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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.

Thesis (M.S.)--Baylor University, 2007. / Includes bibliographical references (p. 95-98).

Thesis (Ph. D.)--University of Adelaide, Dept. of Geology and Geophysics, 1987. / Typescript. Maps in back pocket of v. 1. Microfiches in back pocket of v. 2. Microfiches contain petrographic descriptions, total rock XRF analyses and microprobe analyses. Includes bibliographical references (leaves 160-183 (v. 2)).

Thesis (Ph.D.) -- University of Adelaide, Dept. of Geology & Geophysics, 2000? / Appendix 4 and 5 in pocket on back cover. Bibliography: p. 123-130.

Thesis (M.S.)--Ohio State University, 1986. / Includes bibliographical references (leaves 141-146). Available online via OhioLINK's ETD Center

The Tertiary ultrabasic dykes of the Cuillins and the Strathaird peninsula are studied and classified on the bases of their content of cognate xenoliths and textures. Two principal types are, recognised, the Coire Lagan type (similar to those studied by Drever and Johnston, 1958) and the xenolithic Ben Cleat type. The dykes of the Ben Cleat type are investigated in detail. The Ben Cleat dykes are composed principally of olivine (Fa11), plagioclase (Ang4 with normally zoned margins) and clinopyroxene (Ca43 Mg46 Fe11) with accessory chrome spinel: the compositions of these minerals are constant throughout the dykes. The transverse variations in modal amount and crystal size of the three principal minerals within selected representative dykes have been determined and it is established beyond doubt that the dykes are differentiated. The petrogenetic hypothesis of composite intrusion previously proposed for these dykes by Bowen (l928) is examined in the light of this evidence and found to be inadequate. It is suggested that the dykes were intruded as suspensions of olivine crystals and rock fragments in an ultrabasic liquid from which plagioclase, pyroxene and a small amount of olivine subsequently crystallised. It is demonstrated that the dykes are unlikely to have been differentiated in their present positions and the possibility that the differentiation occurred during their emplacement is examined. The processes by which, crystals might migrate in flowing magma are considered, and it is shown that the mineral distributions and crystal size variations occurring in the dykes are analogous to those expected, from the results of theoretical and experimental investigations, to arise during laminar flow of suspensions of solid particles in a viscous fluid in vertical conduits. Several of the apparently anomalous differentiation phenomena are also interpreted in the light of theoretical fluid mechanics as the results of flow in near-vertical fissures. It is concluded that (i) the dykes were each intruded as a single pulse of ultrabasic liquid containing large amounts of olivine phenocsrysts,?(ii) the distinctive type of differentiation which is characteristic of these dykes occurred during their intrusion and (iii) the mechanism involved was flowage differentiation. The petrographiea of the cognate xenoliths are studied and their distribution and orientation explained on the basis of laminar flow of the dyke magma. The age of the xenolithic ultrabasic dykes in relation to the other intrusions of the Cuillin Tertiary igneous complex is reconsidered and it is suggested that the dykes were emplaced contemporaneously with the Sgurr Dubh ultrabasic intrusion. Petrogenetic hypotheses are advanced for both the dykes; and the cognate xenoliths and it is tentatively proposed that both were derived by partial fusion of a deep-seated peridotitic rook.

The petrogenetic relationships of the different varieties of kimberlite in the De Beers Mine and Letseng-Ia-terai composite diatremes have been investigated using petrographic and chemical methods. Kimberlites in the Letseng-Ia-terai diatreme were found to be strongly contaminated by crustal material, mainly basalt. A method to correct for the effects of the contamination has been developed and applied to these kimberlites. Using the corrected data, the four kimberlite types in each group appear to be related to each other by crystal/liquid fractionation models. However the two groups cannot be related to each other. The De Beer Mine has two varieties of kimberlite, a monticellite apatite and calcite rich variety which intruded first, and a phlogopite rich type forming a discrete cylindrical body within the earlier kimberlite. These two kimberlites do not appear to be related by any of the fractionation models discussed. An examination of the data from this work and published sources, suggests that kimberlites are derived from below the low velocity zone by small degrees of partial melting involving garnet lherzolite with subordinate phlogopite and carbonate. Diamonds are probably incorporated as xenocrysts in the magma. Upward movement and emplacement of kimberlite appears to have been very rapid. The diatremes were probably eroded and shaped by gas, derived from the kimberlite magma, escaping to surface along weak zones in the earth's crust. Xenoliths of crustal material incorporated in the kimberlite on intrusion have also been studied and various features due to alteration by the magma are described, including the formation of natrolite and cebollite. The latter is a rare mineral that has not been described from kimberlite before. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

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