Dissertations / Theses on the topic 'Barberton Greenstone belt'

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The source of the K2O in the K2O-rich ~3.45 Ga felsic intrusive rocks of the H6 unit in the Hooggenoeg Formation of the Onverwacht Group in the Barberton Granite Greenstone Terrain (BGGT) is examined in this study. This is of particular research interest because the Paleoarchaean rock record is considered to lack K2O-rich magmatic rocks. Previous studies on the felsic igneous rocks of the H6 unit have proposed that these rhyolites are K-metasomatised eruptive equivalents of the sodium-rich ~3.45 Ga TTGs of the BGGT and that the K-feldspar crystals in the rocks formed as a consequence of subsolidus replacement of plagioclase by K-feldspar. Furthermore, the timing of K-metasomatism has previously been related to the formation of the Buck Ridge Chert (BRC), which overlies the H6 unit. However, it has recently been demonstrated from granitic clasts in the conglomerate layer at the base of the Moodies sucession that K2O-rich magmatic rocks formed concurrently with TTG magmas during each of three episodes of TTG magmatism observed in the BGGT. Consequently, the hypothesis of a metasomatic origin for the K2O-rich character of the felsic rocks of the H6 unit requires further examination. Previous studies of the chemistsry of felsic volcanic rocks within the H6 unit were based on relatively low numbers of samples. This study has examined a substantial set of the freshest material available. Two varieties of felsic volcanic rocks were identified; K2O-rich, CaO-poor, Na2O-poor rhyolites and Na2O-rich, CaO-poor, K2O-poor Na-rhyolites. The K2O- rich rhyolite variety is dominant. Consequently, it is possible that the K2O-rich character of these rocks represents a primary magmatic signature. However, this judgment is complicated by the presence of a greenschist-facies metamorphic overprint at 3.2 Ga, which has resulted in complete replacement of micrystalline groundmass and partial replacement of the phenocryst assemblages by greenschist- and sub-greenschist-facies mineral assemblages, which undoubtedly allowed possible shifts in chemical compositions In this thesis, I test the source of K2O in these rocks by using the porphyritic textures of the rocks as an indication of the primary composition of the magmas they were formed from. These textures are typically defined by K-feldspar or albite and quartz phenocrysts within a microcrystalline groundmass. The rocks containing albite are Na-rich (Na-rhyolites) whereas the rocks defined by K-feldspar phenocrysts are rhyolites. XRD study of the structural state of the K-feldspar phenocrysts in the rhyolites indicates that these crystals are orthoclase and intermediate microcline, i.e. medium temperature K-feldspar polymorphs. The modal proportions of K-feldspar, quartz and microcrystalline groundmass in the rhyolites were calculated by using image analysis software. The compositions of the feldspar minerals were determined by electron beam analysis. Minimum bulk rock K2O content of the rhyolites were calculated from the proportions of K-feldspar crystals and their compositions. Even where the proportion of K-feldspar phenocrysts is relatively low (~ 30%), the calculated minimum bulk-rock K2O content is still above 5 wt%. The HREE slope (GdN/LuN) of the felsic porphyritic rocks of the H6 rhyolites is similar to that of ~3.45 Ga TTG plutons and steeper than that of granitic clasts of identical age contained in the basal conglomerate of the Moodies Group. Hence this study has illustrated that the rhyolites of the H6 unit were primary K-feldspar-rich, K2O-rich magmas that formed contemporarily with the ~3.45 Ga TTGs. This implicitly means that rhyolitic volcanism was more wide spread than previously thought in the Paleoarchaean and that it occurred together with the intrusion of the ~3.45 Ga TTGs in the BGGT.
AFRIKAANSE OPSOMMING: Die bron van die K2O in die K2O-ryk ~ 3,45 Ga felsiese vulkaniese rotse van die H6-eenheid in die Hooggenoeg formasie van die Onverwacht Groep in die Barberton Graniet Groensteen Terrein (BGGT) is in hierdie studie ondersoek. Dit is van besondere navorsingsbelang omdat die Paleoargeïse gesteenterekord beskou word as vry van magmatiese K2O ryke gesteentes. Vorige studies oor die felsiese vulkaniese rotse van die H6 eenheid het voorgestel dat hierdie rioliete K-gemetasomatiese eruptiewe ekwivalente van die natrium-ryke ~ 3,45 Ga TTGs van die BGGT is en dat die K-veldspaat kristalle in die gesteentes gevorm is as gevolg van subsolidus vervanging van plagioklaas deur K-veldspaat. Verder is die tydsberekening van K-metasomatisme voorheen gekoppel aan die vorming van die Buck Ridge Chert (BRC) wat die felsiese H6 eenheid bedek. Dit is egter onlangs aangetoon dat K2O-ryke magmatiese rotse gelyktydig met TTG magmas gevorm is tydens elk van drie episodes van TTG magmatisme waargeneem in die BGGT. Gevolglik vereis die hipotese van 'n metasomatiese oorsprong vir die K2O-ryke karakter van die felsiese gesteentes van die H6 eenheid verdere ondersoek. Vorige studies van die felsiese vulkaniese gesteentechemie in die H6 eenheid is gebaseer op 'n relatief klein getal monsters. Hierdie studie het 'n aansienlike stel van die varsste materiaal beskikbaar vir analise ondersoek. Twee variëteite van peralumineuse felsiese vulkaniese gesteentes naamlik 'n K2O-ryk, CaO-arm, Na2O-arm rioliet en Na2O-ryk, CaO-arm, K2O-arm Na-rioliet. Die K2O-ryke rioliet variëteit is meer oorheersend as die Na-rioliete. Dit is dus moontlik dat die K2O-ryk karakter van hierdie rotse 'n primêre magmatiese kenmerke verteenwoordig. Hierdie uitspraak is egter bemoeilik deur die teenwoordigheid van 'n groenskisfasies metamorfe oorprint op 3,2 Ga, wat gelei het tot die volledige vervanging van mikrokrisstalyne grondmassa en gedeeltelike vervanging van fenokrist samestellings deur groenskis en sub-groenskisfasies minerale samestellings en wat ongetwyfeld toegelaat het vir 'n moontlike verskuiwing in chemiese samestelling. In hierdie tesis toets ek die bron van K2O in hierdie gesteentes deur gebruik te maak van die vulkaniese teksture van die gesteentes as 'n aanduiding van die primêre samestelling van die magmas waaruit hulle gevorm het. Hierdie teksture word gewoonlik gedefinieer deur K-veldspaat of albiet en kwarts fenokriste binne 'n grondmassa van wat vroeërglasoorblyfsels was. Die rotse wat albiet bevat is Na-ryk (Na-rioliete) terwyl die rotse gedefinieer deur K-veldspaat fenokriste rioliete is. XRD studie van die strukturele toestand van die K-veldspaat fenokriste in die rioliete dui aan dat hierdie kristalle ortoklaas en intermediêre mikroklien is, dit wil sê die hoër temperatuur K-veldspaat polimorfe. Die modale proporsies van K-veldspaat, kwarts en glasoorblyfsels in die rioliete is akkuraat bereken deur gebruik te maak van beeld analise sagteware. Verder is die samestellings van die veldspaat minerale bepaal deur die elektronstraal analise. Minimum grootmaat rots K2O inhoud van die rioliet is berekén vanaf die fase verhouding van K-veldspaat en hul komposisies. Resultate dui daarop dat selfs waar die verhouding van K-veldspaat phenocrysts is relatief laag (~ 30%), die berekende minimum K2O grootmaat rots samestelling is nog steeds bo 5 wt%. Die REE-helling (GDN / Lun) van felsiese porphyritic rotse van die H6 is soortgelyke relatief tot die REE helling van ~ 3,45 Ga TTGs en steiler REE helling relatief tot granitiese klaste vervat in die basale konglomeraat van die Moodies-groep. Dus het hierdie studie getoon dat die rioliete van die H6-eenheid primêre K-veldspaat-ryke, K2O-ryke en peralumineuse magmas was wat gevorm is terselfdertyd met die ~3,45 Ga TTGs. Dit beteken implisiet dat riolitiese vulkanisme meer wyd verspreid was as wat voorheen gedink is in die Paleoargeïkum en dat dit tesame met die indringing van die ~ 3,45 Ga TTGs in die BGGT plaasgevind het.

Includes bibliographical references.
Images of the electrical conductivity of the subsurface below the Barberton Greenstone Belt (BGB) reveal two electrically conductive zones that extend to a depth of at least 5km. These high conductivity zones correlate well with regional shear zones geologically mapped at surface. The serpentinised Stolzburg Layered Ultramatic Body (SLUB) occurs along one of these shear zones, the Saddleback-Inyoka Shear Zone (SISZ). In an attempt to identify the conductive rocks or phases responsible for the observed electrical conductivity anomalies, impedance spectroscopy measurements on samples collected from regional rock types and shear zone related lithologies were undertaken, and show that the rocks from the BGB are generally very resistive. Sulphide rich greenschists and greywackes collected at depth from the northern extension of the SISZ have elevated conductivities, but are not comparable to the anomalies observed in inversions of the magnetotelluric data. Magnetite veins from the SLUB were the only materials that had electrical resistivities low enough to be comparable with the conductivity anomalies. In order to better understand the structural evolution of the western extent of the greenstone belt, a field investigation was undertaken in the SLUB.

Thesis (MSc (Geography and Environmental Studies))--University of Stellenbosch, 2005.
81 Leaves printed on single pages i-xi, preliminary pages and numbered pages 1- 70. Includes bibliography, list of tables and list of figures.
Digitized at 300 dpi color PDF format (OCR), using KODAK i 1220 PLUS scanner.
ENGLISH ABSTRACT: Geological field mapping is often limited by logistical and cost constraints as well as the scope and extent of observations possible using ground-based mapping. Remote sensing offers, among others, the advantages of an increased spectral range for observations and a regional perspective of areas under observation. This study aimed to determine the accuracy of a collection of image classification techniques when applied to ASTER reflectance data. Band rationing, the Crosta Technique, Constrained Energy Minimization, Spectral Correlation Mapping and the Maximum Likelihood Classifier were evaluated for their efficiency in detecting and discriminating between greenstone and granitoid material. The study area was the Archaean Barberton Greenstone Belt in the eastern Mpumalanga Province, South Africa. ASTER reflectance imagery was acquired and pre-processed. Training and reference data was extracted from the image through visual inspection and expert knowledge. The training data was used in conjunction with USGS mineral spectra to train the five classification algorithms using the ERDAS's software package. This resulted in abundance images for the target materials specified by the training data. The Maximum Likelihood Classifier produced a classified thematic map. The reference data was used to perform a rigorous classification accuracy assessment procedure. All abundance images were thresholded to varying levels, obtaining accuracy statistics at every level. In so doing, threshold levels could be defined for every abundance image in such a way that the reliability of the classification was optimized. For each abundance image, as well as for the output map of the Maximum Likelihood Classifier, user's- and producer's accuracies as well as kappa statistics were derived and used as comparative measures of efficiency between the five techniques. This information was also used to assess the spectral separability of the target materials. The Maximum Likelihood Classifier outperformed the other techniques significantly, achieving an overall classification accuracy of 81.1% and an overall kappa value of 0.748. Greenstone rocks were accurately discriminated from granitoid rocks with accuracies between 72.9% and 98.5%, while granitoid rocks showed very poor ability to be accurately distinguished from each other. The main recommendations from this study are that thermal infrared and gamma-ray data be considered, together with better vegetation masking and an investigation into object orientated techniques.
AFRIKAANSE OPSOMMING: Geologiese veldkartering word algemeen beperk deur logistiese en koste-verwante faktore, sowel as die beperkte bestek waartoe waarnemings met veld-gebasseerde tegnieke gemaak kan word. Afstandswaarneming bied, onder andere, 'n vergrote spekrale omvang vir waarnemings en 'n regionale perspektief van die area wat bestudeer word. Hierdie studie was gemik daarop om die akkuraatheid van 'n versameling beeld-klassifikasie tegnieke, toegepas op ASTER data, te bepaal. Bandverhoudings, die Crosta Tegniek, "Constrained Energy Minimization", Spektrale Korrellasie Kartering, en Maksimum Waarskynlikheid Klassifikasie is evalueer op grond van hul vermoë om groensteen en granitoied-rotse op te spoor en tussen hulle te onderskei. Die studiegebied was die Argalese Barberton Groensteengordel in die oostelike Mpumalanga Provinsie in Suid Afrika. 'n ASTER refleksie beeld is verkry, waarop voorverwerking uitgevoer is. Opleidings- en verwysingsdata is van die beeld verkry deur visuele inspeksie en vakkundige kennis. Die opleidingsdata is saam met VSGO mineraalspektra gebruik om die vyf klassifikasie algoritmes met behulp van die ERDAS sagteware pakket op te lei. Die resultaat was volopheidsbeelde vir die teikenmateriale gespesifiseer in die opleidingsdata. Die Maksimum Waarskynlikheid algoritme het 'n geklassifiseerde tematiese beeld gelewer. Met behulp van die verwysingsdata is 'n streng akkuraatheidstoetsing prosedure uitgevoer. Vir alle volopheidsbeelde is 'n reeks drempelwaardes gestel, en by elke drempelwaarde is akkuraatheidsstatistieke afgelei. Op hierdie manier kon 'n drempelwaarde vir elke volopheidsbeeld vasgestel word sodat die drempelwaarde die betroubaarheid van die klassifikasie optimeer. Vir elke volopheidsbeeld, asook vir die tematiese kaart verkry van die Maksimum Waarskynlikheid klassifikasie, is gebruikers- en produsent-akkuraathede en kappa statistieke bereken. Hierdie waardes is gebruik as vergelykende maatstawwe van akkuraatheid tussen die vyf tegnieke, asook van die spektrale skeibaarheid van die onderskeie teikenmateriale. Die Maksimum Waarskynlikheid klassifikasie het die beste resultate gelewer, met 'n algehele klassifikasie akkuraatheid van 81.1%, en 'n gemiddelde kappa waarde van 0.748. Groensteenrotse kon met hoë akkuraathede van tussen 72.9% en 98.5% van granitoiedrotse onderskei word, terwyl granitoiedrotse 'n swak vermoë getoon het om van mekaar onderskei te word. Die belangrikste aanbevelings vanuit hierdie studie is dat termiese uitstralingdata asook gamma-straal data geimplimenteer word. Beter verwydering van plantegroei en 'n studie na die lewensvatbaarheid van objekgeorienteerde metodes word ook aanbeveel.

Geology
M.S.
Carbonaceous materials found in Archean rocks have been the source of study and controversy for the last two decades due to questions of the biogenecity of these particles. One of the key locations for these studies is the Barberton Greenstone Belt (BGB), in South Africa which contains some of the oldest known rocks on Earth, ranging in age from 3.5 to 3.2 billion years old. Preserved within the Onverwacht and Fig Tree Groups of the BGB are spherules that formed by the condensation of an impact-produced global vapor plume. The spherules are distal deposits that would have been deposited globally, but are only preserved at this location and in western parts of Australia. Like several other sediments in the BGB, there is evidence of minor amounts of carbonaceous particles contained within the spherule beds. Four individual impact events are preserved in distinct beds designated as S1, S2, S3, and S4. Due to the wide distribution of this bed in a variety of depositional settings, including both protected shallow and deep water depositional settings where there is little evidence of reworking, the S3 bed is an ideal choice for mineralogical, geochemical, and petrographic studies of impact spherules. This research examines samples from four different locations of the S3 spherule bed layer, the Barite Syncline, Maid-of-the-Mist, Sheba Mine, and Loop Road locations, in order to determine the origin of carbonaceous particles contained within the bed. Several geologic processes could account for the presence of the carbonaceous materials within the S3 spherule bed layer. These processes include: (1) Diagenetic processes, (2) Fisher-Tropsch Synthesis, (3) Microbial activity, and (4) Primary condensates from the impact plume. In order to distinguish between these processes, the spatial distribution of the carbonaceous matter was mapped, noting the mineral associations with these grains. Petrographic and electron microanalytical studies of the S3 samples reveal the presence of carbonaceous material in the sections with highly concentrated spherules, Barite Syncline, Loop Road, and Sheba Mine locations, but not in the samples from the Maid-of-the-Mist location, where there is a low concentration of spherules and abundant admixed volcanic detritus. Only Fischer-Tropsch Synthesis can be excluded as a process responsible for the origin of carbonaceous materials in the S3 beds. Though there is no direct evidence of the biogenecity of the observed carbonaceous materials, other textual observations within the S3 spherule bed are consistent with microbial activity, including Ambient Inclusion Trails and an unusual feature with a cyanobacteria-like morphology. While microbial activity cannot be ruled out as a process responsible for the origins of the carbonaceous materials, the findings of this study indicate that the carbon was mobilized from within the spherules during diagenesis. The location of carbon along spherule rims and microfractures within the spherules can also be attributed to diagenetic processes, such as fracture flow, dissolution, and replacement. A plausible explanation is that the carbon was a primary condensate from the impact plume, but has been diagenetically remobilized locally into microfractures and along the rims of the spherules.
Temple University--Theses

A palaeomagnetic study of some of the best preserved Palaeoarchaean (3.2 -3.6 Ga) rock successions in the world – the Barberton Greenstone Belt, South Africa – has been carried out in order to shed light on Early Earth processes. The aim is to improve the understanding of the long term evolution of the Earth and the surface conditions under which the first forms of life originated through using palaeomagnetic records. The study follows on from work by Layer et al., (1998), Yoshihara & Hamano (2004), Usui et al., (2009), Tarduno et al., (2010) and Biggin et al., (2011) that indicate that rocks from the Barberton Greenstone Belt have the potential to record a near-primary direction of remanence and a reversing geomagnetic field at ca. 3.5 Ga. The rocks of the Barberton Greenstone Belt are excellently preserved and have only been subjected to low grade metamorphism (greenschist facies), making them good candidates for palaeomagnetic studies. Here, new data obtained from three Onverwacht Group Formations and from the Nelshoogte Pluton are presented. The reliability of the new palaeomagnetic data is affected by the complex history and the age of the rocks but no more so than any other published study of rocks of this age. The Noisy Complex and the Nelshoogte Pluton are affected by lightning induced isothermal remanent magnetisations (IRMs) which result in poor quality results. Nevertheless, two new poles, produced by combining the new findings with previously published data, are calculated for the Komati and Hooggenoeg Formations. The new Komati pole shows improved clustering when compared to previous studies. Whilst the data of the Hooggenoeg Formation are encouraging, the results are ambiguous and open to interpretation. When combined with the results of Biggin et al., (2011) they exhibit considerably improved clustering when the directions are corrected for the tectonic deformation resulting in the formation of the Onverwacht Fold, dated at 3.23 Ga. The new results presented here support the findings of previous palaeomagnetic studies of the Barberton Greenstone Belt and support the existence of a stable geomagnetic field at ca. 3.5 Ga. The results presented here support the findings of Biggin et al., (2011) of moderate latitudinal plate motion during this time and do not rule out the hypothesis that the Pilbara Craton (Western Australia) and the Kaapval Craton (South Africa) were conjoined in the Palaeoarchaean.

Thesis (MSc)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: The southern portions of the Early- to Mid-Archaean Barberton granitoid-greenstone terrain of South Africa consists of a high-grade metamorphic granitoid-gneiss terrain that is juxtaposed against the low-grade metamorphic supracrustal sequence of the Barberton Greenstone Belt. The boundary of the two different crustal domains corresponds to the Theespruit Formation, an amphibolite-facies, highly tectonized mélange of metabasites, felsic volcanics and rare, aluminous clastic sediments that occurs along the granitoidgreenstone margins. Amphibolite-facies lithologies in the Theespruit Formation are characterized by strongly prolate mylonitic fabrics that formed in a constrictional tectonic regime. Away from the granitoid-greenstone margin and towards the central parts of the greenstone belt, these rocks grade to, and are overprinted by, greenschist-facies S-L mylonites that formed during non-coaxial deformation. Both peak and retrograde minerals define, and are aligned parallel to, the fabrics in these rocks, indicating that shearing was initiated under peak metamorphic conditions and continued during retrogression. S-C’ fabric relationships indicate that shearing occurred in an extensional tectonic regime and that, during deformation, the gneiss terrain was uplifted relative to the greenstone belt. Peak metamorphic assemblages of grt-st-bt-chl-pl-qtz and ky-st-btms- pl-qtz in metasediments and grt-ep-hbl-pl-qtz in amphibolite constrain peak metamorphic conditions of 7.4 ± 1.0 kbar and 560 ± 20 ºC that were attained during the main accretionary episode in the Barberton terrain at 3229 ± 25 Ma. Peak assemblages in all rocks are pre-tectonic and were deformed and re-equilibrated during retrogression, resulting in these being minimum estimates of peak metamorphic conditions. Petrographic evidence and retrograde pressure-temperature estimates indicate that retrogression involved near-isothermal decompression of ca. 4 kbar prior to cooling into the greenschist-facies. The style and timing of metamorphism in the Theespruit Formation is similar to that of the granitoid-gneiss terrain, suggesting that the Theespruit Formation shares a geological history with the gneiss terrain and that it is allochtonous to the greenstone belt. The main deformational and fabric-forming event exhibited in the Theespruit Formation occurred during the exhumation of the granitoid-gneiss terrain subsequent to peak metamorphism. Consequently, the juxtaposition of this terrain againstthe greenstone belt was achieved by tectonic underplating and core complex formation at ca. 3.23 Ga. The occurrence of high-grade constrictional mylonites that are overprinted by low-grade non-coaxial mylonites as well as extension in an overall compressional tectonic regime is consistent with exhumation by extensional orogenic collapse. Burial of the high-grade terrain to depths of 25 – 30 km is only possible in a relatively cold and rigid crustal environment, while the extremely low apparent geothermal gradients of ca. 20 ºC/km preserved in this terrain suggest that burial and exhumation occurred rapidly, within a time-span of ca. 15 – 20 Ma. These parameters strongly suggest that metamorphism occurred in response to a lateral plate tectonic process that was operational in the Barberton terrain at 3230 Ma.
AFRIKAANSE OPSOMMING: Die suidelike dele van die Vroeg- tot Middel-Argaïese Barberton graniet-groensteen terrein van Suid-Afrika bestaan uit ‘n hoë-graad metamorfe graniet-gneiss terrein wat die lae-graad metamorfe groenstene van die Barberton Groensteen Gordel begrens. Die grens tussen die twee verskillende kors-domeine hang saam met die Theespruit Formasie, ‘n amfiboliet-fasies, getektoniseerde melange van metabasiete, felsiese vulkaniese gesteentes en skaars, alumineuse klastiese sedimente wat langs die graniet-groensteen kontakte voorkom. Amfiboliet-fasies gesteentes in die Theespruit Formasie word gekenmerk deur sterk prolaat milonitiese maaksels wat in ‘n vernouende tektoniese omgewing gevorm het. Hierdie rotse word weg van die graniet-groensteen kontak en na die sentrale dele van die groensteen gordel oordruk en vervang deur groenskis-fasies S-L miloniete wat tydens nie-koaksiale vervorming gevorm het. Beide piek en retrograad minerale definieer, en is georienteer parallel aan, die maaksel in die rotse, wat daarop dui dat skuifskeur onder piek metamorfe toestande begin het en volgehou het tydens retrogressie. S-C’ maaksels dui daarop dat skuifskeur in ‘n verlengende tektoniese omgewing plaasgevind het en dat die gneiss terrein opgehef is relatief tot die groensteengordel tydens vervorming. Piek metamorfe versamelings van grt-st-bt-chl-plqtz en ky-st-bt-ms-pl-qtz in metasedimente en grt-ep-hbl-pl-qtz in amfiboliet bepaal piek metamorfe toestande van 7.4 ± 1.0 kbar en 560 ± 20 ºC wat bereik is gedurende die hooffase van akkresie in die Barberton terrein teen 3229 ± 25 Ma. Die piek metamorfe versamelings in alle rotse is pre-tektonies en is vervorm en geherekwilibreer tydens retrogressie, wat maak dat die beramings minimum skattings van piek metamorfe toestande is. Petrografiese getuienis asook druk-temperatuur beramings dui daarop dat retrogressie gepaard gegaan het met byna-isotermiese drukverligting van naastenby 4 kbar voor afkoeling tot in die groenskis-fasies. Die styl en tydsberekening van metamorfose in die Theespruit Formasie is vergelykbaar met metamorfose in die granietgneiss terrein, wat daarop dui dat die Theespruit Formasie ‘n geologiese geskiedenis met die gneiss terrein deel en allochtoon is tot die groensteen gordel. Die hooffase van vervorming en maakselvorming in die Theespruit Formasie het plaasgevind gedurende die herontbloting van die graniet-gneiss terrein na piek metamorfose. Gevolglik is dieteenplasing van dié terrein teen die groensteen gordel vermag deur tektoniese onderplasing en kernkompleksvorming teen ongeveer 3.23 Ga. Die verskynsel van hoëgraadse vernoude miloniete wat oordruk word deur lae-graadse nie-koaksiale miloniete asook verlenging in ‘n algeheel saamdrukkende tektoniese omgewing dui daarop dat herontbloting plaasgevind het deur middel van verlengende orogenetiese ineenstorting. Die begrawing van die hoë-graadse terrein tot dieptes van 25 – 30 km is net moontlik in ‘n relatief koel en star kors-omgewing, terwyl die uitermate lae geotermiese gradiente van ongeveer 20 ºC/km wat in die terrein behoue gebly het daarop dui dat begrawing en herontbloting vinnig geskeid het, binne ‘n tydsverloop van ongeveer 15 – 20 Ma. Hierdie beperkings is ‘n sterk aanduiding dat metamorfose plaasgevind het as gevolg van ‘n laterale plaattektoniese proses wat werksaam was in die Barberton terrein teen 3230 Ma.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Doctor of Philosophy
This thesis provides a comprehensive account of the geology of the Archaean granitoid-greenstone terrane centred around Three Sisters in the northeastern sector of the Barberton Mountain Land. The supracrustal succession in the region comprises a diverse variety of altered volcanic and sedimentary rock types that have been correlated with the principal lithostratigraphic units of the Barberton greenstone belt (BGB) as fellows: 1) schistose basic and ultrabasic lithologies correlated with the Theespruit Formation of the Gnverwacht Group are mainly developed in a narrow unit fringing the northern margin of the BGB; 2) ferruginous shale greywacke - banded iron-formation assemblages correlated with the Jheba and Belvue Road Formations constitute the dominant Fig Tree Group imks in the region. A sec «ence or silicic » .-stavolcaniclastic rocks, now altered to a variety of micaceous schists, occurs west, north ar.a northeast of Three Sisters. Viljoen and Viljoen (1970) cc rrela ted these schists ith the Theespruit Formation. In this study, the schists have been assigned'to a new lithostratigraphic unit, referred to as the Bien Venue Formation, which forms the uppermost formation of the Fig Tree Group in the northeastern part of the BGB. Isotopic studies on zircons indicate that the schists have an age of 3256 ± Ma, which is some 200 Ma younger titan the most recent age estimates for the lower portions of the Gnverwacht Group. Chemically, the silicic schists resemble calc-alkaline rocks found in modem arcs, suggesting that the Bien Venue Formation represents a period of arc-like volcanism; and 3) conglomeratic and quartzitic rocks constitute the dominant lithologies within the Moodies Group, which uncoriorroably or paraconformably overlies lithologies of the Fig Tree and Onverwacht Groups. North of the BGB is a complex suite of granitoid rocks, previously investigated by Robb et al. (1983) who defined a large (—60 kn ng and —6 km wide), elongate plutonic body of tonalitic-to-trondhjemitic composition known as the Stentor pluton. It was suggested that this pluton is correlatable with the irondhjemite gneiss plutons that intrude the southwestern parts of the BGB. Field evidence indicates, however, that the Stentor pluton forms a much smaller (* .14 km long and ~ 4 km wide) ovoid body located immediately north of the village of Louw’s Creek. Furthermore, the pluton consists of equigranular-textured graiodiorite-adamcllite, totally unlike any of the trondhjemite gneisses. In terms of texture, mineralogy and chemical composition, the Stentor pluton closely resembles the Hebron and Berlin plutohs which constitute a phase of the Nelspruit batholith. Thus, it is concluded that the Stentor pluton also forms an integral part of the batholith. Three deformation phases have been identified. The regional event affected all stratigraphic units in response to a northerly oriented compressions! stress and gave rise to east-northeasterly trending, tight-.« 5soclinal, upright and north-verging folds that are bounded by southward-dipping longitudinal reverse faults. The regional deformation occurred both prior and subsequent to the emplacement of the Stentor pluton at circa 3100 Ma. Deformation associated with the diapiric intrusion of the Stentor pluton into the greenstone assemblage during the regional deformation pnase, led to the formation of large-scale folds that have modified earlier formed structures. The final deformation episode is manifested by the presence of nortnwest- to northeast-striking, oblique-slip normal faults that exhibit both left- and right-lateral strike-slip components.
AC 2018

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Doctor of Philosophy
This thesis provides a comprehensive account of the geology of the Archaean granitoid-greenstone terrane centred around Three Sisters in the northeastern sector of the Barberton Mountain Land. The supracrustal succession in the region comprises a diverse variety of altered volcanic and sedimentary rock types that have been correlated with the principal lithostratigraphic units of the Barberton greenstone belt (BGB) as fellows: 1) schistose basic and ultrabasic lithologies correlated with the Theespruit Formation of the Gnverwacht Group are mainly developed in a narrow unit fringing the northern margin of the BGB; 2) ferruginous shale greywacke - banded iron-formation assemblages correlated with the Jheba and Belvue Road Formations constitute the dominant Fig Tree Group imks in the region. A sec «ence or silicic » .-stavolcaniclastic rocks, now altered to a variety of micaceous schists, occurs west, north ar.a northeast of Three Sisters. Viljoen and Viljoen (1970) cc rrela ted these schists ith the Theespruit Formation. In this study, the schists have been assigned'to a new lithostratigraphic unit, referred to as the Bien Venue Formation, which forms the uppermost formation of the Fig Tree Group in the northeastern part of the BGB. Isotopic studies on zircons indicate that the schists have an age of 3256 ± Ma, which is some 200 Ma younger titan the most recent age estimates for the lower portions of the Gnverwacht Group. Chemically, the silicic schists resemble calc-alkaline rocks found in modem arcs, suggesting that the Bien Venue Formation represents a period of arc-like volcanism; and 3) conglomeratic and quartzitic rocks constitute the dominant lithologies within the Moodies Group, which uncoriorroably or paraconformably overlies lithologies of the Fig Tree and Onverwacht Groups. North of the BGB is a complex suite of granitoid rocks, previously investigated by Robb et al. (1983) who defined a large (—60 kn ng and —6 km wide), elongate plutonic body of tonalitic-to-trondhjemitic composition known as the Stentor pluton. It was suggested that this pluton is correlatable with the irondhjemite gneiss plutons that intrude the southwestern parts of the BGB. Field evidence indicates, however, that the Stentor pluton forms a much smaller (* .14 km long and ~ 4 km wide) ovoid body located immediately north of the village of Louw’s Creek. Furthermore, the pluton consists of equigranular-textured graiodiorite-adamcllite, totally unlike any of the trondhjemite gneisses. In terms of texture, mineralogy and chemical composition, the Stentor pluton closely resembles the Hebron and Berlin plutohs which constitute a phase of the Nelspruit batholith. Thus, it is concluded that the Stentor pluton also forms an integral part of the batholith. Three deformation phases have been identified. The regional event affected all stratigraphic units in response to a northerly oriented compressions! stress and gave rise to east-northeasterly trending, tight-.« 5soclinal, upright and north-verging folds that are bounded by southward-dipping longitudinal reverse faults. The regional deformation occurred both prior and subsequent to the emplacement of the Stentor pluton at circa 3100 Ma. Deformation associated with the diapiric intrusion of the Stentor pluton into the greenstone assemblage during the regional deformation pnase, led to the formation of large-scale folds that have modified earlier formed structures. The final deformation episode is manifested by the presence of nortnwest- to northeast-striking, oblique-slip normal faults that exhibit both left- and right-lateral strike-slip components.
AC 2018

A Dissertation Submitted to the Faculty of Science; University of the Witwatersrand, Johannesburg; for the Degree of Doctor of Philosophy
A volcanological study of the Onverwacht Group in the southwestern part of the Archaean (-3.5 - 3.2 Ga) Barberton greenstone belt (BGB), South Africa, shows that volcanic extrusion rates of the Komati and Hooggenoeg Formations must have been high to have maintained the degree of submarine sheet flooding that is evident. It is concluded that the volcanic attributes of the Komati and Hooggenoeg Formations are not typical of MOR crust, as has been claimed, but rather closely resemble those of modern oceanic plateaus. The shear-zone-bound basal contact of the Komati Formation suggests that the top of the ancient oceanic plateau was allochthonously emplaced and delaminated from its basal (intrusive) part. (Abbreviation abstract)
AC2017

Various methods and techniques developed by researchers worldwide for enhancement and processing ATM, MSS· and TM remotely sensed data are tested. on LANDSAT 5 Thematic Mapper data from a part of the Barberton Greenstone Belt straddling the border between the Republic of South Africa and the Kingdom of Swaziland. Various enhancement techniques employed to facilitate the extraction of structural features and lineaments, and the findings Of the ensuing photogeologlcal interpretation are compared with existing geological maps~ Methods for the detection of zones of hydrothermal alteration. are also considered. The reflectance from vegetation, both natural and cultivated, and the possible reduction of the interference caused by this reflectance, are considered in detail. Partial unmixing of reflectances through the use of various methods and techniques, some of which are readily available from the literature, are performed and its effectiveness tested. Since large areas within the study area are covered by plantations, the interfereiice from the two types of vegetation present (i.e. natural and cultivated), were initially considered separately. In an attempt to isolate the forested areas from the natural vegetation, masks derived through image classification were used to differentially enhance the various features. Results indicate that the use of any particular method to the exclusion of all others will seriously limit the scope of conclusions possible through interpretation of the information present. Enhancement of information in one domain will inadvertently lead to the suppression of information from one or more of the coexisting domains. A series of results from a sequence of procedures interpreted in parallel will in every case produce information of a higher decision making quality.
AC2017

The area around New Consort Gold Mine (NCGM) is complexly deformed during at least 5 distinct events named D1NC – D5NC. D1NC - D3NC events involve progressive shearing and folding linked to the 3250-3225 Ma accretionary history of the Barberton greenstone belt (D1NC and D2NC), and subsequent 3105 Ma emplacement and doming of surrounding batholiths (D3NC). During D3NC the area experienced intense strain partitioning with the development of a network of shear zones, which envelop structural domains characterized by locally unique deformation histories. Around NCGM, D3NC events involved early shearing (D3aNC) along the Consort Bar followed by two episodes of 600m scale folding (D3bNC and D3cNC) resulting in a complex fold interference pattern. Pegmatites intruded during D3NC. D4NC structures comprise a network of extensional brittle-ductile shear fractures and associated kink bands and crenulation folds that formed concomitant with gold mineralization after all the D3NC structures had fully developed, marking a clearly separate event. The D4NC fractures are distributed along 100-200m wide corridors as 10-100m scale, enechelon, Riedel, anti-Riedel and P-shear arrays. D5NC structures represent represent late reverse faults of unknown age. The critical structures controlling gold mineralization are the D4NC fracture zones. The distribution of high-grade ore zones is controlled by the intersection orientation of D4NC fractures and suitable host lithologies, mainly the silicified hinge zones of D1NC folds and the laminated chert of the Consort Bar. Because these host lithologies were complexly folded in D1NC-D3bNC-D3cNC fold interference patterns, the 3-D distribution of ore zones is highly discontinuous and complex. Kinematics analysis and stress inversion using Bingham tensor solutions and an optimized dihedron method, of mineralized D4NC fractures along old gold workings at NCGM, consistently indicate a vertical σ1, and a horizontal NW-SE iii directed σ3, within a pure extensional stress regime indicating that gold mineralization occurred in an extensional tectonic setting. Results for the nearby Clutha, Albion and Woodstock mines are similar. This study suggests that gold mineralization in the NCGM area can be linked to an extensional event that may have developed separately from the accretionary events shaping the craton and may have coincided with the opening of Dominion Group basins.

A Thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirement for the degree of Doctor of Philosophy. Johannesburg March 2016
This study aims to provide a comprehensive description of the Flora, biogeography and diversity of the serpentine outcrops of Barberton Greenstone Belt in Mpumalanga, South Africa in order to set conservation priorities for these areas. About 30 large and many smaller serpentine outcrops form part of the Barberton Greenstone Belt and consist of various combinations of serpentinized minerals. Seven outcrops were selected to be studied in detail. A floristic analysis recorded 744 species and subspecies, 319 genera and 94 families. The flora includes 33 taxa endemic to serpentine soils and six taxa, which are hyperaccumulators of nickel. The endemic taxa make up 41 % of the endemics of the Barberton Centre of Endemism. The serpentine flora was found to be different to the surrounding non-serpentine vegetation in terms of numbers of species per family, the ratios of dicotyledons to monocotyledons and familial composition. The Asteraceae and the Anacardiaceae support a higher number of endemics than expected, which suggests genetic pre-adaptation within these families and specifically within the genera Berkheya, Helichrysum and Ozoroa. Most of the endemic taxa exhibit long-range dispersal suggesting gene flow between populations on different outcrops. The endemics represent a mix of neo-endemics and paleoendemics. Non-parametric species richness estimators used to predict the species richness of each site, indicated that five serpentine outcrops have higher species richness than the surrounding non-serpentine areas. Indices of diversity calculated showed similar patterns to those of the species richness estimates. The Barberton Greenstone Belt serpentine outcrops show relatively high plant diversity when compared to some other serpentine outcrops around the world. Beta diversity calculated for each site was not correlated with altitude and weakly correlated with the size of outcrops. Species turnover between outcrops is high and is positively correlated with the geographical distance between outcrops. Diversity at higher taxonomic levels were calculated, and results suggest that genera have some potential for facilitating the ranking of outcrops in terms of biological richness to select sites for conservation planning. Less than 30% of serpentine outcrops are adequately conserved. Species and genus richness and endemism were used to select five outcrops that have high conservation priority
MT2016

No
The ESA/Roscosmos ExoMars rover will be launched in 2018. The primary aim of the mission will be to find evidence of extinct or extant life by extracting samples from the subsurface of Mars. The rover will incorporate a drill that is capable of extracting cores from depths of up to 2 m, a Sample Preparation and Distribution System (SPDS) that will crush the core into small grains and a suite of analytical instruments. A key component of the analytical suite will be the Raman Laser Spectrometer (RLS) that will be used to probe the molecular and mineralogical composition of the samples. In this work we consider the capability of the proposed Raman spectrometer to detect reduced carbon (possibly associated with evidence for extinct life) and to identify the level of thermal alteration/maturity. The Raman analysis of 21 natural samples of shale (originating from regions exhibiting different levels of thermal maturity) is described and it is shown that reduced carbon levels as low as 0.08% can be readily detected. It is also demonstrated that the Raman spectra obtained with the instrument can be used to distinguish between samples exhibiting high and low levels of thermal maturity and that reduced carbon can be detected in samples exposed to significant levels of oxidation (as expected on the surface of Mars). (C) 2014 Published by Elsevier Ltd.