The Lower Kutai Basin is a Tertiary sedimentary basin located on the eastern coast of Kalimantan, Indonesia, underlying the area around the Mahakam Delta. Concerning overpressuring, previous workers agreed that the principal mechanism of overpressure generation is disequilibrium compaction, with sand–mudrock pressure discrepancies being present above the transition zone into hard overpressure as a result of lateral reservoir drainage. The pressure data, wireline logs and other data such as temperature and vitrinite reflectance data have been re-examined to analyse the overpressuring in this area. Unloading mechanisms have been considered as alternatives to disequilibrium compaction. The reasons for doing so are the high temperatures in this basin, which promote unloading mechanisms, together with some evidence ignored by previous researchers, from wireline log and vitrinite reflectance data, that also suggest unloading mechanisms play an important role. Clear evidence of unloading has been found in the form of trend reversals in sonic and resistivity logs, without coincident reversals in density logs, and of substantial chemical compaction with mudrock densities exceeding 2.6 g/cm3 at the top of overpressure. In the Peciko Field, a field located in the shelfal area of the basin, mudrock density continues to increase with depth in the overpressured section. All these circumstances are in conflict with the disequilibrium compaction hypothesis; instead, the mudrocks are inferred to be overcompacted. The top of the transition zone into hard overpressure coincides with the onset of gas generation indicating that the gas generation is the principal cause of unloading. Chemical compaction processes must also be ongoing in the overpressured zone, including illitization of mixed layer illite-smectite, illitization of kaolinite, and quartz dissolution and reprecipitation. The result of this research is novel and possibly controversial: there is no other Neogene basin where the role of disequilibrium compaction in overpressure generation has been discounted.

Introduction: This study documents the eruption histories and depositional mechanisms of the Poris ignimbrite in Tenerife (Canary Islands) and the Glaramara Tuff in the Ordovician Scafell Caldera, English Lake District. It focuses on the lithofacies architecture of the deposits and on the application of recent concepts of progressive aggradation from the depositional flow boundaries of density currents. The two deposits were chosen because they exhibit considerable lateral and vertical lithofacies variations that are likely to register spatial and temporal changes in current depositional behaviour, and because study of them offered the experience of working with both modern and ancient deposits. Initially it was thought that there might be some similarities between the two deposits in terms of eruptive history and emplacement process, but, aside from some similar lithofacies, the two deposits record very different types of eruptions.

For the past three decades, deep crustal studies of the British Isles have been restricted to the interpretation of 2-D seismic reflection and refraction profiles, mostly acquired offshore. During this period, the British Geological Survey (BGS) seismic monitoring network has developed to an unrivalled density for a region of low intraplate seismicity. In an average year, the modern network records approximately 40 earthquakes in the crust beneath the British Isles with local magnitudes > 2. Statistical tests show the modern and historical pattern is not random. Understanding of the tectonic processes behind the pattern are hindered by the sparseness of onshore deep crustal studies where the majority of earthquakes are concentrated. For the first time local earthquake tomography, a method more commonly applied to tectonically active regions, is used to produce high resolution 3-D images of seismic P-wave velocity (Vp) and the P- to S-wave velocity ratio (Vp/Vs) in the crust beneath England, Wales and the Irish Sea. To account for low seismicity, over 1,000 earthquakes are utilised from the past 25 years of monitoring. The existing BGS digital catalogue is enhanced by a two-fold increase in seismic arrival time picks, significantly reducing earthquake location errors in the input dataset. The tomographic models establish a strong and previously undemonstrated link between Palaeocene magmatism and more widespread earlier phases of Caledonian magmatism. A regional Vp anomaly (> 7.2 km/s) in the lower crust centred on the East Irish Sea Basin is inferred as Palaeocene magmatic underplate with seismicity concentrated around its eastern and southern margins. In the mid- and lower-crust earthquake clusters are evident around the edges of local Vp/Vs anomalies (> 1.80), most significantly beneath the Ordovician volcanic centre in Snowdonia. The models are supplemented by the inversion of 185 independently determined focal mechanisms to consider the influence of local variations in far-field intraplate stresses alongside lithostatic stress from overburden pressure.

This thesis concerns the crustal evolution of Nemegt and Altan Uul in the Gobi Altai mountains of southern Mongolia. Nemegt and Altan Uul consist of polydeformed Palaeozoic rocks uplifted in the Cenozoic at a restraining bend along the active left-lateral Gobi-Tien Shan intra-continental fault system, one of several east-west trending left-lateral intra-continental transpressional fault systems associated with eastward continental extrusion tectonics in Central Asia. The tectonic evolution of southern Mongolia is of particular interest as it forms part of the Central Asian Orogenic Belt, which is the largest area of Phanerozoic continental growth on Earth, and is a natural laboratory for studying processes of continental growth and deformation including terrane accretion, ophiolite obduction, terrane amalgamation, terrane dispersal and crustal reactivation. The uplifted Palaeozoic rocks exposed in Nemegt and Altan Uul offer an opportunity to understand multiple phases of the crustal evolution of southern Mongolia. A series of cross-strike transects of Nemegt and Altan Uul were carried out to document the lithologies and structure of the ranges. Samples were taken along the transects and at several important localities, to constrain the metamorphic petrography of the rocks in the ranges. This data is used to define several distinct east-west trending litho-tectonic sequences in Nemegt and Altan Uul. The ranges have a systematic south to north litho-tectonic variation from greenschist grade meta-volcanic and volcaniclastic rocks, thrust north over a discontinuous ophiolite belt, which is thrust north over greenschist to epidote-amphibolite grade arkosic to mature meta-sedimentary rocks. Four phases of deformation are identified from cross-cutting field relationships and constrained by existing regional data: east-west trending south-dipping cleavage (D1), and north-vergent folds of cleavage and north-directed ductile thrust shear zones (D2) formed during late Carboniferous south to north arc-terrane accretion and ophiolite obduction. East-west and northeast-southwest trending D3 normal faults formed during Cretaceous basin extension. East-west and northwest-southeast trending D4 left-lateral oblique-slip and dip-slip thrust faults formed during Cenozoic transpressional deformation and define the modern mountain ranges. The structures identified are conservatively extrapolated to depth to suggest Nemegt and Altan Uul have a positive flower structure in cross-section. An evolutionary model of Nemegt and Altan Uul suggests that D1 and D2 structures and the ophiolitic rocks in the area may represent south-dipping east-west trending fabrics and rheological weaknesses that have been reactivated in a left-lateral transpressional sense in the Cenozoic.

No description available.

Young igneous rocks from a range of tectonic settings exhibit various Uranium-series (Useries) disequilibria. The U-series systematics of Mid-ocean-ridge basalts (MORBs) have been attributed to mantle melting, while those of arc basalts are widely thought to be slab fluid signatures. Mid-ocean-ridge and arc U-series models generally assume that U4+ is the only oxidation state relevant to mantle melting processes, however the potential for the stabilisation of U5+ and/or U6+ has recently been proposed for some arc lavas. To determine the oxidation state of U in geological melts, and to assess the relative stabilities of U4+, U5+, and U6+ under mantle conditions, X-ray absorption near edge structure (XANES) spectra were recorded from synthetic analogues, including an Fe-bearing MORB composition. Spectra were collected from quenched glasses equilibrated at 1400 °C and oxygen fugacities (fO2s) between logfO2 = -18 and +4.7 (QFM-11.7 to QFM+11), and from equivalent high temperature melts using a custom designed XAS furnace. Spectra were collected at both the U L3- and M4-edges, as the variation of the M4-edge spectral line-shape could be unambiguously linked to oxidation state changes in the glasses, while the higher energy of the L3-edge was better suited to in situ studies. The variation of the XANES spectra as a function of fO2 allowed U5+ to be identified as a major component in both the MORB glasses and their original melts, and a methodology was developed to accurately quantify their U oxidation state proportions. The proportion of U4+ was found to be highly sensitive to fO2 at conditions relevant to mantle melting, with U5+/ΣU varying between ~0.1 and 0.5 between QFM-1 and QFM+2 and pressures equivalent to mantle depths of ≥ 15 km. U-series models assuming melting of a variably oxidised mantle wedge can produce a wide range of U-series signatures that are consistent with many arc basalts. In contrast, the stability of even small proportions of U5+ in the melt may present a problem for those models currently attributing the 230Th excesses of MORBs to mantle melting in the spinel lherzolite field.

No description available.

Continental rifting and incipient seafloor spreading are observed either side of the main Ethiopian rift (MER). EAGLE (the Ethiopia Afar Geoscientific Lithospheric Experiment) included a 400 km-long profile containing 97 passive seismometers to investigate the change from mechanical to magmatic extension by defining the lithospheric structure and extent of magmatism beneath the rifted northern MER. Changes in crustal structure along the cross-rift profile are imaged using forward modelling, H-kappa stacking and non-linear inversion analyses of receiver functions. The lithospheric structure is inherently different beneath the north-western rift flank, rift valley and south-eastern rift flank, with contrasting crustal thickness and composition, upper mantle velocity and lithospheric anisotropy. Magmatic addition is imaged in the form of an 6--18 km-thick underplate lens at the base of the crust beneath the high Ethiopian plateau and zones of intense dyking and partial melt beneath the rift valley. The underplate layer probably formed synchronous with an Oligocene flood basalt event and therefore pre-dates the rifting by ~20 Myr. A 20--30 km-wide magmatic system pervades the entire crust beneath volcanic chains that mark the locus of current rift extension. To the southeast of the rift, a lithospheric suture is inferred, which was created during the Precambrian collision of East and West Gondwana. Collision-related lithospheric fabric is proposed to be the main source of strong anisotropy observed along the entire profile, which is locally augmented by rift-related magmatism. An active followed by passive magma-assisted rifting model that is controlled by a combination of far-field plate stresses, pre-existing lithospheric framework and magmatism is preferred to explain the evolution of the northern MER.

No description available.

Daphne Desiree Charlotte Pochin Mould (15 November 1920 - 29 April 2014) was a photographer, broadcaster, geologist, traveller, pilot and Ireland's first female flight instructor. She received her PhD in Geology from the University of Edinburgh in 1946 entitled 'The Geology of the Foyers Plutonic Complex and the surrounding country'. More information about her life can be found on Wikipedia: https://en.wikipedia.org/wiki/Daphne_Pochin_Mould