L’objectif principal de cette thèse est de décrire et interpréter la mise en place des différents types de minéralisations présents dans le district minier de Nefza (NO de la Tunisie), qui constitue une région complexe et particulière du point de vue géologique dans ce pays. En effet, outre la présence de diapirs triasiques (commune à tout le Nord de la Tunisie), le district minier de Nefza est caractérisé par : (1) la mise en place d’épaisses nappes au Néogène qui forment le substratum sédimentaire régional, et (2) la présence d’une grande variété de roches magmatiques tant plutoniques que volcaniques, d’âge miocène (12,9 à 6,4 Ma),: - la granodiorite de l’Oued Bélif, qui est liée à l’évolution d’un magma calco-alcalin contaminé par la croûte ; - les rhyodacites de Aïn Deflaia, de l’Oued Bélif et du Jebel Haddada, qui résultent du mélange entre ce magma calco-alcalin et un magma de fusion crustale ; - les basaltes de Mokta el Hadid marquant la transition vers un magmatisme alcalin. A proximité des roches magmatiques – et en relation avec ces dernières – on observe différents types de minéralisation, riches en Fe, en Fe-Cu-Au, et en Pb-Zn. Parmi ces minéralisations, ce travail a permis de reconnaître : - un gisement (de volume réduit) de type « Iron Oxide Copper Gold » (IOCG), qui minéralise la brèche de l’Oued Bélif, datée du Miocène supérieur. Le minerai ferrifère (hématite et goethite), riche en F, Cu, REE, U et Au, cimente des clastes de taille variable et de nature principalement triasique ; - deux gisements (de volume modeste) de Pb-Zn, de type « sedimentary exhalative » (Sedex) qui prennent place dans lentilles carbonatées des bassins d’âge miocène supérieur de Sidi Driss et de Douahria. Les minéralisations syndiagénétiques (messiniennes) à galène, sphalérite sphérulitique et pyrite, remplacent : (1) des calcites riches en Fe-Mn et (2) des sulfates (barytine et célestine) qui remplacent eux-mêmes de façon précoce les carbonates (avant la mise en place des sulfures) ; - un gisement économique d’oxydes de Fe de type latéritique (mine de Tamra, minerais datés du Mio-Pliocène), qui résulte vraisemblablement de plusieurs épisodes de reconcentration du fer, en conditions pédogénétiques. Ce minerai enregistre également des apports hydrothermaux qui mènent, entre autres, à la précipitation de minéralisations riches en Mn, Pb, Zn et Ba. Ces unités géologiques sont étroitement liées au contexte géodynamique particulier du Nord de la Tunisie au Néogène. Ce dernier passe d’un régime compressif au Serravallien-Tortonien, qui voit la mise en place des roches magmatiques felsiques, à un régime extensif qui, à partir du Messinien (fini-Tortonien ?), se marque par la mise en place de basaltes et une augmentation du gradient thermique régional. Ce régime extensif favorise/active la circulation de fluides hydrothermaux et leur enrichissement en métaux au contact des formations constitutives du substratum régional. Ces fluides, mélangés aux fluides superficiels (localement riches en soufre au Messinien), mèneraient au dépôt de la plupart des minéralisations observées.

The first section of this work examines melt inclusions in phenocrysts from Volcán Popocatépetl and Volcán de Colima within the Trans Mexican Volcanic Belt (TMVB). These inclusions are dacitic to rhyolitic. Trends in melt inclusion major element and water concentrations form the evolved extension of other Mexican volcanics including those presumably derived directly from primitive melts. Water concentrations in Popocatépetl and Colima melt inclusions are similar (0.3 to 3.4 weight percent Hsub2O). Melt-vapor equilibration pressures calculated from dissolved Hsub2O and COsub2 (Popocatépetl) or Hsub2O (Colima) in melt inclusions correspond to depths of entrapment of 12 km or less. Water and carbon dioxide concentrations correlate negatively with SiOsub2 and potassium. Normalized olivine-augite-quartz compositions are consistent with near cotectic crystallization under vapor-saturated conditions at pressures of 1.5 kb or less. Our results show that Popocatépetl and Colima magmas have undergone vapor-saturated crystallization during ascent in conjunction with varying degrees of mixing between degassed rhyo-dacitic and less degassed, mafic melts in the upper portions of the crust. These data suggest melt evolution occurred in conduits or inter-fingered dikes rather than a large stratified magma chamber. Part II looks at the Masaya caldera in Nicaragua. This volcano has erupted frequently in recorded history, producing lava lakes and very high gas emissions. Melt inclusions from Masaya are basaltic, with low Hsub2O (below 0.5 wt. %), low S (less than 300 ppm) and high COsub2 concentrations (up to approximately 6000 ppm). Relationships between water, sulfur, Cl and F in combination with Masaya's high COsub2 and Ba/Zr and Ba/Nb ratios suggest that Masaya has undergone a multi stage degassing process involving 1) shallow degassing, 2) recycling of magma into a deeper reservoir, and 3) fluxing of previously degassed magma with a nearly pure COsub2 vapor. Trace element signatures of melt inclusions are consistent with contributions that have been variably metasomatized by fluids generated by dehydration of subducted sediments and/or altered oceanic crust.

The Toba caldera located in north Sumatra, Indonesia, is the source of the largest volcanic eruption in the Quaternary (Rose & Chesner 1987). Its enormous volume of 2800 km3 has been a matter of debate for decades and it is still unclear where and how the Toba magma was assembled. This study documents oxygen isotope data for a suite of whole rocks and minerals erupted as part of the Young Toba Tuff (YTT), some 74 ka ago (cf. Chesner et al. 1991). Oxygen isotope data has been obtained in-situ from quartz crystals (SIMS), whole rocks (conventional), as well as quartz, feldspar, amphibole and biotite (laser fluorination). In combination with cathodoluminescence (CL) imaging on the quartzes, the data are used to test the relative roles of shallow magmatic processes such as crystal fractionation, magma-crust interaction and crystal recycling within the Toba magmatic system. In addition, thermobarometric calculations have been performed on plagioclase and amphibole phenocrysts from the YTT to help unravel the magma storage and plumbing system that gave rise to the YTT. The combined evidence will be used to derive a model for shallow magma evolution and storage at Toba some 74 ka ago. The CL images of quartz crystals exhibit defined patterns of magmatic zoning, which broadly coincide with fluctuations in δ18O values in the quartz crystals, allowing correlation of textural and compositional data. Measured δ18Oquartz values range from 6.7 ‰ to 9.4 ‰, independent of position on crystal core or rim. Values for δ18Omagma have been calculated from quartz phenocrysts (assuming Δquartz-magma is 0.7 ‰ at magmatic temperatures). The lowest magma value is 6.0 ‰, apparently reflecting a primitive isotopic signal (Taylor & Sheppard 1986). The maximum calculated magma value is 8.7 ‰, indicating a significant crustal component and thus multiple sources to the Toba magmatic system. Several crystals, however, show internal zoning with gradually lower values towards the rims, pointing to a late-stage low-δ18O input, most probably from the shallow volcanic edifice. The crystals therefore record a complex and heterogeneous origin of the YTT magma, comprising a primitive and an evolved magmatic component topped up with several substantial crustal contributions to finally assemble the massive volume of the 74 ka Toba eruption.

Η εργασία αυτή έχει ως αντικείμενο τη διερεύνηση των τεχνικογεωλογικών συνθηκών με σκοπό την αναζήτηση βραχωδών υλικών ,έπειτα τα από εργαστηριακές δοκιμές ,για ταξινόμησή τους και καταλληλόλητας τους ή μη, ώστε να μπορούν να χρησιμοποιηθούν ως αδρανή υλικά για διάφορες χρήσεις / This work is intended to investigate the geotechnical conditions in pursuit of rocky material, after laboratory tests for classification and Suitability or not, so they can be used as aggregates for various uses.

During the Paleoproterozoic Era (ca. 2.5 Ga to 1.6 Ga), Earth underwent dramatic changes to its tectonic and atmospheric parameters. These changes included: the formation and breakup of the supercontinent Nuna (Columbia) and the gradual rise in atmospheric oxygen levels. The gradual rise in atmospheric oxygen, referred to as the Great Oxidation Event (GOE), altered the behaviour of silicate mineral weathering, and permitted the formation of new types of economic uranium deposits. Beaverlodge Lake, Northwest Territories (NT), allows for the study of a weathering profile and uranium mineralization post GOE. At Beaverlodge Lake, NT, a regolith is preserved in a rhyodacitic porphyry of the ca. 1.93 Ga Hottah plutonic complex, which is unconformably overlain by the ca. 1.9 Ga quartz arenite of the Conjuror Bay Formation. Coincident with the unconformity is a past-producing uranium deposit (called the Tatie U deposit), which was mined out in the 1930s. Other uranium showings have been discovered at Beaverlodge Lake including the Bee showing. The initial purpose of this project was to examine the regolith through field, petrography, electron microprobe analysis (EMPA), whole-rock geochemistry, and mass balance calculations. The weathering profile shows an increase in Al2O3, Fe2O3T, K2O, P2O5, Ba, and Rb, a loss in SiO2, Na2O, MgO, and Sr, and constant and low abundance of CaO. Titanium remains constant in the weathering profile. Rare earth element (REE) analysis reveals remobilization of light REE (LREE) on a micrometer scale, but no cerium anomaly is preserved in the weathering profile. The weathering profile displays characteristics similar to other post GOE paleoweathering profiles developed on felsic parental material. The timing of uranium mineralization at Tatie and Bee was constrained by in-situ U-Pb uraninite dating by Secondary Ion Mass Spectrometer (SIMS), which yielded two variably discordant ages of 1370.2 ± 7.9 Ma and 407 ± 21 Ma. In addition, REE contents of uraninite were determined by in-situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Results revealed two types of uraninite mineralization are preserved at Beaverlodge Lake and they consist of synmetamorphic at Bee and basement-hosted unconformity-type at Tatie similar to those in the Athabasca Basin. The ca. 1370 Ma uraninite (Tatie) is characterized by an asymmetric bell-shaped REE pattern centered on Tb to Er where LREEs are depleted compared to heavy REEs (HREE). The ca. 407 Ma uraninite at Bee has low La concentrations and a flat to slightly negative REE pattern. The Mesoproterozoic age is similar to a Pb loss age of ca. 1400 Ma found in the Athabasca Basin. The younger Devonian age may be related to meteoric fluids cycling and uranium remobilization during the Phanerozoic.

Volatiles (H2O, CO2, S, Cl) play a key role in magmatic processes at subduction zones. In this study, the dissolved volatile contents of olivine-hosted melt inclusions from cinder cones in the Lassen segment of the Cascade arc are used to investigate dehydration of subducted oceanic lithosphere, magma formation in the sub-arc mantle wedge, and mafic magma storage and evolution in the crust. Relatively young, hot oceanic lithosphere subducts beneath the Cascade arc. The hydrogen-isotope and trace-element compositions of melt inclusions, when integrated with thermo-petrologic modeling, demonstrate that fluids in Cascade magmas are sourced from hydrated peridotite in the deep slab interior and that the oceanic crustal part of the slab extensively dehydrates beneath the forearc. In contrast to their slab-derived H, the melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), requiring little to no slab contribution of B, which is also consistent with extensive dehydration of the downgoing plate before it reaches sub-arc depths. Correlations of volatile and trace element ratios in the melt inclusions (H2O/Ce, Cl/Nb, Sr/Nd) demonstrate that geochemical variability in the magmas is the result of variable amounts of addition of a hydrous subduction component to the mantle wedge. Radiogenic isotope ratios require that the subduction component has less radiogenic Sr and Pb and more radiogenic Nd than the Lassen sub-arc mantle and is therefore likely to be a partial melt of subducted Gorda MORB. These results provide evidence that chlorite-derived fluids from the deep slab interior flux-melt the oceanic crust, producing hydrous slab melts that migrate into the overlying mantle, where they react with peridotite to induce further melting. The basaltic magmas that erupted at Cinder Cone near Mt. Lassen trapped melt inclusions during olivine crystallization at ~7-15 km depth. The melt inclusion compositions require that two different mantle-derived magmas were involved in the eruption, and temporal changes show that arrival of the two batches correlates with two explosive phases of activity. Both magmas experienced rapid crustal contamination before erupting, illustrating the complexities of cinder cone eruptions. This dissertation includes previously published and unpublished co-authored material.

>Magister Scientiae - MSc / The Sea Point contact, Cape Town, South Africa, exposes the contact between the Neoproterozoic Malmesbury Group metasedimentary rocks of the Pan-African Saldania belt and the intrusive S-type Peninsula Granite of the Neoproterozoic-Paleozoic Cape Granite Suite (CGS). The exposure outcrops over an area of approximately 170 m × 60 m with the northern end of the exposure being characterized by the country rock–microgranite intrusive contact. Heading further south, the outcrop transitions to the main contact zone, which is a predominantly gradational zone marked by sheets of compositionally variable granitic injections (collectively referred to as hybrid granite phases) concordant to the country rock structure, before reaching the main pluton area comprising the voluminous coarse-grained porphyritic granite. Using a combined study incorporating field, structural, geochemical, isotopic and U-Pb geochronological data, the intrusive contact is investigated to determine the construction history of the pluton and delineate possible emplacement mechanisms.

The Higganum dike of Connecticut is one of the earliest basaltic dikes of the Central Atlantic Magmatic province and is geochemically representative of the widespread low-Ti basaltic lavas (~1 wt % TiO2) that make up the majority of the province in North America. Liquid compositions calculated from Cr-rich clinopyroxene cores from the Higganum dike are significantly more primitive than the bulk rock with average Mg# s of 0.63 compared to the Higganum dike which has Mg #'s ~ 0.55. However, the negative Nb and positive Pb anomalies that are seen in trace element patterns of the low-Ti group are also found in the liquids calculated from the Cr-rich clinopyroxene cores. Ca-rich plagioclase cores that probably come up from depth with the Cr-rich clinopyroxenes were found to be more radiogenic than bulk Earth with 87Sr/86Sri ratios ranging from 0.7057 to 0.7064. We conclude that this enriched isotopic signature and the trace element signatures of primitive liquids calculated from clinopyroxene are inherited from the source. This source is identified as a subduction-enriched metasomatized lithospheric mantle. High-Ti magmas (~2-5 wt % TiO2) that are limited to a small geographic area of the Central Atlantic Magmatic Province were found to be unrelated to the low-Ti magmas. These two groups probably originated from different degrees of partial melting of different sources and follow distinctive differentiation paths.

<p> New U-Pb ages from the Barberton Mountain Land document an 800 m.y. period of Archean magmatism (ca. 3540 Ma to ca. 2740 Ma) that can be divided into five distinct episodes. Magmatic activity during Episode I includes tonalite-trondhjemite gneisses such as the Steynsdorp pluton (3509 +8/-7 Ma) and a tectonically interleaved sliver (3538 +4/-2 Ma) located at the base of the Onverwacht Group. Trondhjemitic magmatism of Episode II is synchronous with volcanism and inferred D1 thrusting of the Onverwacht Group and is represented by plutons such as the Doornhoek (3448 ± 4 Ma), Theespruit (3443 +4/-3 Ma), and Stolzburg (3459 +5/-4 Ma). A quartz-feldspar porphyry dyke, related to Episode II, intrudes the Komati Formation of the Onverwacht Group and yields an age of 3467 +12/-7 Ma. D2-related thrusting, volcanism, sedimentation, and tonalitic plutonism in the north-central part of the Barberton greenstone belt (BGB) occurred during Episode III and are recorded by an ignimbrite which was deposited between the Fig Tree and Moodies Groups during regional deformation (3227 ± 1 Ma), by pre- and post-tectonic porphyries (3227 Ma), and by the emplacement of the Kaap Valley tonalite (3227 ± 1 Ma). Episode IV is characterized by the intrusion of large sheet-like potassic batholiths to the north and south of the BGB and syenitic plutonism at ca. 3107 Ma, and by D3-related deformation at the northern margin of the BGB. Gold mineralization also appears to coincide in time with this episode. The last known period of Archean magmatic activity in the BGB is represented by late phase granite magmatism at ca. 2740 Ma (Episode V).</p> <p> Epsilon Nd values range from +1.3 to -0.7 in rocks varying in composition from gabbro to granodiorite that were emplaced during Episodes I to IV. A gabbro from the Komati Formation, with a baddeleyite age of 3352 +6/-5 Ma, has an ϵNd of +1.3, which is the only value to fall on a depleted mantle growth curve. This value is similar to ϵNd data obtained by others for ca. 3450 Ma basalts from the Onverwacht Group. Three Episode IV plutons have identical ϵNd values of -0.5, and a granite pluton from Episode V has an ϵNd of -4.3, indicating a source compatible with remelting of older crust.</p> <p> In summary, the protracted evolution of the Barberton Mountain Land occurred in a series of discrete events widely separated in time. Each event is characterized by a number of geological processes (magmatism, volcanism, sedimentation) that appear to coincide in time with thrust-related deformation as a result of compressional tectonics. The duration of the main period of crustal growth occurred over ≈365 m.y. from ca. 3470 Ma, with the formation of the main Onverwacht sequence and its associated tonalitic-trondhjemitic rocks through ca. 3230 Ma, with the intrusion of the Kaap Valley tonalite and D2 thrust-related deformation, to ca. 3105 Ma, with the widespread emplacement of sheet-like potassic batholiths bordering the Barberton greenstone belt.</p> / Thesis / Master of Science (MSc)

<p> Nine rock samples from the mafic volcanics of Mamainse Point, Ontario were analysed for boron using Prompt Gamma Neutron Activation Analysis (PGNAA) and Alpha-Track Imaging (ATI). The mean concentration of boron in these rocks was 7.85 ppm with a maximum concentration of 15.5 ppm and a minimum concentration of 4.21 ppm. The Mamainse Point samples are therefore enriched in boron relative to fresh basalts (~ 2 ppm B) but depleted relative to basalts altered on the seafloor (30 - 60 ppm B). From ATI the boron was found to be most highly concentrated in iron oxides, chlorite, stilpnomelane and microscopic fractures throughout the rock. Plagioclase, clinopyroxene, quartz and calcite were all low in boron.</p> <p> These results led to the conclusion that the Mamainse Point Formation is of continental rather than marine origin. The addition of boron to the rock has resulted from penecontemporaneous burial and hydrothermal metamorphism in the zeolite and subgreenschist facies through the interaction of boron-bearing hydrothermal fluids. The source of the boron is thought to be from the surrounding Precambrian terrain (Canadian Shield), the lower continental crust and magmatic fluids associated with volcanism.</p> / Thesis / Bachelor of Science (BSc)