>) Cretaceous unit of serpentinized harzburgite with podiform chromitite and dunite bodies, cut by a series of dolerite dykes and underplated by an amphibolite-grade metamorphic sole: (v) supra-allochthon Palaeogene sediments that unconformably overlie the Lycian Mélange and Oligocene to Lower Miocene terrestrial and shallow-marine sediments of the Tavas Basin. The boundaries between these tectonostratigraphic units display a consistent top-to-the-southeast sense of shear. Therefore, the Lycian Allochthon is interpreted to have originated to the northwest of its present location, i.e. in the Ankara-Izmir Zone north of the Menderes Metamorphic Massif. Evidence for multiple phases of both opening and closure of the southern Tethys ocean were found with the Lycian Thrust Sheets. The earliest evidence of rifting in the region is within Permian rocks, this is manifest by the presence of basalts that have a similar trace-element chemistry to within-plate basalts and are coeval with a deepening event.

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In recent years, the acquisition, processing, imaging and fracture detection capabilities using multicomponent PP- and PS-wave seismic have been improved. Unlike traditional narrow-azimuth P-wave data, multicomponent wide-azimuth data are more sensitive to the presence of seismic anisotropy. Two types of anisotropy are commonly considered within exploration seismology: vertical transverse isotropy (VTI) due to layering of sedimentary rocks, and horizontal transverse isotropy (HTI) due to vertical fracturing. Intensive efforts have been devoted to studying the effects of these types of anisotropy on both PP- and PS-waves.  Nevertheless, there are still some fundamental issues which need to be investigated, and this thesis aims to address some of these issues.

Differential GPS, which can provide a positional accuracy of ±4cm in terms of latitude and longitude and ±8cm in terms of fault elevation, was used to survey the dimensions of normal fault blocks in the field. In general, positional data were collected every metre along the crest and base of each fault scarp and, where possible, along lava flow contacts. Such data, when combined with ⁴⁰Ar/³⁹Ar ages determined form the syn-tectonic lava flows, were used to build up a detailed, quantitative, growth-history of faulting in four field localities; two at the centre and two at the eastern margin of the Kenya Rift. Extensional faulting in the South Kenya Rift appears to have been a very episodic process, expressed as: i) an early phase of rapid vertical fault displacement (up to ~6mmyr^-1) that resulted in the formation of a train of discrete, ‘bell-shaped’, fault blocks with relatively large fault displacement/length (d/L) ratios (~0.05-0.07), prior to, ii) fault growth at much lower displacement rates (0.3-0.7mmyr^-1), characterised by linkage of the pre-existing fault train to form a single fault with a lowered d/L value (~0.01). The observed reduction in fault displacement rates and d/L value may result from down-dip fault interaction with vertical strength contrasts in the volcanic lava pile or, on a more fundamental scale, the base of the effective elastic thickness (T_e). Fault development is also likely to be influenced by the effects of magmatism, since periods of increased fault activity often occur subsequent to renewed phases of rift volcanism and possible dyke emplacement. Episodic fault-growth could therefore be explained by tectono-magmatic cycling within the South Kenya Rift. On a large scale, there is evidence for a progressive migration of strain towards the centre of the rift over the past 2Myr.

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Tethyan suture zones commonly undergo a change from compression to extension shortly after suturing. The mechanics and timing of this change in tectonic regime are poorly understood, and the extensional sedimentary basins of west Turkey, and , in particular, the northern Menderes massif, provide an excellent natural laboratory for the study of the crustal response to these different processes. During this study, field observations of sedimentary, structural and lithological features of the Alasehir Graben, Gördes and Selendi Basins, and their surroundings were combined with new radiometric age data to investigate the onset of N/S crustal extension in west Turkey. This timing of initiation has major implications for the driving mechanism of extension, since alternative models are time dependant. Extension driven by tectonic escape of west Anatolia requires extension to have begun in the Late Miocene, whilst extension driven by orogenic collapse of thickened crust in the region, and extension related to subduction roll-back both are postulated to have commenced in the Early Miocene. Extension in the northern Menderes massif took place on large-scale, presently low-angle (<20°), north-dipping normal (detachment) faults. Two separate detachment basin systems are recognised in the study area. The Gördes and Selendi Basins both trend NE/SW and formed by extension on the same northerly detachment system. This detachment has a strongly corrugated morphology when viewed parallel to extension, with a wavelength of ~30 km and an amplitude of ~1.5 km. The corrugations form the eastern and western margins of the Gördes and Selendi Basins and have produced 'scoop-shaped' depocentres and their characteristic NE/SW basin trend. No upper plate metamorphic lithologies are exposed within the basins and the total extension on the detachment fault system is in excess of 60 km. Syn-extensional sedimentation in the form of coarse alluvial fan conglomerates were deposited from south to north, and subsequently back rotated and tectonically emplaced against the detachment as a result of continuing extension. The initial sediments were followed by northward transported, braided-fluvial to alluvial-plain sandstones and conglomerates. These sediments unconformably overlie the syn-extensional deposits and passively onlap the basin margins.

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