>Magister Scientiae - MSc / The late- to post-collisional Cape Granite Suite (CGS) located in the southwest of South Africa is comprised of S-, I-, and A-type granites, mafic intrusives, and volcanic flows. The CGS is interpreted to have formed during the closing of the Adamastor Ocean during the Late-Proterozoic to Early-Cambrian. Recently, the S-type granites have received much attention concerning their petrogenesis and sources. However, the I- and A-type granites remain poorly understood and little studied. Therefore, with new geochemical and isotopic data the petrogenesis, sources, and tectonic settings of I- (Vredenburg Batholith) and A-type (Cape Columbine) granites of the CGS form the focus for this study. The major and trace element data presented in this thesis show that the granites from the Vredenburg Batholith are weakly peraluminous to metaluminous, ferroan, and alkali-calcic. Associated with the granites are metaluminous, magnesian, and calc-alkalic igneous enclaves. Formerly, the granites have been interpreted to have formed by fractionation. However, with new geochemical analyses and reassessment of such models, it can be shown that such processes are incompatible with accounting for the chemical variation displayed by the granites and their enclaves. Moreover, the I-type granites and enclaves exhibit positive linear trends between whole-rock major and trace elements vs. maficity (Fe + Mg), which can be explained by co-entrainment of peritectic and accessory phases. The lithogeochemical characteristics of the enclaves and host granite reflect melting of a heterogeneous source. Moreover, the granite and enclave"s ?Nd(t) values reflect melting of Paleoproterozoic-aged crustal sources. Finally, with tectonomagmatic discrimination diagrams, it can be shown that the tectonic setting of the granites indicates a transition from a collisional to extensional regime which corroborates the inferences of previous studies. The Cape Columbine Granites lithogeochemical characteristics are ferroan, calc-alkalic and weakly peraluminous. They show typical A-type granite characteristics in having high silica content, high Na + K values, REE enrichment as compared to S- and I-type granites and strong negative Eu anomalies. For this thesis, it can be shown that anatexis of quartzofeldspathic protolith in an extensional regime produced the chemical variation of the Cape Columbine Granite. Moreover, their isotope ratios are typically radiogenic, indicative of a crustal origin. With this new geochemical data evidence is provided against and in support of previous inferences made about the petrogenesis of the I- and A-type granites of the CGS. This also betters our understanding of the magmatic processes involved in the construction of the CGS over time.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in prined format.

Thèse de doctorat--Sciences de la terre--Montpellier II, 2004. / Bibliogr. Titre provenant de l'écran-titre.

Thesis (M. Phil.)--University of Hong Kong, 1984.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

The biotite bearing Schultze Granite (Globe-Miami district) and the biotite-hornblende bearing Ruby Star Granodiorite (Pima district) compose two intrusive centers that produced multiple porphyry copper deposits during the Laramide orogeny. Both magmatic-hydrothermal systems were dismembered and tilted by Tertiary extension, as indicated by tilted Tertiary sedimentary rocks, paleomagnetic data, and geobarometry, thereby producing extraordinary exposures of these magmatic-hydrothermal systems: ~ 1 to ~10 km (Globe-Miami district) and <1 to>12 km (Pima district). Ages of emplacement range from 68 to 61 Ma for the Schultze Granite and 64 to 58 Ma for the Ruby Star Granodiorite. The plutons were formed by rapid accumulation of magma within short periods of time (~1 m.y.). The Schultze Granite is a high-silica granite and did not evolve chemically with time, except during formation of late porphyry and aplite dikes. Phases of the Ruby Star pluton range from granodiorite to granite, but appear to be distinct intrusive events separated in time by several million years. Each pluton is chemically homogenous with depth, probably due to convection. The low iron contents of biotites suggest that magmas related to porphyry copper deposits have higher oxidation states than typical granitic bodies. Hydrothermal alteration was associated with most phases of each pluton, with multiple alteration types overlapping to create complex centers. Veins persist to >10 km beneath porphyry copper deposits. Deep styles of alteration differ in the two plutons. The Schultze Granite contains biotite veins and greisen veins (coarse-grained muscovite) (~10 km). The Ruby Star Granodiorite contains sodic-calcic alteration (4-8 km) and greisen veins (4-12 km). The sodic-calcic alteration is asymmetrically distributed on the eastern side of the Sierrita deposit and is interpreted to have been created by influx of external sedimentary brines from Paleozoic sedimentary rocks that only are present on the eastern side of the pluton. Greisen alteration occurs late in the hydrothermal history and may be the last fluids that were exsolved from the magma as the magma chamber completely crystallized. These deep alteration styles can be used to predict where porphyry copper deposition may have occurred, which can lead to discoveries in extended terranes.

No description available.

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1987.

This study is a detailed investigation concerning the construction of granite plutons by the incremental emplacement of granitic sheets. The modem consensus is that sheeted plutons are often controlled by tectonic structures such shear zones. The Main Donegal Granite (MDG), NW Ireland forms the basis to this study. This pluton is the largest presently exposed member of the Caledonian Donegal Batholith (~405 Ma). Field evidence from this highly deformed pluton, attest to emplacement along the long-axis of a sinistral transcurrent shear zone. The presence of long and persistent xenolith "trains" within the pluton has been taken as evidence of an overall sheeted structure; however detailed maps have not been available to test this hypothesis. Two earlier members of the Donegal Batholith, the Ardara and Thorr plutons, whilst having their main outcrops outside the MDG, also occur as xenoliths within the main body. It can be demonstrated in a number of critical situations that these xenoliths are commonly more deformed than the host MDG facies. Furthermore the presence of original country rock contacts implies these xenoliths were originally in situ. These features imply that the shear zone was active prior to the emplacement of the MDG, with it controlling the emplacement of substantial parts of these earlier plutons. Further evidence from the study of parts of the petrographically similar and younger Trawenagh Bay Granite implies the sinistral shear zone was still operational after the majority of the MDG had crystallised. New, detailed (scale 1:250) and reconnaissance mapping of the MDG, reveals its hitherto unrecognised heterogeneity. At least seven major plutonic zones or packages have been identified. All these units have an NE -SW elongate form parallel to the long axis of the pluton and are often, but not always, separated by extensive "raft-trains" of country rock and older plutons. The major packages in the central regions of the pluton are often complex and are composed of three main granitoid phases, ranging in composition form early granodiorites and tonalites to latest porphyritic and to lesser extent equigranular, monzogranites. The early granodiorite and tonalite sheets are now only preserved as xenolithic rafts within the later monzogranites. The broad range in composition/chemistry together allied with field observations implies a complex intrusion history, with these granitoid packages representing sites of long-standing intrusion within the pluton. In contrast, towards the more marginal areas of the pluton there are large units of monzogranite which are characterised by general homogeneity, but in reality are believed to consist of relatively small compostionally similar sheets. On all scales, either meta-sediments, older plutonic material, or early MDG facies are found to lie along the boundaries of younger intrusive units. This implies the pluton is primarily sheeted in character and that the "raft-trains" are partially disrupted, in situ roof material which has been wedged apart during the intrusion of the sheets. The appearance of sheets within the field is dependent on the rheology of the material into which the granitic material was intruded into, i.e. to what extent has the host was crystallised. The degree of crystallisation in the host is related to how fast later sheets were being intruded, i.e. the rate of emplacement. The field relationships, in the central regions of the pluton, between the granodiorites tonalites and the later monzogranites, are interpreted as representing zones of episodic-to slow emplacement, where earlier phases had become essentially competent by the time later units were intruded (i.e. capable of fracture). These earlier phases may be preserved as angular rafts within later sheets. At moderate emplacement rates earlier sheets may still be crystallising but sufficiently viscous to prevent mixing, except at their immediate boundaries with transitional contacts developing. The more homogeneous zones are believed to be related to rapid emplacement with original contacts between pulses being destroyed at the level of emplacement due to homogenisation of pulses which had similar viscosities and hence allowed mixing. The emplacement of granitic melts within active shear zones can lead to the development of a self- perpetuating situation, where melts in a shear zone will enhance deformation rates and cause greater displacements subsequently allowing more melt to enter the shear zone promoting even greater displacement rates. This process is only halted when melts within the source regions are drained; hence the rate of pluton construction and appearance of sheets within plutons is ultimately related to how fast granitic melts are being generated within the source regions.