http://www.dspace.cam.ac.uk:80/handle/1810/219098 Tue, 18 Jun 2013 23:44:59 GMT 2013-06-18T23:44:59Z http://www.dspace.cam.ac.uk:80/handle/1810/244506 Title: Fluid-rock interactions in a carbon storage site analogue, Green River, Utah Authors: Kampman, Niko Abstract: Reactions between CO2-charged brines and reservoir minerals might either enhance the long-term storage of CO2 in geological reservoirs or facilitate leakage by corroding cap rocks and fault seals. Modelling the progress of such reactions is frustrated by uncertainties in the absolute mineral surface reaction rates and the significance of other rate limiting steps in natural systems. This study uses the chemical evolution of groundwater from the Jurassic Navajo Sandstone, part of a leaking natural accumulation of CO2 at Green River, Utah, in the Colorado Plateau, USA, to place constraints on the rates and potential controlling mechanisms of the mineral-fluid reactions,under elevated CO2 pressures, in a natural system. The progress of individual reactions, inferred from changes in groundwater chemistry is modelled using mass balance techniques. The mineral reactions are close to stoichiometric with plagioclase and K-feldspar dissolution largely balanced by precipitation of clay minerals and carbonate. Mineral modes, in conjunction with published surface area measurements and flow rates estimated from hydraulic head measurements, are then used to quantify the kinetics of feldspar dissolution. Maximum estimated dissolution rates for plagioclase and K-feldspar are 2x10-14 and 4x10-16 mol·m-2·s-1, respectively. Fluid ion-activity products are close to equilibrium (e.g. DGr for plagioclase between -2 and -10 kJ/mol) and lie in the region in which mineral surface reaction rates show a strong dependence on DGr. Local variation in DGr is attributed to the injection and disassociation of CO2 which initially depresses silicate mineral saturation in the fluid, promoting feldspar dissolution. With progressive flow through the aquifer, feldspar hydrolysis reactions consume H+ and liberate solutes to solution which increase mineral saturation in the fluid and rates slow as a consequence. The measured plagioclase dissolution rates at low DGr would be compatible with far-from-quilibrium rates of ~1x10-13 mol·m-2·s-1 as observed in some experimental studies. This suggests that the discrepancy between field and laboratory reaction rates may in part be explained by the differences in the thermodynamic state of natural and experimental fluids, with field-scale reactions occurring close to equilibrium whereas most laboratory experiments are run far-from-equilibrium. Surface carbonate deposits and cementation within the footwall of the local fault systems record multiple injections of CO2 into the Navajo Aquifer and leakage of CO2 from the site over ca. 400,000 years. The d18O, d13C and 87Sr/86Sr of these deposits record rapid rates of CO2 leakage (up to ~1000 tonnes/a) following injection of CO2, but rates differ by an order of magnitude between each fault, due to differences in the fault architecture. Elevated pCO2 enhances rates of feldspar dissolution in the host aquifer and carbonate precipitation in fracture conduits. Silicate mineral dissolution rates decline and carbonate precipitation rates increase as pH and the CO2 charge dissipate. The Sr/Ca of calcite cements record average precipitation rates of ~2x10-6 mol/m2/s, comparable to laboratory derived calcite precipitation rates in fluids with elevated Mn/Ca and Fe/Ca, at cc of ~1 to 3. This suggests that far-from-equilibrium carbonate precipitation, which blocks fracture conduits and causes the leaking system to self-seal, driven by CO2 degassing in the shallow subsurface, can be accurately modeled with laboratory derived rates. Sandstones altered in CO2 leakage conduits exhibit extensive dissolution of hematite grain coatings and are chemically bleached as a result. Measurements of Eh-pH conditions in the modern fluid, and modeling of paleo-Eh-pH conditions using calcite Fe and Mn concentrations, suggests that the CO2-charged groundwaters are reducing, due to their low dissolved O2 content and that pH suppression due to high pCO2 is capable of dissolving and transporting large concentrations of metals. Exhumed paleo-CO2 reservoirs along the crest of the Green River anticline have been identified using volatile hosting fluid inclusions. Paleo-CO2-charged fluids mobilized hydrocarbons and CH4 from deeper formations, enhancing the reductive dissolution of hematite, which produced spectacular km-scale bleached patterns in these sediment. Description: Pagination differs from hardbound copy deposited in Cambridge University Library. Mon, 11 Jul 2011 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244506 2011-07-11T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243629 Title: The evolution of the Baie Verte Lineament, Burlington Peninsula, Newfoundland Authors: Kidd, William Abstract: An area measuring about 5 km by 30 km, of the relatively well-exposed central part of the Baie Verte Lineament, has been mapped in detail. Two major rock divisions are recognised by their differing structural and metamorphic histories. A terrain of psammitic, semipelitic and mafic schists borders the western side of the Lineament. These rocks (part of the Fleur de Lys Supergroup) are in upper greenschist to epidote-amphibolite metamorphic facies, and are affected by a polyphase deformation sequence. They are intruded by post-kinematic granite and tonalite. A large, generally unfoliated, granodiorite (Burlington Granodiorite) borders the eastern side of the Lineament. Outside the map area, it is seen to be either a pre- or early syn-kinematic intrusion into Fleur de Lys schists. The Baie Verte Lineament consists, in the mapped area, of two adjacent narrow-parallel belts; to the west the Baie Verte Group of uncertain (?Arenigian) age, and to the east the early Devonian Mic Mac Lake Group. Large lensoid "alpine-type" (ophiolitic) ultramafic bodies are situated along the tectonic contact between the Fleur de Lys schists and the Baie Verte Group. A narrow discontinuous strip containing bodies of ophiolitic gabbro with parallel diabase dykes is found at the western side of the Baie Verte Group adjoining the tectonic contact. The internal structures and textures of the ophiolitic rocks are described. The Baie Verte Group consists mainly of mafic pillow lava and mafic volcaniclastic sediments, subvertical to moderately west-dipping, and facing east, for which a stratigraphy is defined. At or near the base, a conglomerate, resting on ophiolite gabbro megabreccia, contains clasts mainly referable to the mafic parts of an ophiolite complex, with some clasts identical to the Burlington Granodiorite, and rare clasts referable to previously deformed silicic volcanics and related sediments of the Fleur de Lys Supergroup found to the east of the map area. Redeposited carbonate rocks are very occasionally found near this horizon. The Mic Mac Lake Group rests with spectacular unconformity, including a significant amount of palaeotopographic relief, on the Burlington Granodiorite. It also contains a similar erosion surface within the subaerial sequence of silicic volcanics, mafic and trachyte lava flows, and mostly conglomeratic sediments. A stratigraphy is defined for the Mic Mac Lake Group. The sequence dips west at moderate angles and, with the significant exception of a narrow strip at the western side, faces west. The Baie Verte and Mic Mac Lake Groups share a single steep cleavage and low greenschist facies metamorphic grade. An autochthonous contact between Baie Verte Group and east-facing Mic Mac Lake Group in the southern part of the area indicates that the Mic Mac Lake Group is in a highly-disrupted syncline, and is unconformable on the Baie Verte Group. To the north an attenuated Mic Mac Lake Group is overthrust by the Baie Verte Group, and must eventually be cut out to the north of the map area where the Baie Verte Group directly overthrusts Burlington Granodiorite. It is shown that the deformation of the Baie Verte and Mic Mac Lake Groups, and the tectonic emplacement of the ophiolitic ultramafic bodies into their present position, was wholly later than all the regional polyphase deformation and metamorphism of the Fleur de Lys Supergroup, and that this later deformation is almost wholly localised in the belt of less complexely deformed rock. Joint mapping with J.M. Bird and J.F. Dewey at the northeast end of the Baie Verte Lineament demonstrated the presence of all members of a full ophiolite suite, overlain by mafic volcaniclastic sediments and a thick pile of pillow lava. The internal igneous-relationships of the ophiolite complex are described. These rocks are disposed in three thrust sheets (two being inverted), which are overthrust eastward above previously deformed and metamorphosed Fleur de Lys schists. One model has been proposed that coherently interprets the Palaeozoic evolution of the central and western Newfoundland Appalachians in terms of present-day continental margin / island arc sedimentation, magmatism, and tectonics. The results of this mapping are interpreted within the framework of this model. The Fleur de Lys schists and Burlington Granodiorite represent rifted continental margin sediments, and a volcanic arc built on and intruding them prior to polyphase deformation and metamorphism. The Baie Verte Group is interpreted as the remains of the oceanic crust and mantle floor and mafic volcanic fill of one of several small marginal (inter-arc) basins that developed in the northwestern Newfoundland area in lower Ordovician times. It is interpreted to be in the place where the basin formed relative to the eastern and western Fleur de Lys blocks that border it. The Mic Mac Lake Group is a proximal section to an early Devonian calc-alkaline cordilleran caldera complex which may have been related either to subduction or to continental collision processes. It was laid down over an eroded surface of Burlington Granodiorite and over little to undeformed mafic rocks filling the Baie Verte marginal basin. Both were then deformed during the Acadian continental collision orogeny by contraction of the Baie Verte basin, with medium to high angle eastward overthrusting. Description: Notes for the reader. Thin sections and corresponding rock samples used for this study are deposited in the Harker collection of the Department of Mineralogy and Petrology, University of Cambridge. (Catalogue no. 33, p. 251-253, 255- 283; serial numbers 110403-110456, and 110476-110990). The magnification quoted in captions to photomicrographs is the true scale of the print to the thin section. The prints are about 85 X 57 mm., and their longest side therefore represents about 8.5, 3.4, 2.1 and 0.85 mm. for magnifications of X 10, X 25, X 40 and X 100 respectively. The camera lens cap seen in photographs of outcrop surfaces is 45 mm across. Tue, 29 Oct 1974 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243629 1974-10-29T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/226116 Title: Dynamic Properties of Materials: Phonons from Neutron Scattering Authors: Cope, Elizabeth Ruth Abstract: A detailed understanding of fundamental material properties can be obtained through the study of atomic vibrations, performed experimentally with neutron scattering techniques and coupled with the two powerful new computational methodologies I have developed. The first approach involves phonon-based simulations of the pair distribution function -- a histogram of localised atomic positions generated experimentally from total scattering data. This is used to reveal ordering behaviour, to validate interatomic models and localised structure, and to give insights into how far dynamic behaviour can be studied using total scattering techniques. Most importantly, the long-standing controversy over dynamic disorder in $\beta$-cristobalite is resolved using this technique. Inelastic neutron spectroscopy (INS) allows \emph{direct} study of vibrational modes through their interaction with the neutron beam, and is the experimental basis for the second strand of the new methodology. I have developed new simulation and refinement tools based on the next generation of spectrometers currently being commissioned at the ISIS pulsed neutron source. This allows a detailed powder spectroscopy study of cristobalite and vitreous silica demonstrating that the Bose peak and so-called `fast sound' features can be derived from standard lattice dynamics in both the crystal and the amorphous counterpart, and allowing discussion of their origins. Given the controversy in the literature, this is a key result. The new methodology also encompasses refinement of interatomic models against powder INS data, with aluminium providing a successful test-case. A more complex example is seen in calcite, with experimental data collected during the commissioning of the new MERLIN spectrometer. Simulated one-phonon coherent INS spectra for the single crystal and powder (the latter including approximations to multi-phonon and multiple scatter) are fully convolved with experimental resolution functions. These are used in the analysis of the experimental data, yielding previously unpublished dispersion curves and soft mode information, as well as allowing the effectiveness of powder refinement of more complex materials to be assessed. Finally, I present further applications with technologically important materials -- relaxor ferroelectrics and high temperature pnictide superconductors. The conclusions draw together the different strands of the work, discussing the importance of these new advances together with future developments and scientific applications. Description: Related article - "FORTRAN routines for the new SQW and PDF modules of GULP and TOBYFIT" at http://www.dspace.cam.ac.uk/handle/1810/225173 in the Data sets - Mineral Science Collection Fri, 01 Jan 2010 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/226116 2010-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/218854 Title: Aspects of structural and electronic disorder in network materials: approaches to simulation Authors: Walkingshaw, Andrew D Abstract: Disorder in solids is one of the critical problems facing exponents of simulation-based studies in the mineral sciences. This thesis presents some novel techniques which can be used to probe the structure and dynamics of such systems under simulation. Two techniques are focussed upon. Firstly, the use of simulated charge as a probe to investigate the bonding and electrochromic properties of materials (particularly tungsten trioxide); secondly, derivation of a novel algorithm (Constrained Linear Maximization) for prediction of transition states by simulation, and its application to diffusion simulations in both crystalline network silicates and silica glass. Tue, 06 Mar 2007 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/218854 2007-03-06T00:00:00Z