Of the ten Tertiary and pre-Tertiary alkaline igneous centres in Eastern Uganda, three (Budeda, Tororo and Toror) are described in this thesis, and a summary of a fourth (Napak) is presented. The earliest intrusive rock at Budeda and Napak is melteigite/pyroxenite which in both areas becomes converted to variable ijolite by replacement in the form of diffuse patches and well-defined veins. Melanite, wollastonite and calcite are characteristic of later phases of ijolite at Napak and Tororo. Nepheline syenites are produced by the development of feldspar in the marginal zone of the ijolites. At Budeda, cancrinite and calcite also occur in these rocks. They show intrusive relations with the fenites but are gradational towards the ijolite. At Napak, the cancrinite syenites and related feldspathic types occur as dyke-like masses within the ijolite. Feldspathization also affects the mixed rocks of the agglomerate (including ijolite and nepheline syenite) adjacent to the carbonatite at Tororo, locally producing orthoclasites. At Toror, the gneisses around the carbonatite are in places converted to feldspathic fenites (potash-feldspar rocks). Feldspathic breccias and intrusive rocks of similar composition (about 12% K2O) include trachytes, which evidently represent the mobilized products. The carbonatite at Budeda is a small mass formed by the replacement of melteigite, but at the other complexes it is clearly intrusive. Pyroxene, biotite and magnetite are considered to be derived from assimilated silicate rocks. Around the intrusive complexes fenites were formed by alkali metasomatism of the Basement. At Budeda syenitic fenites are widely developed, and have a foliated character which is related to early crushing. Locally the Budeda fenites are nepheline-bearing; they are also extensively feldspathized. The writer finds no direct evidence (with the exception of the trachytes) of mobilization of fenites to give rocks of the intrusive series. The intrusive rocks are considered to be derived from a melanephelinite magma, which by differentiation and the retention of volatiles led ultimately to the formation of a carbonatite residuum.

The Husfjord area of Soroy essentially comprises a plutonic igneous complex which has been emplaced into Eocambrian meta sediments during the Caledonian orogeney. The metasedimentary envelope of the complex consists mainly of a sequence of psammites, pelites, semi-pelites, calc-silicate-schists, and metalimestones, which have suffered a prolonged regional metamorphism and two principal episodes of deformation. The regional metamorphic event commenced before the first folding episode, reached its peak in the almandine-amphibolite facies between the deformation episodes, and waned during the second period of folding. The various members of the igneous complex were emplaced synchronous with these metamorphic and tectonic events. Contact metamorphie effects produced by some members have been superimposed upon those of the regional metamorphism. The earliest member, the Husfjord metagabbro, was intruded towards the end of the first deformation episode, and has undergone the highest grades of regional metamorphism. A norite and a suite of diorites were emplaced during the second deformation episode and these have only suffered a low-grade regional metamorphism. The Husfjord metagabbro and the diorite complex were emplaced essentially by a mechanism of permissive intrusion. The latest members of the igneous complex were the Vatna gabbro, the Slatten gabbros, and a number of minor intrusions including perthosite sheets, basic dykes, and nepheline-syenite pegmatites. The main diorite suite appears to have developed from a dioritic melt, which was generated deep in the crust by the syntexis of sialic material with basic magma emplaced from beneath. Metamorphic mineral paragenesis in pelitic hornfelses suggests that the depth of emplacement of the Husfjord plutonic complex was in the order of 23 km.

An investigation of the structures and metamorphic petrology of an area of Eocambrian rocks in Soroy, Northern Norway, forms the basis of this dissertation. The area is characterised by metasediments some of which enclose sheared lenticular bodies of metagabbro. Gneisses have been developed as products of granitisation. The stratigraphical order of the metasedimentary succession can be demonstrated by reference to sedimentary structures preserved in massive psammites. From this evidence, it is manifest that strata are Inverted over a large part of N.E. Sry, this inversion being attributed to the presence of early recumbent folds of considerable magnitude. In the surveyed area, major folds of a later, second deformation episode dominate the structural picture and refold the early structures. The second episode of folding was protracted and consists of two distinct phases. The main folding occurred early in this period while the later phase is characterised by a brittle deformation. Generally, second episode folds display monoclinic symmetry though in the south and west there is no uni-directional sense of fold overturning and the symmetry of movement is apparently orthorhombic. This difference of fold symmetry is clearly related to an orthogonal swing of strike direction. Textural studies of the metasediments in relation to the tectonic episodes allow a subdivision of the metamorphic history into a number of phases. A low grade metamorphism accompanied the early folding. The highest grade of regional metamorphism was established late in the static Interval separating the first and second deformation episodes. Coeval with this, a granitisation of the metasediments was effected which continued, in part, into the second episode of folding. Diaphthoretic phenomena characterise the later phase of brittle deformation.

The rocks exposed on the eastern part of the island of Seiland are the metasedimentary envelope to the large basic and ultrabasic plutons that make up the western part of the island and the neighbouring island of Stjernoy. These metasediments have been intensely deformed and metamorphosed, thus all sedimentary structures have been obliterated. The metasedimentary sequence is, therefore, a structural one. The lowest group is the psammitic Komagnes Group. This is followed by the Eidvageid Schist Group which is followed by the relatively thin psammitic Trollvann Group. Structurally above this is the pelitic Olderbugten Group and finally the dominantly psammitic Olderfjord Group. Broadly speaking two major fold-forming deformations have been recognised; F.1 and F.2. The latter part of the first phase, which was responsible for tight isoclinal folds and a penetrative schistosity, was accompanied by intrusion of sheets of basic material parallel to the axial planes of the early folds. During the static interval separating the two deformations the maximum grade of metamorphism was achieved, this, however, varies across the area and a sequence of metamorphic isograds have been recognised. The highest grade occurs in the west and is marked by a kyanite-sillimanite porphyroblastesis, migmatisation and intrusion of adamellitic sheets. The lowest grade in the east is characterised by albite, biotite, epidote, hornblende assemblages in the psammites of the Lower Komagnes Group. These isograds reflect a contemporaneous lateral change in metamorphic grade. Following the development of these high grade assemblages in the west, there was a phase of intense flattening leading to the development of mylonitic textures in the rocks. It is suggested that this deformation phase is related to a rising basic asthenolith. The majority of folds on the area are attributed to F.2.By the onset of F.2. the metamorphic grade appears to have waned to sub-garnet grade conditions. The folds have a very variable style. In the east, they have intensely attenuated long-limbs with a number of vertically-stacked folds in the short-limbs. In the west, the limbs are of more equal length. This change in style is related to the different states of competence of the rocks at the onset of F.2. A ubiquitous feature of F.2. folds on both the major and minor scale, is the curvature of their axial-lines. In the east a number of oblique boudins have been recorded which post-date F.2. They are closely associated with rotated tension-gashes and monoclinal folds. It is suggested that all these structures were formed in response to a progressive deformation sequence. This sequence was also responsible for the development of the late Caledonian thrusts on the mainland. In the north of the area there is a pronounced swing in strike. A number of open folds are associated with this swing. These folds have been designated F.3. Monoclinal warps have been recorded in the east of the area. Their temporal relationship to the F.3. folds in the north is not known. The final phase of movement in the area led to the development of joints, faults and locally kink-folds. The prevailing metamorphic grade during this phase of deformation, and indeed all the phases subsequent to F.2., was the Quartz-Albite-Muscovite-Chlorite Sub-facies of the Greenschist Facies.

This thesis is devoted to a detailed investigation of a piorite sill of Tertiary age intruded into Torridonian strata on the island of Soay, south Skye. It is devided into four parts (1) studies on the petrography of the picrate, (2) the thermal metamorphism of the enclosing Torridonian strata, (3) and (4) a consideration of the genetic problems of the piorite and the metamorphosed and partially fused Torridonian especially in the light of experimental data on silicate systems related in composition thereto. The first section gives in detail the mineralogy and petrography of one of the piorite sills of Harker's "later peridotite" group of intrusions and particular attention is devoted to the question of the habit of the olivine phase in its textural setting through the sill in the light of Bowen's reinterpretation of the condition of intrusion of the Skye later peridotites. Part 2 of the thesis deals with the metamorphism induced in the associated Torridonian sediments. This metamorphism culminated in partial fusion of the sediments. The account of these phenomena, including the hybridism with the picrate is well set out and an analysis provided of a fused xenolith within the sill. In Part 3 an attempt is made in the light of experimental studies on a related silicate system to evaluate the liquidus of a piorite of the composition analysed. The discussion concerns the studies of Ricker on the Ca2Sio4-Mg2Sio4-Fe2Sio4 plane in the quatemary system and the application of the results, with, it must be admitted, considerable extrapolation to the related piorite. It is concluded that these studies indicate that the liquidus of the piorite would be at considerably lower temperatures than suggested by earlier phase equilibrium work. A beginning with some experimental work by the candidate in the picrate itself in the presence of water vapour is reported but no liquidus determinations were recorded. The temperature deduced for the liquidus is roughly placed around 1500oc. With still lower values, if volatiles are allowed for. This temperatures is still very high, at least 300oc. higher than that known for the liquidus of a calcalkali type of basalt. The discussion of the fusion of the Torridonian assemblage in relation to the experimental data on the granite system (Ab-Or-SiO2-H2O) is well presented and probably provided a real picture of the processes involved. The final part of the thesis is devoted to the petrogenesis. Included here are discussions on the significance of the variations in the shape and size of olivine crystals, on the interpretation of porphyritic texture in relation to the olivine phase and the bearing of these phenomena on the question of in situ crystallization of olivine. The evidence considered unfavourable to the hypothesis of intrusion of a basaltic liquid containing a high proportion of olivine crystals is marshalled but not all of the argument can be regarded as cogent evidence. The candidate has however brought forward good evidence from his own detailed studies that there are good grounds for extending the composition of true magmatic liquids beyond the limits given by Bowen.

Quartz-carbonate vein Au deposits in the Timmins-Porcupine gold camp, Abitibi Subprovince, have equivocal protracted parageneses and formed during late to post-Kenoran (2750-2670 Ma) deformation and metamorphism. SIMS U-Pb and delta18O depth-profiling and LA-ICPMS REE depth-profiling techniques were employed on unpolished wallrock zircons to resolve temporal constraints on mineralization and hydrothermal fluid sources at Hoyle Pond and Pamour mines. Depth-profiling techniques successfully uncovered <3 mum alteration domains in zircon rims based on Th/U, REE, and isotopic signatures, and rim 207Pb/206Pb ages are significantly younger than host rock ages. Zircon alteration is from a complex interplay of recrystallization and localized dissolution-reprecipitation of metamict to fully crystalline zircon during hydrothermal fluid flow. Alteration of Hoyle Pond and Pamour zircons at 2660 Ma correlates to intensely mineralized and deformed quartz-carbonate-Au shear veins, and this age represents peak fluid infiltration at the mines coinciding with peak regional metamorphism. Subsequent zircon alteration correlating to thin, shallow-dipping and less altered / mineralized vein networks occurred at 2640 Ma, and this age likely represents a late hydrothermal fluid pulse at the end of regional retrograde metamorphism. Protracted hydrothermal alteration along discrete zones within the camp continued into the Proterozoic. Th/U and 18O values of zircon alteration domains suggest that fluids were most likely derived from lower crustal metamorphic and/or plutonic activity. While the underutilized depth-profiling technique has resolved ∼200 m.y. of continuous crustal evolution and fluid flow in the southern Abitibi, further investigation of the southern Abitibi is required to clarify the genetic relationship between Au mineralization and zircon alteration.

Internally consistent thermodynamic data for 23 phases in the CaO-Al₂O₃-SiO₂-H₂O system are determined by linear programming consistent set analysis. The consistent set analysis is based on published experimental petrology data for equilibrium reactions involving the phases in this system. Inconsistencies in the experimental data are removed by moving four data points beyond the maximum error allowed by the specific authors or by ignoring some portions of the questionable data. The phase relations among the phases between 0 to 2000°C and 0 to 50,000 bars are calculated using the consistent thermodynamic data with the computer program PT-SYSTEM written by T.H. Brown and E.H. Perkins of the Department of Geological Sciences at the University of British Columbia. The stable portions of the 236 stable equilibrium reactions are drawn on pressure-temperature (P-T) diagrams showing the phase relations of each phase. The P-T diagrams can be used to interpret the petrogenesis of metamorphic zones containing the phases. The consistent thermodynamic data in this study can be improved by undertaking petrology experiments which will substantiate and further define the data. Experiments investigating the stability of prehnite, wairakite and heulandite are recommended. Updating of the internally consistent thermodynamic properties for existing and new phases should be carried out for each additional set of experimental data by redoing the linear programming consistent set analysis on the entire experimental data set. The new thermodynamic properties for the phases could then be used to calculate the new phase relations. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

abstract: Volcanoes can experience multiple eruption styles throughout their eruptive histories. Among the most complex and most common are eruptions of intermediate explosivity, such as Vulcanian and sub-Plinian eruptions. Vulcanian eruptions are characterized by small-scale, short-lived, ash-rich eruptions initiated by the failure of a dense magma plug or overlying dome that had sealed an overpressured conduit. Sub-Plinian eruptions are characterized by sustained columns that reach tens of kilometers in height. Multiple eruption styles can be observed in a single eruptive sequence. In recent decades, transitions in eruption style during well-documented eruptions have been described in detail, with some workers proposing explanatory mechanisms for the transitions. These proposed mechanisms may be broadly classified into processes at depth, processes in the conduit, or some combination of both. The present study is focused on the Pietre Cotte sequence because it may have encompassed up to three different eruptive cycles, each representing different degrees of explosivity. The first deposits are composed of repeated layers of fine ash and lapilli composed of latite and rhyolite endmembers, efficiently mixed at sub-cm scales. The thin layers and bubble/crystal textures indicate that the magma underwent numerous decompressions and open-system degassing, and that the eruptions waned with time. The second phase of the sequence appears to have been initiated by cm-scale mixing between a volatile-rich, mafic magma from deeper in the system and a shallow silicic body. Textures indicate that the magma ascended rapidly and experienced little to no open-system degassing. The final phase of the sequence again produced repeated layers of fine ash and lapilli, of uniform trachyte composition, and waned with time. The first and last phases were likely produced in Vulcanian eruptions, while the pumice-rich layers were likely produced in Vulcanian to sub-Plinian eruptions. In summary, the Pietre Cotte sequence is characterized by up to three magma recharge events in ~200 years. The differences in eruptive style appear to have been controlled by variations in the volatile content of the recharge magma, as well as the efficiency and scale of magma mixing and resulting overpressures. / Dissertation/Thesis / Masters Thesis Geological Sciences 2020

Ninety-four samples from two cores drilled in the Uitenhage Group of the Algoa Basin were analysed. The group of sedimentary rocks comprises the Enon, Kirkwood and Sundays River Formations and consists of continental (Enon and Kirkwood Fms.) and marine (Sundays River Fm.) deposits typical of a transgression sequence into an intermontane valley. Only the Kirkwood and Sundays River Formations were intersected in the boreholes but in one - AD 1/68 'basement' of Bokkeveld Group is reached, while the other borehole, CO 1/67, did not reach 'basement'. The Kirkwood Formation sediments are typically red shales interbedded with drab, fine sandstones (wackes) while the Sundays River Formation is typically drab fine to very fine silty sandstones and gray shales of a marine delta environment. Grain size analyses utilizing wet sieving and pippeting methods showed that two populations of grains are dominant, namely fine to very fine silty sand and clay size material. From the granulometric analyses statistical parameters (e.g. mean, standard deviation, skewness, kurtosis) were calculated and plotted in various combinations. Distinctive trends are thus revealed indicating a mixing of the two sediment populations in varying proportions. Compaction has resulted in an increase with depth in specific gravity (which varies from about 2,5 to +2,6 gm cc⁻³). Studies of the heavy mineralogy reveals a dominance of garnet (two varieties, colourless and pink) with zircon, sphene, rutile and some others in considerably lesser amounts. Opaque grains are also present, sometimes in dominant amounts. X-ray diffraction analyses of the <2 μm clay fraction showed that illite is dominant in both the marine and terrestrial deposits and that chlorite is abundant to infrequent, while montmorillonite is more prevalent in the continentally deposited rocks. Selected clay samples were photographed with both the Transmission and the Scanning Electron Microscopes. Thin sections of the arenaceous samples reveal that those which are carbonate cemented are relatively free from matrix, while those which are uncemented are matrix-rich. This latter situation can be ascribed to the breakdown, after burial, of the commonly occurring rock fragments which frequently constitute about one-third of the sandstones. The problem of red beds is considered, and the red pigmentation found in the Kirkwood Formation is believed to be due to oxidation of iron after deposition of the sediment. Intense weathering in the upland source area is not a suitable explanation for the formation of the Kirkwood Formation red beds. The basin as a whole is considered with attention being focussed on the provenance areas (believed to be the Cape and Lower Karroo Supergroups), the dispersal, depositional environments and the lithification and diagenesis. Finally, the economic potential is briefly considered and some suggestions for future research are put forward.

The Luderitz Alkaline Province, as it is at present known, comprises the subvolcanic central complexes of Drachenberg, Pomona, and Granitberg. An attendant dyke swarm strikes NE-SW and crops out between the latitudes of 27°00' and 27°30' S. Stratigraphic indications (now confirmed by a K/Ar age from Granitberg) are that the Luderitz Province is early-Cretaceous in age and therefore older than the Klinghardt phonolites (Eocene) as well as the smaller melilitite and nephelinite intrusions. Granitberg is a circular foyaite complex, in the centre of which is preserved a large fragment of sedimentary rocks that originally formed the roof of the intrusion. The foyaites have been emplaced into the feldspathic sandstones and dolomites of the Bogenfels Formation, and three major intrusive phases can be recognised. The first phase produced chilled nepheline syenites beneath the roof of the intrusion. These chilled rocks grade downwards into coarse-grained foyaites. The second phase was the emplacement of the Inner Foyaite which crystallized as a cylindrically zoned plug, capped by a zone of layered, laminated, and xenolithrich foyaites. The third phase was the emplacement of the Outer Foyaite, into which the Roof Zone and the Inner Foyaite foundered. The Outer Foyaite is zoned with a miaskitic core, and an agpaitic outer zone.