Three gneissose alkaline granitoid intrusives at Ngoye, Bulls Run and Wangu are described. They are located within the Nkomo Nappe of the Tugela Terrane, near the northern margin of the Natal Metamorphic Province. The Ngoye Complex comprises alkaline granites, with minor syenite and monzodiorite phases. According to modal am geochemical criteria the Ngoye granites range from peraluminous (muscovite-bearing), through metaluminous (biotite- and/or hornblende-bearing), to peralkaline (riebeckite-, aegirine- and magnetite-bearing). The granites are A-types according to their modal and geochemical characteristics. Rb-Sr isotopic data for the hornblende granites indicate an age of 1063 ± 17 Ma and the initial ratio (R๐ = 0.7025) provides evidence for derivation from a mantle source. Plotting of the Ngoye geochemistry on tectonic-discrimination diagrams suggests intrusion into rifted continental crust. It is concluded that the gneissose Ngoye granites constitute a deformed central complex, similar to anorogenic complexes in Nigeria and the Sudan. The Bulls Run Complex is situated 30 km west of the Ngoye Complex. A concentric outcrop pattern has been mapped, according to which an envelope of silica-saturated biotite-muscovite syenite surrounds a core of nepheline-bearing syenites. Minor intrusive phases include biotite-rich dykes, sovite carbonatite sheets, silica-oversaturated microsyenite dykes and feldspathic ijolite. The outer envelope of muscovite-rich syenite is interpreted as fenitised pelitic country rock. An alkali-lamprophyre origin is suggested for the biotite-rich dykes. Geochemically the syenites are predominantly miaskitic, apart from the microsyenite dykes which are mildly peralkaline. Rb-Sr isotopic data for the nepheline syenites indicate an age of 1138 ± 45 Ma (Ro = 0.70322). Carbonate separates from the carbonatites provide a similar low initial ratio (Ra = 0.70319) which supports a comagmatic mantle origin. A comparison is drawn between the Bulls Run Complex and miaskitic nepheline syenite gneisses in the mid-Proterozoic Grenville Province of canada. From this, it is suggested that the Bulls Run Complex is pretectonic and was intruded into the rifted passive margin of a continent. The Wangu Granite Gneiss is situated 3 km southwest of the Bulls Run Complex. The granites are fine grained and contain aegirine-augite and/or magnetite, and classify as alkali-feldspar granite. Peralkaline chemistry is characteristic of the Wangu granites, with trace-elenent contents indicating a distinct A-type signature. Biotite-rich mafic dykes intrude the southern part of the Wangu outcrop and, on the basis of major- and trace-element signatures, are suggested to be metamorphosed volatile-rich alkaline lamprophyres similar to those at Bulls Run. Geochemical similarities between the Wangu granites and certain comendites from the Kenya Rift are noted. It is suggested that the Wangu granites were emplaced as high-level dykes, within rifted continental crust. It is proposed that the Ngoye, Bulls Run and Wangu intrusives be united as the Nkwaleni Suite. Comparison of the Tugela Terrane with the Grenville Province reveals many similarities, particularly their mid- to late-Proterozoic age and the occurrence of pre-tectonic anorogenic continental magmatism. It is concluded that, unlike the current model which would have the Tugela Terrane as obducted ophiolite, these new data indicate that the Tugela Terrane is a metamorphosed continental rift system. / Thesis (Ph.D.)-University of Durban-Westville, 1991.

The rocks studied in this thesis have been the subject of considerable discussion as to their original nature. J. D. Bateman of the Geological Survey of Canada considers that they are of igneous origin whereas others believe that they are metamorphosed sediments. It was thought that a petrographical study might provide some information that would help to decide the problem and it was with this object in view that this study was undertaken. Cree Lake, in the vicinity of which the rocks occur, is situated 2 miles North of the Sherritt-Gordon Mine, Manitoba, which lies about 20 miles east of the Manitoba-Saskatchewan border and 120 miles northwest of the north end of L. Winnipeg. The Sherritt-Gordon copper-zinc ore deposit is a very remarkable deposit in that it is a tabular body with a total outcrop length of 16,000 feet and an average width of 15 feet, thus being one of the longest exposed ore bodies in the world. The rocks in question outcrop around Found Lake which lies very close to and just to the southeast of Cree Lake (see Map 44-4) and fall into two groups; firstly, thos that outcrop south of Found Lake in an area which was mapped by J. D. Bateman as an oval body of oligoclase granite (Map 44-4, No. 12) about one mile long and 1/4 mile wide and secondly, those that outcrop as three smaller masses north of Found Lake but enclosed by the arms of Cree Lake and mapped as anorthositic gabbro (Map 44-4, No. 11). [...]

The northern Lau Basin contains the northeastern-most part of the Tonga arc-basin system. Volcanic rocks associated with the recent-arc have been sampled from Tafahi and Niuatoputapu, and young basalts «1.5Ma) have been dredged from Northern Lau Spreading Centre (NLSC), the northeastern limb of the King's Triple Junction. The 1982 'Kallisto' cruise dredged two ophiolite sections, one containing boninitic, and the other tholeiitic, lavas, from the inner wall of the northern Tonga trench. The magma genesis of these lava suites is related to the structural and geochemical controls imposed during the tectonic evolution of the region. The geochemical controls result from processes related to the mantle dynamics in the northern Lau Basin, and to along-trench variations and the degree of influence of the subduction component. The lavas associated with the Central Lau Spreading Centre are derived from the Lau Basin mantle reservoir, which has Indian MORB mantle (!MM) isotopic characteristics. This reservoir has been present under the region since early-arc magmatism, as indicated by the trace elements and !MM isotopic signatures of the tholeiitic lavas from the eastern ophiolite section, and Eocene lavas from 'Eua. A reservoir with the geochemical characteristics of residual Samoan plume mantle underlies the northern Lau Basin. This mantle has been influxing through the rip in the Pacific plate, at the northern termination of the Tonga trench, since the Lau Basin began to open « 6Ma), as a result of processes relating to subduction roll-back. The north Tongan boninites, the lavas from Tafahi and Niuatoputapu have residual plume mantle sources. However, prior to the opening of the Lau Basin, the proto-Tonga trench formed a barrier to this influx, and therefore, the influence of the plume cannot be detected in lavas associated with the early-arc, such as the tholeiites from one of the ophiolite sections and the Eocene lavas from 'Bua. The variations in the trace element and Pb isotopic compositions of the lavas from the Northern Lau Spreading Centre indicate that mixing has occurred between Lau Basin and residual plume mantle end-members in the central northern Lau Basin. The residual plume mantle sources of the north Tongan boninites and the lavas from Tafahi, Niuatoputapu and the Tofua arc have been enriched by a subduction component, the characteristics of which are enrichment in Lll..E, Ph ± LREE. In the south, the subduction component is made up of fluids derived from subducted Pacific altered oceanic crust and pelagic sediments. However, in the north, it is comprised predominantly of fluids derived from Pacific volcanogenic sediments, with a contribution from altered oceanic crust and possibly subducted plume crust.

Ecological and ecophysiological investigations carried out at the ultramafic outcrop near Meikle Kilrannoch, Angus, Scotland are reported. The outcrop is botanically famous for its rare plant species, particularly the endemic Cerastium fontanum ssp. scoticum and the nationally rare Lychnis alnina. The studies were made on the main outcrop (called MK1) which is dome shaped, and on a much smaller low-lying area (called MK1.5) about 300 m from it. The overall aim of the studies was to investigate the relationship between the soil physico-chemical environment and species distribution on the open areas of the ultramafic site and to experimentally test for causality; and to offer an explanation for the open character of the vegetation on the skeletal soils. Variograms which were constructed for soil properties and vegetation data to investigate soil micro-spatial variation and vegetation pattern showed differing levels of spatial dependence, always indicating high intrinsic variability. The cause of this high variability was probably cryoturbation for the soil and morphological characters for plants. The gradient analyses (Principal Components Analysis and its canonical form, Redundancy Analysis) used to study soil - vegetation correlations suggested that A ostis vinealis, Cerastium fontanum ssp. scoticum and Lychnis alpina were most abundant in areas up-slope with lower concentrations of soil magnesium; Cochlearia pyrenaica ssp. alpina and Festuca rubra were associated with bigger stone sizes, and the latter occurred in wetter areas with higher of ions. A comparative solution culture experiment based on the local soil chemistry was used to study the growth responses to magnesium and nickel of Cerastium fontanum ss. scoticum, Cochlearia pyrenaica ssp. al ina and Festuca rubra. The results for Festuca and Cerastium were in agreement with the findings of the gradient analysis: Festuca was indifferent to both magnesium and nickel and Cerastium was susceptible to high magnesium; the reduction of dry weight by nickel in the Cochlearia conflicted with its suggested association with high soil nickel in the gradient analysis. The impacts on the photosynthetic systems of three Cochlearia species of different concentrations of iron and nickel were identifiable only in the non-ultramafic C. pyrenaica where the addition of nickel decreased photosynthesis but the effect could be ameliorated by the addition of high concentrations of iron. The open character of the skeletal soil at the MK1 site was discussed in terms of 'carrying capacity'. Vegetation development was suggested to be controlled at least partly by large stones covering the soil surface. Further factors such as space fragmentation, possible plant-to-plant interactions, and low density of flowering individuals and restricted seed dispersal were also considered. To test if major nutrients were limiting plant growth, major nutrients (NPK) were applied to the MK1.5 skeletal soil. The significantly higher X's and recruitment and change in life history traits (larger rosette sizes, earlier maturing and higher seed production) in the fertilised populations of C. pyrenaica ssp. alpina resulted in a significantly higher plant cover in the fertilised quadrats. The better growth of plants in the fertilised quadrats was reflected in their lower total non-structural carbohydrate (TNC) concentrations in May and their higher TNC in August. The present series of investigations found that magnesium and nickel toxicity had an effect on the intra-site distribution of the ultramafic species and also confirmed earlier reports on the importance of magnesium and nickel toxicity in ultsamafic exclusion. Large stones and low soil phosphorus concentration are proposed as limiting factors for the development of closed vegetation on the skeletal soil areas of the sites.

The Lac Guyer greenstone belt in the James Bay region of New Quebec was a zone of active volcanism in Archean times and constituted part of a system of "rifts" known as the La Grande superbelt. The rifting of continental crust initiated with the deposition of a sequence of volcanics dominated by pillowed basalts. An overlying volcanic sequence began with the deposition of rhyodacites and other felsic volcaniclastics, intercalated with mafic flows and tuffs. These, in turn, are overlain by peridotitic and pillowed pyroxenitic komatiite flows and then by pillowed basalts. The rocks in this Archean belt have experienced at least two periods of deformation and attained amphibolite facies. / The early voluminous basalts of the first sequence probably reflect the eruption of steady state liquids from periodically replenished, periodically tapped, magma chambers located near the interface of an early crust and Archean mantle. With time the mafic crust overlying these magma chambers, melted to produce tonalitic-granodioritic magmas. These magmas rose and experienced amphibole fractionation. Residual liquids produced by this fractionation erupted as rhyodacites contemporanously with later basalts. The eruption of komatiitic liquids indicates a major failure of the crustal screen enabling primitive magmas to reach the surface. The spectrum of primitive komatiitic compositions reflects variable degrees (15 to 40%) of partial melting of a garnet lherzolite in the Archean mantle. Pyroxenitic komatiite magmas represent the least degree of melting with garnet remaining in the mantle residue. Garnet was completely consumed, however, in the more extensive melting involved in the production of the peridotitic komatiite magmas. As the volcanic pile of the second volcanic sequence grew crustal magma reservoirs were re-established. Primitive komatiitic magmas held in these reservoirs underwent extensive crystal fractionation to yield residual steady state liquids which erupted as the upper basalts of the second volcanic sequence.

No description available.

The ultramafic cumulate rocks of the Raglan horizon in the Proterozoic Cape Smith fold belt of northern Quebec have a common parental liquid in equilibrium with olivine of Fo89 composition. Cumulate olivines have experienced a trapped liquid shift to lower forsterite composition proportionally to the fraction of trapped liquid in the cumulate. Anomalously low nickel contents in analyses of both olivine and whole-rock chemistries are observed only in cumulates with the most modal olivine and which are proximal to known Ni-Cu-(PGE) deposits. The calculated compositions of the trapped liquid fraction indicate that most of the Raglan cumulates formed from Fe-rich high-MgO basalts, which are restricted to the base of the Chukotat volcanic stratigraphy. We propose that a lower degree of adiabatic partial melting of a mantle source accounts for the Fe-rich nature of these parental liquids and may provide an explanation for the presence of numerous Ni-Cu-(PGE) deposits in the sills of the Raglan horizon.

No description available.

No description available.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1984. / Bibliography: leaves 219-236. / Microfiche. / xviii, 236 leaves, bound ill. 29 cm