The purpose of architectural theory is to provide a paradigm, or episteme, from which one can address contemporary design issues within the broader cultural context. It comprises any written system of architecture and may be either partial or comprehensive, but it must encompass a framework of cognitive categories that inevitably provide criteria for judgment. If not explicitly stated, it nevertheless implies an epistemology, a substructure for architectural knowledge. Previous studies of tectonics have tended to treat it as an autonomous architectural discourse, focusing on an individual writer and theory, or on a thematic concern such as the relationship between ontology and representation. This study approaches tectonics differently, relating it to the broader shifts within the discourses of architecture and philosophy, thereby sanctioning a more synergistic, as opposed to autonomous, examination. In exploring the epistemological parameters of tectonics theories in the West it isolates three major periods in its development: Classical Tectonics- derived from ancient philosophy, Rational Tectonics- emerging from the epistemology of science and Poetic Tectonics- developed out of concerns raised by the German Counter- Enlightenment and the Romantic Movement. At each stage in its development tectonics has served to provide key principles that collectively constitute its ground. The study reveals that Poetic Tectonics was a reaction against the duality of mind and abstract rationalism- so central to Cartesian thought and the epistemology of science- and its impact on architectural thought. In response Poetic Tectonics while accepting the key principles of Rational Tectonics sought to redirect it along the philosophical lines of the 2 German Enlightenment and Romanticism while also re-presencing the ethical substructure of Classical Tectonics. This study recognizes that through the course of time, the epistemology upon which cultures are formed have and will continue to change and as they do new tectonic theories will need to be negotiated; rendering tectonics in a continual state of 'becoming'. If there is to be a conclusion it lies in the fact that in its historical persistence and continuity tectonics represents a tradition within Western architecture on par with the likes of the Vitruvian, Organic and Functionalist.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 12, 2010 ). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dr. Francisco Gomez, Thesis Supervisor. Includes bibliographical references.

The 6845±50 yrs BP caldera-forming eruption of Mt Mazama (Crater Lake, Oregon) was preceded within 200 years by two plinian eruptions producing voluminous airfall deposits followed by lava flows. This study concentrates on these two airfall deposits as well as the complex airfall deposits from the climactic eruption, which are distributed over = 1.7 million km2 of northwest America. Tephro-stratigraphic mapping of airfall units throughout south-central Oregon has revealed the presence of five lobes of coarse pumice deposits and two widespread ash units which are important marker horizons. Detailed grain size data have been generated by sieving and measurement of maximum clast sizes, and these are used to characterise each deposit and as input data for clast dispersal models of plinian airfall eruptions. Geochemical variations between each deposit generally support the models already developed for Mt Mazama, and geochemical techniques have been used to deduce the source of distal 'Mazama ash'. The role of volatiles in each eruption is reviewed and, along with the rate of vent and conduit erosion, is found to be vital in controlling eruptive evolution. Deduction of column height and mass eruption rate for various stages during each eruption has been possible using clast dispersal models and, when combined with eruptive velocity and vent and conduit dimensions, has produced a detailed physical model of eruptive development. This has then been linked to field characteristics to provide significant new information about the physical volcanology of plinian airfall eruptions. Revised volume estimates for the climactic airfall eruption, including distal fine ash, give a volume of = 20 km3 (dense rock equivalent), with a maximum column height of = 55 km occurring immediately prior to column collapse and ignimbrite generation. This eruption is thus one of the most intense and voluminous ultra -plinian eruptions yet documented.

Most passive margins display a prominent breakup unconformity coinciding with the rift to drift transition. The unconformity, as defined by Falvey, (1974) is of broad regional extent affecting both basins and highs and is easily recognised on seismic sections. Criteria for the recognition of the breakup unconformity include an inflection in the subsidence curve, fault terminations and volcanic strata (and/or evaporites) at the level of the unconformity. Falvey considered that it was caused by "erosion during the final uplift pulse associated with pre-breakup upwelling in the mantle". It is more likely that the uplift is caused by magmatic underplating in response to the passive upwelling of the mantle and the flexural isostatic effects of erosion throughout the syn-rift phase. The primary objective has been to quantify the amount of uplift and erosion associated with the breakup unconformity / breakup megasequence boundary. This is of particular importance in hydrocarbon exploration as it quantifies the potential loss of old reservoirs and predicts the provenance of new reservoir clastics. Two data sets, from the Grand Banks and the Northwest Shelf of Australia, have been studied. In both cases there are multiple breakup events and breakup megasequence boundaries form part of a complex tectono-stratigraphy. Regional seismic lines have been interpreted, depth converted and modelled using a new technique of combined reverse post-rift and forward syn-rift modelling. The results of this process, together with seismic megasequence analysis, show that the morphology of the breakup megasequence boundary varies systematically across a passive margin. It is strongly erosional at about 70 km landward of the continentocean boundary, where regional "breakup" uplift outweighs extensionally controlled subsidence, but may be depositional on either side of this zone. A coupled, quantitative magmatic-tectonic model has been constructed by combining the Bickle-McKenzie melt generation model with the flexural cantilever model for continental extension. The magnitude of underplating can be estimated using the Bickle-McKenzie model, in which the amount of melt produced is controlled by the extension factor, ß, and the proximity of a mantle plume convection cell.

The formation and evolution of sedimentary basins are best understood within the context of prevailing tectonic conditions. This dissertation presents an integrated geologic and geophysical study of the southeast Caribbean–northeast South American margin which is characterized by a 300-km-long curved transition from subduction to strike-slip plate boundary interaction. Tomography models are generated to image the geometry and orientation of the subducting slab and associated upper mantle structures, and integrated with observations made from gravity, magnetic and seismicity data. The plate boundary interaction changes laterally from: (1) direct subduction where oceanic South American lithosphere dips towards the west at up to 65° beneath the Caribbean plate; to (2) collision where South American transitional-continental type lithosphere dips 44°–24° beneath the Caribbean plate; to (3) east-west oriented strike-slip interaction where the slab is detached from the South American continent. A tectonostratigraphic framework based on the interpretation of ~10,000 km of 2-D seismic and abundant well data is used to study the evolution of the structures and basin fill of the margin. The basins are characterized by composite and superimposed structural styles which differ from basins formed in pure strike-slip or convergent margins. A NW–SE oriented tear fault aligned with the South American continent-ocean-boundary defines the boundary between different contractional styles in the sedimentary succession of the subduction and collision provinces. An examination of bathymetric conditions and the upper Pleistocene succession of the continental shelf suggest a bimodal sediment transport process, linked to shoreline changes. Current-driven, strike-parallel sediment distribution systems dominate during highstand, generating unique shelf-bound channels and fills. Lowstand across the area is characterized by dip-directed, sediment distribution systems with SW–NE oriented channels that direct sediments to the shelf edge and deep basin environments. The results of this study illustrate that plate boundary conditions and associated lithospheric arrangement at depth, play a significant role in influencing the form of shallow structures, basins and surface geomorphology. Crustal-scale structures; influenced by deeper lithospheric-scale configuration, act over longer time-scales to create and deform depocenters; while sea-level stand exerts significant control on the timing and location of sedimentation over shorter time periods. / text

A study of Devonian syn-extensional silicic volcanism in the Rhenohercynian Zone (RHZ) of Northern Europe was undertaken to determine their evolution and petrogenesis within the changing tectonic and sedimentological environment of a developing intra-plate rift zone. Silicic volcanics in the Lower Devonian of south Devon and Northern Germany are classified as subalkaline rhyolites-rhyodacites with minor peralkaline variants. Middle Devonian silicics from the Lahn-Dill syncline are peralkaline trachytes with minor subalkaline equivalents. All Lower and Middle Devonian Rhenohercynian silicic volcanics are tectonomagmatically classified as within-plate granitoids and are interpreted to represent syn-rift A-type silicic volcanics. However, a distinction is made with respect to age, in that all Lower Devonian silicics are N-type, whereas the Middle Devonian trachytes are AI-type. The McKenzie & Bickle (1988) theoretical evaluation of magmatism associated with crustal extension provides an excellent explanation for the changing geochemical and isotopic signatures of RHZ Lower and Middle Devonian silicic volcanics. The distinct geochemical and isotopic signatures between Lower and Middle Devonian volcanics reflects progressive lithospheric attenuation within the RHZ with the extension factor P<2 for Lower Devonian to P>2 (for Middle Devonian). The Lower Devonian southwest England silicic magmas, generated during the initial stages of extension, show evidence of crustal contamination and were probably derived from subduction-modified lithospheric mantle. Lower Devonian rhyolites from Northern Germany were generated via partial melting of crustal materials, the thermal energy for which was generated by the injection of basaltic melts which ponded at their equilibrated density level. Middle Devonian trachytes display mantle-dominated chemical patterns and represent extreme differentiates of alkali basalts derived from an omlike mantle source. The southwest-northeast trend of the major volcanic masses indicates the direction of faulting which has controlled the timing and extrusion of these syn-extensional melts. The volume of extrusive products appears strongly linked to the rate of extension and sediment accumulation. The greatest period of subsidence (Givetian) and sediment accumulation (200 metres per million years) coincides with the most volumetric period ofRHZ silicic volcanism

No description available.

Whether by accretion, magmatic addition, or refinement of more mafic lithologies, continental arcs are likely zones for the creation of "average" continental crust with intermediate silica content. This dissertation contains the results of broadband seismic studies carried out in two field areas, an active subduction zone and the remnants of an extinct arc, with the aim of understanding lithospheric evolution at convergent margins. The analytical techniques of receiver function calculation and surface wave tomography are applied to data sets collected above the Andean subduction zone in Chile and western Argentina and in the Coast Mountains Batholith of central British Columbia. We present the first in-depth comparison of receiver functions calculated using the high frequencies available in records of intermediate-depth local earthquakes with those calculated from the lower frequency data in records of larger teleseismic events. The comparison reveals that the lower crust beneath the Western Sierras Pampeanas contains a gradational velocity increase over ~20km above a small velocity step at the Moho. Surface wave tomography confirms the existence of an unusually high velocity anomaly in the mantle above the slab and yields estimates of slab thickness on the order of 50 km. To the south of the flat slab region, we see evidence of active mantle wedge convection above the steep slab, but no evidence of the lithosphere-asthenosphere boundary beneath the subducting Nazca plate. In the Coast Mountains Batholith (CMB), receiver functions image a bright, continuous Moho throughout the study region. Combined with petrologic modeling, the receiver function data point toward convective removal of any ultramafic root that formed beneath the CMB. Low absolute shear wave velocities in the upper mantle resolved via surface wave analysis strengthen the case for root removal beneath the eastern section of the CMB. On the far western edge of the CMB, we find evidence of a partially reformed lithosphere outboard of a major tectonic boundary. These observations shed light on the distillation of felsic to intermediate continental crust from more mafic primary magmas in active subduction zones and the eventual return of the complementary ultramafic residuals to the convecting mantle.

The widespread recognition of (ultra)high-pressure ((U)HP) metamorphic rocks in orogens worldwide suggests that subduction and exhumation of crustal rocks from mantle depths are normal processes at convergent plate margins. However, the dynamics of these processes, in particular the comparative roles of erosion and crustal extension, and the driving forces of extension during (U)HP rock exhumation, remain controversial. This thesis presents numerical modeling and field/analytical studies that address the geodynamics of crustal subduction and exhumation in two intensely studied orogens, the Alps and the Caledonides. The 2D numerical models show how different scales and durations of orogeny and plate motions can lead to marked contrasts in the style of orogenic growth, crustal subduction, and (U)HP exhumation. In the Western Alps, rapid exhumation (1-3 cm/a) can be explained by local, syn-orogenic extension driven by the buoyant ascent of deforming (U)HP crust from the subduction channel. Later trans-crustal exhumation probably resulted from the combined effects of syn-convergent thrusting, local extension, and erosion. The low temperatures (500-700°C) of Alpine (U)HP metamorphism are attributable to the small size of the orogen and short duration of subduction/exhumation. Contrary to recent suggestions, neither erosion nor absolute extension is required to explain (U)HP exhumation in the Alps. The Western Gneiss Region (WGR) (Norwegian Caledonides), in contrast, can be explained by subduction to (U)HP conditions followed by plate divergence. Gravitational spreading of a thick, hot orogenic wedge leads to a short period of coeval thrusting and extension. Exhumation of (U)HP crust from the subduction channel is achieved by normal-sense shearing along the top of the (U)HP terrane, with minor associated shortening. Trans-crustal exhumation by vertical thinning of the orogenic wedge results from continued absolute extension and erosion. The comparatively high temperatures (700-800°C) achieved by Caledonian (U)HP rocks reflect the orogen's greater size, slower exhumation rates, and possible stalling of the (U)HP terrane at depth. These contrasting models underscore the variety of possible mechanisms responsible for (U)HP exhumation, and represent new benchmarks in the understanding of Alpine and Caledonian tectonics and (U)HP rock exhumation in general.

<p> Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_U-Pb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf).</p><p> <b>Appendix A</b> is a combination of detailed isopach maps of the Upper Cretaceous Western Interior, flexural modeling and a comparison to dynamic subsidence models as applied to the region. Using these new isopach maps and modeling, I place the previously recognized but poorly constrained shift from flexural to non-flexural subsidence at 81 Ma.</p><p> <b>Appendix B</b> is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation.</p><p> <b>Appendix C</b> is a geo-thermochronologic study to measure the lag time of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. The maximum depositional ages using DZ U-Pb match existing biostratigraphic age controls. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4&ndash;5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed from &lt;8&ndash;9 km depth. Apatite U-Pb analyses indicate that volcanic contamination is a significant issue, without which, one cannot exclude the possibility that the youngest detrital AFT population is contaminated with significant amounts of volcanogenic apatite and does not represent source exhumation. AFT lag times are &lt;5 Myr with relatively steady-state to slightly increasing exhumation rates. Lag time measurements indicate exhumation rates of ~0.9->>1 km/Myr.</p>