Department of Earth Sciences

Differentiation and stabilisation of the Archean continental crust, the example of the northern edge of the Kaapvaal craton, South Africa

2017-06-09T08:29:11Z

Differentiation and stabilisation of the Archean continental crust, the example of the northern edge of the Kaapvaal craton, South Africa Vezinet, Adrien ENGLISH ABSTRACT: The Earth is one of the only solid celestial bodies displaying, at present day, an internal activity significant enough to modify its surface. This activity is mostly pictured by plate tectonic motions, which triggers the magmatic activity of mid-ocean ridges as well as subduction zones and mountain ranges development. These geodynamics are the locus of the creation of the oceanic crust, the continental crust and the reworking of older crustal material respectively that deeply modify both physical and chemical properties of the Earth’s lithosphere. One of the main consequences of these processes is the chemical layering of the continental crust, composed of granodioritic to granitic upper levels while lower crustal levels are more mafic. Two crustal processes are assumed to be responsible for such a structure: (i) the crustal growth taking place at subduction zones and (ii) the crustal differentiation taking place within collision and accretionary orogens. The PhD work presented in this manuscript focuses on the recognition and the manifestation of Archean crustal differentiation processes. The Archean eon which represents 1/3 of the geological record is featured by both lithologies unrecognized in younger eons and cryptic geodynamics. Most of investigations concentrate on the characterisation of aluminium-rich lithologies that allow an accurate determination of the pressure-temperature evolution underwent by crustal materials during crustal thickening geodynamics. However, aluminium-rich lithologies - mainly represented by metasediments - account for only 10 % on average of Archean terranes whereas orthoderived gneisses (TTG + granite) - which also testify for crustal differentiation processes - form around 75 % of these terranes. The following contribution depicts an Archean composite grey gneiss complex located at the northern edge of the Kaapvaal craton is South Africa. Results carried out during this PhD study have major consequences on Archean geodynamics. Firstly, the Uranium-Lead isotope study of zircon grains from igneous lithologies of the northern Kaapvaal craton indicates an uninterrupted recording from ca. 2.97 Ga to ca. 2.68 Ga, namely during more than 300 Ma (which is the time that separates the Carboniferous/Permian transition from present day). This protracted recording sheds light on Archean tectonics and questions the ways and means of such geodynamics. Our isotope investigation, associated with field investigation and whole rock major and trace elements chemistry, are assumed to picture accretionary orogen geodynamics that contribute to a moderated crustal thickening. Secondly, the Lutetium-Hafnium isotope signature of the same zircon grains displays unprecedented results. Our analyses indicate that igneous lithologies from the northern Kaapvaal craton evolve on a single crustal trend through time. This is interpreted as the absence of exotic material involved in the accretionary orogen, i.e. the crustal block evolved in a thermodynamically closed system. It is therefore crucial to monitor the evolution of the grey gneiss complex forming phases through time. Geochemical analyses of dated phases show a noteworthy sequence of events with: . Emplacement of a basic complex (produced by partial melting of a depleted mantle) at ca. 2.97 Ga, which is subsequently partially melted, implying the, . Production and emplacement of TTGs during 100 Ma, from ca. 2.95 Ga to ca. 2.85 Ga, themselves subsequently differentiated into, . Granites which intrude the continental crust from ca. 2.85 Ga to ca. 2.75 Ga. These geodynamics are also marked by the emplacement of greenstone belts and associated sedimentary basins. The burying of supracrustal lithologies is recognized while ongoing accretionary orogen, however, no partial melting feature is described. After the intrusion of granites at ca. 2.85-2.75 Ga, partial melting reactions are recognized within supracrustal formations. Therefore, this study aims to demonstrate the key role of a rheologically strong granitic crust for the onset of an efficient burying process. Finally, the burying of supracrustal formations towards lower crustal levels triggers mantle metasomatism, ensued partial melting, production of mantle derived granite and therefore stabilisation of the entire crustal block. The PhD work presented here shed light on the Archean tectonics. This eon is perceived as a time where geodynamics were faster than present day due to a hotter and thus a more active Earth. Nevertheless, our results show that composite grey gneiss complexes may be built over a protracted time span, achieved through self-refinement of crustal materials. Grey gneiss complexes are only moderately investigated even though information enclosed in these lithologies is complementary with those from aluminium-rich rocks. Therefore, deeper investigations of these geological objects must be a central scope in order to improve the knowledge of the Archean eon and appears necessary for the building of even more realistic geotectonic models.; AFRIKAANSE OPSOMMING: Die Aarde is een van die enigste solide hemelliggame wat huidig ‘n interne aktiwiteit beduidend genoeg toon om sy oppervlak te verander. Hierdie aktiwiteit word meestal voorgestel deur tektoniese plaat bewegings wat die magmatiese aktiwiteit van mid-oseaanrûe sowel as subduksiesones en bergreeks ontwikkeling veroorsaak. Hierdie geodinamika is die lokus van die skepping van die oseaankors, die kontinentale kors en die herwerking van ouer korsmateriaal onderskeidelik, wat beide die fisiese en chemiese eienskappe van die Aarde se litosfeer hoogs modifiseer. Een van die hoof gevolge van hierdie prosesse is die chemiese gelaagdheid van die kontinentale kors wat granodiorities tot granities in die boonste korsvlakke is terwyl die laer korsvlakke meer mafies is. Twee korsprosesse word aangeneem om verantwoordelik te wees vir so ‘n struktuur: (i) die korsgroei wat plaasvind in subduksiesones en (ii) die korsdifferensiasie wat plaasvind binne-in botsende en akkresie orogene. Die PhD werk wat aangebied word in hierdie manuskrip fokus op die herkenning en die manifestasie van Argeïese korsdifferensiasie prosesse. Die Argeïkum eon wat ‘n derde van die geologiese rekord verteenwoordig word gekenmerk deur litologieë beide onherkenbaar in jonger eone en kriptiese geodinamika. Meeste van die ondersoeke konsentreer op die karakterisering van aluminium-ryke litologieë wat die akkurate bepaling van die druk-temperatuur evolusie toelaat wat deur die korsmateriaal ervaar is tydens korsverdikkings geodinamika. Alhoewel, aluminium-ryke litologieë – hoofsaaklik verteenwoordig deur metasedimente – verantwoordelik is vir net 10 % gemiddeld van Argeïese terreine terwyl orto-afgeleide gneise (TTG + graniet) – wat ook getuig van korsdifferensiasie prosesse – vorm rondom 75 % van hierdie terreine. Die volgende bydra beeld ‘n Argeïese saamgestelde grys gneiskompleks uit wat aan die noordelike rand van die Kaapvaal kraton in Suid-Afrika geleë is. Resultate verkry gedurende die uitvoering van hierdie PhD studie het groot gevolge op Argeïese geodinamika. Eerstens, die Uraan-Lood isotoop studie van sirkoonkorrels vanaf stollingslitologieë van die noordelike Kaapvaal kraton dui ‘n ononderbroke opname van ca. 2.97 Ga tot ca. 2.68 Ga aan, naamlik gedurende meer as 300 Ma (wat die tydperk is wat die Karboon/Permium oorgang van hedendaagse tyd skei). Hierdie verlengde opname werp lig op Argeïese tektonika en bevraagteken die wyses van sulke geodinamika. Ons isotoopondersoek, geassosieër met veldondersoek en heelrots hoof- en spoorelement chemie, word aangeneem om deur akkresie orogeen geodinamika bereik te word en sodoende by te dra aan matige korsverdikking. Tweedens, die Lutesium-Hafnium isotoop karakteristiek van dieselfde sirkoonkorrels vertoon ongekende resultate. Ons analises dui aan dat stollings litologieë van die noordelike Kaapvaal kraton evoleer op ‘n enkele korstendens deur tyd. Dit word interpreteer as die afwesigheid van eksotiese materiaal betrokke in die akkresie orogeen., m.a.w. die korsblok het evoleer in ‘n termodinamiese geslote stelsel. Dit is dus noodsaaklik om die evolusie van die grys gneiskompleks wat fases deur tyd vorm te monitor. Geochemiese analises van gedateerde fases wys ‘n opmerklike opeenvolging van gebeurtenisse met: . Inplasing van ‘n basis kompleks (geproduseer deur gedeeltelike smelting van ‘n uitgeputte mantel) teen ca. 2.97 Ga, wat daarna gedeeltelik gesmelt word wat impliseer dat, . Produksie en inplasing van TTGs gedurende 100 Ma, vanaf ca. 2.95 Ga tot ca. 2.85 Ga, hulself daarna gedifferensieër in, . Graniete wat die kontinentale kors indring vanaf ca. 2.85 Ga tot ca. 2.75 Ga. Hierdie geodinamika word ook gemerk deur die inplasing van groensteenstroke en geassosieerde sedimentêre komme. Die begrawing van suprakorslitologieë word erken alhoewel daar geen gedeeltelike smelting kenmerke vir deurlopende akkresie orogene beskryf is nie. Na die indringing van graniete teen ca. 2.85-2.75 Ga, word gedeeltelike smeltingsreaksies erken in suprakorsformasies. Dus, beoog hierdie studie om die sleutelrol van ‘n reologiese sterk granitiese kors om die aanvang van ‘n doeltreffende begrawingsproses te demonstreer. Uiteindelik sal die begrawing van suprakors formasies na die laer vlakke van die kors mantel metasomatisme veroorsaak, gevolg deur gedeeltelike smelting, produksie van mantelafgeleide graniet en dus stabilisering van die hele korsblok. Die PhD werk wat hierin aangebied is werp lig op die Argeïese tektonika. Hierdie eon word beskou as ‘n tyd waar geodinamika vinniger was as vandag as gevolg van ‘n warmer en dus ‘n meer aktiewe Aarde. Nietemin, ons resultate wys dat saamgestelde grys gneiskomplekse gevorm kan word oor ‘n verlengde tydperk, bereik deur self-verfyning van korsmateriaal. Grys gneiskomplekse is net matig ondersoek alhoewel informasie bevat in hierdie litologieë die informasie van aluminium-ryke gesteentes komplimenteer. Dus moet dieper ondersoeke van hierdie geologiese voorwerpe die sentrale punt wees in orde om kennis van die Argeïkum eon te verbeter en blyk dit ook noodsaaklik vir die bou van selfs meer realistiese geotektoniese modelle.; FRENCH RESUME: La planète Terre est l’un des rares corps céleste solide connu qui possède présentement une activité interne suffisamment importante pour en modifier sa surface. Cette activité s’observe principalement au sein de l’écorce terrestre par le biais des mouvements des plaques tectoniques qui induisent l’activité magmatique des dorsales médio-océaniques, les zones de subduction ainsi que les chaînes orogéniques. Ces différentes géodynamiques sont le théâtre de processus de création de croûte océanique (dorsales), continentale (zone de subduction) mais aussi de remaniement de croûte antérieure (zones de collisions/accrétion) et modifient en profondeur les propriétés physico-chimiques de la lithosphère. Il en résulte une stratification de la croûte continentale terrestre, marquée par une croûte supérieure granodioritique à granitique - donc chimiquement acide - et une croûte inférieure plus riche en phases ferromagnésiennes, chimiquement basique à intermédiaire. Deux processus amènent à ce type de configuration : (i) la croissance crustale se déroulant dans les zones de subduction et (ii) la différenciation crustale se déroulant dans les zones de collision/accrétion. Le travail de thèse reporté dans ce manuscrit se focalise sur la reconnaissance ainsi que l’expression des processus de différenciation crustale à l’Archéen. Cet éon représente à lui tout seul 1/3 des temps géologiques, et se caractérise notamment par des lithologies diagnostiques, ainsi que des contextes géodynamiques complexes. La majorité des études sont portées sur l’investigation des phases alumineuses qui permettent de contraindre précisément les divers événements métamorphiques au cours d’une géodynamique d’épaississement crustal. Toutefois, ces phases alumineuses - incarnées principalement par les méta-sédiments - représentent rarement plus de 10 % des terrains archéens, alors qu’ils sont faits à plus de 75 % de gneiss orthodérivés (TTG + granite), témoignant eux aussi des processus de différenciation crustale. L’étude qui suit est une caractérisation du complexe de gneiss gris composite de la marge Nord du craton archéen du Kaapvaal en Afrique du Sud. Les résultats produits durant cette investigation ont amené à plusieurs conclusions importantes au regard de la géodynamique archéenne. Tout d’abord, l’étude isotopique Uranium-Plomb des zircons provenant des lithologies magmatique du Nord-Kaapvaal montre un enregistrement continu de ca. 2.97 Ga à ca. 2.68 Ga, soit sur une période de plus de 300 Ma, correspondant à la durée qui sépare la transition Carbonifère/Permien de l’actuel. Un tel enregistrement prolongé dans le temps, jamais décrit auparavant, apporte une nouvelle optique sur la tectonique archéenne. En effet, cela pose la question des modalités de la durée d’une telle géodynamique. Les résultats isotopiques, couplés aux données recueillies sur le terrain ainsi qu’aux analyses géochimiques, sont interprétés comme issus d’une géodynamique d’orogenèse d’accrétion qui a permis un épaississement modéré de la croûte continentale archéenne durant une période prolongée. De plus, l’analyse isotopique du couple Lutétium-Hafnium sur ces mêmes grains de zircon a montré un résultat, là aussi, jamais décrit auparavant. Ces analyses indiquent que l’ensemble des lithologies magmatiques présentes sur la marge Nord du craton du Kaapvaal progressent sur une unique direction d’évolution crustale au-cours du temps. Ce résultat est interprété comme attestant de l’absence de phase allochtone impliquée dans les processus de différenciation crustale, i.e. l’orogenèse évolue en système thermodynamiquement fermé. Il apparaît alors important de tracer l’évolution dans le temps des différentes phases qui constituent le complexe de gneiss gris étudié. Les analyses géochimiques des différentes phases datées du complexe de gneiss gris ont montré une séquence assez remarquable avec notamment : . La formation d’un complexe basique à 2.97 Ga produit par fusion partielle d’un manteau appauvri, qui subit un épisode de fusion partielle amenant à, . La mise en place de granitoïdes à signature géochimique TTG entre ca. 2.95 Ga et ca. 2.85 Ga, qui eux-mêmes subissent un épisode de fusion partielle permettant la formation de, . Granites intrusifs mis en place sur la période ca. 2.85 - ca. 2.75 Ga. Cette géodynamique est aussi marquée par la mise en place de ceintures de roches vertes et de bassins sédimentaires associés. Ces formations supracrustales sont enfouies durant l’orogenèse, mais pas suffisamment pour atteindre les conditions de fusion partielle. Cette configuration est modifiée après l’intrusion des granites sur la période 2.85-2.75 Ga, où des épisodes de fusion partielle sont observés au sein les formations supracrustales. Cette étude tend donc à démontrer que l’intrusion de granite différencié dans la croûte continentale est l’élément clé dans l’établissement de processus de remaniement par fusion partielle des lithologies surfaciques. Enfin, l’enfouissement des formations supracrustales a permis la métasomatome du manteau sous continental, amenant à la fusion partielle de ce dernier et donc à la cratonisation de l’ensemble du bloc continental. Ce travail apporte donc une nouvelle vision de la tectonique archéenne. En effet, l’Archéen est souvent perçu comme une période durant laquelle les processus géodynamiques sont rapides du fait d’une Terre plus chaude et donc plus active qu’à l’actuel. Or, l’étude réalisée au-cours de ce projet de thèse montre que la construction d’un complexe de gneiss gris composite correspond à une géodynamique prolongée dans le temps, accomplie au-travers de processus de différenciations crustales internes à la zone accrétée. Les complexes de gneiss gris ne sont que modérément étudiés, toutefois, les informations contenues dans ces lithologies sont complémentaires avec celles obtenues par les études métamorphiques sur les lithologies alumineuses. Il est donc nécessaire d’approfondir les investigations sur ces corps afin de mieux comprendre les modalités de mise en place des lithologies orthodérivées archéenne et construire des modèles géodynamiques les plus proches de la réalité. Thesis (PhD)--Stellenbosch University, 2017.

Repeated partial melting events in the polymetamorphic Carlos Chagas batholith : implications for the tectono-metamorphic evolution of the Araçuaí orogen (southeastern Brazil)

2017-06-09T10:13:30Z

Repeated partial melting events in the polymetamorphic Carlos Chagas batholith : implications for the tectono-metamorphic evolution of the Araçuaí orogen (southeastern Brazil) De Melo, Marilane Gonzaga ENGLISH ABSTRACT: The Araçuaí orogen (AO), located in the southeastern Brazil, and its African counterpart, the West Congo belt, is part of the Pan-African-Brasiliano orogenic system developed between the Congo and São Francisco paleocontinents. From the earliest (ca. 630 Ma) pre-collisional plutons to the latest (ca. 480 Ma) post-collisional intrusions, the Araçuaí orogen records an outstanding succession of granite production events in space and time. This study investigates the petrogenesis of the Carlos Chagas batholith (CCB), a very large body (~ 14,000 km2) composed of S-type granites ascribed to the collisional plutonism (G2 supersuite) in the back-arc region of the AO, to the east of the Rio Doce magmatic arc. CCB extends in a N-S direction between latitudes 17°S and 19°30’S in the states of Espírito Santo, Minas Gerais and Bahia. The CCB includes a dominant granite richer in garnet than in biotite, in which three mineral assemblages can be identified: 1) Qz + Pl + Kfs + Bt + Grt + Ilm ± Rt; 2) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil; and 3) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil + Spl. Rocks which contain mineral assemblage 2 and 3 all contain two generations of garnet. Textural evidence for the presence of former melt, recognized in all studied CCB samples, includes: silicate melt inclusions in poikiloblastic garnet, pseudomorphed thin films of melt surrounding both generations of garnet, pseudomorphed melt pools adjacent to garnet and biotite, and plagioclase and quartz with cuspate-lobate shapes occurring among matrix grains. Both generations of garnet crystals (Grt1 and Grt2) are unzoned in terms of major element concentration, contain small rounded inclusions of Ti-rich biotite and, in addition, the Grt2 crystals also contain inclusions of remnant sillimanite needles. Microstructural evidence, in combination with mineral chemistry, indicates that the garnet crystals grew during two distinct metamorphic-anatectic events, as the peritectic products of fluid-absent melting reactions which consumed biotite, quartz and plagioclase, in the case of Grt1, and which consumed biotite, quartz, plagioclase and sillimanite in the case of Grt2. P-T pseudosections calculated via Theriak-Domino, in combination with U-Pb monazite and zircon dating, provide new constraints on the thermal evolution of the back-arc region of the Araçuaí orogen. Data from assemblage 1 suggests P-T conditions for the first granulite-facies metamorphic event (M1) at 790-820 ºC and 9.5- 10.5 kbar, while the assemblage 2 records P-T conditions for a second granulite-facies metamorphism (M2) of around 770 ºC and 6.6 kbar. Ti-in-zircon thermometry is consistent with the phase equilibrium modelling, indicating that the two metamorphic events in the batholith reached granulite facies conditions. A wide range of monazite and zircon ages (> 825 Ma to ca. 490 Ma) have been found in CCB rocks, recording a complex history of crustal recycling and inheritance, magmatic crystallization and anateksis during the evolution of the AO. 582 Ma magmatic zircons are marked by similar Hf isotope compositions and REE patterns to those of inherited cores (ca. 825-600 Ma), indicating that the chemical signature of these crystals has likely been inherited from the source. The U-Pb ages and initial 176Hf/177Hf ratios from anatectic and/or metamorphic zircon domains are consistent with a two-stage metamorphic evolution marked by contrasting mechanisms of zircon growth and recrystallization during the orogeny. The oldest metamorphic episode (ca. 570-550 Ma) is recorded by development of thin anatectic overgrowths on older cores and by growth of new anatectic zircon crystals. Both domains have higher initial 176Hf/177Hf values compared to relict cores and display REE patterns typical of zircon that grew contemporaneously with peritectic Grt1 through biotite-absent fluid partial melting. U-Pb ages obtained in monazite and zircon (ca. 569-552 Ma) included in Grt1, further support the interpretation that the Grt1 crystals grew during the first anatectic episode. Hf isotopic and chemical evidences indicate that a second anatectic episode (ca. 535-500 Ma) is only recorded in part from the CCB rocks (assemblage 2 and 3). In these rocks, the growth of new anatectic zircon and/or overgrowth is marked by high initial 176Hf/177Hf values and also by generation of Grt2, as indicated by petrographic observations and REE patterns. On the other hand, some rocks have zircon grains formed by solidstate recrystallization of pre-existing zircon, which exhibit similar Hf isotope composition those to inherited/magmatic core domains. The M1 event likely corresponds to the striking crustal thickening and widespread anateksis in the CCB. The M2 event can be associated to asthenosphere upwelling during extensional thinning and gravitational collapse of the orogen, this produced anateksis in parts from the CCB that had been re-fertilized by retrogression along shear zones following the first granulite facies event.; AFRIKAANSE OPSOMMING: Die Araçuaí orogen (AO), geleë in die suidooste van Brasilië, en sy Afrikaanse eweknie, die Weste Kongogordel, is deel van die Pan-Afrika-Brasiliano orogenetiese stelsel ontwikkelde tussen die Kongo en São Francisco kratons. Van die vroegste (ongeveer 630 Ma) pre-botsing plutone om die nuutste (ongeveer 480 Ma) post-botsing rotse, die Araçuaí orogen rekords 'n uitstekende opvolging van graniet produksie gebeure in ruimte en tyd. Hierdie studie ondersoek die petrogenese van die Carlos Chagas batoliet (CCB), 'n baie groot liggaam (~ 14.000 km2) bestaan uit S-tipe graniet toegeskryf word aan die botsing plutonism in die back-boog streek van die AO, om die oos van die Rio Doce magmatiese boog. CCB strek in 'n N-S rigting tussen breedtegrade 17°S en 19°30'S in die state van Espírito Santo, Minas Gerais en Bahia. Die BSB sluit 'n dominante graniet ryker in granaat as in biotiet, waarin drie mineraal samestellings kan geïdentifiseer word: 1) Qz + Pl + Kfs + Bt + Grt + Ilm ± Rt; 2) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil; en 3) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil + Spl. Tekstuur bewyse vir die teenwoordigheid van die voormalige smelt, erken in al bestudeer CCB monsters, sluit in: silikaat smelt insluitings in granaat, pseudomorphed dun films van smelt omliggende beide generasies van granaat, pseudomorphed smelt poele aanliggend aan Garnet en biotite, en plagioklaas en kwarts met cuspate-lobate vorms voorkom tussen matriks korrels. Beide geslagte van granaat kristalle (Grt1 en Grt2) is unzoned in terme van belangrike element konsentrasie, bevat klein ronde insluitings van Ti-ryk biotiet en, benewens, die Grt2 kristalle bevat insluitings van oorblyfsel sillimanite naalde. Mikrostrukturele bewyse, in kombinasie met minerale chemie, dui daarop dat die granaat kristalle gegroei gedurende twee afsonderlike metamorfiese-anatectic gebeure, soos die peritektiese produkte van vloeistof-afwesig smelting reaksies wat verbruik biotiet, kwarts en plagioklaas, in die geval van Grt1, en wat verbruik biotiet, kwarts, plagioklaas en sillimanite in die geval van Grt2. P-T bereken deur Theriak-Domino, in kombinasie met die U-Pb monasiet en sirkoon dating, verskaf nuwe beperkings op die termiese evolusie van die back-boog streek van die Araçuaí orogen. Data van mineraal samestellings 1 dui PT toestande vir die eerste granulietterreine-fasies metamorfiese gebeurtenis (M1) by 790â820 ºC en 9.5â10.5 kbar, terwyl die mineraal samestellings 2 rekords PT toestande vir 'n tweede granulietterreine-fasies metamorfose (M2) van sowat 770 ºC en 6.6 kbar. Ti-in-sirkoon thermometry is in ooreenstemming met die faseewewig modellering, wat daarop dui dat die twee metamorfe gebeurtenisse in die batoliet bereik granulietterreine fasies voorwaardes. 'N Wye verskeidenheid van monasiet en sirkoon ouderdomme (> 825 Ma tot ongeveer 490 Ma) is gevind in CCB rotse, opname van 'n komplekse geskiedenis van kors herwinning, magmatiese kristallisasie en anateksis gedurende die evolusie van die AO. 582 Ma magmatiese sirkone is gekenmerk deur soortgelyke Hf isotoop komposisies en REE patrone aan dié van geërf kern (ongeveer 825-600 Ma), wat aandui dat die chemiese ondertekening van hierdie kristalle het waarskynlik geërf uit die bron. Die U-Pb ouderdomme en aanvanklike 176Hf / 177Hf verhoudings van anatectic en / of metamorfiese sirkoon domeine is in ooreenstemming met 'n twee-stadium metamorfiese evolusie gekenmerk deur kontrasterende meganismes van groei sirkoon en dekristallisatie gedurende die orogenie. Die oudste metamorfiese episode (ongeveer 570-550 Ma) is aangeteken deur die ontwikkeling van dun anatectic oorgroei op ouer gebiede en deur groei van nuwe anatectic sirkoon kristalle. Beide gebiede hoër aanvanklike 176Hf / 177Hf waardes in vergelyking met oorblyfsel cores en vertoon REE patrone tipies van sirkoon wat gelyktydig gegroei met peritektiese Grt1 deur vloeistof-vrye biotiet smelting. U-Pb ouderdomme verkry in monasiet en sirkoon (ongeveer 569-552 Ma) ingesluit in Grt1, verder te ondersteun die interpretasie dat die Grt1 kristalle gegroei gedurende die eerste anatectic episode. HF isotope en chemiese bewyse dui daarop dat 'n tweede anatectic episode (ongeveer 535-500 Ma) is slegs aangeteken in sommige CCB rotse (mineraal samestellings 2 en 3). In hierdie rotse, is die groei van nuwe anatectic sirkoon en / of oorgroei word gekenmerk deur 'n hoë aanvanklike 176Hf / 177Hf waardes en ook deur die opwekking van Grt2, soos aangedui deur petrografiese waarnemings en REE patrone. Aan die ander kant, sommige rotse het sirkoon korrels gevorm deur vastetoestand dekristallisatie van voorafbestaande sirkoon, met 'n soortgelyke Hf isotoop komposisie diegene te geërf / magmatiese domeine. Die M1 gebeurtenis waarskynlik ooreenstem met die treffende kors verdikking en wydverspreide anateksis in die CCB. Die M2 gebeurtenis geassosieer kan word om opwelling astenosfeer gedurende extensieve dunner en gravitasie ineenstorting van die orogen, hierdie geproduseer anateksis in dele van die CCB wat was weer bevrug deur agteruitgang saam skuifskeursones na aanleiding van die eerste granulietterreine-fasies metamorfiese.; PORTUGUESE RESUMO: O orógeno Araçuaí (OA) localizado no sudeste do Brasil e sua contraparte africana (cinturão Congo Ocidental) constituem o sistema orogênico Brasiliano Pan Africano desenvolvido entre as paleocontinentes Congo e São Francisco. O orógeno Araçuaí registra uma notável sucessão de eventos de produção de granitos no espaço e no tempo, que engloba desde os primeiros plútons pré-colisionais (~ 630 Ma) até as mais recentes intrusões póscolisionais (~ 480 Ma). Este estudo investiga a petrogênese do batólito Carlos Chagas (BCC), um enorme corpo (~ 14.000 km2) composto por granitos do tipo S atribuídos ao plutonismo colisional (supersuíte G2) na região de retro arco do OA, a leste do arco magmático Rio Doce. BBC estende-se em uma direção N-S entre as latitudes 17 ° S e 19°30'S, nos estados de Espírito Santo, Minas Gerais e Bahia. BBC inclui predominantemente granitos ricos em granada, em que três assembleias minerais podem ser identificadas: 1) Qz + Pl + KFS + Bt + Grt + Ilm ± Rt; 2) Qz + Pl + KFS + Bt + Grt + Ilm + Sil; e 3) Qz + Pl + KFS + Bt + Grt + Ilm + Sil + Spl. As rochas que contêm as assembleias 2 e 3 contêm duas gerações de granadas. Evidências microestruturais para a presença de melt são identificadas em todas as amostras estudadas, tais como: inclusões de melt silicático em granadas poiquiloblásticas, finos filmes de melt pseudomorfizados ao redor de ambas gerações de granada, “piscinas” de melt adjacentes a granada e biotita, além de plagioclásio e quartzo com formas cuspade a lobulados que ocorrem entre os grãos da matriz. Ambas gerações de granada (Grt1 e Grt2) não apresentam zoneamento em termos de elementos maiores e contêm pequenas inclusões arredondadas de biotita rica em Ti. Além disso, os cristais Grt2 também contêm inclusões de remanescentes agulhas de sillimanita. Evidências microestruturais, em combinação com a química mineral, indicam que os cristais de granada cresceram durante dois eventos metamórficos/anatéticos distintos, como produtos peritéticos de reações de fusão parcial em regime de fluido ausente que consumiram biotita, quartzo e plagioclásio, no caso de Grt1, e que consumiram biotita, quartzo, plagioclásio e silimanita, no caso de Grt2. Pseudoseções calculadas via Theriak-Domino forneceram novas condições metamórficas para a região do retro arco do OA. Dados da assembleia mineral 1 sugerem que o primeiro evento metamórfico de fácies granulito (M1) ocorreu a temperaturas de 790-820 ºC e pressões de 9.5-10.5 kbar, enquanto a assembleia mineral 2 registra condições PT para um segundo metamorfismo de fácies granulito (M2) a aproximadamente 770 ºC e 6.6 kbar. Dados do geotermômetro Ti em zircão são consistentes com modelamento metamórfico, indicando que os dois eventos metamórficos no batólito atingiram condições de fácies granulito. Variadas idades foram encontradas em grãos de monazita e zircão (> 825 Ma a 490 Ma) das rochas do BCC, registrando uma complexa história de reciclagem crustal e herança, cristalização magmática e anatexia durante a evolução do OA. Os zircões magmáticos (~ 582 Ma) mostram composição isotópica de Hf e padrões de ETR similar aos dos núcleos herdados (825-600 Ma), indicando que a assinatura química destes cristais provavelmente foi herdada da fonte. Idades U-Pb e razões iniciais 176Hf/177Hf dos domínios de zircões anatéticos e/ou metamórficos são consistentes com dois estágios metamórficos caracterizados por processos de crescimento/sobrecrescimento e recristalização de grãos de zircão durante a orogenia. O episódio metamórfico mais antigo (570-550 Ma) é caracterizado pelo sobrecrescimento anatético em núcleos mais velhos e pelo crescimento de novos cristais de zircão anatético. Ambos os domínios têm elevados valores iniciais de 176Hf/177Hf em comparação com núcleos mais antigos e exibem padrões de ETR típicos de zircão que cresceu simultaneamente com granada peritética (Grt1) através de reações de fusão parcial em regime de fluido ausente. Idades U-Pb obtidas em grãos de monazita e zircão (569-552 Ma) inclusos na Grt1, corroboram a interpretação de que os cristais Grt1 cresceram durante o primeiro episódio anatético. Composição isotópica de Hf e evidências químicas indicam que um segundo episódio anatético (535-500 Ma) é registrado em parte das rochas do batólito (assembleias 2 e 3). Nestas rochas, o crescimento e/ou sobrecrescimento de novos zircões anatéticos é marcado por elevada razão inicial de 176Hf/177Hf e também pela geração da Grt2, como indicado pelas observações petrográficas e padrões de ETR. Por outro lado, algumas rochas têm grãos de zircão formados por processos de recristalização no estado sólido de zircão pré-existente, que exibem composição isotópica de Hf similar àqueles domínios magmáticos/herdados. O evento M1 é associado ao espessamento crustal e anatexia no batólito. O evento M2 pode ser associado a ascensão da astenosfera durante o colapso gravitacional do orógeno. Isto produziu anatexia em partes do BCC que tinham sido refertilizado ao longo de zonas de cisalhamento após o primeiro evento de fácies granulito. Thesis (PhD)--Stellenbosch University, 2017.

The biogeochemistry of bioactive trace elements cadmium and cobalt in the Southern Ocean, Atlantic Sector

2017-06-09T09:18:37Z

The biogeochemistry of bioactive trace elements cadmium and cobalt in the Southern Ocean, Atlantic Sector Loock, Jean Christian ENGLISH ABSTRACT: The biogeochemical cycling of the bio-active dissolved trace metals cadmium (DCd) and cobalt (DCo), are reported on a meridional transect of the Southern Atlantic, spanning 36°S to 68°S. Seawater samples were collected using an adaptation of the GEOTRACES clean sampling method concurrent to the austral mid-summer (2015). A multi-element inductively coupled plasma mass spectrometry (ICP-MS) technique, coupled with the commercially available seaFAST pre-concentration module was set up and validated for 8 trace elements (Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb). The method proved highly precise (≤10%RSD) in the repeated analysis of an in-house control (TM4A), and accurate in the analysis of the SAFe (D2) international natural seawater reference material. Iron (Fe) quantification proved precise (≤5%RSD) and accurate under repeat analysis. Furthermore, two GEOTRACES standards, GSP and GSC, were analysed for contributing to the determination of their consensus values. DCo concentrations within the oligotrophic sub-surface waters (500m) of the Sub-Tropical Zone (STZ) are heavily depleted (12.57 pmol/kg) owing to strong bio-utilization. Conversely, sub-surface Antarctic Intermediate Waters (AAIW) near the Sub-Antarctic Front (SAF) were elevated (36.1 pmol/kg). Concentrations subsequently decline meridionally through the Antarctic Circumpolar Current (ACC) steadying within the Weddell Gyre (20.3 pmol/kg). STZ DCd sub-surface concentrations are notably depleted (74.1 pmol/kg). However, sub-surface concentrations increase within the ACC at the SAF (450 pmol/kg), continuing into the Weddell Gyre (700.8 pmol/kg). DCd exhibits a typical nutrient-like profile, with bio-utilization in the surface (MLD), followed by regeneration and conservation. The nutrient like behaviour of bio-utilized DCd was exemplified by an excellent Cd/P sub-surface correlation in the ACC, waning somewhat in the sub-optimal productivity of the Weddell Gyre. However, abiotic factors may have contributed to DCd concentrations. The complete water column concentrations ranged from 8.4 ± 0.05 pmol/kg to 902 ± 22.71 pmol/kg. Conversely, DCo demonstrated a typical hybrid-type vertical distribution – nutrient uptake and remineralization in the surface succeeded by scavenging controlled by heterogeneous oxidising bacteria. The complete water column concentrations ranged from 4.1 ± 0.02 pmol/kg to 38.9 ± 0.3 pmol/kg. Elevated DCo concentrations in the sub-surface and a poor but significant DCo/Salinity correlation, suggest DCo flux in the expanse surrounding 46°S and 68°S. Keywords: Biogeochemical cycling, Dissolved Co and Cd, GEOTRACES, ICP-MS, Iron (Fe), seaFAST, Southern Atlantic.; AFRIKAANSE OPSOMMING: Die biogeochemiese sirkulering van die bio-aktiewe opgelosde spoor metale kadmium (DCd) en kobalt (DCo), word berig op 'n meridionale transeksie van die Suider-Atlantiese Oseaan, wat van 36 °S tot 68 °S strek. Seewater monsters was ingesamel met behulp van 'n aanpassing van die GEOTRACES skoon steekproefmetode tydens die middel van die suidelike somer (2015). 'N Multi-element induktiefgekoppelde plasma massaspektrometrie (ICP-MS) tegnologie, tesame met die kommersieel beskikbare seaFAST pre-konsentrasie module is opgestel en bekragtig vir 8 spoorelemente (Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb). Die metode bewys hoogs akkuraat (≤10% RSD) in die herhaalde analise van 'n in-huis beheer (TM4A), en akkuraat in die ontleding van die SAFe (D2) internasionale natuurlike seewater verwysingsmateriaal. Yster (Fe) kwantifisering bewys presies (≤5% RSD) en akkuraat onder herhaalende analise. Verder, twee GEOTRACES standaarde, GSP en GSC, is ontleed om by te dra tot die bepaling van hul konsensus waardes. DCo konsentrasies binne die oligotrofiese sub-oppervlak water (500m) van die Subtropiese Sone (STZ) is swaar uitgeput (12,57 pmol/kg) as gevolg van 'n sterk bio-benutting. Aan die ander kant was Sub-Antarktiese Front (SAF) sub-oppervlak water (AAIW) verhef (36.1 pmol/kg). Konsentrasies daal daarna meridionally deur die Antarktiese Circumpolaire Huideging (ACC) en bedaar binne die Weddell Gyre (20.3 pmol/kg). STZ DCd sub-oppervlak konsentrasies was veral arm (74,1 pmol / kg). Maar, sub-oppervlak konsentrasies verhoog binne die ACC naby die SAF (450 pmol / kg), voortgesette in die Weddell Gyre (700,8 pmol/kg). DCd toon 'n tipiese voedingstof-agtige profiel, met bio-benutting in die oppervlak (MLD), gevolg deur die wedergeboorte en bewaring. Die voedingstowwe soos gedrag van bio-gebruik DCd is vergestalt deur 'n uitstekende Cd/P sub-oppervlak korrelasie in die ACC, besig om te kwyn ietwat in die sub-optimale produktiwiteit van die Weddell Gyre. Dit kan egter wees dat abiotiese faktore bygedra het tot DCd konsentrasies. Die volledige waterkolom konsentrasies het gewissel van 8.4 ± 0.05 pmol/kg tot 902 ± 22,71 pmol/kg. Aan die ander kant, demonstreer DCo 'n tipiese baster-tipe vertikale verspreiding - voedingsopname en remineralisatie in die oppervlak, opgevolg deur aas beheer tekoms heterogene oksideer- bakterieë. Die volledige waterkolom konsentrasies het gewissel van 4.1 ± 0,02 pmol/kg tot 38,9 ± 0,3 pmol/kg. Verhoogde DCo konsentrasies in die sub-oppervlak en 'n arm, maar beduidende DCo/Zoutgehalte korrelasie, raai DCo vloed in die uitspansel rondom 46 °S en 68 °S. Sleutelwoorde: biogeochemiese sirkulering, opgelosde Co en Cd, GEOTRACES, induktiefgekoppelde plasma massaspektrometrie (ICP-MS), yster (Fe), seaFAST, Suider-Atlantiese Oseaan Thesis (MSc)--Stellenbosch University, 2017.

Measurement of bioactive trace metals (Cu and Zn) in the Southern Ocean : validation of sampling protocol and ICP-MS based analytical method

2017-06-09T09:58:37Z

Measurement of bioactive trace metals (Cu and Zn) in the Southern Ocean : validation of sampling protocol and ICP-MS based analytical method Cloete, Ryan ENGLISH ABSTRACT: A method comprising an improved seawater collection protocol and subsequent Inductively Coupled Plasma Mass Spectrometry (ICP-MS) based analytical technique was validated through an intercalibration exercise performed with the University of Plymouth (UK), multiple cross-over stations and analyses of certified reference materials (SAFe, GEOTRACES and NASS-5). The commercially available seaFAST-pico preconcentration module was employed for the simultaneous extraction of a suite of trace metals (Mn, Fe, Ni, Cu, Zn, Co, Cd and Pb) from their seawater matrix prior to ICP-MS analysis. Extremely low detection limits (< 0.228 nmol/kg) combined with low blank values ensured quantitive recovery on ICP-MS and minimal interferences arising from alkali and alkaline earth metals (Na, K, Mg and Ca) present in the saline matrix. The results of the certified reference materials were in excellent agreement with their corresponding consensus values and validated the methods precision and accuracy. During ICP-MS analysis, repeatability and reproducibility were monitored through analysis of an internal Stellenbosch University (SU) TM4 control and various commercially available quality controls, the results of which further confirmed a high level of precision. The distribution of Dissolved Copper (DCu) and Dissolved Zinc (DZn) was investigated in the Atlantic sector of the Southern Ocean. DCu displayed typical nutrient type behaviour reflected by sub-nanomolar surface concentrations increasing steadily until maximum observed concentrations of 2 – 3 nmol/kg in the Antarctic Bottom Waters (AABW). DZn concentrations ranged between approximately 1 and 12 nmol/kg and exhibited characteristic nutrient-type behaviour although intermediate and deepwater distributions were more conservative compared to DCu. Local subsurface minima coincided with elevated levels of chlorophyll-a (chl-a) indicating biological utilisation by phytoplankton in the euphotic zone. Remineralisation of sinking organic matter, predominantly diatom frustules, from Antarctic Surface Water (AASW) resulted in deeper sub-surface maxima for DZn. The dominant supply of trace metals to surface waters south of the Antarctic Polar Front (APF) was advective upwelling of nutrient rich Upper Circumpolar Deep Water (UCDW) and AABW. Atmospheric inputs and melting ice accounted for minor surface influxes where there was a poor DCu/salinity correlation. Both trace elements displayed significant correlations with the macronutrient silica, evidence of their role in the biological cycle. An overall Cu:Si relationship of Cu (nM) = 0.011 Si (μM) + 0.851 (R2 = 0.85, n=98) was obtained for this study while the corresponding Zn:Si relationship was Zn (nM) = 0.043 Si (μM) + 1.021 (R2 = 0.80, n=98). The APF exerted a strong control over nutrient distributions separating low nutrient low chlorophyll (LNLC) subtropical waters to the north from high nutrient low chlororphyll (HNLC) waters to the south. Keywords: Southern Ocean, Dissolved Copper, Dissolved Zinc, GEOTRACES, seaFAST, ICP-MS; AFRIKAANSE OPSOMMING: 'n Metode wat bestaan uit 'n verbeterde seewater versameling protokol en die daaropvolgende Inductively Coupled Plasma Mass Spectrometry (ICP-MS) gebaseer analitiese tegniek is bekragtig deur 'n onderlinge oefening uitgevoer met die Universiteit van Plymouth (UK), verskeie ‘cross-over’ stasies en ontleding van gesertifiseerde verwysingsmateriaal (SAFe, GEOTRACES en NASS-5). Die kommersieel beskikbare seaFAST-pico preconcentration module is aangewend vir die gelyktydige onttrekking van 'n versameling van spoor metale (Mn, Fe, Ni, Cu, Zn, Co, Cd en Pb) van hul seewater matriks voor ICP-MS analise. Uiters lae opsporings perke (<0,228 nmol / kg) gekombineer met 'n lae leegwaardes verseker kwantitatiewe herstel op ICP-MS en minimale inmenging wat voortspruit uit alkalie en alkalie-aard metale (Na, K, Mg en Ca) teenwoordig is in die sout matriks. Die resultate van die gesertifiseerde verwysingsmateriaal was in 'n uitstekende ooreenkoms met hul ooreenstemmende konsensuswaardes en bekragtig die presisie en akkuraatheid van die metodes. Tydens ICP-MS analise, herhaalbaarheid en reproduseerbaarheid is gemonitor deur analise van 'n interne Universiteit Stellenbosch (US) TM4- beheer en verskeie kommersieel beskikbare kwaliteit beheer, die resultate waarvan 'n hoë vlak van akkuraatheid verder bevestig. Die verspreiding van opgeloste Koper (DCu) en opgeloste Zinc (DZn) is ondersoek in die Atlantiese sektor van die Suidelike Yssee. DCu vertoon tipiese tipe voedingstofagtige gedrag weerspieël deur sub-nanomolar oppervlak konsentrasies steeds toenemende tot maksimum waargenome konsentrasies van 2 - 3 nmol / kg in die Antarctic Bottom Waters (AABW). DZn konsentrasies wissel tussen ongeveer 1 en 12 nmol / kg en vertoon voedingstofagtige gedrag hoewel intermediêre- en diepwaterverspreidings meer konserwatief in vergelyking met DCu was. Plaaslike ondergrondse minima saamgeval met verhoogde vlakke van chlorofil-a (Chl-a) dui biologiese benutting deur fitoplankton in die euphotic sone aan. Remineralisasering van sink organiese materiaal, hoofsaaklik diatom frustules van Antarctic Surface Water (AASW) tot gevolg gehad vir ‘n dieper sub-oppervlak maksima vir DZn. Die dominante verskaffing van spoor metale om water oppervlak suid van die Antarctic Polar Front (APF) was advektiewe opwelling van voedingstofryke Upper Circumpolar Deep Water (UCDW) en AABW. Atmosferiese insette en smeltingsys is verantwoordelik vir klein oppervlak strome waar daar was 'n swak DCu / soutgehalte korrelasie. Beide spoorelemente vertoon beduidende korrelasies met die makro-silika, bewyse van hul rol in die biologiese siklus. 'N Algehele Cu:Si verhouding van Cu (nM) = 0,011 Si (μm) + 0,851 (R2 = 0.85, n = 98) is verkry vir hierdie studie, terwyl die ooreenstemmende Zn: Si verhouding was Zn (nM) = 0,043 Si (μM ) + 1,021 (R2 = 0.80, n = 98). Die APF oefen sterk beheer uit oor voedingstof verspreiding wat low nutrient low chlorophyll (LNLC) subtropiese waters in die noorde skei high nutrient low chlorophyll (HNLC) water na die suide. Trefwoorde: Suidelike Yssee, opgeloste Koper, opgeloste Zinc, GEOTRACES, seaFAST, ICP-MS Thesis (MSc)--Stellenbosch University, 2017.

The geometry of Karoo dolerite dykes and saucers in the Highveld Coalfield : constraints on emplacement processes of mafic magmas in the shallow crust

2017-02-24T10:27:04Z

The geometry of Karoo dolerite dykes and saucers in the Highveld Coalfield : constraints on emplacement processes of mafic magmas in the shallow crust Coetzee, Andre ENGLISH ABSTRACT: This dissertation is a compilation of two case studies that integrates an extensive underground mining and drilling data set on Karoo dolerite intrusions in the Highveld Coalfield to constrain the emplacement processes of the upper-crustal plumbing system of the Karoo large igneous province. Chapter 3 describes by means of a three-dimensional strata model the geometry of a regional-scale Karoo-age (ca. 180Ma) saucer complex locally referred to as the number 8 sill. The saucer complex consists of three saucers largely confined to the Karoo Supergroup underlain by a shallow dipping basement feeder. The model demonstrates the lateral emplacement of magma where a single basement feeder gives rise to several split level saucers that subsequently coalesces into one vast saucer complex. Furthermore, these relationships show a strong spatial and geometric dependency of saucers to their underlying feeders. Lithological interfaces and weak layers control and facilitate the lateral emplacement of magma during the development of saucers in the Karoo Supergroup. The common occurrence of localised dome- and ridge-shaped structures along the flat inner sill of the saucers are likely generated from lobate magma flow processes. Inflation of individual magma lobes induce overlying strata failure along multiple curved faults that facilitates the formation of circular inclined sheets feeding a flat lying roof seated at a higher stratigraphic level. Chapter 4 examines the spatial and temporal relationships between dolerite dykes and the saucers that make up the larger number 8 sill complex. These dykes have distinct short strike lengths, curved geometries and form interconnected and cross-cutting patterns. Moreover, the dykes are often rooted along the upper surface of underlying saucers and cannot be seen to extend below the base (inner sill) of the saucers. Contact relationships show a mainly coeval or contemporaneous emplacement of dykes to the inner sill and inclined sheets of the underlying saucer. The dykes can be described as two diverse sets, namely systematic and non-systematic dykes. Systematic dykes form a well-organised interconnected boxwork or ladder-like pattern of two near-orthogonal dyke sets confined to the inner sill of the underlying saucer. The formation of these dykes is related to the uplift and stretch of the strata directly overlying propagating magma lobes along the inner sill of the underlying saucer. Conversely, non-systematic dykes display a more irregular array of structures that not only overlie the inner sill but often cross-cut or extend outwards from the inclined sheets of the saucer. These dykes are likely the product of multi-directional stretch induced during the emplacement of coeval and adjacent saucers forming a so called “cracked lid” similar to field descriptions of stacked saucers in Antarctica. Dyke-saucer relationships of the Highveld Coalfield highlight the influence of magma emplacement processes and the deformation of host strata rather than far-field tectonic stresses.; AFRIKAANS OPSOMMING: Geen opsomming beskikbaar Thesis (MSc)--Stellenbosch University, 2016.

The lithostratigraphy and structural components of the Eureka Shear Zone, southern Namibia

2017-02-24T09:56:22Z

The lithostratigraphy and structural components of the Eureka Shear Zone, southern Namibia Angombe, Moses Tuutaleni ENGLISH ABSTRACT: The newly recognised Eureka Shear Zone (ESZ) in southern Namibia is a Late-Mesoproterozoic to Early Neoproterozoic high strain zone in the Namaqua sector of the Namaqua Natal Metamorphic Province (NNMP). Its current outcrop trace is closely aligned with the previously identified terrane boundary between the Paleoproterozoic Richtersveld Subprovince and the Mesoproterozoic Gordonia Subprovince (South Africa) or Grünau Terrane (Namibia). This has given rise to the question of what this high strain zone represents in terms of its lithostratigraphy and tectonic history. A joint mapping program between the Geological Survey of Namibia and the Council for Geoscience in South Africa has redefined and clarified aspects of the regional geology and the relationship between different crustal blocks within the Namaqua sector. Chief amongst these are the redefinition of: (1) the Paleoproterozoic Richtersveld Subprovince into the Richtersveld Magmatic Arc (comprised of the greenschist-facies Vioolsdrif Domain and the amphibolite-facies Pella Domain) in both South Africa and Namibia; (2) the Mesoproterozoic Grünau Terrane into the Kakamas Domain in Namibia; (3) the SW-vergent, subhorizontal Lower Fish River-Onseepkans Thrust (LFROT) that juxtaposes the granulite-facies Kakamas Domain on top of the Pella Domain and (4) a zone of highly deformed and imbricated units on top of the LFROT that reworks the Kakamas Domain, referred to as the Lower-Fish-River-Onseepkans Thrust Zone (LFROTZ) and which also includes unique units not found in the Kakamas or Pella domains. In this study, detailed field mapping, petrography, structural analysis and U-Pb zircon dating on the ESZ was undertaken to understand its relationship to the LFROTZ and the nearby Marshall Rocks-Pofadder Shear Zone (MRPSZ) with a view to understanding the evolution of the ESZ in the broader context of the Namaqua sector and NNMP. The ESZ is a ~2 to 5 km wide, 50 km long and WNW-trending zone of intense shearing. It is dominantly composed of two distinct lithostratigraphic packages: (1) the Eureka Complex (EC) in the north, a heterogeneous sheared garnet-bearing gneiss with isolated m-scale and lens-shaped remnants of pelitic granulite whose metamorphic grade and detrital zircon patterns correlate it to the Kakamas Domain; and (2) fault/thrust-bounded packages of interlayered quartz-feldspar gneiss and amphibolite (MQ), that occur as sigmoid-shaped mega-lenses within the EC and which are correlated to units considered to be unique to the LFROTZ. South of the EC and MQ units, the ESZ shears migmatitic volcanoclastic rocks of the Pella Domain. Petrographic studies indicate that the rocks of the ESZ were affected by retrograde metamorphism at mid to upper greenschist facies during shearing. Fault rock textures in the ESZ vary from phyllonite to cataclasite dominant, with rarer mylonitic textures. This implies a complex interplay between rheological contrast, slip rate and crustal depth under shearing conditions where potassium feldspar was brittle and quartz was plastic. The orientation of the shear fabrics varies with the ESZ but maintains a dominant WNW strike steeply dipping shear foliation accompanied by a NE trending and moderately to steeply plunging lineation. The ESZ was intruded by a significant volume of foliation sub-parallel, sheet-like, pegmatite and leucocratic equigranular granite dykes which date to ~1000 Ma and constrain the age of the shear zone. The geometry, age and strain regime of ESZ is similar to the adjacent MRPSZ, but its lithostratigraphy reveal the presence of rocks found in the LFROTZ making the ESZ a younger shear zone exploiting the older terrane boundary between the Kakamas and Pella domain.; AFRIKAANS ABSTRACT: Geen opsomming beskikbaar Thesis (MSc)--Stellenbosch University, 2016.

The effect of winery wastewater irrigation on the properties of selected soils from the South African wine region

2017-02-20T08:19:25Z

The effect of winery wastewater irrigation on the properties of selected soils from the South African wine region Mulidzi, Azwimbavhi Reckson ENGLISH ABSTRACT: Due to an increase in wine production as well as an intensification of environmental legislation in South Africa, the need for guidelines for sustainable management of winery wastewater has increased. To address this, the first part of the study focused on the seasonal dynamics of the volumes and quality of undiluted winery wastewater. The soil chemical dynamics were monitored in two different soils that were irrigated with undiluted winery wastewater for three years. Over-irrigation with undiluted winery wastewater in combination with winter rainfall caused large amounts of cations, particularly K+ and Na+, to leach beyond 90 cm soil depth. Consequently, the leached elements are bound to end up in natural water resources over time. Irrigation with undiluted winery wastewater did not have a pronounced effect on soil pH(KCl). This was probably due to the decomposition of organic matter and the fact that the applied salts as well as dissolved organic or mineral acids leached beyond 90 cm depth. The practical application of irrigation with diluted winery wastewater was assessed in a pot experiment. Irrigations were applied under a rain shelter over four simulated irrigation seasons. Four soils varying in texture were irrigated with winery wastewater that was diluted to 3000 mg/L chemical oxygen demand (COD). The four soils were irrigated with municipal water as a control. The rate of K+ increase in the soil containing 20% clay was higher than in soils containing 13% clay, or less. This suggested that heavy soils will aggravate the risk of high K+ levels. The risk of Na+ accumulation increased linearly with the clay content in the soil. Low Ca2+ and Mg2+ concentrations in the diluted wastewater had no effect on the soil, irrespective of clay content. Irrigation with diluted winery wastewater increased soil pH(KCl) substantially in all soils over four simulated seasons. The soil pH increase was attributed to the addition of organic and mineral salts via the diluted winery wastewater to the soil. The effect of simulated rainfall on soils irrigated with winery wastewater was also assessed in a pot experiment. Six soils with different clay content were irrigated with winery wastewater diluted to 3000 mg/L over one simulated irrigation season. Thereafter, good quality river water simulating winter rainfall was added to the pots. The rainfall was simulated according to the long term averages of the regions were the soils originated. Leaching of cations, particularly K+ and Na+ occurred only from four of the six soils when winter rainfall was simulated. In one of the sandy soils, the simulated rainfall was too low to allow leaching. In the case of other soil where there was no leaching, high clay content of 35% in combination with low rainfall prevented leaching. Where three soils received the same amount of rainfall, more cations leached from the sandy soils compared to the two heavier soils. These trends indicated that leaching of cations was a function of soil texture and rainfall.; AFRIKAANS OPSOMMING: As gevolg van die toename in wynproduksie, asook ‘n verskerping in omgewingswetgewing in Suid-Afrika, het die behoefte vir riglyne vir volhoubare bestuur van kelderafvalwater ‘n belangrike aspek van wynproduksie geword. Om dit aan te spreek, het die eerste deel van die studie op die seisoenale dinamika van die volumes en gehalte van onverdunde kelderafvalwater gefokus. Die grondchemiese dinamika in twee verskillende gronde wat met onverdunde kelderwater besproei is,by twee verskillende kommersiële kelders oor drie seisoene gemonitor. Oorbesproeiing met die onverdunde kelderafvalwater, in kombinasie met winterreënval, het veroorsaak dat groot hoeveelhede katione, veral K+ en Na+, dieper as 90 cm gronddiepte geloog het. Die nagevolg hiervan is dat die geloogde elemente oor tyd in natuurlike water hulpbronne sal beland. Besproeiing met onverdunde kelderafvalwater het nie ‘n noemenswaardige effek op grond pH(KCl) gehad nie. Dis was heel waarskynlik te wyte aan die feit dat die organiese materiaal ontbind het, en dat die toegediende katione as opgeloste organiese of mineraal soute verby 90 cm diepte geloog het. Die praktiese toepasbaarheid van besproeiing met verdunde kelderafvalwater is in ‘n potproef ondersoek. Besproeiings is onder ‘n reënskuiling oor vier gesimuleerde seisoene toegedien. Vier gronde met verskillende teksture is besproei met kelderafvalwater wat tot 3000 mg/L chemiese suurstof aanvraag (Eng. = chemical oxygen demand, of kortweg COD). As ‘n kontrole is die vier gronde met munisipale water besproei. Die K+ toename in die grond wat 20% klei bevat het, was hoër as in gronde wat 13% of minder klei bevat het. Dit het aangedui dat die risiko van K+ aansameling hoër is in swaarder gronde. Die risiko van Na+ toename het reglynig toegeneem met klei inhoud in die grond. Lae Ca2+ en Mg2+ konsentrasies in die verdunde afvalwater het geen effek in die gronde gehad nie, ongeag die klei-inhoud. Besproeiing met verdunde kelderafvalwater het die grond pH(KCl) in al die gronde oor die vier gesimuleerde seisoene betekenisvol laat toeneem. Die pH toename in die gronde kon aan die toediening van organiese en mineraal soute deur middel van die verdunde kelderwater toegeskryf word. Die effek van gesimuleerde winterreënval op gronde wat eers met verdunde kelderafvalwater besproei is, is ook met behulp van ‘n potproef ondersoek. Ses gronde met verskillende kleiinhoude is vir een gesimuleerde besproeingseisoen met kelderafvalwater wat tot 3000 mg/L COD verdun is, besproei. Daarna is gesimuleerde winterreënval in die vorm van hoe kwaliteit rivierwater op die gronde toegedien. Die reënval is volgens die langtermyn gemiddeldes van die streke waar die gronde voorgekom het, gesimuleer. Loging van katione, veral K+ en Na+ het slegs by vier van die ses gronde tydens die gesimuleerde winterreënval voorgekom. In die geval van een van die sanderige gronde, was die gesimuleerde reënval te min om loging te veroorsaak. In die geval van die ander grond waar geen loging voorgekom het nie, het die hoë-klei inhoud van 35%, in kombinasie met lae winterreënval, loging verhoed. Waar drie gronde dieselfde hoeveelheid reënval ontvang het, het meer katione uit die sanderige grond in vergelyking met die twee swaarder gronde geloog. Hierdie tendense het aangedui dat loging van katione ‘n funksie van grondtekstuur en reënval is. Thesis (PhD)--Stellenbosch University, 2016.

Magma accumulation and segregation during regional-scale folding : the Holland’s dome granite injection complex, Damara belt, Namibia.

2017-02-20T07:52:09Z

Magma accumulation and segregation during regional-scale folding : the Holland’s dome granite injection complex, Damara belt, Namibia. Kruger, Tolene Mia ENGLISH ABSTRACT: Mid-crustal, upper amphibolite-facies rocks in the south Central Zone magmatic arc of the Damara belt in central Namibia contain kilometre-scale networks of intrusive, sheet-like leucogranites. These granite injection complexes are spatially and temporally closely associated with regional folds, particularly antiformal structures, and document the presence and geometries of magma permeability networks in suprasolidus (T ~700-750 °C, P ~5 kbar) crust, close to the anatectic zone. The Holland’s dome is a northeast-trending, upright, isoclinal, gently doubly plunging antiform that formed during northwest-southeast shortening in supracrustal rocks above the basement-cover contact in the south Central Zone. Highly fractionated leucogranite sheets have intruded the Holland’s dome as three main orthogonal sets. The predominant set of subvertical granite sheets is roughly axial planar to the fold dome and is intersected at right angles by a subvertical and subhorizontal set of leucogranites normal to the fold axial plane. Contacts between the three main sets are mostly continuous pointing to the broadly coeval emplacement of leucogranites, while the internal sheeting of granites documents the incremental growth of larger granite sheets through successively injected smaller magma batches. The granites constitute between 40-80 % of the outcrop area, but wall-rock fragments have undergone little or no rotation with little evidence for a whole-scale flow and disruption of the succession. All three leucogranite sets cross-cut subvertical wall rocks. This underlines the late-kinematic emplacement of the granite sets during fold lock-up and flattening of the fold. Structural relationships between leucogranite sheets and the Holland’s dome point to a stepwise evolution of the injection complex during folding from (1) the dilatancy-driven segregation and accumulation of granitic magmas in the core of the fold during fold amplification above the basement-cover detachment, followed by (2) fold tightening and compaction-driven segregation of a melt from the initially accumulated magma in the core of the fold. This stage corresponds to the formation of the injection complex at the present-day erosional level of the Holland’s dome. The successive assembly of the granite network through the injection of probably thousands of smaller melt batches ensures compatibility between regional strain rates during fold amplification and the rates of magma segregation and emplacement. The orientation of sheets closely reflects the regional stress field and folding of the cover sequence during regional shortening. Strain localization associated with the late-stage injection of a three-dimensional melt network also facilitates tightening of the Holland’s dome beyond the fold lock-up stage during ongoing regional shortening. Granite injection complexes similar to that of the Holland’s dome are common in the mid-crust of the Damara belt. The presence of the injection complexes highlights the significance of regional-scale folding for the formation of temporary magma accumulation sites and the redistribution of progressively more fractionated melts during deformation in suprasolidus crust.; AFRIKAANS OPSOMMING: Middel-aardkors, boonste-amfiboliet fasies gesteentes in die suid-Sentrale Sone magmatiese boog van die Damara gordel in sentraal Namibië bevat kilometer-skaalse netwerke van intrusiewe, leukograniet plate. Hierdie graniet injeksiekomplekse is ruimtelik en tydelik nou verwant aan regionale plooie, spesifiek antiforme strukture, en dokumenteer die teenwoordigheid en geometrie van magma deurlatendheid netwerke in bo-solidus (T ~700-750 °C, P ~5 kbar) aardkors, naby aan die anatektiese sone. Die Holland’s koepel is ‘n noordoos-strekkende, regop, isoklinale, liggies dubbel-duikende plooi wat tydens noordwes-suidoos verkorting van die bokorsgesteentes gevorm het bo die vloer-bedekkingsgesteente kontak in die suid-Sentral Sone. Hoogs gefraksioneerde leukograniet plate het die Holland’s koepel ingedring en vorm drie ortogonale stelle. Die dominante stel van subvertikale plate is asvlakplanêr met die koepel en word reghoekig gesny deur ‘n subvertikale en subhorisontale stel van leukograniete loodreg teenoor die plooi se asvlak. Kontakte tussen die drie hoof plaatstelle is meestal deurlopend en verwys na die gelyktydige inplasing van leukograniete, terwyl die interne plaatvorming van graniete die inkrementele groei van groter plate deur middel van agtereenvolgende injeksie van kleiner magma hoeveelhede dokumenteer. Die graniet maak tussen 40-80 % van die dagsoomarea op, maar wandgesteente fragmente het minimale of geen rotasie ondergaan nie, met amper geen bewyse van ‘n heelskaalse vloei en ontwrigting van die suksessie nie. Al drie leukograniet stelle kruissny subvertikale wandgesteentes. Dit beklemtoon die laat-kinematiese inplasing van die graniet stelle tydens plooisluiting en afplatting van die plooi. Strukturele verhoudings tussen die leukograniet plate en die Holland’s koepel dui op die stapgewyse evolusie van die injeksiekompleks tydens plooiing vanaf (1) die dilatante-gedrewe segregasie en akkumulasie van granietiese magmas in die kern van die plooi gedurende plooi versterking bo die vloer-bedekkingsgesteente afstropingsvlak, gevolg deur (2) plooi vernouing en kompaksiegedrewe segregasie van ‘n smeltsel van die aanvanklik ge-akkumuleerde magma in die kern van die plooi. Hierdie stadium korrespondeer met die vorming van die injeksiekompleks in die hedendaagse verweringsvlak van die Holland’s koepel. Die agtereenvolgende samestelling van die granietnetwerk deur middel van die injeksie van seker duisende kleiner smeltsel hoeveelhede verseker die verenigbaarheid tussen regionale vervormings tempo gedurende plooi versterking en die tempo van magma segregasie en inplasing. Die orientasie van plate reflekteer die streeksstresveld en die plooiing van die bedekkingsgesteentesuksessie gedurende regionale verkorting. Spannings lokalisering verwant aan die laat-stadium injeksie van ‘n drie-dimensionele smeltsel netwerk fasiliteer vernouing van die Holland’s koepel verby die plooisluitingsstadium gedurende aanhoudende regionale verkorting. Graniet injeksiekomplekse soortgelyk aan die van die Holland’s koepel is algemeen in die middel-aardkors van die Damara gordel. Die teenwoordigheid van die injeksiekomplekse beklemtoon die betekenis van die regionaalskaalse plooiing vir die vorming van tydelike magma akkumulasie gebiede en die herverdeling van progressiewe meer gefraksioneerde smeltsels gedurende vervorming van die bo-solidus aarkors. Thesis (MSc)--Stellenbosch University, 2016.

The emergence of modern sea ice cover in the Arctic Ocean

2016-11-11T09:13:35Z

The emergence of modern sea ice cover in the Arctic Ocean Knies, Jochen; Cabedo-Sanz, Patricia; Belt, Simon T.; Baranwal, Soma; Fietz, Susanne; Rosell-Mele, Antoni Arctic sea ice coverage is shrinking in response to global climate change and summer ice-free conditions in the Arctic Ocean are predicted by the end of the century. The validity of this prediction could potentially be tested through the reconstruction of the climate of the Pliocene epoch (5.33–2.58 million years ago), an analogue of a future warmer Earth. Here we show that, in the Eurasian sector of the Arctic Ocean, ice-free conditions prevailed in the early Pliocene until sea ice expanded from the central Arctic Ocean for the first time ca. 4 million years ago. Amplified by a rise in topography in several regions of the Arctic and enhanced freshening of the Arctic Ocean, sea ice expanded progressively in response to positive ice-albedo feedback mechanisms. Sea ice reached its modern winter maximum extension for the first time during the culmination of the Northern Hemisphere glaciation, ca. 2.6 million years ago. CITATION: Knies, J. et al. 2015. The emergence of modern sea ice cover in the Arctic Ocean. Nature Communications, 5, Article number: 5608, doi:10.1038/ncomms6608.; The original publication is available at http://www.nature.com/ncomms

Ice sheet deformation in the Table Mountain group, Western Cape

2016-05-11T11:00:51Z

Ice sheet deformation in the Table Mountain group, Western Cape Blignault, H. J. ENGLISH ABSTRACT: The Lower Paleozoic glaciogenic sediments of the Table Mountain Group are interpreted as the result of two ice sheet advances into the active Table Mountain embayment. Subglacial deformation during the first advance gave rise to the Fold Zone. Macro- and micro-fabric data of deformed and undeformed sediments provide valuable constraints on the interpretation of the rheology of sediment transport media and the contemporaneously deformed sediments. It is shown that the structural characteristics of the Fold Zone are consistent with the progressive infill of the Table Mountain embayment by an ice sheet. The distribution, size and geometry of the folds are dependent on the effective load of the ice sheet and the type and direction of ice sheet flow; compressive and extending flow resulted in pure shear and simple shear deformation respectively.; AFRIKAANSE OPSOMMING: Die glasiogene sedimente van die Onder-Paleosolese Tafelberggroep word verklaar as die sedimentasie-produk van twee ysplaatbewegings in die aktiewe Tafelberginham. Die Plooisone word geassosieer met onderysplaatdeformasie tydens die eerste ysplaatbeweging. Die rheologie van die sedimentasietransportmedia en die gedeformeerde sedimente van die Plooisone is ondersoek deur gebruik te maak van maakselanalises. 'n Model is opgestel waarvolgens die struktuur van die Plooisone ooreenstem met die progressiewe opvulling van die Tafelberginham deur 'n ysplaat. Hiervolgens is die verspreiding, grootte en geometrie van die plooie 'n funksie van die effektiewe ysplaatbelading en tipe en rigting van ysplaatvloei; kompressiewe en verlengingsvloei het oorlangse en eenvoudige skuifskeurvervorming respektiewelik veroorsaak. Thesis (MSc)--Stellenbosch University, 1970.; Maps may be of poor quality due to digitisation process.

Geology, structural evolution and controls of hydrothermal gold mineralization in the Eastern Karagwe-Ankole fold belt, North Western Tanzania

2016-05-31T06:50:30Z

Geology, structural evolution and controls of hydrothermal gold mineralization in the Eastern Karagwe-Ankole fold belt, North Western Tanzania Koegelenberg, Corne ENGLISH ABSTRACT: In central-east Africa, the north-western margin of the Archaean Tanzania Craton (TC) is overlain by imbricated, low grade, volcano-sedimentary rocks of the Karagwe-Ankole belt’s (KAB) Eastern Domain (ED). Centred in the ED, vast stretches of a sheared and Au mineralized basement-cover contact are exposed along margins of the Mugera-Nyakahura (MN) inlier. To date, no detail research has been done in the area and the regional geology has been described from only broad reconnaissance studies. As part of an exploration project the first high resolution geological maps of key prospects and larger, more encompassing, scale maps of the basement-cover region was compiled. Mapping was supplemented by a regional scale structural traverse of the ED and selected sampling for analysis of micro-structures, geochronology and oxygen isotopes. The collective structural data has indicated that basement gneisses of the MN inlier may be considered as part of a forethrusted tectonic wedge caused by regional top-to-the-SE thick skinned thrusting. Above and in front of the wedge diagnostic back-thrusts and the reversal of kinematic fabrics in weak, often graphitic, metapelitic rocks of the Muyaga Group depict top-to-the-NW, hinterland-directed, tectonic transport along the main “roof” detachment. To the east under-thrusting of the coarse clastic Bukoba Group by the Muyaga Group has also created a distinct triangle zone at the frontal termination of the KAB. 39Ar-40Ar muscovite ages of detachment mylonites in the easternmost, and latest developing, parts of the KAB has constrained timing of D2 to at least 1326 ± 10 Ma. This age corresponds with the youngest end of the main phase of granite plutonism and mafic dyke emplacement in the KAB (1380 – 1328 Ma) and may point towards a Mesoproterozoic collisional event between the Congo- and Tanzania Cratons. U-Pb detrital zircon ages of the Muyaga- and Bukoba Groups have indicated uplift, erosion and subsequent reworking of Muyaga Group sediments and layered volcanics into the Bukoba basin after 1780 Ma, but before 1568 Ma. The Bukoba Group thus correlates with the Bwezigoro Group in SW Uganda, indicating the presence of an extensive Paleo- and/or Mesoproterozoic foreland basin overlying the western margin of the TC and Uganda Block. Lastly, controls of D2 fluid flow and mineralization along the low angle phyllonitic detachment are linked to NE trending ramp structures that were most favourable for the initiation of slip and development auriferous quartz vein networks. Upwards into the Muyaga Group progressive fold amplification and eventual fold-lock of second order anticlines, cored by competent and chemically re-active ferruginous mafic sills, are responsible for the late-kinematic development of auriferous quartz veins. Oxygen isotope values of D2 quartz veins and host rocks have indicated that fluids are derived from dehydrated clastic sediments of the Kagera Supergroup and, as such, may suggest that gold associated with greenstones of the TC have not been remobilized during D2 fold-and-thrust development in the ED. Collectively these findings greatly enhance the understanding of the geological evolution of the KAB’s easternmost parts and provides future research and exploration with a much improved geological background.; AFRIKAANSE OPSOMMING: In Sentraal- en Oos-Afrika is die noord-westelike rand van die Argeïese Tanzanië Kraton (TK) oorlê deur geimbrikeerde, lae-graadse, vulkaan-sedimentêre gesteentes van die Karagwe-Ankole plooistelsel (KAP) se Oostelike Segment (OS). Sentraal in die OS is daar groot lengtes van ‘n gouddraende skuifskeur kontak tussen vloer- en bedekking gesteentes wat blootgestel is aan die rante van die Mugera-Nyakahura (MN) venster. Daar was nog geen navorsing in die omgewing gedoen nie en die regionale geologie is slegs vanuit breedvoerige verkenning beskryf. As deel van ‘n eksplorasie projek is die eerste hoë resolusie kartering van sleutel prospekte en groter, meer omvattende, skaal kaarte van die skuifskeur kontak vervaardig. Kartering is aangevul deur ‘n regionale skaal struktuur dwars-snit van die OS en selektiewe monsters vir die analiese van mikro-strukture, geokronologie and suurstof isotope. Algehele struktuur data het aangedui dat basale gneisse van die MN venster wel deel mag wees van ‘n voor-stootverskuifde tektoniese wig gedurende regionale bo-na-die-SO dik vel stooting. Bo-op en voor die wig is kenmerkende terug-stote en die omkeer van kinematiese foliasies in swak, somtyds grafietise, meta-pelitiese gesteentes van die Muyaga Groep ‘n aanduiding van bo-na-die-NW, agterland gestuurde, tektoniese vervoer op die hoof “dak” vloeroorskuiwing. Na die ooste is onder-stoot van die Bukoba Groep deur die Muyaga Groep verantwoordelik vir die vorming van ‘n “driehoek” sone and die voorkant van die KAP. 39Ar-40Ar muskoviet ouderdomme van vloeroorskuiwing miloniete in die mees oostelike, en laasgevormde, dele van die KAP het D2 vervorming beraam tot en met 1326 ± 10 Ma. Die ouderdom vergelyk met die jongste fase van granite plutonisme and mafiese gang indringing in die KAP (1380 – 1328 Ma) en mag aanduidend wees van ‘n Mesoprotersoïese botsing tussen die Congo- en Tanzanië Kratons. U-Pb ditrale zirkoon ouderdomme van die Muyaga- en Bukoba Groepe het aangedui dat tektoniese oplig, erosie en gevolglike herwerk van Muyaga sedimente en vulkaniese lae binne in die Bukoba kom in na 1780 Ma, maar voor 1568 Ma. Die Bukoba Groep vergelyk dus met die Bwezigoro Groep van SW Uganda, wat aanduiding gee tot ‘n uitgebreide voorland kom oor die westerlike rand van die TK en Uganda blok. Laastens, is die beheer van D2 vloeistof migrasie en mineralisasie langs die milonietiese vloeroorskuiwing gekoppel aan NO strekkende skuinstes wat mees gepas is vir begin van skuifskeer glip en ontwikkeling van goud-yster draende kwarts aar netwerke. Opwaarts in die Muyaga Groep is aanhoudende vou-versterking en uiteindelike vou-sluiting van sekondêre antiklinale, gekern met harde en chemiese-reaktiewe plate, verantwoordelik vir die laat-kinematiese onwikkeling van goud-yster draende kwarts-are. Suurstof-isotoop waardes van D2 kwarts-are en gasheergesteentes dui aan dat vloeistowwe afkomstig is van gedehidreerde klastiese sedimente van die Kagera Supergroep en, gevolglik, aandui dat goud geassosieer met groenstene van die TK nie gemobiliseer was gedurende D2 verforming nie. In die geheel het al die bevindinge grootliks bygedra tot die verstaan van die geologiese ontwikkeling van die KAP se OS en verskaf dit toekomstige navorsing en eksplorasie met ‘n verbeterde geologiese agtergrond. Thesis (DSc)--Stellenbosch University, 2016.

Mineralogical and geochemical variations in the UG2 reef at Booysendal and Zondereinde mines, with implications for beneficiation of PGM

2016-05-31T07:31:34Z

Mineralogical and geochemical variations in the UG2 reef at Booysendal and Zondereinde mines, with implications for beneficiation of PGM McCall, Michael-John ENGLISH ABSTRACT: The layered intrusion of the Bushveld Complex, South Africa hosts the world’s largest concentration of platinum group elements (PGE), which are principally mined from three mineralised horizons namely, the Merensky reef, the Upper Group Two (UG2) reef and the Platreef. The PGE contents of these horizons are conventionally beneficiated via comminution, froth flotation and smelting techniques. The mineralogical and geochemical characteristics of the platiniferous reefs, and any variations thereof, are known to be intimately connected with the performance of the above-mentioned techniques. In particular, the chromite-rich UG2 reef presents a variety of complications, for example the ore/gangue relationships, mineral chemistry and textural characteristics, which can impact upon its beneficiation potential. This study was primarily aimed at evaluating and constraining the mineralogical and geochemical characteristics of two UG2 reef mining cuts from Booysendal mine (eastern Bushveld Complex) and Zondereinde mine (western Bushveld Complex). The results of comprehensive petrographic (2-D and 3-D), compositional and geochemical investigations were then placed within the context of the milling and flotation process in order to comment on the impact that any variability might have during the beneficiation of the PGE contents. In addition to these aims, the validity of results obtained from 3-D microfocus X-Ray Computed Tomography (XCT) were assessed within the context of this study. In this study it was found that the main ore zone from each UG2 reef sample is characterised by cumulate chromite grains with variable characteristics depending on the grain size, composition, degree of compaction and grain shape. The Zondereinde UG2 reef in particular was interpreted as having experienced a significant degree of compaction due to the lack of intercumulate silicate phases within the chromitite units. All mineral phases within both UG2 reef sample sets exhibit variable alteration features which results in the replacement of primary silicates by hydrous silicate minerals. PGE grade is commonly distributed with a top- and bottom-loaded profile in the main chromitite layers. Some PGE exist as platinum group minerals (PGM) with average grain sizes of less than 3 μm, associated predominantly with nickel and copper sulphide minerals. The Booysendal UG2 reef is dominated by a PGE-sulphide assemblage whereas Zondereinde is dominated by PGE-alloys. The mineralogical and geochemical characteristics further described in this study can be utilised to refine the milling regime and flotation parameters in order to maximise plant efficiencies. It is suggested that the Booysendal UG2 reef’s lesser degree of compaction within the chromitite horizons and predominance of PGE-sulphide mineral compositions may yield better liberation and faster recoveries of PGM contents when compared to the Zondereinde UG2 reef. In the case of the Zondereinde UG2 reef, the homogeneity of chromite textures might serve to simplify the refinement of milling regimes so as to not over- or under-grind the reef contents. This, coupled with a strong association of PGM with comparably higher sulphide mineral proportions will benefit the beneficiation process. The interpretation of results obtained from 3-D XCT proved the technique to be a powerful tool in terms of the broad-scale characterisation of chromite textures and PGM distribution. The technique however suffers from resolution limitations when attempting to accurately discern individual PGM grains. This is interpreted to be an artefact of the typically small grain size of PGM from the UG2 reef.; AFRIKAANSE OPSOMMING: Nie beskikbaar nie. Thesis (MSc)--Stellenbosch University, 2016.

Bulk geochemical, biomarker and leaf wax isotope records of Mfabeni peatland, KwaZulu Natal, South Africa since the late Pleistocene

2016-05-16T07:34:53Z

Bulk geochemical, biomarker and leaf wax isotope records of Mfabeni peatland, KwaZulu Natal, South Africa since the late Pleistocene Baker, Andrea ENGLISH ABSTRACT: Southern Africa is a topographically diverse region that is influenced by temperate, sub-tropical and tropical climates encompassing varying rainfall zones. The core regional contemporary climatic drivers are the large sea surface temperature (SST) gradients between the Atlantic and Indian Oceans, and seasonal fluctuations in the Inter Tropical Convergence Zone (ITCZ). Our understanding of how these two mechanisms interacted in the past and how ecosystems responded to these climate drivers is ambiguous, mainly due to a lack of continuous archives as a consequence of the region‘s semi-arid climate. The Mfabeni peatland is a 11 m thick continuous peat sequence that has been dated to ca. 47 kcal yr BP. It is the only known coastal peatland record in the summer rainfall zone of Southern Africa to transcend the Last Glacial Maximum (LGM), and gives us the opportunity to reconstruct high-resolution palaeoenvironment records under both glacial and interglacial conditions on the south eastern coastline of the African continent. A diverse set of geochemical techniques and analysis (bulk C and N elemental and stable isotopes; different biomarkers and leaf wax δ13C isotope) was undertaken on a 810 cm long core to reconstruct primary productivity, organic matter (OM) sources, rates of OM remineralisation, peatland hydrology and relative contributions of C3 and C4 plant matter into the peat deposit. These geochemical climatic indicators were used to infer precipitation intensities and relative temperatures at time of sedimentation and, in conjunction with other regional archives, the dominant mechanisms (Indian Ocean SST changes versus changes in the position of ITCZ) driving climatic fluctuations since the late Pleistocene were explored. We established the Mfabeni peatland to be a well-preserved and unique palaeoecological archive that recorded both environmental and climatic signals throughout the depositional history of the peatland. Even though the dominant OM source of the peat was terrestrial and emergent plants, there were definitive periods of predominant submerged macrophyte input, suggesting elevated water levels. A general positive trend was observed between the temperature and moisture proxies, however the local plant physiology (n-alkane chain lengths; ACLalk) and plant types (terrestrial vs aquatic and their influence on OM lability; CPIalk) was dominated by moisture availability as opposed to temperature variations, arguably due to the relatively moderate cooling experience in the sub-tropics during the LGM. The leaf wax C isotope data set established variability in the proportional balance of C3 and C4 plants, with interchanges between plant clades and inter family C3 and C4 switches in response to changes in environmental conditions. However, plant assemblage shifts were absent during some of the more ephemeral climatic events which we concluded was due to local hydrological overprinting. The Mfabeni archive correlates strongly with Mozambique Channel SST records, suggesting the dominant climate forcing factor in south eastern Africa to be the evaporation potential and advection of moisture from the adjacent Indian Ocean since the late Pleistocene. It was also noted that the Mfabeni record exhibited overall opposite environmental responses to Northern Hemisphere climatic events, suggesting an anti-phase coupling between the two hemispheres.; AFRIKAANSE OPSOMMING: Suidelike Afrika is a topografies diverse streek wat beïnvloed word deur gematigde, sub-tropiese en tropiese climate omvattende wisselende groeiseisoen reënval sones. Die kern streeks kontemporêre klimaatsdrywers is die groot see-oppervlak temperatuur (SST) gradiënte tussen die Atlantiese en Indiese Oseane, asook seisoenale skommelinge in die Intertropiese Konvergensiesone (ITCZ). Ons begrip van hoe die interaksie tussen die twee meganismes in die verlede was en hoe ekostelsels reageer het teenoor hierdie klimaatsdrywers is dubbelsinnig grootliks as gevolg van ‗n tekort aan deurlopende argiewe as ‗n gevolg van die streek se semi-droë klimaat. Die Mfabeni veenland is ‗n 11 meter dik aaneenlopende veen reeks gedateer ongeveer 47 kcal jaar BP. Dit is die enigste bekende kus veenland rekord in die somerreënval sone van Suider-Afrika wat die Laaste Ystydperk Maksimum (LGM) oortref het en gee ons die geleentheid om hoë resolusie paleo-omgewings rekords te rekonstrueer onder beide ystydperk en tussen-ystydperk toestande op die suid-oostelike kuslynvan die Afrika continent. ‗n Diverse stel geochemiese tegnieke en analise was (grootmaat C en N elementele en stabiele isotope; biomerkers en blaarwas δ13C isotoop) onderneem op ‗n 810 cm lang kern om primêre produktiwiteit , organiese material (OM) bronne, tempo van OM hermineralisasie, veenland hidrologie en relatiewe bydraes van C3 en C4 plantmateriaal tot die veen afsetting te rekonstrueer. Ek het toe hierdie geochemiese klimaat aanwysers gebruik om neerslag intensiteite en relatiewe temperature gedurende sedimentasie af te lei en, in samewerking met ander streeksargiewe, het ek die dominante meganisme (Indiese Oseaan SST veranderinge vs. veranderinge in die posisie van ITCZ) wat die klimaatskommelinge vanaf die laat Pleistocene tydperk dryf afgelei. Ons het vasgestel dat die Mfabeni veenland ‗n goed gepreserveerde/bewaarde en unieke paleo-ekologiese argief is wat beide omgewings- en klimaatsseine deurlopende die afsettings geskiedenis van die veenland opneem. Alhoewel die dominante OM bron van die veen land- en ontluikende plante was, was daar definitiewe periodes van oorheersende onderwater makrofiet insette wat verhoogde watervlakke voorstel. ‗n Algemene positiewe tendens was opgemerk tussen die temperature en vog gevolgmatigdes. Die plaaslike plantfisiologie (n-alkaan ketting lengtes; ACLalk) en plantsoorte (land vs. akwaties en hulle invloed op OM labiliteit) was egter gedomineer deur vogbeskikbaarheid daarteenoor temperatuur variasies, waarskynlik as gevolg van die relatiewe matige afkoeling wat ervaar was in die subtropiese areas gedurende die LGM. Die blaarwas C isotoop datastel het vasgestel dat variasie in die proporsionele balans van C3 en C4 plante plaasvind, met verwisseling tussen plant klades en interfamilie C3 en C4 skakelaars in reaksie tot veranderinge in omgewings toestande. Die plantsamestelling-skuif was egter afwesig gedurende sommige van die meer efemere klimaatstoestand gebeurtenisse en ons het vasgestel dat dit ‗n nagevolg van plasslike hidrologiese oordrukking is. Die Mfabeni argief korreleer sterk met Mozambiek Kanaal SST rekords en stel voor dat die dominante klimaat dwingende faktor in suid-oostelike Afrika die verdampingspotensiaal en adveksie van vog is van die aangrensende Indiese Oseaan vanaf die laat Pleistocene tydperk. Dit was ook opgemerk dat die Mfabeni rekord algeheel teenoorgestelde omgewings reaksies toon teenoor die Noordelike Halfrond klimaatsgebeurtenisse, wat daarop dui dat daar ‗n anti-fase koppeling is tussen die twee Halfronde. Thesis (PhD)--Stellenbosch University, 2016.

The processes of melt segregation, magma ascent and pluton emplacement in the continental crust of the Damara Belt, Namibia

2016-05-25T07:18:03Z

The processes of melt segregation, magma ascent and pluton emplacement in the continental crust of the Damara Belt, Namibia Hall, Duncan James ENGLISH ABSTRACT: Theoretical models of meso- and macroscale granitic melt/magma transport commonly invoke a prominent role for dilatant fracturing of the wall rocks, but supporting field evidence is in many cases only scantly presented. This dissertation is a compilation of three case studies that integrate some of the theoretical models with field-based aspects from the obliquely exposed south Central Zone magmatic arc of the Damara Belt in Namibia. Chapter 3 describes interconnected leucogranite networks that accommodate the transport of melt at the outcrop-scale in homogeneous, high-grade near-source gneisses in the western parts of the south Central Zone. The net-structured leucogranite networks include small intrafolial stringers, larger shear-band-hosted veins and still larger fracture-hosted leucogranite sheets, which display a size-based hierarchical distribution that results from the self-organisation of the near-source melt transport pathways. The development of the networks is controlled intrinsically by variations in the rate of melt supply. During periods of elevated melt supply and under conditions of low differential stress, melt-induced extensional fracturing generates hydraulic gradients that result in the formation of melt sheets which represent potential far-field ascent conduits (dykes sensu lato). However, the orientations of the sheets are controlled by wall-rock structures and regional and local stress fields, resulting in this case in the preservation and eventual crystallisation of shallowly-dipping leucogranite sheets that were unfavourably orientated to accommodate buoyancy-driven melt/magma drainage. Chapter 4 describes the actual drainage of magma along steeply-dipping fracture conduits initiated in well-layered upper amphibolite-facies basement gneisses ~30 km SE of the outcrops presented in chapter 1. Here, the moderately-dipping gneisses contain large-scale leucogranite networks that include deca- to hecto metre-scale subvertical leucogranite lenses interpreted to document the near-source accumulation of magma necessary for efficient far-field ascent. Field relationships also document the drainage of the subvertical lenses at critical lengths and volumes in excess of 100 m and ~2.4×105 m3 respectively. These values as well as the field relationships are broadly consistent with theoretical models of magma transport along mobilised (self-propagating) hydrofractures. Self-propagating hydrofractures propagate at their tips and close simultaneously along their tails, leaving behind only very subtle and easily overprinted evidence, which may account for the elusiveness of granite conduits in the mid-crust. This work presents the first field evidence of large-scale magma drainage along self-propagating hydrofractures and has important consequences for the subsequent transport of magma through and eventual incremental emplacement within the subsolidus crust. Chapter 5 examines in more detail the implications of fracture-controlled magma ascent for granite pluton emplacement in lower amphibolite-facies wall rocks ~80 km northeast of the near-source features presented in chapters 3 and 4. Three closely-spaced tabular granitoid plutons that were emplaced roughly contemporaneously at widely-varying structural levels are investigated. Each of the plutons demonstrates the effect of mechanical contrasts in the wall-rock that favour fracture arrest rather than ascent, particularly rigidity and rheological contrasts. However, contrary to the theoretical models, it is shown that rigidity contrasts which cause fracture arrest need not be associated with lithological contacts and the role of increasing differential stress during the fracture-controlled ascent of magma towards the brittle-to-ductile transition is highlighted. The three chapters outlined above highlight the importance of fracture-controlled magma transport at all scales in the Damara Belt and substantiate some of the theoretical concepts, but also highlight prominent discrepancies between the models and natural systems.; AFRIKAANSE OPSOMMING: Teoretiese modelle van meso- en makroskaalse granitiese smeltsel/magma vervoer roep oor die algemeen ‘n prominente rol van dilatante breukvorming van die wandgesteentes, maar ondersteunende veldbewyse is in baie gevalle op ‘n onvoldoende wyse voorgestel. Hierdie proefskrif is ‘n samestelling van drie gevallestudies wat teoretiese modelle en veld gebaseerde aspekte vanuit die skuins ontblote suid-Sentrale Sone magmatiese boog van die Damara Belt in Namibië integreer. Hoofstuk 3 beskryf ‘n onderlinge verbindings netwerk van leukograniet wat die vervoer van smeltsel op dagsoomskaal akkommodeer in hoë-graad naby-bron gneise in die westelike dele van die suid-Sentrale Sone. Die netgestruktureerde leukograniet netwerke sluit in klein intrafoliese smeltselstringe, groter aar-draende skuifskeursones asook groter breukaangedrewe leukograniet plate wat grootte ‘n gebaseerde hiërargiese-verspreiding vertoon as gevolg van die self-georganiseerdheid van die naby-bron smeltsel vervoer bane. Die ontwikkeling van die netwerk is intrinsiek beheer deur variansie in die tempo van smeltsel-toevoer. Smeltsel-geïnduseerde uitstrekkingsbreuking tydens periodes van lae differensiële spanning en verhoogde smeltsel toevoer genereer groot hidroliese gradiënte wat die vorming van groot smeltsel-plate dryf en gevolglik vêr-veld magma dreinerings leikanale kan vorm (gange sensu lato). Egter, die orientasie van die resultante breuke en gange word beheer deur strukture in die wandgesteentes asook regionale en lokale spanningsvelde, wat gevolglik lei tot die ontwikkeling en uiteindelike stolling van die vlak-inklinasie smeltsel plate wat ongunstig georienteer was om druifaangedrewe smeltsel dreinering te akkommodeer. Hoofstuk 4 adresseer die werklike dreinering van magma deur steil leikanale/gange wat in goed-gelaagde boonste amfiboliet fasies vloergneise sowat ~30 km SO van die dagsome wat aangebied is in hoofstuk 1. In die geval van die matig-hellende vloergneise met grootskaalse leukograniet netwerke, word deka- tot hektometerskaalse subvertikale leukograniet lense ingesluit en word geïnterpreteer om naby-bron akkumulasie van magma wat noodsaaklik is vir doeltreffende vêr-veld vervoer te dokumenteer. Veld verhoudings dokumenteer onderskeidelik ook die dreinering van die subvertikale lense teen kritiese lengtes en volumes in oormaat van 100 m en ~2.4×105 m3. Hierdie waardes sowel as die veld verhoudings is oor die algemeen in ooreenstemming met teoretiese modelle van magma vervoer deur middel van gemobiliseerde self-propagerende hidrobreuke. Self-propagerende hidrobreuke propageer by hul toppunte en maak terselfdertyd toe by hul sterte en los dus baie subtiele en maklik-oordrukte bewyse agter wat moontlik rekening staan vir die ontwynkendheid van graniet leikanale in die middel-kors. Hierdie verteenwoordig die eerste veld gebaseerde bewyse van grootskaalse magma dreinering deur self-propagerende hidrobreuke en het belangrike gevolge vir die daaropvolgende vervoer van die magma deur en die uieindelike inkrementele inplasing daarvan binne in die subsoliduse kors. Hoofstuk 5 ondersoek in meer detail die implikasies van breuk-beheerde magma styging vir graniet pluton inplasing in laër-amfiboliet fasies wandgesteentes ~80 km noordoos van die naby-bron strukture wat in hoofstukke 3 en 4 bespreek is. Drie nou-gespasieerde tabletvormige granietiese plutone wat ongeveer gelyktydig ingeplaas was teen wyd uiteenlopende strukturele vlakke in wandgesteentes is ondersoek. Elkeen van die plutone demonstreer die effekte van meganiese kontraste in die wandgesteentes wat breuk propagasie tot stilstand bring eerder as om voorsetting van propagasie te bevoordeel. Meer spesifiek, die drie plutone beklemtoon die rolle wat vertolk word deur vervormingvastheid en reologiese kontraste. Egter, in een geval is dit gewys dat die meganiese kontraste wat breuk propagasie stopsit word nie noodwendig geassosieer met litologiese kontakte nie, soos aanbeveel deur teoretiese modelle van magma inplasing, deur die belangrikheid van toenemende differensieële spanning te beklemtoon soos wat temperature langs die stygingspad die brosheid-smeebaarheids-oorgang bereik. Die drie hoofstukke uiteengesit hierbo beklemtoon die belangrkheid van breukbeheerde magma vervoer op alle skale in die middel-kors van die Damara Belt en substansieer sekere van die teoretiese konsepte, maar lig ook uit prominente teenstrydighede tussen die modelle en natuurlike stelsels. Thesis (DSc)--Stellenbosch University, 2016.

Relationship of historical copper mining to the transport and accumulation of trace metals and salts in semi-arid environments : an example from Buffels River, Northern Cape, South Africa

2016-05-11T08:02:46Z

Relationship of historical copper mining to the transport and accumulation of trace metals and salts in semi-arid environments : an example from Buffels River, Northern Cape, South Africa Dunford, Alexander ENGLISH ABSTRACT: The town of Kleinzee, located in the Northern Cape, South Africa exists solely to mine alluvial diamonds found in the Buffels River. Given the very low precipitation of the area (generally <150mm/yr) groundwater is the principal supply of domestic and industrial water to the town. In an effort to increase the water supply needed, the town installed an underground membrane across the Buffels River approximately 5.5km upriver from the town. However, climatic conditions, long term copper and diamond mining and poor groundwater management practices have combined to produce very poor quality groundwater within the Buffels River Valley. The purpose of this study is to look at the impact of the membrane on the quality of both the shallow groundwater system as well as the soils within the river bed. To do this, 46 sites were selected for soil analysis starting below the membrane and continuing above the membrane upriver for a distance of approximately 5 km. Additionally, a further 15 groundwater samples were collected at the end of the wet season in October when groundwater was available. Cation and anion analysis of the shallow groundwater and the saturated paste extracts shows significant peaks in SO4 2- and Mg2+ immediately above the membrane in the sediments in addition to Na+ and Cl-, diminishing upstream away from the membrane. Cu2+ and Zn2+ did not show an elevated concentrations in the groundwater or sediments above the membrane as originally thought. Experiments on atacamite, a Cu2+-hydroxide, which forms naturally in the Spektakel soils within the Buffels River Valley, indicates that although generally stable at moderate pH, large rain events may increase the solubility of atacamite resulting in its transport downstream. However, the source of sulphate is probably linked to processing of Cu2+ ores further up the river valley. The transport mechanism of the groundwater salts and trace metals is via dissolution mobilization. The membrane is accumulating trace metals and salts in sediments behind the membrane and not in groundwater found behind the membrane. Thus accumulation is due principally to evaporative concentration.; AFRIKAANSE OPSOMMING: Nie beskikbaar nie. Thesis (MSc)--Stellenbosch University, 2016.

An experimental investigation into the ‘fate’ of entrained peritectic minerals in I-type granite magmas intruded at below 2kbar.

2016-05-05T07:57:05Z

An experimental investigation into the ‘fate’ of entrained peritectic minerals in I-type granite magmas intruded at below 2kbar. Zarrebini, Sara Kathryn ENGLISH ABSTRACT: Entrainment of a peritectic mineral assemblage, formed through the incongruent melting of biotite and hornblende in a source of intermediate composition, has been proposed to account for the fact that I-type granites are commonly more mafic in composition than the melts from which they are derived. Magma consisting of variable proportions of melt and a distinct peritectic assemblage (Pl + Cpx + Opx + Ilm ± Grt) has been proposed to explain the substantial compositional range of I-type granitic rocks. Geochemical evidence to support the entrainment of a peritectic assemblage includes the strong, positive correlation between Ti vs maficity (atomic Fe + Mg) (with correlation coefficients typically higher than 0.9 for suites from individual plutons), as well as the very weak correlation between K and maficity in all granitic rocks. Despite this compelling geochemical evidence for the entrainment of a peritectic mineral assemblage, there is distinct lack of both mineral textural and mineral compositional evidence of these peritectic phases within I-type granites. In order to ascertain the ‘fate’ of the proposed entrained peritectic phases; the mechanisms and reactions by which these phases equilibrate with the surrounding magma, as well as the corresponding rates of these reactions needs to be established. This research used experimental techniques to determine the kinetic processes involved in the digestion of a high-pressure peritectic assemblage within a granodioritic magma under plutonic conditions within the upper crust (~2kbar and 763 to 720°C). A synthetic silicate gel (representative of the melt fraction) was mixed with a hypothetical, natural peritectic mineral assemblage (13.1Pl + 9.3Cpx + 1.1Opx + 0.8Ilm ± 5.7Grt) in a 7:3 ratio to form the experimental starting material. The peritectic mineral assemblage comprised of natural minerals of suitable compositions that were crushed and sieved to produce crystals with an average 200μm - 600μm size range. The 1.60 wt. % water within the starting composition was accommodated as kaolinite, which was added to the completed silicate gel in the correct stoichiometric proportions. The overall mineral-melt mixture was intended to represent the bulk composition of an I-type granodioritic magma produced by the fluid-absent melting of biotite and hornblende within an intermediate source composition at 10kbar and 850 - 900°C. The starting material (melt + mineral mixture) was loaded into gold capsules, which were then welded shut. The material was then reacted at pressures of 1.90kbar and 1.40kbar and at temperatures of 763 – 723°C within a cold-seal pressure vessel, with each experiment lasting 10 days. The findings of this research identified two principal reaction processes by which the high-pressure peritectic minerals react out within the experimental run products, namely; dissolution-precipitation and mineral-melt reactions. A coupled dissolution-precipitation mechanism is proposed to account for the rapid re-equilibration of ‘peritectic’ phases that are predicted (by phase equilibrium modelling) to be stable, but out of compositional equilibrium with the surrounding magma at the investigated PT conditions. ‘Peritectic’ plagioclase was seen to dissolve completely and reprecipitate a more albitic composition across all experimental pressure and temperature conditions, and within the experimental run-time (10 days). Consequently, a coupled dissolution-precipitation mechanism is inferred to be a sufficiently rapid and efficient process to account for the predominantly magmatic origin of feldspathic crystals within natural granitic rocks. At corresponding PT conditions, unstable mineral phases were seen to change both compositionally and texturally according to a separate reaction process, i.e. reaction with the surrounding melt portion. High pressure and temperature ferromagnesian minerals, such as garnet and orthopyroxene, which were not stable phases in the magma at the condition of the experiments were seen to react with the melt to produce reaction rims of biotite, which was a stable phase in the magma. The rapid growth rate of biotite resulting from this process suggests phaneritic textural features typically associated with granite bodies do not require long residency times to form within upper crustal magma chambers. The persistence of both garnet and orthopyroxene at the low pressure (1.40 – 1.90kbar) and temperature (763 - 720°C) conditions of experimentation indicates that at these conditions the mineral-melt reactions were too ‘sluggish’ to completely digest these phases. The rapid dissolution-precipitation rates of plagioclase within the experiments suggests that where garnet and orthopyroxene crystals are evident in natural granitic rocks these minerals bear no compositional or textural resemblance to the originally entrained ‘peritectic’ phases. The findings of this research corresponds well with the theory that I-type granites’ compositional trends form as a consequence of a peritectic mineral assemblage (Pl + Cpx + Opx + Ilm ± Grt) being entrained within a leucocratic melt. However, this research has far-reaching implications in terms of other formational theories, such as; fractional crystallization, magma mixing at depth and restite entrainment, that similarly involve the production of crystal-rich magmas at depth. Regardless of which process is responsible for generating the vast compositional heterogeneity of I-type granitic rocks, if the temperature conditions of the granitic magmas remain sufficiently high (>700°C) the magma will have the propensity to either partially or fully equilibrate any crystal component that is not in equilibrium with the surrounding magma.; AFRIKAANSE OPSOMMING: Optel-en-meevoer van ‘n peritektiese mineraal versameling gevorm deur die ongelykvormige smelting van biotiet en hornblende in ‘n bron van intermediêre samestelling, was voorgestel om die I-tiepe graniet in ag te neem. Die I-tiepe graniet is oor die algemeen meer mafies in samestelling as wat smelt is. Magma bestaan uit verskillende hoeveelhede van smelt en ‘n spesifieke peritektiese versameling (Pl + Cpx + Opx + Ilm ± Grt) was voorgestel om die aansienlike komposisionele reeks van I-tiepe graniet smelt te verduidelik. Geochemiese bewyse om die optel-en-meevoer van die peritektiese versameling te ondersteun sluit in ‘n sterk, positiewe korrelasie tussen die Ti vs mafiese (atomies Fe + Mg) (met ‘n korrelasiekoëffisiënt wat gewoontlik hoër as 0.9 is vir rock groepe van individuele plutone) asook die baie swak korrelasie tussen K en mafiese in alle graniet klippe. Ten spyte van hierdie geochemiese bewyse van die optel-en-meevoer van die peritektiese mineraal versameling, is daar ‘n duidelike gebrek van bewyse vir beide mineraal tekstuur en mineraal komposisie van hierdie peritektiese fases in die I-tiepe graniet. Om die ‘lot’ van die voorgestelde optel-en-meevoer peritetiese fases te bepaal, moet die meganismes en reaksies van hierdie ewewigsfases, sowel as die magma in die omliggende en hul ooreenstemmende tempos, bepaal word. Hierdie navorsing het van eksperimentele tegnieke gebruik gemaak om die kinetiese prosesse te bepaal. Die prosesse is betrokke in die vertering van ‘n hoë druk perifiese mineraal versameling in ‘n granodioritiese magma onder plutoniese omstandighede in die boonste kors (~2kbar en 763 tot 720°C). ‘n Sintetiese silikahouende gel (verteenwoordiger van die smelt fraksie) was gemeng met ‘n hipotetiese, natuurlike peritektiese mineraal versameling (13.1Pl + 9.3Cpx + 1.1Opx + 0.8Ilm ± 5.7Grt) in ‘n 7:3 verhouding om die eksperimentele begin materiaal te vorm. Die peritektiese mineraal versameling bestaan uit natuurlike minerale van geskikte komposisies wat vergruis en gesif was sodat die kristalle ‘n gemiddeld grootte van 200μm - 600μm het. Die 1.6 wt. % water in die begin komposisie was geakkommodeer as kaoliniet, wat bygelas was om die silikahouende gel in die regte stoïgiometriese proporsies volledig te maak. Die hele mineraal mengsel was bedoel om die mederheid komposisies van ‘n I-tiepe granodiorite magma voor te stel en was geproduseer by die vloeistof-afwesige smelting van biotiet en hornblende in ‘n intermediêre bron komposisie by 10 kbar en 850 - 900°C. Die begin materiaal (smelt + mineraal mengsel) was in ‘n goue capsule gelaai, wat dan toe gesweis was. Die materiaal het gereageer by ‘n druk van 1.9 kbar en 1.4 kbar en by die temperatuur van 763 - 720°C wat in ‘n koue geseëlde drukvat geplaas was met elke eksperiment wat 10 dae lank geduur het. Die resultate van hierdie navorsing identifiseer twee beginsel reaksie prosesse, ontbinding-neerslag en minerale-smelt hidrasie reaksies, waar die hoë druk peritektiese minerale reageer in die eksperimentele resultante. ‘n Gekoppelde oplossings-presipitasie meganisme is voorgestel om die vinnige herewewigsproses van peritektiese fases in ag te neem wat voorspel is (deur fase ewewig modellering) om stabiel te wees, maar uit komposisionele ewewig saam met die magma in die omliggende gebied by die ondersoekte PT omstandighede. Peritektiese plagioklaas was gesien en het heeltemal opgelos en neerslag ‘n meer albeitiese komposisie oor al die eksperimentele druk en temperatuur omstandighede, asook in die eksperimentele looptyd (10 dae). Gevolglik is ‘n gekoppelde oplossings-presipitasie meganisme afgelei as ‘n effektiewe proses teen voldoende tempo om die oorwegende magmatiese oorsprong van feldspatiese kristalle in natuurlike graniet klip waar te neem. By ooreenkomstige PT omstandighede was daar onstabiele mineraal fases gesien wat volgens die afsonderlike reaksie fase in beide komposisionele en teksturele minerale verander het, bv. reaksies met die omgewind smelt proporsies. Hoë druk en temperatuur minerale met hoë Fe en Mg konsentrasies, soos granaat en ortopirokseen, was nie in stabiele fases in die magma by die omstandighede van die eksperiment nie en waargeneem dat dit reageer met die smelt om reaksie rande van ‘n stabiele biotiet fases te vorm. Dit was waargeneem dat ortopirokseen in laer druk eksperimente (1.40 kbar) reageer met die omliggende smelt proporsie om biotiet vervang ortopirokseen te vorm teen ‘n spoed van omtrent vier keer stadiger as die herewewig van peritektiese plagioklaas by die oplossings-presipitasie proses. Die vinnige groeitempo van biotiete, as gevolg van hieride proses, stel voor dat ‘phaneritic’ teksturele funksies wat tipies geassosieer word met graniet liggame, vereis nie lang verblyf tye om te vorm in die boonste kristal magma kamers nie. Die volharding van beide granaat en ortopirokseen by die lae druk (1.40 – 1.90kbar) en temperatuur (763 - 720°C) omstandighede van eksperimentasie toon dat by hieride omstandighede van eksperimentasie die mineraal-smelt hidrasie reaksies was te trae om volledig te verteer in hierdie fases. Die vinnige oplossings-presipitasie tempos van plagioklaas in die eksperimente dui duidelik aan dat granaat en ortopirokseen kristalle in natuurlike graniet klippe is. Hierdie minerale hou geen komposisionele of teksturele ooreenkoms met die oorspronklike opgetel en weggedra peritektiese fases nie. Die resultate van die navorsing stem goed ooreen met die teorie dat I-tiepe graniete komposisionele tendense vorm as ‘n gevolg van ‘n peritektiese mineraal versameling (Pl + Cpx + Opx + Ilm ± Grt) wat opgetel en weggedra is in ‘n leukokratiese smelt. Maar hierdie navorsing het verreikende gevolge in terme van ander magmatiese teorieë, bv. fraksionele kristalisering, magma vermenging in diepte en die optel-en-meevoer van die oorblywende minerale uit die bron, wat soortgelyk die produksie van kristalryk magmas in diepte insluit. Ongeag van watter van hierdie prosesse verantwoordelik is vir die generering van die oorgrote komposisionele heterogeniteit van I-tiepe graniet klippe, as die temperatuur omstandighede van die graniet magmas by voldoende hoë hoeveelhede bly (>700°C), dan sal die magma die geneigdheid hê om gedeeltlik of heeltemal ewewig te bereik met enige kristal komponent wat nie in komposisionele ewewig met die omliggende magma is nie. Thesis (MSc)--Stellenbosch University, 2016.

Application of hydrochemistry and residence time constraints to distinguish groundwater systems in the Karoo Basin prior to shale-gas exploration

2016-05-12T06:15:39Z

Application of hydrochemistry and residence time constraints to distinguish groundwater systems in the Karoo Basin prior to shale-gas exploration Swana, Kelley ENGLISH ABSTRACT: The possibility of shale-gas development in the semi-arid Karoo Basin, South Africa has created the need to develop a hydrochemical baseline for deep Karoo groundwater. However, it is uncertain how the process of hydraulic fracturing (fracking) will affect the surrounding groundwater and environments, particularly shallow groundwater sources. Therefore, it is important to have a good understanding of the characteristics of the deep groundwater and its connectivity to the shallower groundwater systems which are of utmost importance to the farmers and local communities in the region. As a result of the requirement for information regarding the deeper groundwater in the Karoo Basin, this project was initiated in order to create a baseline of the deeper groundwater and assess how it differentiates from the shallow groundwater. Nineteen groundwater samples were collected from 8 locations throughout the Karoo Basin. At each site a deep sample was collected from a warm spring or borehole, and a corresponding shallow site was collected from a nearby shallow borehole. Following an initial assessment of the groundwater samples, three groups were identified; deep, shallow and mixed. The shallow samples could be identified by temperatures less than 25°C, high alkalinities, the presence of Mg2+, NO3- and U, as well as higher δ2H and δ18O values. Warmer temperatures usually above 25°C, low alkalinities less than 80 mg.L-1 HCO3-, elevated Na+ and F- as well as lower δ2H and δ18O values were characteristic of the deep samples. The results of the mixed samples consistently feel between those of the deep and shallow samples, indicates that natural mixing occurs between the deep and shallow aquifer systems. This has important implications as upward migration of poor quality deep groundwater and contaminants resulting from fracking activities have been known to occur in the USA. Significant differences are observed between the deep and shallow samples, resulting from different controls on the groundwater chemistry. For example, the process of nitrification occurs in the shallow groundwater resulting in elevated NO3- concentrations, whereas the dissolution of fluorite results in elevated F- concentrations in the deep groundwater. Furthermore, increased contact time with the host lithologies results in increased Na concentrations in the deep groundwater. Residence times of the groundwater samples were calculated using four isotopic tracers, namely, tritiogenic helium, radiocarbon, helium-4 and chrlorine-36. Overall, the deep groundwater samples showed much longer residence times than shallow groundwater, with radiocarbon producing the most probable residence times. Pollution and contamination of shallow aquifers as a result of fracking is possible. Therefore, continuous baseline monitoring is essential before, during and after fracking activities in order to identify abnormalities that could be associated with fracking.; AFRIKAANSE OPSOMMING: Nie beskikbaar nie. Thesis (MSc)--Stellenbosch University, 2016.

Disequilibrium melting of plagioclase during biotite fluid-absent anatexis of metapelites in the South Marginal Zone of the Limpopo belt, South Africa

2016-05-25T06:58:23Z

Disequilibrium melting of plagioclase during biotite fluid-absent anatexis of metapelites in the South Marginal Zone of the Limpopo belt, South Africa Madlakana, Nonkuselo ENGLISH ABSTRACT: This study investigated the behaviour of plagioclase during fluid-absent biotite melting in a metapelitic source from which peraluminous granite magma had segregated. The study focused on the Bandelierkop Quarry (South Marginal Zone of the Limpopo belt), where stromatic and discordant nebulous leucosomes contain peritectic garnet crystals produced by the following melting reactions; Bt + Sil + Qtz + Pl = Grt + Ilm + Melt; and, Bt + Qtz + Pl = Grt + Ilm + Opx + Crd + Melt. In rare cases, large (10 to 20mm) garnet crystals within both leucosome types are growth zoned. These garnet crystals host plagioclase inclusions, which are commonly euhedral and occur as single crystals, clusters of crystals and as polymineralic inclusions which typically consist of biotite, rutile and orthopyroxene. The inclusions display considerable chemical heterogeneity. Matrix plagioclase in both leucosome types ranges in composition from An27 to 35, whilst that in the residuum adjacent to the leucosomes ranges from An32 to 39. Euhedral plagioclase inclusions are considerably more calcic with compositions that range from An50 to 83. Composition of the inclusions shows no relationship with position within the garnet crystal, or with size of the plagioclase crystal. These crystals are also significantly zoned, yet their zoning is not systematic, with inclusions displaying both Na- and Ca-enriched rims. Garnet zonation around the inclusions was investigated in detail and demonstrates that the Ca-rich nature of the inclusions is not a consequence of Ca-uptake from garnet. In contrast, anhedral plagioclase within large amoeboid polymineralic inclusions displays compositions similar to the matrix plagioclase. Garnet also hosts very small (≤ 10μm) inclusions of quartz + plagioclase ± biotite. These micro-granite inclusions are interpreted as melt inclusions. The complexity of plagioclase behaviour recorded within the peritectic garnet crystals is interpreted to reflect disequilibrium during anatexis due to slow diffusion in plagioclase; only the outer portions of the plagioclase crystals participate in the melting reaction and they do so by combined dissolution and precipitation of new, Ca-rich crystals. Modelling demonstrates that the Ca-contents of these new crystals is inversely proportional to the amounts of plagioclase that participate in the reaction. Consequently, the euhedral plagioclase inclusions are interpreted to be peritectic, where these occur as polymineralic inclusions they are small and plagioclase is volumetrically dominant, so the melt volume in the inclusion was low. The more Ca-rich rims in euhedral plagioclase inclusions may reflect zonation produced by the melting reaction, whilst Na-rich rims may reflect crystals that are too calcic to equilibrate with melt within the time-scale available for melting , the volume of equilibrium is extremely locally controlled, which in turn induces Na-rich rims. The preservation of these garnet crystals, possibly due to rapid and efficient melt loss from the leucosome structures, provides a rare insight into the details of the anatectic process. In the vast majority of migmatitic granulites these are lost due to comprehensive extensive recrystallization and homogenization of mineral compositions.; AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die gedrag van plagioklaas gedurende vloeistof-vrye biotiet smelting in ‘n metapelitiese bron vanwaar peraluminous graniet magma geskei het. Die studie fokus op die Bandelierkop Steengroef (Suid Marginale Zone van die Limpopo belt), waar stromatiese en afwykende newelagtige leukosome peritektiese granaatkristalle bevat wat produseer is deur die volgende smeltingsreaksies; Bt + Sil + Qtz + Pl = Grt + Ilm + Smelt; en, Bt + Qtz + Pl = Grt + Ilm + Opx + Crd + Smelt. In seldsame gevalle is groot (10 tot 20mm) granaatkristalle vanuit beide leukosoom tipes gesoneer tydens die groeiproses. Hierdie granaatkristalle bevat plagioklaas insluitings wat in die algemeen euëdries is en as enkel kristalle, kristal clusters en as polimineraliese insluitings wat tipies bestaan uit biotiet, rutiel en ortopirokseen. Die insluitings vertoon aansienlike chemiese heterogeniteit. Matriks plagioklaas in beide leukosoom tipes vertoon ‘n reeks komposisies van An 27 tot 35, waaartydens die in die residium aangrensend tot die leukosome verskil van An 32 tot 39. Euëdriese plagioklaaskristalle is aansienlik meer kalies met ‘n reeks komposisies van An 50 tot 83. Komposisies van die insluitings wys geen verhouding met posisie binne die granaat kristal of met die grootte van die plagioklaas kristal nie. Hierdie kristalle is ook merkwaardiglik gesoneer maar die sonering is nie sistematies nie, waar die insluitsels beide Na en Ca-ryke vellings vertoon. Granaat sonering rondom die insluitings was in detail ondersoek en dit demonstreer dat die Ca-ryke natuur van die insluitings nie ‘n oorsaak van Ca-opname vanaf granaat is nie. In kontras vertoon die oneievormige plagioklaas vanbinne groot amobidale polimineraliese insluitings komposisies soortgelyk aan die matriks plagioklaas. Granaat bevat ook baie fyn (≤ 10μm) isometriese insluitings van quartz + plagioklaas ± biotiet. Hierdie mikrogranietinsluitsels word as smeltingsinsluitsels geïnterpriteer. Die kompleksiteit van die gedrag van plagioklaas is aangeteken vanbinne die peritektiese granaatkristalle en is geïnterpriteer as die refleksie van onewewigtigheid gedurende anateksis as gevolg van stadige diffusie in plagioklaas. Slegs die buitenste gedeelte van die plagioklaaskristalle neem deel aan die smeltingsreaksie en hul doen dit deur gekombineerde ontbinding en presipitasie van nuwe Ca-ryke kristalle. Modellering demonstreer dat die Ca-inhoud van hierdie nuwe kirstalle ongekeerd eweredig is tot die hoeveelheid plagioklaas wat deel neem aan die reaksie. Gevolgelik is die euëdriese plagioklaas insluitings as peritekties geïnterpreteer. Waar hierdie voor kom as polimineraliese insluitings, is hulle klein en plagioklaas is volumetries dominant, so die smelt volume in die insluitsel was klein. Die meer Ca-ryke vellings in euëdriese plagioklaasinsluitings mag sonering as gevolg van die smeltingsreaksie reflekteer, waartydens Na-ryke vellings die kristalle reflekteer wat te kalies is om te ekwilibreer met die smelt. Die volume van ewewig is uiters plaaslik beheer wat dan Na-ryke vellings insluit. The bewaring van hierdie unieke granaatkristalle, moontlik as gevolg van spoedige en effektiewe verlies aan smelt van die leukosoomstrukture, bied ‘n rare insig in die proses van anatekse. In die oorweldige meerderheid van magmatiese granuliete is hierdie kirstalle verlore as gevolg van omvattende uitgebreide herkristallisasie en homogenisering van mineraalkomposisies. Thesis (MSc)--Stellenbosch University, 2016.

Rcrust : a tool for calculating path-dependent open system processes and application to melt loss

2016-05-09T11:27:56Z

Rcrust : a tool for calculating path-dependent open system processes and application to melt loss Mayne, Matthew Jason ENGLISH ABSTRACT: Earth‘s continental crust is stabilised by crustal differentiation that is driven by partial melting and melt loss: Magmas segregate from their residuum and migrate into the upper crust, leaving the deep crust refractory. Thus, compositional change is an integral part of the metamorphic evolution of anatectic granulites. Current thermodynamic modelling techniques have limited abilities to handle changing bulk composition. New software is developed (Rcrust) that via a path-dependent iteration approach enables pressure, temperature and bulk composition to act as simultaneous variables. Path-dependence allows phase additions or extractions that will alter the effective bulk composition of the system. This new methodology leads to a host of additional investigative tools. Singular paths within Pressure-Temperature-Bulk composition (P-T-X) space give details of changing phase proportions and compositions during the anatectic process, while compilations of paths create path-dependent P-T mode diagrams. A case study is used to investigate the effects of melt loss in an open system for a pelite starting bulk composition. The study is expanded upon by considering multiple P-T paths and considering the effects of a lower melt threshold. It is found that, for the pelite starting composition under investigation, open systems produce less melt than closed systems and that melt loss prior to decompression drastically reduces the ability of the system to from melt upon decompression.; AFRIKAANSE OPSOMMING: Korsdifferensiasie stabiliseer die kontinentale kors van die aarde tydens gedeeltelike smelting. Magma segregeer van hul residuum en migreer in die vlakker kors in. As gevolg daarvan raak die diepkors meer vuurvas. Dus speel komposisionele verandering ‗n belangrike rol in die evolusie van anatektiese granuliete. Hedendaagse termodinamiese modelleringstegnieke het beperkte vermoëns om 'n veranderende grootmaatsamestelling te hanteer. Nuwe sagteware is ontwikkel (Rcrust) wat 'n roete-afhanklike iterasie benadering volg. Hierdie metode laat die druk, temperatuur en grootmaatsamestelling toe om as gelyktydige veranderlikes te funksioneer. Roete-afhanklikheid laat fasetoevoegings of ekstraksies toe om die effektiewe grootmaatsamestelling van die stelsel te verander. Die nuwe metode bied ‗n magdom verskeie maniere aan om ondersoek in te stel. Enkel roetes van P-T-X ruimte beskryf die fase proporsies en komposisies tydens die proses anatektiese, terwyl kombinasies van roetes, roete-akhanklike pseudosections skep. 'n Gevallestudie is op uitgebrei om die gevolge van smeltverlies te ondersoek. Dit is bevind dat oop stelsels minder produktief by smelt vorming is as geslote stelsels, en dat dekompressie smelt minder produktief as verwarming is. Die verlies in smelt produktiwiteit van die oop stelsel impliseer beperkings op die maksimum massa dekompressie smelt wat kan vorm. Tektoniese modelle wat dekompressie smelt as bron van groot volumes smelt gebruik moet dus herevalueer word.

Photosynthetic response of Southern Ocean phytoplankton under iron and light limitations : bioassay experiments

2016-01-21T06:51:59Z

Photosynthetic response of Southern Ocean phytoplankton under iron and light limitations : bioassay experiments Van Horsten, Natasha ENGLISH ABSTRACT: The Southern Ocean (SO) is of significant interest in the understanding of the global carbon cycle and therefore many studies have been conducted to determine the limiting factors controlling the biological pump within the region. During photosynthesis phytoplankton require various nutrients such as NO3, PO4, inorganic carbon and the micronutrient Fe. The SO is a High-Nutrient Low-Chlorophyll region, therefore no macronutrient limitation is experienced by resident phytoplankton but instead the micronutrient Fe is a significant limiting factor within these waters due to limited inputs. Due to deep mixed layer depths, ice cover, low sun angles and cloud cover throughout parts of the year, light is also considered a limiting factor in the SO. Fe and light limitation cause a decrease in photosynthetic efficiency and therefore a decrease in carbon fixation capabilities. During this study we conducted five bioassay shipboard incubation experiments during two cruises along the Greenwich meridian between South Africa and the ice edge, SOSCEx during March and SAFePool during January to February, in which we varied Fe concentrations and light levels to determine the effects of Fe and light limitation or co-limitation within resident phytoplankton. Spatial and temporal variations in phytoplankton response were studied to determine varying effects of limitation across water masses and different stages of bloom decline within the study area. The combined addition of Fe and light gave the largest increase in biomass, photosynthetic capacity and nutrient uptake. In support of the hypotheses tested changes in the photosynthetic apparatus led to changes in the photosynthetic efficiency and growth of the SO phytoplankton, as a result of variations in Fe and light availability. Variability was also observed in the response of phytoplankton to Fe and light amendments due to spatial and temporal variation in resident phytoplankton communities. It was therefore concluded that both Fe and light are significant controls in the resident phytoplankton photosynthetic apparatus, photosynthetic capabilities, organic carbon fixation and therefore the biogeochemical cycles within the Atlantic sector of the SO.; AFRIKAANSE OPSOMMING: Die Suidelike Oseaan (SO) is van beduidende belang in die begrip van die globale koolstofsiklus en dus is baie studies gedoen om die beperkende faktore te bepaal wat die biologiese pomp in die streek beheer. Tydens fotosintese benodig fitoplankton verskillende voedingstowwe soos NO3, PO4, anorganiese koolstof en die mikrovoedingstof Fe. Die SO is 'n High-Nutrient Lae-Chlorofil streek, dus word geen makrovoedingstof beperking ervaar deur inwoner fitoplankton maar in plaas daarvan is die mikrovoedingstof Fe 'n beduidende beperkende faktor binne hierdie waters weens beperkte insette. As gevolg van diep gemengde laag dieptes, ysbedekking, lae son hoeke en wolkbedekking deur dele van die jaar, word lig ook beskou as 'n beperkende faktor in die SO. Fe en lig beperking veroorsaak 'n afname in die fotosintetiese doeltreffendheid en dus 'n afname in koolstof binding vermoëns. Tydens hierdie studie het ons vyf biotoets inkubasie eksperimente aan boord die skeep gedoen tydens twee vaarte langs die Greenwich meridiaan tussen Suid-Afrika en die ys rand, SOSCEx gedurende Maart en SAFePool gedurende Januarie tot Februarie, waarin ons Fe konsentrasies en lig vlakke gewissel het om die gevolge van Fe en lig beperking, of medebeperking, binne inwoner fitoplankton te bepaal. Ruimtelike en temporale variasies in fitoplankton reaksie was bestudeer om wisselende gevolge van die beperking oor watermassas en verskillende stadiums van bloei afname in die studie area te bepaal. Die gekombineerde byvoeging van Fe en lig het die grootste toename in biomassa, fotosintetiese kapasiteit en voedingsopname gegee. Ter ondersteuning van die getoetste hipoteses, veranderinge in die fotosintetiese apparaat het gelei tot veranderinge in die fotosintetiese doeltreffendheid en groei van die SO fitoplankton, as 'n gevolg van variasies in Fe en lig beskikbaarheid. Veranderlikheid is ook waargeneem in die reaksie van fitoplankton om Fe en lig wysigings weens die ruimtelike en tydelike variasie in inwoner fitoplankton gemeenskappe. Dus was dit by die gevolgtrekking gekom dat beide Fe en lig beduidende kontrole in die inwoner fitoplankton fotosintetiese apparaat, fotosintetiese vermoëns, organiese koolstof binding en daarom die biogeochemiese siklusse binne die Atlantiese sektor van die SO. Thesis (MSc)--Stellenbosch University, 2015.