Thesis (PhD) -- Stellenbosch Univesrsity, 1972. / The Darling batholith is characterised by large scale hybridisation, but mainly consists of the coarsely porphyritic Darling granite. This granite changes gradationally into a biotite-rich variety which occupies a roughly elliptical area with a major, northwesterly trending axis of 30 km. The biotite granite envelops a large irregular body of hybrid granodiorite. Small intrusions of younger granite occur within the batholith namely the Klipberg and Contreberg granites and possibly the biotite-rich Dassenberg granite. Dassen Island is underlain by fine-grained granite which could be related to either the younger or coarsely porphyritic granites. A prominent northwesterly trending mylonite zone can be traced through Darling to Swartberg, and ultimately to Trekoskraal in the Saldanha batholith, but is not continuous since it occasionally changes into gneissic granite and is also interrupted by the younger intrusives. Quantitative mapping included measurement of matrix grain size, average maximum phenocryst length, xenolith distribution density, quartz nodule distribution density and average size, lineation, dark mineral index and gneissosity. On Dassen Island the distribution of tourmaline nodules was , determined. The results are displayed as small scale contour maps which show strong correlation between the various parameters. The average values of matrix grain size, average phenocryst length and xenolith distribution density are respectively 2-5mm, 20-60mm and 0-1,5 per m² for the Darling granite, and 1-2 mm, 5-20 mm and 1-9 per m² for the hybrid granodiorite. It was found that the matrix grain size decreases with increase in hybridisation. The spotty distribution pattern of tourmaline nodules on Dassen Island indicates addition of boron by assimilation of metamorphites and a late stage liquid immiscibility process. The granites :.have normal mineralogy and the K-feldspar of the phenocrysts is maximum microcline (Δ = 0,9 - 1,0). The hybrid granodiorite contains much pinitised cordierite and locally garnet. The deeply pleochroic bioti te is probably of the 2M1 polytype and has a higher Fe:Mg ratio in the hybrid granodiorite than in the granite (2,8 - 3,0 vs. 2,2 - 2,3). The intimately associated chlorite seems to be of the Ia polytype. The cordierite is of the normal and low temperature type with average intensity index of 2,7 , distortion index of 0,3 and 2 a of 63°. The xenoliths are predominantly quartzitic metagraywackes, but lime-rich types holding sphene and diopside were occasionally encountered. Thirteen new chemical analyses and thirty-one previously published analyses are used to calculate average composite analyses of the various rock types. The results of calculations employing Barth standard cell values indicate that the hybrid granodiorite could have originated by reaction between granite magma and Malmesbury quartzitic metagraywacke and pe-lite with a little limestone. A "granite differentiation index" based on weight percentages of (Ti02 + MgO + FeO + Fe2O3) and (Si02 + Na2O + K2O) shows a linear relationship between the granites in probable order of age. The magmatic differentiation trend is separated from the hybridisation trend on a 6alk - 2(al - alk) - (100 - 2al) diagram. Mesonorms and their cordierite variants are used to effect comparison with the experimental granitic system of von Platen (1965). The Darling and Contreberg granites plot near the relevant cotectic surfaces. A pilot experimental study of melting behaviour indicates that the Contreberg granite is closer to a minimum melt composition than the Darling granite. Comparison of alkali values with a M Na2O - M K2O Schreinemakers diagram of Korzhinskii (1959), shows that the alkali ratio of the older analyses may be incorrect, and indicates that the dark minerals have a greater effect on plagioclase composition than the amount of K-feldspar. The classification of granites by means of Harpum diagrams is shown to have little relevance to the reconstruction of the ancient thermodynamical variants. The Darling granite is correlated with the Hoedjies Point granite of the Saldanha batholith and on geochronological evidence probably corresponds in age (500- 600 m.y.) with the Cape Peninsula granite. The younger granites of Darling are tentatively correlated with the Cape Columbine granite of the Saldanha batholith. The northeastern boundary of the Darling batholith is a major fault, the Colenso fault, which is considered to extend as far as Northwest Bay, Saldanha. It is proposed that the Darling batholith occupies a down-faulted block within a graben and that the hybrid granodiorite represents a remnant synform of the roof rocks intruded by the granite. The younger granites constitute only four percent by volume of the batholith and may represent anatectic melts from a nearby subjacent source.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: To date, the only volcanic rocks described from the Cape Granite Suite are ignimbrites that crop out along the western margin of Langebaan lagoon, to the south of Saldahna. These ignimbrites, with an age of 515 ± 3 Ma, represent the youngest rocks within the Suite. This study aims to investigate the petrogenesis of fine grained granitic rocks exposed to the north of Langebaan lagoon, as well as to reassess the classification of these rocks as a sub-volcanic quartz porphyritic intrusive. These rocks exhibit a dark grey to brown micro- to crypto-crystalline matrix containing prominent feldspar and quartz phenocrysts that are often embayed and broken. Phenocrysts of biotite and orthopyroxene (Fs50-70) can be identified microscopically, as can replacement of both phases by chlorite. Ilmenite commonly occurs in close association with the orthopyroxene phenocrysts. A second generation of poikiloblastic biotite overgrows the matrix and is clearly formed through sub-solidus reaction. The feldspar phenocrysts are commonly microcline microperthite. Contact exposures can be observed in the study area which indicates that the finer grained rock intruded older coarser grained granites. The predominance of broken phenocrysts as well as the presence of fiamme present in outcrop in rocks with a microcrystalline matrix is indicative of a volcanic origin, suggesting that these rocks be classified as ignimbrite as opposed to quartz porphyry. The foregoing observations and features could be interpreted to represent a welded ignimbrite deposit which is underlain by coarse grained granite. The finer grained ignimbrite would then represent a subsequent intrusion by a later pulse of similar magma along the contact with the coarser grained granite. The ignimbrites are silicic with SiO2 ranging between 69 and 76 wt. %; they are mildly peraluminous with values for ASI (ASI = mol. Al2O3/ (CaO+Na2O+K2O)) ranging from 1.02 to 1.09; and ASI is negatively correlated with Mg + Fe (hereafter maficity). Tight to very tight inter-element correlations exist for several major elements as well as trace elements when plotted against maficity. The following R² values apply: Al =0.94; Ca = 0.98; Si = 0.97; Ti = 1.00; Na =0.90; Zr =0.95; La = 0.87. These elements are all positively correlated with maficity, except for Si which is negatively correlated. Orthopyroxene and ilmenite represent early formed, high temperature minerals in the magma. In the biotite-poor rocks, ilmenite represents the main reservoir of titanium whilst orthopyroxene represents the main MgO and FeO reservoir. The exceptionally tight Ti: maficity correlation requires that both these minerals always be present at the same molecular ratio in the magma, despite the significant range in maficity portrayed by the rocks and despite the fact that these minerals have different size-density relationships. This exceptionally tight correlation can be readily interpreted to reflect entrainment of a peritectic assemblage consisting of ilmenite and orthopyroxene. The Al, Ca and Na correlations require the entrainment of peritectic plagioclase. The decreasing trend for ASI requires the entrainment of peritectic clionopyroxene. A near perfect match with the concentrations of these elements in the ignimbrites is produced by modelling entrainment of a peritectic assemblage consisting of plagioclase, ilmenite, orthopyroxene and clionopyroxene in stoichiometric proportions dictated by the melting reaction. A peritectic assemblage formed by these phases’ points to the partial melting of a source undergoing coupled biotite and hornblende fluid-absent melting, with hornblende being subordinate. The opx- and ilmenite-rich micro-domains in the rocks represent zones in the magma rich in original peritectic orthopyroxene and ilmenite. In contrast, the peritectic plagioclase demanded by the chemistry of the rocks has melted during ascent due to overheating and decreasing water solubility in the melt. The phenocrystic potassium feldspar observed in the rocks crystallised after significant cooling and the physical behaviour of these crystals does not shape the chemistry of the magma. K contents of the ignimbrites are however not well replicated by this modelling, which predicts a significant K decrease due to dilution. K in the rocks is not correlated with maficity. This may reflect the fact that the K behaviour represents two slightly different source protoliths with differing K contents. / AFRIKAANSE OPSOMMING: Tot op hede is die enigste vulkaniese rots van die Kaapse Granietgroep wat al beskryf is ignimbriete wat teen die westelike grens van die Langebaan-lagune, na die suide van Saldanha, aan die oppervlak kom. Hierdie ignimbriete, met ’n ouderdom van 515 ± 3 Ma, verteenwoordig die jongste gesteentes in die Groep. Die doel van hierdie studie was om die petrogenese van fynkorrelrige granietrots wat na die noorde van die Langebaan-lagune blootgestel is, te ondersoek, en ook die klassifikasie van hierdie rotse as ’n subvulkaniese kwartsporfier- intrusiewe gesteentes te assesseer. Hierdie gesteentes toon ’n donker grys tot bruin mikro- tot kriptokristalvormige matriks wat prominente veldspaat en kwartsfenokriste bevat wat dikwels bogtig en gebreek is. Fenokriste van biotiet en ortopirokseen (Fs50-70) asook vervanging van albei fases deur chloriet kan mikroskopies geïdentifiseer word. Ilmeniet kom dikwels naby ortopirokseenfenokriste voor. ’n Tweede generasie poikiloblastiese biotiet groei die matriks toe en is duidelik deur subsolidusreaksie gevorm. Die veldspaatfenokriste is gewoonlik mikroklien-mikropertiet. Kontakblootstelling kan in die studiegebied waargeneem word, wat aantoon dat die fynkorrelrige rots ander grofkorrelrige granietgesteentes intrudeer het. Die oorheersing van gebroke fenokriste asook die teenwoordigheid van ‘fiamme’ strukture in die rotsdagsoom met ’n mikrokristalvormige matriks dui op vulkaniese oorsprong, wat aan die hand doen dat hierdie gesteentes as ignimbriete eerder as kwartsporfier geklassifiseer kan word. Hierdie waarnemings en eienskappe kan geïnterpreteer word as verteenwoordigend van ’n gelaste ignimbriet-afsetting wat deur grofkorrelrige graniet onderlê word. Die fynkorrelrige ignimbriet stel dan ’n daaropvolgende intrusie voor deur ’n latere puls van soortgelyke magma teen die kontak met die grofkorrelrige graniet af. Die ignimbriete is silisies met SiO2 wat wissel tussen 69 en 76 wt. %; hulle is matig peralumineus met waardes vir ASI (ASI = mol. Al2O3/ (CaO+Na2O+K2O)) wat wissel van 1.02 tot 1.09; en ASI is negatief gekorreleer met Mg + Fe (hierná mafiese komponent). Nou tot baie nou inter-elementkorrelasies bestaan vir verskeie groot elemente asook spoorelemente wanneer dit teen die mafiese komponent gestip word. Die volgende R²-waardes is van toepassing: Al =0.94; Ca = 0.98; Si = 0.97; Ti = 1.00; Na =0.90; Zr =0.95; La = 0.87. Hierdie elemente is almal positief met die mafiese komponent gekorreleer, buiten Si, wat negatief gekorreleer is. Ortopirokseen en ilmeniet verteenwoordig vroeg gevormde, hoëtemperatuur-minerale in die magma. In die biotiet-arme rotse stel ilmeniet die hoofreservoir van titaan voor, terwyl ortopirokseen die vernaamste MgO- en FeO-reservoir voorstel. Die buitengewoon nou Ti: mafiese-korrelasie vereis dat albei hierdie minerale altyd in dieselfde molekulêre verhouding in die magma teenwoordig moet wees, ondanks die beduidende omvang van die mafiese komponent wat deur die gesteentes getoon word en ondanks die feit dat hierdie minerale verskillende grootte–digtheidsverhoudings het. Hierdie buitengewoon nou korrelasie kan geredelik geïnterpreteer word om meesleping van ’n peritektiese groep te weerspieël wat uit ilmeniet en ortopirokseen bestaan. Die Al-, Ca- en Na-korrelasies vereis die meesleping van peritektiese plagioklaas. Die verminderende neiging tot ASI vereis die meesleping van peritektiese klionopirokseen. ’n Byna perfekte passing met die konsentrasies van hierdie elemente in die ignimbriete word voortgebring deur die modellering van meesleping van ’n peritektiese groep bestaande uit plagioklaas, ilmeniet, ortopirokseen en klionopirokseen in stoïgiometriese verhoudings wat deur die smeltreaksie bepaal word. ’n Peritektiese groep wat deur hierdie fases gevorm word, dui op die gedeeltelike smelting van ’n bron wat gekoppelde biotiet- en horingblende- vloeistofafwesige smelting ondergaan, met horingblende wat ondergeskik is. Die ortopirokseen- en ilmeniet-ryke mikrodomeins in die gesteentes verteenwoordig sones in die magma wat ryk is aan oorspronklike peritektiese ortopirokseen en ilmeniet. Hierteenoor het die peritektiese plagioklaas wat deur die chemie van die gesteentes vereis word tydens styging gesmelt weens oorverhitting en dalende wateroplosbaarheid in die smeltsel. Die fenokristiese kaliumveldspaat wat in die rotse waargeneem is wat ná aanmerklike afkoeling gekristalliseer het en die fisiese gedrag van hierdie kristalle vorm nie die chemie van die magma nie. Die K-inhoud van die ignimbriete word egter nie goed deur hierdie modellering gerepliseer nie, wat ’n aanmerklike K-afname weens verdunning voorspel. K in die rotse is nie met mafiese komponente gekorreleer nie. Dit kan die feit weerspieël dat die K-gedrag twee effens verskillende bronprotoliete met verskillende K-inhoud voorstel.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Rhythmic magmatic layering in granites is an intriguing feature that has been reported from plutons with contrasting chemical compositions from a wide range of tectonic settings. Layered granites are rare and occur in association with volumetrically dominant non-layered rocks having similar composition. Understanding the origin of such layering in granites, particularly from well exposed outcrops, may give crucial insights on the physical-chemical conditions and processes (such as fractional crystallization, size and composition of individual magma batches, efficiency of mixing between batches etc.) within magma chambers during their construction. In the Cape Granite Suite, rhythmic layering is exceptionally well preserved in outcrops of the S-type granodioritic to monzogranitic Peninsula pluton along the coastline of the small town of Llandudno. At Llandudno, the granodioritic facies of the Peninsula pluton is exposed as a coarse-grained, cordierite and K-feldspar phenocrystic granite (referred to as Llandudno granodiorite in this study). Layering within the Llandudno granodiorite occurs within several lens-shaped bodies, of which the largest, with a thickness of about 5 m. The studied rhythmic sequence comprises 50 layers with thicknesses ranging between 5 and 50 cm. Each layer is typically characterised by a sharp lower contact overlain by a biotite-rich portion containing approximately 50 vol. % biotite. This mafic lower portion, grades upwards into a strongly leucocratic upper portion enriched in quartz, plagioclase and K-feldspar. The layered rocks host a substantially lower abundance of K-feldspar megacrysts and cordierite than the surrounding Llandudno granodiorite. In particular, cordierite crystals are five times less abundant in the layered zone than the un-layered Llandudno granodiorite. The K-Feldspars megacrysts that do occur within the layering are generally concentrated in the mafic part of some of the layers and are commonly oriented parallel to the layering. The K-feldspar megacrysts are significantly smaller than those in Llandudno granodiorite, but were found to be similar in composition. The whole rock compositions of the layered rocks are peraluminous with A/CNK >1.4. They have lower Mg#s (51 to 58) than the Llandudno granodiorite (51 to 65). The Na2O/CaO ratio of mafic and leucocratic portions is higher than in the Peninsula pluton. The mafic portions show an enrichment of trace and rare earth elements relative to the leucocratic portions and Peninsula pluton. The difference in bulk rock composition as well as trace and rare earth elements composition shows that the layered rocks were not formed by magmas produced by differentiation of the Llandudno granodiorite. The differences in biotite composition in basal sections of adjacent layers suggest that each layer represents a separate magma pulse, with the mafic portions of the layers largely representing an accumulation of the crystals in the magma batch at the time of injection and that these crystals mostly consist of orthopyroxene and biotite. This is in agreement with the findings based on the whole rock chemistry of the layers compared with the Llandudno granodiorite. The inclusion of K-feldspar megacrysts from the host granite into the layering, as well as the exceptional state of preservation of the layering, suggests that the layering formed relatively late in the crystallization sequence of the granite. This, in combination with the evidence for subtle differences in the chemistry of the magmas that formed separate layers, suggests that the layers represent a frozen feeder zone in the Peninsula pluton recording small successive pulses of magma addition. Frequent occurrence of the less-preserved layered biotite schlieren in the pluton may represent the equivalents of the layering that have become partially digested and texturally equilibrated with the host magma. / AFRIKAANSE OPSOMMING: Ritmiese magmatiese gelaagdheid in graniet is ’n interessante kenmerk van plutone met teenstellende chemiese samestellings in ’n wye verskeidenheid tektoniese omgewings. Gelaagde graniet is seldsaam en kom saam met volumetries dominante, niegelaagde gesteentes met soortgelyke samestellings voor. ’n Begrip van die oorsprong van hierdie gelaagdheid in graniet, veral in goed sigbare dagsome, kan belangrike insig verleen in die fisies-chemiese omstandighede en prosesse (soos fraksionele kristallisasie, die grootte en samestelling van individuele volumes magma, die doeltreffendheid van volume-vermenging, ensovoorts) in magmakamers gedurende die vorming daarvan. In die Kaapse granietgroep het ritmiese gelaagdheid besonder goed behoue gebly in dagsome van die S-tipe granodioritiese tot monsogranitiese Skiereilandse plutoon langs die kuslyn van die voorstad Llandudno. Die granodioritiese fasies van die Skiereilandse plutoon by Llandudno manifesteer in die vorm van ’n grofkorrelrige, kordiëritiese en K-veldspatiese fenokris-graniet (wat in hierdie studie Llandudno-granodioriet genoem word). Gelaagdheid in die Llandudno-granodioriet kom voor in verskeie lensvormige massas, waarvan die grootste sowat 5 m dik is. Die bestudeerde ritmiese opeenvolging bestaan uit 50 lae met diktes van tussen 5 cm en 50 cm. Elke laag word gekenmerk deur ’n skerp onderste kontakvlak wat bedek is met ’n biotiet-ryke gedeelte wat uit sowat 50 vol % biotiet bestaan. Hierdie mafiese onderste gedeelte gradeer opwaarts in ’n sterk leukokratiese boonste gedeelte wat ryk is aan kwarts, plagioklaas en K-veldspaat. Die gelaagde gesteentes bevat beduidend minder K-veldspatiese megakriste en kordiëriet as die omliggende Llandudno-granodioriet. Die kordiëritiese kristalle in besonder kom vyf keer minder in die gelaagde sone as in die niegelaagde Llandudno-granodioriet voor. Die K-veldspatiese megakriste wat wél in die gelaagdheid voorkom, is oor die algemeen in die mafiese gedeelte van sommige lae gekonsentreer, en is meestal parallel met die gelaagdheid georiënteerd. Die K-veldspatiese megakriste is aansienlik kleiner as dié in die Llandudno-granodioriet, maar het ’n soortgelyke samestelling. Die heelrots-samestellings van die gelaagde gesteentes is peralumineus, met A/CNK >1,4. Dit toon ook laer Mg#s (51 tot 58) as die Llandudno-granodioriet (51 tot 65). Die Na2O/CaO-verhouding van die mafiese en leukokratiese gedeeltes is hoër as in die Skiereilandse plutoon. In die mafiese gedeeltes is daar ‘n verryking in spoor- en skaarsaarde-elemente relatief tot die leukokratiese gedeeltes sowel as die Skiereilandse plutoon. Die verskil in heelrots-samestelling sowel as spoor- en seldsame-aardelementsamestelling toon dat die gelaagde gesteentes nié gevorm is deur magmas wat uit differensiasie van die Llandudno-granodioriet ontstaan het nie. Uit die verskille in die biotiet-samestelling van basissnitte uit aanliggende lae word afgelei dat elke laag ’n afsonderlike magmapuls verteenwoordig, terwyl die mafiese gedeeltes van die lae hoofsaaklik ‘n versameling van kristalle verteenwoordig wat tydens inplasing van die magma volume gevorm het, meestal ortopirokseen en biotiet. Dít stem ooreen met die bevindinge rakende die heelrots-chemie van die lae in vergelyking met die Llandudno-granodioriet. Die insluiting van K-veldspatiese megakriste vanaf die moedergraniet by die gelaagdheid, dui daarop dat die gelaagdheid betreklik laat in die kristallisasie-orde van die graniet gevorm het. Dít, tesame met bewyse van subtiele verskille in die chemie van die magmas waaruit afsonderlike lae gevorm is, dui daarop dat die lae ’n bevrore toevoersone in die Skiereilandse plutoon uitmaak wat kort, opeenvolgende pulse van magmatoevoeging vasgevang het. Die gereelde voorkoms van swakker bewaarde, gelaagde biotiet-sliere in die plutoon kan moontlik dui op sones van die gelaagdheid wat gedeeltelik verteer is en tekstureel met die moedermagma ge-ekwilbreer het.

The Ngoye Granite Gneiss Formation is located in the Natal sector of the Proterozoic Namaqua-Natal Mobile Belt, about 10 km southwest of Empangeni. It forms a prominent east-west trending elongate whalebacked massif some 30 km in length, within amphibolitic gneisses and schists of the Tugela Group. A suite of twelve different, gneissic granitoids has been-recognised within the Ngoye Formation on the basis of field relationships, mineralogy and supportive geochemistry. They range in composition from peraluminous syenite to peralkaline granite. Peraluminous varieties are typically muscovite and garnet-bearing whereas metaluminous granites in the formation contain olivegreen biotite and/or hornblende and sphene. Riebeckite, aegerine and yellow-brown biotite, with accessory fluorite and zircon are characteristic of the peralkaline granites. Geochemically, the samples analysed display a range in SiO₂ from 63,79 - 78,47∞, are extremely depleted in CaO and MgO, while being enriched in Na₂O and K₂O. Depletion of CaO relative to alkalis is shown by an alkali-lime index of only 36, suggestive of an alkalic character. The agpaitic index (A. I. = mole Na₂O + K₂O/AL₂O₃) of the peralkaline samples ranges between 1,02 and 1,16; which classifies them as granites of comenditic affinity. Various chemical classification schemes have been tested and evaluated, of which the RI - R2 multicationic diagram provides results most similar to modally-derived terminology. Accordingly, the Ngoye granitoids are shown to range from minor syenites and alkali granites to predominant monzo - and syeno-granites. Trace element data indicate that the peralkaline granites are enriched in Nb, Zr and Zn relative to the other, non-peralkaline, granites in the formation. In addition, radioactive, magnetite-bearing quartz-rich rocks associated with the peralkaline granites, have extremely enhanced contents of Nb, Zr, Y, Zn, U, Th and to a lesser extent Sn and W. Peraluminous and near-peraluminous granites have the highst Rb/Sr and Rb/Ba ratios of all samples analysed, as well as enhanced Sn, U and Th contents while Zr is notably depleted. Small, muscovite-rich pods associated with muscovite-bearing granites are highly enriched in Sn. The application of certain discriminants based on modal and geochemical parameters has shown the Ngoye Formation to comprise typical "A" - type granites. "A" - type granites are characteristically intruded as ring complexes into anorogenic or post-orogenic tectonic settings in attenuated or epiorogenically-domed continental crust. Comparison of the Ngoye Formation wi th the well-known "younger granite" complexes of Nigeria and Saudi Arabia reveals marked similarities. The inference is therefore that the Ngoye Formation represents a metamorphosed "postorogenic" granite complex with most of the hallmarks of "A" type or "within-plate" magmatism. Four phases of deformation (D₁ to D₄) are recognised within the area mapped. Evidence of D₁ deformation is rare, but rootless folds within the transposed layering in the amphibolitic country rocks reflect the intensity of this prograde metamorphic event, M₁, during which upper amphibolite grades were achieved. Field evidence shows that the Ngoye granites were intruded after the D₁ event and prior to D₂. This latter event caused widespread folding about east-west F₂ axes, with the development of a pervasive S₂ planar fabric within the antiformally folded Ngoye Formation. S₂ is locally developed in the amphibolitic country rocks. The D₂ event culminated in the development of northward-directed overthrusting and retrogressive ,M₂, metamorphism of mylonitic thrust planes. Lateral shearing characterizes D₃, with development of macroscopic mylonites and mesoscopic conjugate shear zones. This was in response to a sinistral sense of movement, as indicated by prominent sub-horizontal extension lineations (L₃) and microscopic asymmetric augen structures. D₄ is deduced from stereograms and is indicated as cross-folding of F₃ fold axes. / Thesis (M.Sc.)-University of Durban-Westville, 1985.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: This study focussed on the comparison of accessory mineral chemistry and paragenesis in the S-, I- and A-type granites of the Cape Granite Suite. The objective of the study was to use differences in accessory mineral chemistry and petrography to give insight in the evolution, recycling and formation of continental crust as affected by the Cape Granite Suite. Because of the high partition coefficients of the REE and trace elements into accessory minerals these minerals play an important role to explain granite evolution. The accessory mineral features are used as discriminators between barren and mineralized S-, I- and A-type granites in the suite. The petrography of the suite reflects the allanite-monazite dichtonomy with allanite and titanite occurring in the I -type granites while monazite occurs in S-type granites. Monazite becomes unstable in high Ca melts such as I-type granites. Apatite occurs in all the plutons which reflects its stability over a wide range of geological conditions. Rounded crystal habits of apatite and monazite in S-type granites indicate they are relics of sedimentary source rocks. Concentric growth- and sectoral zoning, as observed with CL and SEM, are common features in minerals that crystallized in barren plutons. The overprinting of magmatic textures reflects secondary processes, such as those that occurred in mineralized plutons, by "patchy" zoning and irregular alteration rims (coronas) in the mineralized plutons' accessory minerals. CL and SEM observations revealed that REE are redistributed into these coronas. Mineral chemistry of the accessory minerals reflects mostly the whole rock chemistry and physical conditions of the magmas. (Al~ Fe) substitution in titanite is controlled by P-T conditions, together with Ca, Mn and Mg substitution which is controlled by whole-rock chemistry, are good discriminators in S- and I-type granites. LREE and Sr content in allanite discriminate between the plutons and reflect the whole-rock chemistry. Apatite, because it occurs in all the plutons, is the most useful accessory mineral for discriminating between the plutons. From previous studies it is known that ASI controls the two main substitutions in apatite: Ca+P~Si+REE and Na+REE~2Ca, Fe and Mn content in apatite (0,1 pfu Mn and 0,05 pfu Fe contents are the cut-off between S-and Itype granites) are controlled by oxidation state of the magma and Sr, REE and Mg reflect whole-rock chemistry. The content of these elements in apatite can be used as discriminators between the plutons as their ASI, oxidation states and whole-rock chemistry differ. REE patterns of monazite and allanite are LREE enriched without exception, while apatite and titanite REE patterns are mostly birdwing profiles with occurrences of LREE or HREE enrichment. These patterns are influenced by crystallization of coexisting REE-bearing phases, fractionation history of the pluton and by crystallization sequence of the accessory minerals. Phase relationships were investigated experimentally for monazite and allanite under magmatic conditions (870 °C, 1,8 kbar) in peraluminous to metaluminous granitic melts. Monazite became unstable when aqueous CaCh solutions of 0.7-7 g CaCh/10cc H20 where added to peraluminous melts (ASI> 1 ). Monazite broke down to Cl-apatite and corona textures were observed. Allanite was tested in peraluminous (ASI> 1) and metaluminous (ASI=1) melts with different P20 5 (0.08 - 0.25 wt%) concentrations. Allanite became unstable at high phosphorus and peraluminous melt conditions and broke down to LREE-P± Al, Ca, K phases. Corona (kelyphitic) textures were observed. It is also clear that phosphorus played an important role, with Al, in the melt structure as can be seen from the absence or presence of crystals in the glasses of the different melts. This is possible because adding of phosphorus to the melt results in a depression of the T of the granitic melts' liquidus. Because of an interaction of phosphorus with Si networks and formation of complexes it also depolymerize aluminosilicate melts. The solubility of monazite was also tested in aqueous solutions under atmospheric conditions and low T (100-350 °C) to investigate low TIP alteration. Solutions ofCaCb +NaCl (1:1) chlorides were very reactive and dissolved the monazite completely, while solutions of CaCb were less reactive and only partly dissolved the monazite. These experiments demonstrate the concentrations required in hydrothermal solutions to destabilize monazite and explain textures found in natural rocks. Accessory minerals are useful discriminators between S-, I- and A-type granites and also their mineralized counterparts. Discrimination does depend on what accessory minerals are present and therefore apatite is the best mineral because it occurs in all the plutons. Petrography of these minerals is an indicator of primary or secondary processes. / AFRIKAANSE OPSOMMING: Die fokus van hierdie studie was om die mineraalchemie en paragenese van bykomstige minerale in S-, 1- en A-tipe graniete van die Kaapse Graniet Suite te vergelyk. Die doelwit van hierdie studie was om die verskille in chemie en petrografie van bykomstige minerale te gebruik as insig in die evolusie, herwinning en ontstaan van kontinentale kors soos geaffekteer deur die Kaapse Graniet Suite. Omdat SAE en spoorelemente hoe partisiekoeffisiente het vir bykomstige minerale speel hierdie minerale 'n belangrike rol om graniet evolusie te verklaar. Genoemde kenmerke van bykomstige minerale is ook gebruik om te onderskei tussen ongemineraliseerde en gemineraliseerde S-, 1- en A-tipe graniete in die suite. Die petrografie van die Kaapse Graniet Suite weerspieel die tweeledigheid van allanietmonasiet deurdat allaniet en titaniet in 1-tipe graniete en monasiet in S-tipe graniete voorkom. Monasiet word dus onstabiel in hoe Ca, 1-tipe, graniete. Apatiet kom in al drie tipes voor wat die mineraal se stabiliteit in verskeie geologiese omgewings weerspieel. Geronde kristalvorme , of reliekteksture, van apatiet en monasiet in S-tipe graniete weerspieel die sedimentere oorsprong van hierdie graniete. Konsentriese groei - en sektorale sonering kom algemeen voor in bykomstige minerale in ongemineraliseerde plutone. Sekondere veranderings rande (koronas) en onreelmatige sonering in gemineraliseerde plutone se bykomstige minerale is 'n aanduiding dat primere teksture gedeeltelik vemietig is deur sekondere prosesse. Katodeluminisensie en skandeerelektron mikroskopie ondersoeke het bewys dat SAE gehermobiliseer word na die koronas. Heelrotschemie en fisiese toestande van die magma word weerspieel in die mineraalchemie van bykomstige minerale. (Al~Fe) substitusie in titaniet word beheer deur P-T toestande en is, saam met Ca, Mn en Mg inhoud wat heelrotschemie weerspieel, goeie diskriminators in S- en 1-tipe graniete. LSAE en Sr inhoud in allaniet onderskei goed tussen plutone omdat hierdie elemente die heelrotschemie weerspieel. Omdat apatiet in al die plutone voorkom is dit die bruikbaarste mineraal om as diskriminant te gebruik. V anuit vorige werk is dit bekend dat die aluminium versadigings indeks die twee hoofsubstitusies: Ca+P~Si+SAE en Na+SAE~2Ca beheer, Fe en Mn inhoud in apatiet (0,1 pfu Mn en 0,05 pfu Fe is die afsnypunt tussen S- en 1-tipe graniete) weerspieel die oksidasietoestand van die magma en Sr, SAE en Mg weerspieel heelrotschemie. Saam kan hierdie elemente dus gebruik word as diskriminatore tussen die verskillende plutone. SAE patrone van allaniet en monasiet is sonder uitsondering verryk in die LSAE, terwyl apatiet en titaniet meestal "birdwing" profiele wys, maar kan ook verryk wees in LSAE of SSAE. Hierdie patrone word beinvloed deur kristallisasie van ander SAE-draende minerale, fraksionering van minerale uit die magma en die kristallisasie volgorde van die mineral e. Faseverwantskappe is eksperimenteel getoets tussen monasiet en allaniet in magmatiese toestande (780 °C en 1,8 kbar). Monasiet word onstabiel in 'n peralumineuse smelt (Aluminium versadigingsindeks >1) as waterig oplossings met konsentrasies van 0.7-7 g CaCh/1 0 cc H20 bygevoeg word. Cl-apatiet vorm as veranderingsproduk om die rande (koronas ). Allaniet is getoets in peralumineuse (Aluminium versadigingsindeks > 1) en metalumineuse smelte (Aluminium versadigingsindeks =1) met wisselende konsentrasies P20s (0.08 - 0.25 wt%). Allaniet het onstabiel geraak in peralumineuse smelte en hoe fosfor konsentrasies en het afgebreek na fases van LSAE+P± Ca, Al, K. Korona (kelifitiese) teksture is waargeneem. Hierdie eksperimente bewys dat fosfor, saam met Al, 'n belangrike rol speel in smeltstruktuur. Dit kan gesien word in die teenwoordig- of afwesigheid van kristalle in die glas. Dit is moontlik deurdat die byvoeging van fosfor 'n verlaging in die graniet likwidus temperatuur veroorsaak. Fosfor depolimeriseer ook aluminiumsilikaat smelte deur interaksie en kompleksvorming tussen fosfor en silika netwerke. Die oplosbaarheid van monasiet is ook getoets in waterige oplossings onder atmosferiese toestande en lae T (100-350 °C) om lae PIT veranderinge te ondersoek. 'n Versadigde oplossing van CaCh en NaCl (1:1) chloried het monasiet heeltemal opgelos terwyl 'n versadigde oplossing van CaCh monasiet net gedeeltelik opgelos het. Hierdie eksperimente dui op die konsentrasies nodig vir hidrotermale vloeistowwe waar bykomstige minerale onstabiel raak en verklaar teksture in natuurlike rotse. Bykomstige minerale kan dus gebruik word as diskriminators tussen ongemineraliseerde en gemineraliseerde plutone en ook tussen S-, I- en A-tipe graniete. Hulle kan egter net gebruik word as hulle teenwoordig is en daarom is apatiet die beste omdat dit in al die plutone aanwesig is. Petrografie is 'n aanduiding van magmatiese of sekondere prosesse.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The close spatial and temporal relationship of shear-zones and magmas is commonly interpreted to indicate positive feedback between magma migration, granitic emplacement and shear-zone-associated deformation. Emplacement geometries and structural fabrics are however rarely preserved, hampering the study of shear-zones and granitic magmas interactions. This study focuses on an area around the Pofadder Shear Zone (PSZ) in Namibia and South Africa as a case study for granitic bodies, mainly as pegmatite sills and dykes, and their spatial and temporal relationships to a crustal-scale shear-zone. The PSZ is a NW-SE trending, dextral, Mesoproterozoic-Neoproterozoic transpressional shear-zone in Namaqualand, interpreted to have accommodated late-stage lateral escape of the Namaqua Metamorphic Complex in response to southward indentation of the Kaapvaal Craton around 1030 – 1080 Ma. In this study it is shown that the shear-core records an asymmetrical strain variation across the PSZ. This is indicated by pervasively banded ultramylonites, mylonites and the significant development of pervasive phyllonites at the southern margin, defining the internal ductile to brittle-ductile fabrics of the shear, during a progressive deformational evolution. Mapping of the PSZ fabrics and associated pegmatites documents how pegmatites are emplaced in structurally distinctive sites within, and adjacent to the PSZ. New U-Pb monazite ages derived from this study, show how pegmatite emplacement has occurred at different times of shear-zone development. The pegmatites are emplaced into earlier ductile to later brittle-retrograde fabrics that accompanied the ca. 45 Ma shear-zone exhumation. Pegmatites concentrated along the northern PSZ-margin are interpreted to be controlled by anisotropies developed axial planar to large km-scale and parasitic folds during the initial, predominately strike-slip stages of shearzone deformation that occurred as early as 1005 ± 5 Ma. Within the PSZ core, pegmatite emplacement is controlled by the syn-kinematic development of (a) subvertical, mylonitic and phyllonitic foliations and (b) fracture permeabilities created by synthetic Riedel shears and dextral dilatant jogs. The most significant pegmatite development around the PSZ is the Skimmelberg Pegmatite Stockwork (SPS) which forms an extensive interconnecting network of concurrent, foliation-parallel sills and thick (> 50 m) discordant dykes within the southern footwall of the PSZ. The dykes intrude as late as 958 ± 5 Ma into feather-shaped N-S extensional fractures (mode I) that developed due to episodic stick-slip at the boundary between the PSZ core and footwall rocks during periods of late-stage transpression. The SPS forms a steeply dipping fracture network that not only creates space needed for emplacement but effectively acts as a conduit for magma transport along the margin of the PSZ. The large extensional fractures of SPS create the necessary hydraulic gradients to tap the magma source of a regional trending pegmatite belt and form a sheeted complex adjacent to the PSZ. Therefore, this study documents how, during the progressive exhumation of a largescale transcurrent shear-zone, magma emplacement is not only concentrated within the highly permeable, high-strain domains (cores) of shear-zones but may be concentrated in diachronous, structurally controlled sites along the shear-zone margins. / AFRIKAANSE OPSOMMING: Die noue ruimte-tydsverband tussen skuifskeure en magmas word algemeen geïnterpreteer as ‘n aanduiding van positiewe terugkoppeling tussen magma migrasie, graniet-inplasing en skuifskeurgeassosieerde vervorming. Geometrie en struktuurmaaksels van inplasings word egter selde bewaar en belemmer die studie van interaksies tussen skuifskeure en graniet-magmas. Die studie fokus op ‘n area rondom die Pofadder Skuifskeur (PSS) in Namibië en Suid-Afrika as ‘n gevallestudie vir graniet-liggame, hoofsaaklik as pegmatiet plate en gange, asook voorafgenoemde se ruimte-tydsverband met ‘n grootskaalse skuifskeur. Die PSS is ‘n NW-SO-waarts strekkende, regs-laterale, Mesoproterosoïse-Neoproterosoïse transpressieskuifskeur in Namakwaland, wat geïnterpreteer word om die latere-stadium laterale ontsnapping van die Namakwa Metamorfiese Kompleks te akkomodeer in reaksie op die suidwaartse indrukking van die Kaapvaal Kraton omstreeks 1030-1080 Ma. In hierdie studie word getoon dat asimmetriese vervormingsvariasie deur die skuifskeurkern aangeteken word. Hierdie word aangetoon deur gebande ultramilioniete, milioniete en die noemenswaardige ontwikkeling van filoniete wat die suidelike rand deurtrek en definiëer die interne plastiese- tot bros-plastiese maaksels van die skuifskeur gedurende ‘n progressiewe vervormingsevolusie. Kartering van die PSS maaksels en geassosieerde pegmatiete dokumenteer hoe pegmatiete, aangrensend en binne die PSS, in eiesoortige strukturele terreine binnedring. Nuwe U-Pb monasiet ouderdomme, afgelei vanuit hierdie studie, toon aan hoe inplasing plaasgevind het gedurende verskillende tye van skuifskeurontwikkeling. Pegmatiete het vroeëre plastiesetot latere bros-retrogressiewe maaksels binnegedring wat die herontbloting van die ca. 45 Ma skuifskeur meegaan. Pegmatiete, gekonsentreerd langs die noordelike rand van die PSS, word geïnterpreteer as beheer deur anisotrope wat parallel aan die asvlak van groot km-skaalse en ondergeskikte plooie ontwikkel gedurende die aanvanklike, hoofsaaklik strekkingwaarste, stadiums van skuifskeurontwikkeling wat so vroeg as 1005 ±5 Ma plaasgevind het. Binne die kern van die PSS word die inplasing van pegmatiete beheer deur die sinkenimatiese ontwikkeling van (a) subvertikale, milionitiese- en filonitiese foliasies en (b) breukdeurdringbaarheid wat gevorm is deur sintetiese riedelskuifskeure en regslaterale uitsettende “jogs”. Die mees noemenswaardige pegmatiet ontwikkeling rondom die PSS is die Skimmelberg Pegmatiet Stokwerk (SPS) wat ‘n intensiewe netwerk vorm van intergekonnekteerde konkurrente plate, parallel aan die foliasie, en dik (>50m) diskordante gange binne die suidelike vloer van die PSS. Die gange dring in so laat as 958 ± 5 Ma binne-in veervormige N-S uitbreidende breuke (modus1) wat ontwikkel het as gevolg van die episodiese hak-en-glip op die grens tussen die PSS kern- en vloergesteentes gedurende periodes van laat-stadium transpressie. Die SPS vorm ‘n styl hellende breuk-netwerk wat nie net spasie maak vir indringing nie, maar dien ook effektief as ‘n geleidingsweg vir die vervoer van magma langs die rand van die PSS. Die groot uitbreidende breuke van die SPS skep die nodige hidroliese gradiënt om die magma bron van ‘n regionale pegmatiet gordel te tap en vorm ‘n bladvormige kompleks aangrensend tot die PSS. Gevolglik dokumenteer die studie hoe, gedurende die progressiewe ontbloting van ‘n grootskaalse torsieskuifskeur, magma inplasing nie net gekonsentreer is binne die hoogs deurdringbare, hoogsvervormde areas (kerne) van skuifskeure nie, maar ook hoe magma kan konsentreer in diachroniese, struktuur beheerde gebiede teen die rande van skuifskeure.