ENGLISH ABSTRACT The Late Devonian to Early Carboniferous kinematic evolution of the Teplá-Barrandian/Moldanubian boundary The Staré Sedlo complex (SSC) is a relic of meta-igneous arc-related pluton in the southern part of the Sedlčany-Krásná Hora roof pendant, intruded by granitoids of the Central Bohemian Plutonic Complex along the boundary of Teplá-Barrandian (TBU) and Moldanubian units (MU), Bohemian Massif. The SSC mainly comprises deformed orthogneisses of calc-alkaline granodiorite to tonalite protoliths of Late Devonian age (380−365 Ma; Košler et al., 1993) that were commonly mingled with minor basic magmas. Locally preserved subhorizontal intrusive contacts of the orthogneisses against their meta-sedimentary host rock indicate that these magmas intruded as a sill complex. The SSC preserves a rather unusual flat-lying subsolidus foliation (dip <40ř) associated with subhorizontal ~NE-SW-trending mineral lineation. Mesoscopic structures, anisotropy of magnetic susceptibility (AMS), and deformational microstructures indicate prolate shape of the strain ellipsoid with dominant coaxial pure shear regime. The solid state microstructures record cooling of the orthogneiss protolith down to the ambient greenschist facies conditions followed by its static recrystallization due to the intrusion of the younger...

A detailed structural study of Rock Canyon (near Provo, Utah) provides insight into Wasatch Range tectonics and fold-thrust belt kinematics. Excellent exposures along the E-W trending canyon allow the use of digital photography in conjunction with traditional field methods for a thorough analysis of Rock Canyon's structural features. Detailed photomontages and geometric and kinematic analyses of some structural features help to pinpoint deformation mechanisms active during the canyon's tectonic history. Large-scale images and these structural data are synthesized in a balanced cross section, which is used to reconstruct the structural evolution of this portion of the range. Projection of surficial features into the subsurface produces geometrical relationships that correlate well with a fault-bend fold model involving one or more subsurface imbrications. Kinematic data (e.g. slickenlines, fractures, fold axes) indicate that the maximum stress direction during formation of the fault-bend fold trended at approximately 120°. Following initial thrusting, uplift and development of a thrust splay produced by duplexing may have caused a shift in local stresses in the forelimb of the Rock Canyon anticline leading to late-stage normal faulting during Sevier compression. These normal faults may have activated deformed zones previously caused by Sevier folding, and reactivated early-stage decollements found in the folded weak shale units and shaly limestones. Movement on most of these normal faults roughly parallels stress directions found during initial thrusting indicating that these extensional features may be coeval with thrusting. Other zones of extension and brittle failure produced by lower ramp geometry appear to have been activated during Tertiary Basin and Range extension along the Wasatch Fault Zone. Slickenline data on these later normal faults suggest a transport direction of nearly E-W distinguishing it from earlier events.

The Arlanda area is a construction intensive area facing problems with risk of leaching of arsenic (As) from the bedrock to surface- and groundwater. Construction projects in the area have had problems with high levels of As in the bedrock and the risk of leaching increases through processing of aggregates and blasting of the bedrock. Additionally, there are high concentrations of As in potable water and elevated concentrations are correlated with occurrences of metasedimentary rock, but may also be related to other rock types. The existing geological information of the area was collected in the 1960´s and modern petrographic information as well as modelling of P-T and redox conditions are needed to understand the As mineralogy of the bedrock. Methods used in this project include field work, optical microscopy, electron microprobe analyses, geothermometry calculations, pseudosection modelling in Perple_X and geochemical modelling in PHREEQC. The results indicate that the As-rich bedrock domain include rocks of both igneous and sedimentary origin. As-bearing minerals löllingite and arsenopyrite were found in the matrix of two of the metasedimentary rock samples, while no As-minerals were found in metavolcanic samples. P-T estimates from several geothermobarometry models all suggest amphibolite facies metamorphism for the area, with pressure of 3.0-5.5 kbar and temperature of 490-640 °C. Simple modelling of equilibration of löllingite and arsenopyrite in pure water indicate that As(III) is the dominating oxidation state of As and that the molality of As increases with increasing T and decreasing pH. The results of this thesis provide new information on the petrography and P-T conditions for metamorphism of As-bearingsupracrustal rocks in the Arlanda area, but future research is needed to be able to predict the spatial occurrence of As in the bedrock. / Arlandaområdet är ett av de mest expansiva områdena i Sverige där en stor mängd infrastrukturprojekt är planerade under de närmaste 5-20 åren. Tidigare byggnadsprojekt i området har dock stött på problem med höga bakgrundshalter av arsenik (As) i berggrunden och det finns även en risk för urlakning av As från berggrunden till både yt-och grundvatten. Denna risk ökar under byggnadsarbeten i och med till exempel sprängning av berg. Ytterligare ett problem är att det i området runtomkring Arlanda ofta är höga halter av arsenik i dricksvattenbrunnar. Från data över As-halter i bergborrade brunnar har man kunnat se att höga halter av As ofta förekommer i metasedimentära bergarter, men även kan uppträda i andra bergarter. Den tillgängliga geologiska informationen över området är insamlad på 60-talet och ny petrografisk information, samt modellering av tryck- och temperaturförhållanden är nödvändig för att förstå förekomst av As i berggrunden. Målet med detta projekt är att med hjälp av fältarbete, optisk- och elektronmikroskopering, samt termodynamisk modellering få djupare kunskap kring ytbergarterna i området och utvärdera förekomsten av arsenik i dessa. Under vilka tryck- och temperaturförhållanden som de metamorfa bergarterna omvandlats studeras genom beräkningar från mineralsammansättningar samt modellering i programmet Perple_X. Resultatet från projektet visar att bergarter i As-anrikade zoner är av både magmatiskt och sedimentärt ursprung. Arsenikmineralen löllingit och arsenikkis dokumenterades endast i bergarter av sedimentärt ursprung. Bergarternas kemiska sammansättning tyder också på att de högsta As-halterna finns i de metasedimentära bergarterna. Modellering i PHREEQC visar att As(III) är den dominerande formen av As när löllingit och arsenikkis reagerar med vatten. Tryck- och temperaturberäkningar samt tryck- och termodynamisk modellering tyder på metamorfos under amfibolitfacies, med tryck omkring 3.0-5.5 kbar och temperatur omkring 490-640 °C. Resultaten från detta projekt ger ny information om de metamorfa bergarterna i Arlanda området och förekomst av As i dessa. Vidare studier är nödvändiga för att kunnaförutse i vilken form och i vilka bergarter As förekommer.

Thin fallout tuffs in the Duchesne River Formation in the Uinta Basin, Utah are evidence that volcanism was active in northern Nevada and Utah in the late Eocene. The Uinta Basin is a sedimentary basin that formed during the Laramide orogeny. Ponded lakes of various salinity filled and emptied and during the late Eocene the northern rim was dominated by a wetland/floodplain depositional setting. Most of the tuffs have rhyolitic mineral assemblages including quartz, biotite, sanidine, and allanite. Rhyolitic glass shards were also found in one of the ash beds. Biotite compositions have Fe/(Fe+Mg) ratios typical of calc-alkaline igneous rocks and clusters of biotite compositions suggest 3 or 4 volcanic events. Sanidine compositions from five samples grouped at Or73 and Or79. Only one sample had plagioclase with compositions ranging between An22 - An49. Some beds also contained accessory phases of titanite, apatite, and zircon. Whole rock compositions of the altered volcanic ash beds indicate these tuffs underwent post-emplacement argillic alteration, typical of a wetland/floodplain depositional setting. Immobile element ratios and abundances, such as Zr/Nb and Y are typical of a subduction zone tectonic setting and rhyolitic composition. 40Ar/39Ar ages constrain the timing of volcanism. One plagioclase and one sanidine separate from two different tuff beds yielded ages of 39.47 ± 0.16 Ma and 39.36± 0.15 Ma respectively. These dates, along with the compositional data seem to limit the eruptive source for these fallout tuffs to the northeast Nevada volcanic field. These new ages, along with previously published ages in the Bishop Conglomerate which unconformably overlies the Duchesne River Formation, constrain the timing of two uplift periods of the Uinta Mountains at 39 Ma and 34 Ma. Finally, the ages also date the fauna of the Duchesnean Land Mammal Age to be about 39.4 Ma as opposed to less precise earlier estimates that placed it between 42 and 33 Ma.

Thin fallout tuffs in the Duchesne River Formation in the Uinta Basin, Utah are evidence that volcanism was active in northern Nevada and Utah in the late Eocene. The Uinta Basin is a sedimentary basin that formed during the Laramide orogeny. Ponded lakes of various salinity filled and emptied and during the late Eocene the northern rim was dominated by a wetland/floodplain depositional setting. Most of the tuffs have rhyolitic mineral assemblages including quartz, biotite, sanidine, and allanite. Rhyolitic glass shards were also found in one of the ash beds. Biotite compositions have Fe/(Fe+Mg) ratios typical of calc-alkaline igneous rocks and clusters of biotite compositions suggest 3 or 4 volcanic events. Sanidine compositions from five samples grouped at Or73 and Or79. Only one sample had plagioclase with compositions ranging between An22 - An49. Some beds also contained accessory phases of titanite, apatite, and zircon. Whole rock compositions of the altered volcanic ash beds indicate these tuffs underwent post-emplacement argillic alteration, typical of a wetland/floodplain depositional setting. Immobile element ratios and abundances, such as Zr/Nb and Y are typical of a subduction zone tectonic setting and rhyolitic composition. 40Ar/39Ar ages constrain the timing of volcanism. One plagioclase and one sanidine separate from two different tuff beds yielded ages of 39.47 ± 0.16 Ma and 39.36± 0.15 Ma respectively. These dates, along with the compositional data seem to limit the eruptive source for these fallout tuffs to the northeast Nevada volcanic field. These new ages, along with previously published ages in the Bishop Conglomerate which unconformably overlies the Duchesne River Formation, constrain the timing of two uplift periods of the Uinta Mountains at 39 Ma and 34 Ma. Finally, the ages also date the fauna of the Duchesnean Land Mammal Age to be about 39.4 Ma as opposed to less precise earlier estimates that placed it between 42 and 33 Ma.

No description available.

Paleomagnetic data from 25 sites (5 samples per site) in andesite flows of the Gringo Gulch Volcanics in Santa Cruz County, Arizona, were analyzed to determine a lower Paleocene paleomagnetic pole. Alternating-field demagnetization to 500 oe peak field was sufficient to erase secondary viscous components. The mean direction of magnetization (inclination = -58.8°, declination = 167.5 °) was obtained by averaging the site mean directions of the 25 sites, which are all reversed. The resultant lower Paleocene pole position is at lat. 77.0 °N, 1on. 201.0 °E (dp = 1.2 °, dm = 1.7 °).

This study contributes to the understanding of major river evolution in Southeast Asia during the Cenozoic. In order to trace the evolution of a hypothesized palaeo-Yarlung Tsangpo-Irrawaddy River, this work undertakes the first systematic provenance study of detrital minerals from Cenozoic synorogenic fluvial and deltaic sedimentary rocks of the Central Burma Basin, employing a combination of high precision geochronology, thermochronology, and geochemistry analytical techniques on single grain detrital zircon and white mica. The dataset is compared to published isotopic data from potential source terranes in order to determine source provenance and exhumation history from source to sink. A Yarlung Tsangpo-Irrawaddy connection existed as far back as ca. 42 Ma and disconnection occurred at 18–20 Ma, based on provenance changes detected using a combination of U-Pb ages and εHf(t) values on detrital zircons, and ⁴ºAr/³⁹Ar dating on detrital micas. During the Eocene and Oligocene, units are dominated by U-Pb age and high positive εHf(t) values, characteristic of a southern Lhasa Gangdese magmatic arc source. An antecedent Yarlung Tsangpo-Irrawaddy River system formed the major river draining the eastern Himalaya at this time. A significant change in provenance is seen in the early Miocene, where detritus is predominantly derived from bedrock of the eastern Himalayan syntaxis, western Yunnan and Burma, a region drained by the modern Irrawaddy-Chindwin river system characterized by Cenozoic U-Pb ages and negative εHf(t) values. This is attributed to the disconnection of the Yarlung-Irrawaddy River and capture by the proto-Brahmaputra River, re-routing Tibetan Transhimalayan detritus to the eastern Himalayan foreland basin. Re-set zircon fission track ages of 14-8 Ma present in all units is used to infer post-depositional basin evolution related to changes in the stress regime accommodating the continued northward migration of India. The early Miocene initiation of the Jiali-Parlung-Gaoligong-Sagaing dextral shear zone and the continued northward movement of the coupled India-Burma plate aided in focusing deformation inside the syntaxis contributing to the disconnection of the Yarlung Tsangpo-Irrawaddy system, linking surface deformation and denudation with processes occurring at deeper crustal levels.

L’analyse des données magnétiques et gravimétriques de la partie nord de la ceinture trans-saharienne a permis de proposer une carte de compartimentalisation géophysique et rhéologique des structures crustales et de visualiser les terranes du bouclier Touareg sur plus de 1000 km au nord, sous les bassins sédimentaires sahariens et plusieurs aspects ont pu être discutés. Un pseudo réseau de quatre générations successives de paléovallées et incisions a été mis en évidence dans la succession glaciaire de l’Ordovicien supérieur au NE du bassin d’Illizi sur la base des données sismiques de haute résolution. Pour chaque incision, la géométrie ainsi que les faciès sismiques de leur remplissage ont été déterminés. Un parallélisme entre la distribution de certaines paléovallées et l'orientation des anomalies magnétiques a été observé, mais aucune relation stratigraphique entre ces structures n'a été identifiée sur les sections sismiques. Un réseau complexe de vallées tunnel glaciaires du Pléistocène en mer du Nord a été identifié sur la base de données aéromagnétiques à haute résolution. Une analyse magnétique détaillée a été réalisée en combinant plusieurs méthodes magnétiques. A la fin, des modèles magnétiques synthétiques 2D ont été calculés pour les incisions ordoviciennes, appliqué pour le cas du bassin d’Illizi. Les résultats obtenus montrent que leur détection magnétique est possible, si toutes fois un levé magnétique à haute résolution serait disponible. / The magnetic and gravimetric data analysis of the northern part of the trans-saharan belt allowed to propose a geophysical and rheological compartmentalization map of its crustal structures and to visualize the Tuareg shield terranes over 1000 km to the north, under the saharan sedimentary basins and several aspects have been discussed. A pseudo network of four successive generations of paleovalleys and incisions has been identified on the upper Ordovician glacial succession in the north-eastern part of the Illizi basin on the basis of high-resolution seismic data. For each incision, the geometry and seismic facies of their filling have been determined. Parallelism between the distribution of some paleovalleys and magnetic anomaly orientations has been observed, but no stratigraphic relationship between them has been identified on seismic sections. A complex network of Pleistocene glacial tunnel valleys in the North Sea has been identified on the basis of high-resolution aeromagnetic data. A detailed magnetic analysis was performed by combining several magnetic methods. Finally, 2D synthetic magnetic models were calculated for Ordovician incisions, applied in the case of the Illizi basin. The results obtained show that their magnetic detection is possible, if a high-resolution magnetic survey would still be available.

The tectonic significance and age of carbonatite intrusions in the western Foreland Belt of the Canadian Cordillera are poorly constrained. Recent 1:5,000 scale field mapping of one of these carbonatite intrusions, the Aley carbonatite (NTS 94 B/5), has demonstrated that it was emplaced as a syn-kinematic sill, coeval with a major nappe-forming tectonic event. Determining the age of the Aley carbonatite therefore provides a means of directly dating tectonism related to carbonatite magmatism. A U-Pb titanite age of 365.9 +/- 2.1 Ma was obtained from the Ospika pipe, an ultramafic diatreme spatially and genetically related to the carbonatite. We interpret the Late Devonian age of the Ospika pipe to be the minimum possible age of the carbonatite and syn-magmatic nappe-forming tectonic event. The maximum possible age of the carbonatite is constrained by the Early Devonian age of the Road River Group (ca. 410 Ma), the youngest strata intruded by carbonatite dykes and involved in the nappe forming event. Our dating results for the Aley carbonatite closely correlate with U-Pb zircon and perovskite ages obtained for the Ice River carbonatite complex in the western Foreland Belt of the southern Canadian Cordillera, and support the interpretation of carbonatite intrusions of the western Foreland Belt as genetically linked components of an alkaline-carbonatitic magmatic province. Structural, stratigraphic, and geochronological data from the Aley area indicate that deformation was similar in style to, and coeval with, structures attributable to the Antler Orogeny, and are consistent with the Antler orogen having extended the length of Cordilleran margin from the southern United States to Alaska. Deformed alkaline-carbonatite intrusions that characterize continental suture zones in Africa and Tibet may provide an analogue for the Aley carbonatite and correlative alkaline-carbonatite complexes in the western Foreland Belt. / Graduate / 0372 / mcleish@uvic.ca