The south-west portion of the main caldera was mapped and a stratigraphy for the caldera-fill was constructed. The exact timing of formation of the main caldera is unclear; However, caldera collapse either predates or was synchronous with the eruption of the Campagnola Tuff. The proximal facies of the Campagnola Tuff exists as a complex relation of ignimbrite, lithic breccia and pyroclastic surge deposits. Overlying this the Galluccio Tuff a compound ignimbrite, ~6 km3 D.R.E, forms the base of the exposed caldera fill. Caldera lakes then became well established and following activity was predominantly phreatomagmatic. Pyroclastic surge deposits possess sand wave structures of several types and their migration direction was apparently controlled by the velocity/flow regime of the surge rather than the moisutre content. The morphology of juvenile clasts from phreatomagmatic deposits indicates that the eruptions were driven by a combination of vesiculation and magma/water interaction. The uppermost pyroclastic deposits are thought to represent the early phase of dome building where water still had access to the vent. The construction of the lava domes brought activity to a close within the main caldera. The Galluccio Tuff on the flanks of the volcano may be divided into three compositionally distinct eruptive units. The Lower Galluccio Tuff, correlated with the bulk of the Galluccio Tuff filling the main caldera. The Middle Galluccio Tuff commenced with the eruption of pumice-rich pyroclastic flows followed by flows enriched in both the size and amount of lithic fragments forming lithic-rich ignimbrite and co-ignimbrite lithic breccias of which several types exist. The Upper Galluccio Tuff is composed of lithic-rich ignimbrite which possess dense pumice fragments and are thought to be the product of a combination of both vesiculation and magma water interaction. Field relations indicate that pyroclastic flows were sometimes generated in quick succession and may have overrun earlier slower moving flows. Occasionally internal shear may have caused the overriding of portions of the same flow, these often coincide with lithic breccias and represent the climax of the eruptive phases. The grading of lithic fragments indicates that the expansion and fluidization decreased and yield strength increased with time in a pyroclastic flow.

The aim of this study is to investigate the petrography, geochemistry and evolution of quartz-tourmaline-rich rocks occurring in a wide breccia zone within the Late Cretaceous Kerkenez Granitoid (Central Anatolian Crystalline Complex (CACC), Turkey). The approximately 40-m wide main breccia zone has a NE-SW trend and is characterized by intense cataclastic deformation. The breccia zone can be traced several kilometers towards the west and generally occurs as tourmaline-filled faults and 1mm-30cm-thick veins within the granitoid. On the basis of mineralogical and textural features, rocks within this zone are defined as tourmaline veins, tourmaline-breccias and quartz-tourmaline rocks. These rocks are generally composed of quartz, tourmaline and granitic fragments. Petrographical investigations and electron-microprobe analyses indicate that, there are three optically and chemically different tourmaline generations. From oldest to youngest, the tourmalines are classified as blue pleochroic feruvites, blue-green pleochroic schorls and green-light green pleochroic schorls. The chemistry of the tourmalines suggests that these tourmalines crystallized from boron rich fluids derived from an evolving magma. Consequently, the quartz tourmaline-breccia zone is considered to have formed by the injection of overpressured boron rich fluids into faults and fractures present within the Kerkenez Granitoid. Fluid-filled faults and fractures were sealed by quartz-tourmaline crystallization. This led to further fractionation in the magma, new fluid pressure accumulations, reactivation of faults and crystallization of different tourmaline generations. Tourmaline-breccia zones are scarce in the literature and the presence of such rocks within the CACC is first reported in this study.

Thesis (M.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 153-163). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Four folded plates in pocket. Includes bibliographical references (leaves 285-303). Available also in a digital version from Dissertation Abstracts.

Thesis (M.Sc.) -- Memorial University of Newfoundland. / Typescript. Bibliography : leaves 266-289. Also available online.

<p> SE Botswana, located in the NW part of the Kaapvaal Craton is a long lived tectonically stable environment dominated by brittle deformation for more than 2.6 Ga. </p> <p> Relative chronologies in the development of fractures are rationalized according to major unconformities that developed during the Proterozoic in areas around Moshaneng and Kanye in SE Botswana. Periods of brittle deformation are divided into pre-Transvaal Supergroup, post-Transvaal Supergroup/ pre-Waterberg Group and post-Waterberg Group times. Pre-Transvaal lineaments trend ENE and NE and were probably formed as fractures in a rifting environment Dikes are intruded along some of these lineaments. Post-Transvaal/ pre-Waterberg fractures consist of strike-slip faults that form a conjugate system of two major sets trending NE and NW. These fractures probably formed as a result of E-W compression. The displacement along the NE trending faults depicts reactivation along pre-existing fractures. Regional patterns of fault termination are discemable. Epidermal folds and thrusts were produced in the Transvaal Supergroup rocks. Rotational bulk strain is locally significant. PostWaterberg deformation was dominated by dip-slip faults, vertical displacements and drape folds. </p> <p> An orthogonal system of bedding-normal joints predominates in the layered rocks. Inversion of the relative magnitudes of a2 and a3 probably accounts for a two phase tensile failure of layered rocks during the formation of the joint system. A diagonal system of bedding normal joints is superimposed on the orthogonal system possibly because of pre-existing folds that perturb the remote stress field. Joint spacings have a negatively skewed normal frequency distribution. Systematic joints show that spacing of set1 <set2 <set3 <set4. </p> <p> Relics of joint patterns in chert breccia provide insight about post-Transvaal/ pre-Waterberg karstification residuum. The joint pattern accounts for the initial process of fragmentation that resulted in the formation of chert breccia. </p> <p> On the subcontinental scale, high strain tectonic belts provide a chronology of large scale stress fields that could explain the intracratonic brittle deformations. </p> / Thesis / Doctor of Philosophy (PhD)

In the northern part of Swedish Caledonides, north of Lake Torneträsk is a 7 km long exposure of a breccia layer. The layer thins westwards and eastwards from the central part where it is up to 27 m thick. It is called the Vakkejokk Breccia after the type section. The breccia has been described in literature since about a century, but its origin is enigmatic. The breccia layer is since the summer of 2012 investigated by three geologists specialized in impact craters, Paleozoic sediments, and the Caledonian orogeny. They put forward evidence for the breccia being formed by a hypervelocity impact during the Lower Cambrian at approximately 520 Ma (Ormö et al. 2017). At that time the target area was a shallow epicontinental sea that surrounded the mainly peneplanized continent Baltica. An impact into the sea is known to generate tsunami waves as well as resurge deposits when the water brings ejected and rip-up material back into the crater. Ormö et al. (2017) suggest the top part of the Vakkejokk Breccia to include such resurge deposits. The depositional marine environment is also known to rapidly protect an impact crater from further erosion. It is possible that only the topographic rim of the Vakkejokk crater was eroded during the millions of years it may have taken before the crater was covered by younger sediments. About 100 m.y. after the formation, it was completely covered by overthrust nappes during the Caledonian orogeny, when Baltica and Laurentia collided. The crater itself is not exposed today, merely parts of what is thought to be the ejecta layer and resurge deposits. This Bachelor of Science project aimed to investigate the putative resurge deposits to learn more about the process of formation and the provenance in the target of the clasts in the deposits. This was carried out by three short drillcores through the resurge deposit part of the Vakkejokk Breccia layer. The place to drill the boreholes was chosen at an outcrop which is proximal to the putative hidden crater. The retrieved drillcores were cut longitudinally, then polished and photographed in high resolution. Each core was then analyzed in an image analysis software with respect to clast granulometry and lithology. To the results are presented as graphs showing clast size, size sorting, clast shape, of the relative amounts of different lithologies and the matrix content. The results are discussed with respect to well-documented analogue marine-target craters

M.Sc. (Geology) / Three anomalous borehole core sequences from the north eastern Karoo Basin are examined. The boreholes are located up to 30 km from each other and are lithostratigraphically completely atypical for the Vryheid Formation, Ecca Group, Karoo Supergroup. The lithologies of the three boreholes are intensely brecciated for the most part, while all of the surrounding boreholes reveal normal stratigraphy; their sedimentary strata are normally horizontal with no faulting present. The only known disturbances to the Vryheid Formation in the study area are the occurrence of intrusive mafic dolerite sills and dykes, which are known to have been contemporaneous with and immediately following the eruption of the Drakensburg Group basaltic lavas. The borehole core lithologies are described in detail with reference to their textural, mineralogical and petrographic characteristics. Mineral and bulk rock chemical data are presented. Several modes of origin of the brecciated core sequences are considered, with the primary hypothesis that the brecciation is due to diatreme activity. A review of diatremes and their mode of emplacement is proposed with reference to their occurrence within the Karoo Igneous Province, as some diatremes in the Karoo are associated with dolerite sill emplacement. The isolated occurrences, lithologies, petrography, alteration and geochemistry of the sequences are used to argue that the Vryheid Formation, intersected in the form of the three anomalous boreholes, was disturbed by diatreme activity, which are genetically related to the late dolerite sill emplacement into the Karoo Supergroup rocks.

Les séismes intermédiaires (40-325 km de profondeur) ont été largement documentés dans les plaques océanique en subduction mais leur mécanismes déclencheurs restent énigmatiques et très peu compris en raison (I) des incertitudes instrumentales sur l'acquisition des données géophysiques et (II) de la rareté des exemples de roches métamorphisées dans des conditions du faciès éclogites et préservant (sans ambiguïté) les structures produites par des séismes intermédiaires. Bien que toujours limité, il y a de plus en plus de preuves que les lambeaux « fossiles » de lithosphère océanique exhumée de taille pluri-kilométrique peuvent enregistrer les processus chimiques et mécaniques caractéristiques de la sismicité de profondeur intermédiaire. Ce projet de doctorat étudie l'impact de la libération et de l'infiltration des fluides métamorphiques sur la génération des brèches éclogitiques disséminées dans une zone de cisaillement de 15 km de long, exposée dans un fragment presqu’intact de lithosphère océanique Tethysienne, subduite jusqu'à 80 km de profondeur (2.6 GPa - 550 ° C, unité du Lago Superiore): le complexe métaophiolitique du Mont Viso (W Alps, Italie). Trois zones de cisaillement majeures ont été étudiées, et en particulier la Lower Shear Zone (LSZ), dans laquelle des blocs de métagabbros mylonitiques éclogitisés et brechifiés (potentiellement lors d’une phase sismique) sont dispersés, avec des blocs métasédimentaires, dans la matrice serpentineuse de la zone de cisaillement.Dans cette dernière zone de cisaillement, une attention particulière a été portée à la caractérisation pétrologique et structurale de 196 blocs exhibant ces brèches (dans lesquels plus de 100 échantillons ont été récoltés), notamment à travers l’étude (i) de leur répartition dans la zone de cisaillement et (ii) de leurs caractéristiques morphologiques (longueur, largeur, hauteur, volumétrie relative de la matrice par rapport aux clastes et nature des clastes). Ces données ont été synthétisées dans une nouvelle carte géologique détaillée des méta-ophiolites du Mont Viso à l’échelle 1 : 20.000. L’étude pétro-structurale a permis de montrer que la formation des brèches résulte de passages transitoires de la déformation ductile à cassante dans le faciès éclogitique, comme le montre la foliation mylonitique dues métagabbros (composée de l’assemblage omphacite + rutile ± grenat et quartz) recoupé par des plans de brèches cimentées par des matrices riches en omphacite ± grenat et lawsonite. Elle montre également que la formation des brèches n'est pas liée à des événements pré-alpins (brèches sédimentaires ou tectoniques superficielles) comme d’autres auteurs l’ont proposé (Balestro et al. 2013; Festa et al. 2015). L'analyse des éléments en trace (in-situ et dans la roche totale), en lien avec une caractérisation rigoureuse des microstructures dans les blocs de brèches, a permis de mettre en évidence un changement progressif des fluides circulant pendant la bréchification. Les premières ruptures fragiles (locales, M1) ont été déclenchées par des fluides dérivés localement (e.g. metagabbros) avec une injection progressive de fluides «exotiques» (dérivés de la déshydratation de serpentinite) provoquant la bréchification dans l'intégralité des LSZ and ISZ (avec la cristallisation de M2 et M3). En raison de l'extension limitée des affleurements, l'origine sismique des brèches eclogitiques reste spéculative. Néanmoins, plusieurs preuves (par exemple, les minéraux fracturés et décalés le long des niveaux micrométriques riches en omphacite) suggèrent que les brèches d'eclogite du Monviso ont été générées par rupture fragile instantanée. / Intermediate-depth earthquakes (40-325 km depth) have been extensively documented within subducting oceanic slab but their triggering mechanisms remain enigmatic due to (I) the instrumental uncertainties on geophysical data acquisition and (II) the scarcity of examples of exhumed (and unambiguously recognized) eclogite-facies earthquake-derived rocks. Although still limited, there is growing evidence that large-scale, “fossil” exhumed portions of subducted lithosphere may record both chemical and mechanical processes operating in the depth range of intermediate-depth seismicity. This thesis project investigates the role of metamorphic fluids in the formation of the eclogitic breccias (resulting from potentially seismic deformation) found in a 15 km-long shear zone developed in an almost intact fragment of Tethyan oceanic lithosphere metamorphosed to eclogite-facies peak metamorphic conditions (2.6 GPa - 550 °C) during Alpine subduction: the Monviso metaophiolite complex (W. Alps). Three major shear zones cutting across the complex at low angle were studied, with a major focus on the Lower Shear Zone -LSZ-, where blocks of variably brecciated (and potentially seismically-derived) Fe-Ti and Mg-Al metagabbros are embedded, together with metasedimentary blocks, in a talc and tremolite-rich serpentinite matrix. Particular attention was paid to the petrological and structural characterization of 196 breccia blocks (in which more than 100 samples were collected), with (i) detailed analysis and mapping of their distribution in the LSZ and (ii) morphological characterization (block size, relative volume of matrix with respect to clasts and matrix-clast composition). These data have been synthesized in a new detailed geological map of Monviso meta-ophiolite at a scale of 1: 20,000. The mylonitic foliation of intact Mg-Al-rich metagabbros (composed of omphacite + rutile ± ex-lawsonite ± quartz and locally garnet) cut by breccia planes (cemented by omphacite + garnet ± ex-lawsonite) univocally indicates brecciation at eclogite facies conditions. In the breccias the occurrence of a first omphacite-rich matrix (M1) cut by a second matrix rich in garnet + lawsonite pseudomorphs (M2) witnesses multiple brittle rupture events (probably shortly spaced in time) prior to a stage of massive eclogite facies fluid ingression (matrix M3). Trace elements analysis (in-situ and bulk) coupled to rigorous microstructural characterization of samples suggest a progressive change of fluids circulating during the brecciation. First brittle event M1 was triggered by locally-buffered fluids (e.g., from metagabbros) with later ingression of “exotic” fluids (e.g., from serpentinites) triggering the brecciation events M2 and M3. Due to the limited extension of outcrops, the coseismic origin of the eclogitic breccia remains somehow speculative; nevertheless several evidences (e.g., minerals fractured and offset along omphacite-bearing planes) suggest that Monviso eclogite breccias were generated by instantaneous brittle rupture.

No description available.