364,031 research outputs found
Zinc Contents of Mafic Micerals in Granitic Rocks, with Special Reference to Ore Chemistry
No full textIn order to know the reason why the Cu/Zn-Pb ratios of skarn-type deposits related with the ilmenite-series granitic rocks are markedly higher than those related with the magnetite-series, comparative mineralogical studies were carried out for the two types of granitic rocks in the Chugoku district. An attention was focused on the be-havior of Zn during the crystallization of granitic magma, because Zn contents of mafic minerals can be obtained by non-destructive electron microprobe analyses.
Microscopic observation indicats that no sphalerite occurs in the magnetite-series granitic rocks, which im-plies that the magmas corresponding to the granitic rocks were undersaturated in respect to ZnS. Electron micro-probe analyses revealed that the Fe/(Fe+Mg) ratios of mafic minerals such as biotite and hornblende in the ilmen-ite-series granitic rocks are remarkably higher than those in the magnetite-series, and the Zn contents are posi-tively correlated with the Fe/(Fe+Mg) ratios in the ilmenite-series granitic rocks. Also the Zn/Fe rations seem to be slightly higher in the ilmenite-series granitic rocks. In contrast, the correlation between Zn contents and Fe/(Fe+Mg) ratios is ambiguous in magnetite-series granitic rocks.
With a progress of crystallization differentiation, therefore, Zn may be removed more effectively in the il-menite-series granitic magma, and the contents may be growing scarce in the fractionated ilmenite-series granitic magma. On the other hand, magnetite-series granitic magma probably increases the Zn-contents in the advanced stage of the crystallization. The hydrothermal fluids genetically related to the fractionated magnetite-series grani-tic magma are likely to be enriched in Zn, being favorable for the formation of Zn-rich deposits
Shock-Induced Damage in Rocks: Application to Impact Cratering
No full textShock-induced damage beneath impact craters is studied in this work. Two representative terrestrial rocks, San Marcos granite and Bedford limestone, are chosen as test target. Impacts into the rock targets with different combinations of projectile material, size, impact angle, and impact velocity are carried out at cm scale in the laboratory.
Shock-induced damage and fracturing would cause large-scale compressional wave velocity reduction in the recovered target beneath the impact crater. The shock-induced damage is measured by mapping the compressional wave velocity reduction in the recovered target. A cm scale nondestructive tomography technique is developed for this purpose. This technique is proved to be effective in mapping the damage in San Marcos granite, and the inverted velocity profile is in very good agreement with the result from dicing method and cut open directly.
Both compressional velocity and attenuation are measured in three orthogonal directions on cubes prepared from one granite target impacted by a lead bullet at 1200 m/s. Anisotropy is observed from both results, but the attenuation seems to be a more useful parameter than acoustic velocity in studying orientation of cracks.
Our experiments indicate that the shock-induced damage is a function of impact conditions including projectile type and size, impact velocity, and target properties. Combined with other crater phenomena such as crater diameter, depth, ejecta, etc., shock-induced damage would be used as an important yet not well recognized constraint for impact history.
The shock-induced damage is also calculated numerically to be compared with the experiments for a few representative shots. The Johnson-Holmquist strength and failure model, initially developed for ceramics, is applied to geological materials. Strength is a complicated function of pressure, strain, strain rate, and damage. The JH model, coupled with a crack softening model, is used to describe both the inelastic response of rocks in the compressive field near the impact source and the tensile failure in the far field. The model parameters are determined either from direct static measurements, or from indirect numerical adjustment. The agreement between the simulation and experiment is very encouraging.</p
Pore structure characterization of low permeability rocks
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2014.Hoje as pesquisas em rochas de baixa permeabilidade (grande tendência no mundo e em breve na indústria petrolífera brasileira) se voltam à escala de poros seja para investigação petrofísica, morfológica, de distribuição de tamanhos de grãos ou poros ou escoamento de fluidos, prática descrita pelos valores de permeabilidade. A avaliação destas propriedades por sua vez, é essencial ao desenvolvimento e exploração de reservas de hidrocarbonetos. No entanto, a determinação de parâmetros do sistema poroso nessas rochas, arenitos de baixa permeabilidade (TGS) e rochas selantes (SR), continua a ser um grande desafio devido à extrema variabilidade de ambientes deposicionais e complexa microestrutura composta por argilas e tamanhos de poros de submícrons a ångströms. Nesta tese empregou-se um conjunto de técnicas experimentais para a caracterização da estrutura porosa de TGS e SR. De tal modo, o trabalho foi dividido em dois tópicos principais: (i) Caracterização do sistema poroso e propriedades petrofísicas em TGS utilizando-se as técnicas de permeabilidade por decaimento de pulso (PDP), NMR de baixo campo, adsorção gasosa N2 (N2GA), porosimetria por intrusão Hg (MICP), nano- e microtomografia de raios X (res. Abstract : Nowadays, significant research effort in low-permeability rocks (a wide tendency elsewhere and soon in the Brazilian petroleum industry) has been focused on pore-scale petrophysics, morphologies and distributions, as well as fluid flow circulation described by the values of permeability. The evaluation of these properties in turn is essential for the assessment and exploitation of hydrocarbon reserves; however, determining pore system parameters in such rocks as tight gas sandstones (TGS) and seal rocks (SR) remains challenging because of the extreme variability in depositional environments resulting in complex pore structures comprised by clays and length scales from sub-microns to Angstroms. In this work we applied a set of techniques to characterize submicron-pore structures in TGS and SR. Therefore it was divided into two main topics of interest: (i) Characterization of petrophysical properties and pore systems in very low permeability TGS using Pulse-Decay Permeability (PDP), Low Field Nuclear Magnetic Resonance (LFNMR), Nitrogen Gas Adsorption (N2GA), Mercury Intrusion Capillary Pressure (MICP) and Multi-scale 3D X-ray Nano- and MicroCT (down to 0.7 µm resolution) techniques; (ii) Study of Photoacoustic Spectrometry (PAS) for determining thermal diffusivity (TD) and porosity in three seal rocks originating from dissimilar fields as a key issue for safe exploration, storage purposes (CO2 sequestration) and developments in shale characterization. The values obtained for TD were between 0.01667 and 0.09298 (cm2/s) while porosity ranged from 1.42 to 9%. For the analyzed TGS the 3D pore-structure characterization lead to pore tortuosity and shape factors ranges of 2.19-5.47 and 3.2-8.5, respectively, and pore size distributions tended to be bimodal for MICP, trimodal for 3D multi-scale and tetramodal for LFNMR measurements. The porosity values ranged from 1.94 to 11.96% obtained by the combination of N2GA and MICP techniques and permeability from 0.036 to 0.00066 mD by PDP technique. The measured pore-structure parameters were also used to predict empirical permeability in TGS (using e.g. Carman-Kozeny (Dullien, 1992) and Coates (1999) models). The set of applied methods has shown to be a useful tool for the unconventional reservoir characterization since it allows obtaining pore morphological and quantitative parameters which account for the permeability values
Seismic anisotropy in siliciclastic reservoir rocks
No full textThe interpretation of geophysical field measurements of seismic anisotropy is presently limited by our knowledge of the controls of the elastic anisotropy of sedimentary rocks
in the subsurface. Traditionally, laboratory ultrasonic velocity measurements have been used to provide important information on bulk aggregate seismic anisotropy, however,
they do not allow the discrimination of the contribution from the various microstructural parameters (e. g., crystallographic lattice preferred orientation (LPO), preferentially aligned porosity, aligned fractures and the non-random spatial distribution of mineral phases). In this study the results from scanning electron microscope-electron backscattered diffraction (SENI-EBSD), quantitative X-ray diffraction (QXRD), image analysis,
ultrasonic velocity measurements, palaeomagnetism, anisotropic magnetic susceptibility, and numerical modelling are combined to elucidate the controls of the elastic anisotropy of siliciclastic sedimentary rocks from an oil reservoir.
SEM-EBSD was used to measure both the overall and individual constituent mineral phase LPO (Maddock et al. 2004). As phyllosilicates are both very fine-grained, with
a high aspect-ratio and low crystallinity, their LPO contribution was established via a combination of image analysis and numerical modelling (Bingham approximation).
These analytical and predictive methods for determining phyllosilicate fabric intensity produced consistent results. For the first time, the azimuthally preferred orientation of elongate grains within sedimentary rocks was determined using anisotropic magnetic susceptibility of ferrous minerals and were compared to those predictions obtained using EBSD.
The strength of the fabric-texture (J), as determined by EBSD, is proportional to the maximum compressional and shear-wave anisotropy, as calculated from the Christoffel
equation, by taking a Hill average of the bulk aggregate elastic constants. The quartz and feldspar velocity maxima aligned in a constructive fashion throughout most of the
samples. It is possible that the preferred alignment of crystals detected by EBSD reflects the palaeoflow direction. The predicted symmetries of velocity anisotropy ranged from orthorhombic in the phyllosilicate-free, well-sorted, mature sandstones to strong vertical transverse isotropy in the unfractured phyllosilicate-rich mudstones. Vertical transverse isotropy is predicted to be oriented, such that, the plane of azimuthal isotropy is aligned
parallel to bedding i. e., parallel to the horizontally aligned clays and micas. Similarly, orthorhombic symmetry is predicted to be oriented, such that, one plane of symmetry is aligned approximately parallel to bedding whilst the other symmetry plane is aligned parallel to the single most dominant fracture set. The results from this study provide the input needed for a general mathematical model for the reservoir allowing the prediction
of seismic anisotropy for any rock in the reservoir given accurate modal proportions. The resulting model is an advance on the empirical correlations that are usually used to determine how seismic velocities are affected by factors such as clay content and porosity. In particular, the bulk aggregate elastic stiffness tensor obtained during this study can be integrated with high-pressure ultrasonic measurements to enable the prediction of the additional contribution from grain-scale effects such as shape-preferred orientations, and grain boundary compliances (Hall et al. 2007). The results from this study have also
provided the basic data to allow field seismic data to be inverted to obtain estimates of in situ fracture density and orientation (Kendall et al. 2006).
In summary, analysis of a suite of siliciclastic hydrocarbon reservoir rocks has shown that the LPO of constitutive minerals can offer information about the nature of a reservoir. The results suggest that seismic anisotropy is not only indicative of lithology but can
also be an indicator of reservoir quality and palaeoflow direction
The emplacement and deformation of granitic rocks in a transpressional shear zone: the ox mountains igneous complex
No full textThe structural evolution of the Ox Mountains Granodiorite {478±12Ma) during and after its emplacement is described. This pluton has been emplaced within and synchronously with, a major transpressional shear zone which is expressed as a 11km wide belt of strongly deformed NE-SW striking, steeply dipping metasediments. The steep shear zone cleavage is intensified to a mylonitic fabric in a braided system of high strain zones formed through out the Ox Mountains Inlier. Pervasive ductile, sinistral deformation in the shear zone is interupted by the emplacement of the pluton and by the synchronous development in the country rocks of series of brittle thrust structures, which produced a displacement upwards and towards the centre of the shear zone. These thrusts are intimately associated with the emplacement of moderately inclined granodiorite sheets belonging to the main intrusive phase indicating a component of vertical extension in the country rocks at this time. The CMC is a heterogeneous, four component pluton internally composed of a series of large sheets or dykes. Minor muscovite granite sheets emplaced along the northern contacts, preceeded the main intrusive sheets of Group 1 and Group 2 granodiorite with associated diorites. Sheets of tonalites and minor components completed the emplacement history. A prolonged history of sinistral transpressional shearing has deformed the pluton. Discrete sinistral shears indicate an early localization event is overprinted by a main ductile penetrative fabric which cross-cuts ail internal contacts. This fouation is deformed by extensive sinistral S-C fabrics. Later deformation becomes increasingly partitioned into late sinistral and dextral shear zones which are locally mylonitic. Microstructural evidence suggests that the main foliation was formed under lower amphibolite facies and deformed by a steady state flow process. The S-C fabric and late shear zone formation, best developed in the granodiorites and granites, may have been initiated by a switch in the predominant alkalifeldspar deformation mechanism from crystal plastic to a diifusive mass transfer process. This may be a retrogessive effect, and the product is a grain size reduction which may lead to ultramylonite production. The emplacement model for the Ox Mountains Granodiorite is constrained by the original geometry of the dykes or sheets. These data rule out emplacement of the OMG in a releasing bend or pull-apart structure. Strain data does not allow a forceful mechanism and a permissive emplacement model is preferred, in which vertical extension during the intrusive episode created an area of dilation in which dyking occurred. This was caused by oblique movements on two upwardly converging high strain zones outside the pluton. Two satellite plutons, the Lough Talt Adamelhte and the Easkey Lough Adamellite were emplaced in extensional cavities created by reactivated sinistral movements on one of the high strain zones at a much later date. (c400Ma).Transpressional shear zones may initiate or enhance melting in the lower crust and mantle lithosphere where thermal perturbation has occurred. The shear zones may provide conduits for the melts and emplacement sites, especially where high transpressional strains are accommodated by vertical uplift
Geology of the Ordovician rocks between Leadhills and Abington, Lanarkshire
No full textNE-SW faults in the Abington area of the Northern Belt of the Southern Uplands define blocks up to 3.2 km wide. The strata, folded and locally overturned, young predominantly to the NW but blocks to the SW contain younger sequences. Analogous configurations occur in modern accretionary margins. The oldest rocks, generally of pelagic and hemipelagic origin, are Arenig basalts, dolerites, cherts and brown mudstones underlying red mudstones, possibly Llanvirn, and black fossiliferous mudstones and cherts of Llandeilo and Caradoc age. Trench sediments overlying pelagic sequences represent a range of depositional mechanisms. Rudites and associated fine-grained lithologies of lateral origin relate to a lower trench-slope canyon system, whilst axially transported sands, originating on the lower trench slope, were deposited by turbidity currents and related flows. Sandstone petrography varies markedly across strike, with quartz-rich compositions suggesting a recycled orogen source, and ferromagnesian-rich compositions a dissected magmatic arc provenance. Faults, initially low-angle thrusts, facilitated thrust nappe formation; faults and bedding were rotated through the vertical within the accretionary complex, predating or accompanying slaty cleavage development. Soft sediment deformation, two fold phases and a kink-band set are recognised. Imbricate fault zones, located in incompetent pelagic sequences, are equated with tectonic melange of other accretionary complexes. Index minerals, illite crystallinity and 'vitrinite' reflectance establish metamorphic grade as prehnitepumpellyite facies
Some aspects of the mechanical behaviour of "structured" soils and soft rocks .
No full textSoft rocks and many soils all over the world are "structured" due to presence of weak bonds between individual particles. In this paper some examples re-garding the role of bonding on both deformability and strength are reported. Considering the common aspects which associate these materials, an unified framework is proposed
'Critische Dichtkunst vor die Deutschen': Gottscheds Poetik
No full textDer Beitrag erschließt Gottscheds 'Versuch einer Critischen Dichtkunst' in ihren systematisch relevanten Aspekten und in ihren historischen Perspektiven. In einem ersten Schritt wird die kulturpolitische Dimension der Poetik untersucht, um daran anschließend ihre kritische Kontur herauszustellen. Kritik firmiert hier einerseits als ein konzeptueller Schlüsselbegriff und zählt andererseits als Praktik des Kritisierens ganz wesentlich zum poetologischen Verfahrensarsenal. Drittens expliziert der Beitrag die intertextuelle Dimension der Poetik, indem er Gottscheds Referenzen auf die Antike gleichermaßen wie auf Autor*innen des neuzeitlichen England und Frankreich aufzeigt. Auf dieser Basis baut Gottsched die deutsche Systemphilosophie auf und um. Viertens entwickelt Gottsched ein Modell des guten Poeten, der im Schulterschluss mit Kritiker*innen und Rezipient*innen über auszubildende Vermögen – insbesondere mit Hilfe des Geschmacks – gute Literatur verbürgt. Diese gute Literatur ist für Gottsched immer gattungsmäßig organisiert, was der Beitrag abschließend mit besonderer Berücksichtigung des Besonderen Teils von Gottscheds Poetik erläutert
The provenance of the norber erratics, and the formation of post-devensian-deglaciation pedestal rocks with carboniferous limestone pedestals in England, Ireland and Wales
No full textThis study investigates a Devensian glacial conundrum, the provenance of the Norber erratics in North Yorkshire, and the
origins of a post-Devensian-deglaciation landform, pedestal rocks with Carboniferous limestone pedestals in England,
Ireland and Wales.
Investigations to determine the provenance of the Norber erratics were undertaken in a study area of about 2000ha. Mapping
erratic dispersal and measuring striae strike revealed that the provenance is Crummackdale, and that Devensian ice crossed
over only the Crummack, Sowerthwaite and Austwick formations en route to Norber. Petrographical and physical surveys
further revealed that the erratics are derived from the Austwick Formation only, and that provenance is a glacially-plucked
‘amphitheatre’ in the vicinity of the Old Limekiln (SD 770707).
Investigations to determine the formation of post-Devensian-deglaciation pedestal rocks with Carboniferous limestone
pedestals were undertaken at 19 sites in England, Ireland and Wales, where 162 pedestal rocks and a pedestal rock field
were examined. The study was divided into two, the formation of perched and mushroom pedestal rocks. An examination of
weathering and erosion processes at Norber, where only perched pedestal rocks with vertical sidewalls are found, revealed
that lowering of the inter-pedestal limestone surface has taken place primarily in a sub-regolith karstic environment, and
that little or no pedestal formation occurred prior to ca.10000BP. In contrast, the lowering of the inter-pedestal limestone
surface about perched pedestal rocks with sloping sidewalls, such as at Scales Moor (North Yorkshire) and the Burren
(County Clare), has taken place primarily in a subaerial environment. Moreover, pedestal formation commenced in
ca.14500BP in England and Wales, and ca.13700BP in Ireland. The pedestals of mushroom pedestal rocks have formed due
to lateral dissolution under regolith that has largely been eroded, probably following deforestation in ca.3000BP
Complex examination of the Upper Paleozoic siliciclastic rocks from southern Transdanubia, SW Hungary—Mineralogical, petrographic, and geochemical study
No full textA vertical section of Upper Paleozoic sandstones from southern Transdanubia (Mecsek-Villány area, Tisza mega-unit, Hungary) has been analyzed for major and trace elements, including rare earth elements (REEs). In addition, the clay mineralogy of the sandstone samples and the petrography and geochemistry of gneiss and granitoid clasts extracted from the associated conglomerates have been determined.
Geochemistry of the sandstone samples analyzed in this study shows that these rocks were predominantly derived from a felsic continental source; nevertheless, compositions vary systematically up-section. The Pennsylvanian (Upper Carboniferous) Téseny Formation has higher SiO(2) and lower Na(2)O, CaO, Sr, high field strength element (HFSE), and ΣREE contents relative to the Permian strata. Its high K(2)O and Rb contents together with the presence of abundant illite-sericite suggest a potassium metasomatism in this formation. Clay mineralogy and large ion lithophile element (LILE) contents of the Lower Permian Korpád Formation vary spatially and are interpreted as local variations in composition of the source region and postdepositional conditions. Zr and Hf abundances and REE patterns, however, show that this formation was derived from mature upper continental crust. The Upper Permian Cserdi Formation has higher TiO(2), Th, U, Y, Cr, and heavy (H) REE contents, and higher Cr/Th and Cr/Zr ratios relative to the underlying formations. These trends can be explained by a sedimentary system dominated by highly weathered detritus derived from combined recycled-orogen, basement-uplift, and volcanic-arc provenance in the Téseny Formation, with an increased proportion of less weathered detritus derived from combined volcanic and basement-uplift provenances in the Permian formations. Characteristics of the Cserdi unit may reflect relatively proximal derivation from a felsic volcanic source
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