Originally built for agricultural purposes by Acadians, dykes and dykelands have now found wider uses in protecting life and property in Nova Scotia and require regular maintenance. This research identifies some values that can be associated with dykes and dykelands and people’s perceptions of them. Semi-structured face-to-face interviews comprising open- and closed-ended questions were used in data collection. Agriculture, flood prevention and Acadian history and heritage were the most important values to most respondents in both open- and closed-ended responses. The results identified differences in people’s perceived values when they were provided with more information. The values placed on dykes and dykelands depended on their physical location, available information, and the activities and properties around the dykes. Peoples’ connections with dykes and dykelands had little influence on their values and perceptions. These findings provide important baseline information for further discussion about dyke and dykeland values and the case for effective maintenance.

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Understanding dykes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions. The 2014-15 Bárðarbunga-Holuhraun rifting event comprised the best-monitored dyke intrusion to date and the largest eruption in Iceland in 230 years. Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano, Iceland, along a 48 km path before erupting in the Holuhraun lava field on 29 August 2014. A huge variety of seismicity was produced, including over 30,000 volcano-tectonic earthquakes (VTs) associated with the dyke propagation at ∼ 6 km depth below sea level, and long-period seismicity - both long-period earthquakes (LPs) and tremor - associated with the eruption processes. The Cambridge University seismic network in central Iceland recorded the dyke seismicity in unprecedented detail, allowing high resolution analyses to be carried out. This dissertation comprises two parts: study of 1) the volcano-tectonic dyke-induced seismicity and 2) the long-period seismicity associated with eruption processes. Volcano-tectonic earthquakes induced by the lateral dyke intrusion were relocated, using cross-correlated, sub-sample relative travel times. The ∼ 100 m spatial resolution achieved reveals the complexity of the dyke propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dyke and seismicity. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dyke, and following this - after dyke opening - indicate a relationship with magma pressure changes (i.e. dyke inflation/deflation), followed by a general 'post-opening' decay. Seismicity occurs only at the base of the dyke, where dyke-imposed stresses - combined with the background tectonic stress (from regional extension over > 200 years since last rifting) - are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dyke section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric. Long-period earthquakes and tremor were systematically detected and located during the dyke propagation phase and the first week of the eruption. Clusters of highly similar, repetitive LPs were identified, with a peak frequency of ∼ 1 Hz and clear P and S phases followed by a long-duration coda. The source mechanisms were remarkably consistent between clusters and also fundamentally different to those of the VTs. The clusters were accurately located near each of three ice cauldrons (depressions formed by basal melting) that were observed on the surface of Dyngjujökull glacier above the path of the dyke. Most events were in the vicinity of the northernmost cauldron, at shallower depth than the VTs associated with lateral dyke propagation. At the two northerly cauldrons, periods of shallow seismic tremor following the clusters of LPs were also observed. Given that the LPs occurred at ∼ 4 km depth and in swarms during times of dyke-stalling, it is inferred that they result from excitation of magmatic fluid-filled cavities and indicate magma ascent. The tremor may then represent the climax of the vertical melt movement, arising from either rapid, repeated excitation of the same LP cavities, or sub-glacial eruption processes. This long-period seismicity therefore highlights magma pathways between the depth of the dyke-VT earthquakes and the surface. Notably, no tremor is detected associated with each cauldron, despite melt reaching the base of the overlying ice cap, a concern for hazard forecasting.

The dykes from the Igaliko Nepheline Syenite complex belong to at least 3 individual swarms (i) a Mid-Gardar swarm in the Østfjordsdal valley, (ii) a Late-Gardar, Si-oversaturated swarm associated with the Younger Giant Dykes of Tugtutôq and (iii) a Si-undersaturated swarm intimately associated with the Late Gardar Igaliko Nepheline Syenite Central Complexes. In addition Early Gardar activity is recorded by the presence of some ultramafic lamprophyres which predate the Motzfeldt centre, sparse trachytes which are truncated by intrusions within the Motzfeldt centre and a possible BD(_0) dolerite which is also cut by the Motzfeldt centre. Most dykes however are bracketed between the Early and Late Igdlerfigssalik syenite intrusions. The main oversaturated and undersaturated suites can be separated on their Zr/Nb ratios (≈6.4 and 3.9 respectively). In addition, the undersaturated basic rocks have smooth chondrite normalised incompatible element spidergrams whereas the oversaturated basic rocks are characterised by negative Nb and positive P anomalies. Evolution of both suites can be modelled in terms of fractional crystallisation of feldspar, clinopyroxene, olivine, apatite and opaques from basaltic parents to either phonolitic or rhyolitic minimum compositions. In each instance these evolved composi tions are extremely rich in incompatible trace elements (REE, Nb, Zr, Rb). In some cases a high CO(_2) content in the undersaturated rocks may lead to the formation (by liquid immiscibility) of late stage carbonatite magmas. High CO(_2) also produces high ƒo(_2) in these magmas and it is argued that in some cases this can suppress the development of negative Eu anomalies on feldspar fractionation. The undersaturated swarm may have evolved from lamprophyric parental magmas, eg. camptonites, which are relatively abundant basic dykes. Ultramafic lamprophyres, often early, may have formed as extremely small degree partial melts at the onset of Gardar rifting. In the Late Gardar, magma genesis is related to the different extensional tectonic regimes which were operative at that time. Mineralogical evolution follows paths similar to several other Gardar suites and records a higher ƒo(_2) in the undersaturated rocks. Zr becomes concentrated in interstitial residual liquids in benmoreites and substitutes into amphibole as the newly proposed end-member zirconian-arfvedsonite.

The wood’s Point dyke swarm, Victoria, consists of a set of abundant subparallel narrow dykes with occasional elliptical expansions (“bulges”) intruded into strongly folded Lower Palaeozoic sediments. The swarm represents a hisly differentiated calc-alkaline rock series derived by fractional crystallization of a single parent magma, possibly of periodotitic composition. The rock types present include both high and low Cr-Ni periodotites, pyroxenite, hornblendite, hornblende diorite and monzonite, biotite leucodiorite, and minor residual granophyre. Apart from this hornblende-bearing rock series, a few hornblende-free basaltic dykes of related chemical composition but intruded later, are petrographically and mineralogically distinct, displaying tholeiitic tendencies. The latter dykes appear to be genetically related to volcanics underlying the Upper Devonian Acheron and Cerberean cauldron subsidences. / Fractional crystallization, flowage differentiation, crystal accumulation and chilling were important factors in the development of the members of the dyke swarm, whilst assimilation in situ was not. The dykes are zonod, ultramafic types having more basic interiors (“cores”) whereas basic to intermediate composition bulges have more basic margins (“rims”). / Magmalic copper-nickel sulphides rich in precious metals (Pt, Pd, Au) occur in dyke bulges of all compositions, especially close to margins where they accumulated by gravitational settling or were trapped by chilling. The sulphides have high Cu/Ni (and Co/Ni) ratios indicative of a highly evolved magma and, along with Au, Pd and Ir are fractionated between dykes of different silicate compositions. The base metal contents of silicates and sulphides vary sympathetically. / The dykes have undergone pervasive hydrothermal alteration during which sulphides were largely recrystallised and Au was leached from some copper-nickel sulphides. A zonal arrangement of increasing intensity of alteration inwards was observed in one ultramefic dyke bulge. Later the dykes were deformed and the basic to intermediate composition dykes were fractured and veined, and major gold deposits formed. The veins have associated wall rock alteration which may be mineralogically subdivided into inner and out zones. / Dyke bulges, ultramafic rocks, copper nickel sulphides and Au mineralization are all concentrated along two main lineations paralleling the fold axes of the sedimentary trough. The eastern and more important trend (at the centre of the trough) marks the eastern limit of the dyke swarm except at its northern end. These lineations may represent deep-seated fractures which controlled the later upward migration of Au-bearing hydrothermal solutions from depth. The source of the Au could have been various rock types present at depth, including copper-nickel sulphides and Lower Palaeozoic sediments.

<p> A baked contact test was carried out between the Otto Stock, dated at 2114 Ma by Bell and Blenkinsop (1976) and its host rock, represented by the magnetically stable, Matachewan Dyke swarm dated at 2690 Ma by Gates and Hurley (1973). Paleomagnetic results from this study confirm the recently revised dating or the Otto Stock and Matachewan dykes at 2680±1 Ma and 2452+3/-2 Ma, resectively (Corru et.al. 1989; Heaman, 1988) . </p> <p> Matachewan dykes both distant and within the contact aureole or the Otto Stock all carry the same southwesterly shallow characteristic Matachewan direction or magnetization. The absense or an Otto Stock overprint on the Matachewan dykes implies that the intrusion or the Otto Stock must have occurred before the intrusion or the Matachewan Dyke swarm. </p> <p> The relative ages or the Otto Stock and Matachewan dyke magnetizations are inconsistent with the conventional early Proterzoic apparent polar wander path (APWP) for North America, which decreases in age from the Matachewan dyke pole t o the Otto Stock pole. It can be concluded that this part or the APWP is running backwards and must now be redefined. </p> / Thesis / Bachelor of Science (BSc)

The multiphase Ice River Alkaline Complex is located in the Main Ranges of the Rocky Mountains about 40 km east-southeast of Golden, BC, and comprises, in order of decreasing age: (1) a rhythmically-layered mafic complex; (2) carbonatite (concentrated as a plug in the centre of the complex); (3) a zoned nepheline syenite complex, and; (4) a dyke suite consisting of syenitic dykes, late alkaline lamprophyres, and carbonatites. Petrographic, geochemical, and isotopic analysis of the dykes occurring along the eastern margin of the Ice River Alkaline Complex indicates that the syenitic dykes are the product of extensive fractional crystallization (Zr/Hf = 39 – 80; Nb/Ta = 19 – 305). These syenitic dykes can be subdivided based on mineralogy and composition into a nepheline syenite – nephelinolite group, a syenite – monzodiorite group, and an alkali feldspar granite dyke. The calculated Sm-Nd isochron age of the syenitic dykes (369 ± 15 Ma) is consistent with the accepted age of the complex (359 ± 3 Ma), and is supported by the Rb-Sr errorchron for the same samples, as well as preliminary U-Pb zircon dating. A solidification front (fractional crystallization) model has been described for the development of the Ice River Alkaline Complex, where the syenitic dykes represent structurally controlled periodic discharges from an evolving magma chamber. Isotopic evidence coupled with a U-Th-Pb EPMA date of 165 ± 8 Ma for one of the examined discordant REE-rich carbonatite dykes, indicates that at least some of the carbonatites within the Moose Creek Valley are temporally and magmatically isolated from the Ice River Alkaline complex.

Across Britain, there are over 100 possible early-medieval linear earthworks commonly termed dykes; in total, they stretch for over 400 kilometres. They vary in size from those just 100 metres in length to the famous Offa’s Dyke, which is over 95 kilometres long. There have been studies of individual dykes (Noble and Gelling 1983 for example) and general discussions of the larger examples (Squatriti 2002 for example), but no systematic attempt to catalogue and analyse them all. Their size and number suggests these earthworks were probably an important aspect of early-medieval life and have the capacity to tell us a great deal about the societies that built them. Dating such earthworks is difficult even with modern archaeological techniques and, as few early-medieval written sources survive, historians have often incorrectly ascribed enigmatic dykes to this period. This present study ascertained which dykes probably belong to the early-medieval period and contains a comprehensive gazetteer of them in the appendix. It also discusses how the dykes relate to the surviving written records, how many people were involved in their construction, what were their functions and what dykes can tell us about the processes that created early-medieval Britain. It calculated that far fewer people were needed to build them than many previous studies had supposed. While some were estate boundaries and King Offa may have ordered the building of the dyke that bears his name to bolster his power, it is argued that many of these earthworks were designed to prevent raiding. The dykes were a symptom of the endemic low-intensity warfare and small-scale forays into neighbouring territories that often characterised this period.

Although Thomas Dyke Tellefsen’s mazurkas have been considered mere imitations of Chopin’s musical idiom, his mazurkas are closely related to Norwegian folk elements. Tellefsen adopted Norwegian folkloric elements from his own country and infused Norwegian spirit into his works to create his own musical language. To trace the Norwegian folk influence, this study examines folk dance (the springar), folk instruments (the hardanger fiddle and the langeleik), and folk melodic and rhythmic motifs. As the result, this research demonstrates that Tellefsen’s mazurkas were influenced by a phrase structure of Norwegian springar dance music and the exact sound effect of folk instruments (the hardanger fiddle and the langeleik) as well as Norwegian folk rhythmic and melodic formulas which are frequently used in Norwegian folk tunes. Furthermore, the comparison between Tellefsen and Chopin’s mazurkas demonstrates that although their mazurkas seem to have a similar musical style, Tellefsen’s mazurkas include his own traditional Norwegian folk aesthetic, which present original contributions to the genre.