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1
Lane, Monica Leonie. "Nickel sulphide mineralization associated with Archean komatiites." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005594.
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The distribution of Archean Nickel sulphide deposits reflects tectonic controls operating during the evolution of the granitoid greenstone terrains. Important deposits of komatiitic-affinity are concentrated within, and adjacent to, younger (∼2.7 Ga), rift-related greenstone belts (e.g. Canada, Western Australia and Zimababwe). Two important classes of Archean Nickel sulphide deposits exist, formerly known as "Dunitic" and "Peridotitic", these are now referred to as Group I and Group II deposits, based on their characteristic structure and composition. Mineralization varies from massive and matrix to disseminated, and is nearly always concentrated at the base of the host unit. Primary ores have a relatively simple mineralogy, dominated by pyrrhotite-pentlandite-pyrite, and to a lesser degree millerite. Metamorphic grades tend to range from prehnite-pumpellyite facies through to lower and upper amphibolite facies. Genesis of Group I and II deposits is explained by the eruption of komatiites into rift-phase greenstone belts, as channelized flows, which assimilated variable amounts of footwall rocks during emplacement. Sulphide saturation was dependent on the mode of emplacement and, the amount of sulphidic sediments that became assimilated prior to crystallization. This possibly accounts for variations in ore tenor. The Six Mile Deposit (SMD) in Western Australia, is an adcumulate body of the Group IIB-type, exhibiting disseminated mineralization. The ore has been "upgraded" due to hydration and serpentinization. A profound weathering sequence exists, which was subsequently utilized during initial exploration. Exploration techniques has been focused on Western Australia, as it is here that the most innovative ideas have emerged.
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Green, Michael Godfrey. "Early archaean crustal evolution evidence from 3̃.5 billion year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia /." Connect to full text, 2001. http://hdl.handle.net/2123/505.
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Thesis (Ph. D.)--University of Sydney, 2002.Title from title screen (viewed Apr. 23, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Geosciences, Division of Geology and Geophysics. Degree awarded 2002; thesis submitted 2001. Includes bibliography. Also available in print form.
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Rivard, Benoit. "Petrochemistry of a layered Archean magma chamber and its relation to models of basalt evolution." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66046.
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Fedo, Christopher M. "Geologic evolution of the Archean Buhwa Greenstone Belt and surrounding granite-gneiss terrane, southcentral Zimbabwe." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164845/.
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Skulski, Thomas. "The tectonic and magmatic evolution of the central segment of the Archean La Grande greenstone belt, central Québec /." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65986.
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Green, Michael Godfrey. "Early Archaean crustal evolution: evidence from ~3.5million year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia." Thesis, The University of Sydney, 2001. http://hdl.handle.net/2123/505.
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In the Pilgangoora Belt of the Pilbara Craton, Australia, the 3517 Ma Coonterunah Group and 3484-3468 Ma Carlindi granitoids underlie the 3458 Ma Warrawoona Group beneath an erosional unconformity, thus providing evidence for ancient emergent continental crust. The basalts either side of the unconformity are remarkably similar, with N-MORB-normalised enrichment factors for LILE, Th, U and LREE greater than those for Ta, Nb, P, Zr, Ti, Y and M-HREE, and initial e(Nd, Hf) compositions which systematically vary with Sm/Nd, Nb/U and Nb/La ratios. Geological and geochemical evidence shows that the Warrawoona Group was erupted onto continental basement, and that these basalts assimilated small amounts of Carlindi granitoid. As the Coonterunah basalts have similar compositions, they probably formed likewise, although they were deposited >60 myr before. Indeed, such a model may be applicable to most other early Pilbara greenstone successions, and so an older continental basement was probably critical for early Pilbara evolution. The geochemical, geological and geophysical characteristics of the Pilbara greenstone successions can be best explained as flood basalt successions deposited onto thin, submerged continental basement. This magmatism was induced by thermal upwelling in the mantle, although the basalts themselves do not have compositions which reflect derivation from an anomalously hot mantle. The Carlindi granitoids probably formed by fusion of young garnet-hornblende-rich sialic crust induced by basaltic volcanism. Early Archaean rocks have Nd-Hf isotope compositions which indicate that the young mantle had differentiated into distinct isotopic domains before 4.0 Ga. Such ancient depletion was associated with an increase of mantle Nb/U ratios to modern values, and hence this event probably reflects the extraction of an amount of continental crust equivalent to its modern mass from the primitive mantle before 3.5 Ga. Thus, a steady-state model of crustal growth is favoured whereby post ~4.0 Ga continental additions have been balanced by recycling back into the mantle, with no net global flux of continental crust at modern subduction zones. It is also proposed that the decoupling of initial e(Nd) and e(Hf) from its typical covariant behaviour was related to the formation of continental crust, perhaps by widespread formation of TTG magmas.
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Brocks, Jochen J. "Molecular fossils in Archean rocks." Phd thesis, School of Geosciences, 2001. http://hdl.handle.net/2123/14300.
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Barovich, Karin Marie. "Behavior of lutetium-hafnium, samarium-neodymium and rubidium-strontium isotopic systems during processes affecting continental crust." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185602.
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Combined Lu-Hf, Sm-Nd and Rb-Sr isotopic studies of continental crustal rocks were undertaken to assess the relative effects of secondary crustal processes on isotopic systematics of whole-rock systems. The processes studied include ductile deformation, and three cases of hydrothermal alteration, involving fluids of varying composition. The Rb-Sr system proved to be easily disturbed during all secondary processes, while Sm-Nd and Lu-Hf systems were, for the most part, resilient. These results show that Nd or Hf isotopic information obtained from old rocks that have undergone typical crustal deformational and alteration events can be counted on to be equally reliable. Nd and Hf isotopic analyses were performed on four suites of Early Archean felsic gneiss complexes from Greenland, Labrador, Swaziland, and Michigan to explore questions associated with Early Archean crustal growth. The Sm-Nd isotopic data yield initial ∊(Nd) values that are mostly consistent with published age data for the suites. Calculations show limited scatter may be attributed to subtle changes in the Sm/Nd ratio or Nd isotopic composition. The Hf isotopic results are more variable and complex than the Nd results. The relevance of the studies on isotopic mobility in the first part of this work is that they have demonstrated that Nd and Hf isotopes are equally resilient during a range of secondary crustal processes. Given the robustness of the Nd isotopic data from the Archean samples, however, it seems unreasonable to attribute the much wider variation in Hf isotopic data to post-Archean isotopic disturbances. Differences in initial Hf isotopic ratios from differing magma sources seem called for. Nd and Hf whole-rock analyses of a Late Archean pristine garnet-bearing granitoid complex from northern Canada point out the importance of garnet in fractionating Lu/Hf ratios, and in developing anomalous ∊(Hf) signatures in potential source regions. Calculations show that even short-lived upper mantle/lower crustal heterogeneities, products of previous partial melting events involving garnet fractionation, can develop the range of positive and negative ∊(Hf) values seen in the Early Archean samples.
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Hodkiewicz, Paul. "The interplay between physical and chemical processes in the formation of world-class orogenic gold deposits in the Eastern Goldfields Province, Western Australia." University of Western Australia. Centre for Global Metallogeny, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0057.
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[Formulae and special characters can only be approximated here. Please see the pdf version of the abstract for an accurate reproduction.] The formation of world-class Archean orogenic gold deposits in the Eastern Goldfields Province of Western Australia was the result of a critical combination of physical and chemical processes that modified a single and widespread ore-fluid along fluid pathways and at the sites of gold deposition. Increased gold endowment in these deposits is associated with efficient regional-scale fluid focusing mechanisms and the influence of multiple ore-depositional processes at the deposit-scale. Measurement of the complexity of geologic features, as displayed in high-quality geologic maps of uniform data density, can be used to highlight areas that influence regional-scale hydrothermal fluid flow. Useful measurements of geological complexity include fractal dimensions of map patterns, density and orientation of faults and lithologic contacts, and proportions of rock types. Fractal dimensions of map patterns of lithologic contacts and faults highlight complexity gradients. Steep complexity gradients, between domains of high and low fractal dimensions within a greenstone belt, correspond to district-scale regions that have the potential to focus the flow of large volumes of hydrothermal fluid, which is critical for the formation of significant orogenic gold mineralization. Steep complexity gradients commonly occur in greenstone belts where thick sedimentary units overly more complex patterns of lithologic contacts, associated with mafic intrusive and mafic volcanic units. The sedimentary units in these areas potentially acted as seals to the hydrothermal Mineral Systems, which resulted in fluid-pressure gradients and increased fluid flow. The largest gold deposits in the Kalgoorlie Terrane and the Laverton Tectonic Zone occur at steep complexity gradients adjacent to thick sedimentary units, indicating the significance of these structural settings to gold endowment. Complexity gradients, as displayed in surface map patterns, are an indication of three-dimensional connectivity along fluid pathways, between fluid source areas and deposit locations. Systematic changes in the orientation of crustal-scale shear zones are also significant and measurable map features. The largest gold deposits along the Bardoc Tectonic Zone and Boulder-Lefroy Shear Zone, in the Eastern Goldfields Province, occur where there are counter-clockwise changes in shear zone orientation, compared to the average orientation of the shear zone along its entire length. Sinistral movement along these shear zones resulted in the formation of district-scale dilational jogs and focused hydrothermal fluid-flow at the Golden Mile, New Celebration and Victory-Defiance deposits. Faults and lithologic contacts are the dominant fluid pathways in orogenic gold Mineral Systems, and measurements of the density of faults and contacts are also a method of quantifying the complexity of geologic map patterns on high-quality maps. Significantly higher densities of pathways in areas surrounding larger gold deposits are measurable within 20- and 5-kilometer search radii around them. Large variations in the sulfur isotopic composition of ore-related pyrites in orogenic gold deposits in the Eastern Goldfields Province are the result of different golddepositional mechanisms and the in-situ oxidation of a primary ore fluid in specific structural settings. Phase separation and wall-rock carbonation are potentially the most common mechanisms of ore-fluid oxidation and gold precipitation. The influence of multiple gold-depositional mechanisms increases the potential for significant ore-fluid oxidation, and more importantly, provides an effective means of increasing gold endowment. This explains the occurrence of negative δ34S values in ore-related pyrites in some world-class orogenic gold deposits. Sulfur isotopic compositions alone cannot uniquely define potential gold endowment. However, in combination with structural, hydrothermal alteration and fluid inclusion studies that also seek to identify multiple ore-forming processes, they can be a useful indicator. The structural setting of a deposit is also a potentially important factor controlling ore-fluid oxidation and the distribution of δ34S values in ore-related pyrites. At Victory-Defiance, the occurrence of negative δ34S(py) values in gently-dipping dilational structures, compared to more positive δ34S(py) values in steeply-dipping compressional structures, is potentially associated with different gold-depositional mechanisms that developed as a result of fluid-pressure fluctuations during different stages of the fault-valve cycle. During the pre-failure stage, when fluids are discharging from faults, fluid-rock interaction is the dominant gold-depositional mechanism. Phase separation and back-mixing of modified ore-fluid components are dominant during and immediately after faulting. Under appropriate conditions, any, or all, of these three mechanisms can oxidize orogenic gold fluids and cause gold deposition. The influence of multiple gold-depositional mechanisms during fault-valve cycles at dilational jogs, where fluid pressure fluctuations are interpreted to be most severe, can potentially explain both the large gold endowment of the giant to world-class Golden Mile, New Celebration and Victory-Defiance deposits along the Boulder-Lefroy Shear Zone, and the presence of gold-related pyrites with negative δ34S values in these deposits. This study highlights the interplay that exists between physical and chemical processes in orogenic gold Mineral Systems, during the transport of ore fluids in pathways from original fluid reservoirs to deposit sites. Potentially, a single and widespread orogenic ore-fluid could become oxidized, and lead to the formation of ore-related sulfides with variable sulfur isotopic compositions, depending on the nature and orientation of major fluid pathways, the nature of wall-rocks through which it circulates, and the precise ore-depositional processes that develop during fault-valve cycles.
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Delvigne, Camille. "The Archaean silicon cycle insights from silicon isotopes and Ge/Si ratios in banded iron formations, palaeosols and shales." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209652.
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The external silicon cycle during the Precambrian (4.5-0.5 Ga) is not well understood despite its key significance to apprehend ancient dynamics at the surface of the Earth. In the absence of silicifying organisms, external silicon cycle dramatically differs from nowadays. Our current understanding of Precambrian oceans is limited to the assumption that silicon concentrations were close to saturation of amorphous silica. This thesis aims to bring new insights to different processes that controlled the geochemical silicon cycle during the Archaean (3.8-2.5 Ga). Bulk rock Ge/Si ratio and Si isotopes (δ30Si) offer ideal tracers to unravel different processes that control the Si cycle given their sensitivity to fractionation under near-surface conditions. First, this study focuses on Si inputs and outputs to ocean over a limited time period (~2.95 Ga Pongola Supergroup, South Africa) through the study of a palaeosol sequence and a contemporaneous banded iron formation. The palaeosol study offers precious clues in the comprehension of Archaean weathering processes and Si transfer from continent to ocean. Desilication and iron leaching were shown to be the major Archaean weathering processes. The occurrence of weathering residues issued of these processes as major component in fine-grained detrital sedimentary mass (shales) attests that identified weathering processes are widely developed and suggest an important dissolved Si flux from continent to the ocean. In parallel, banded iron formations (BIFs), typically characterised by alternation of iron-rich and silica-rich layers, represent an extraordinary record of the ocean-derived silica precipitation throughout the Precambrian. A detailed study of a 2.95 Ga BIF with excellent stratigraphic constraints identifies a seawater reservoir mixed with significant freshwater and very limited amount of high temperature hydrothermal fluids as the parental water mass from which BIFs precipitated. In addition, the export of silicon promoted by the silicon adsorption onto Fe-oxyhydroxides is evidenced. Then, both Si- and Fe-rich layers of BIFs have a common source water mass and a common siliceous ferric oxyhydroxides precursor. Thus, both palaeosols and BIFs highlight the significance of continental inputs to ocean, generally under- estimated or neglected, as well as the close link between Fe and Si cycles.
In a second time, this study explores secular changes in the Si cycle along the Precambrian. During this timespan, the world ocean underwent a progressive decrease in hydrothermal inputs and a long-term cooling. Effects of declining temperature over the oceanic Si cycle are highlighted by increasing δ30Si signatures of both chemically precipitated chert and BIF through time within the 3.8-2.5 Ga time interval. Interestingly, Si isotope compositions of BIF are shown to be kept systematically lighter of about 1.5‰ than contemporaneous cherts suggesting that both depositions occurred through different mechanisms. Along with the progressive increase of δ30Si signature, a decrease in Ge/Si ratios is attributed to a decrease in hydrothermal inputs along with the development of large and widespread desilication during continental weathering.
Le cycle externe du silicium au précambrien (4.5-0.5 Ga) reste mal compris malgré sa position clé dans la compréhension des processus opérant à la surface de la Terre primitive. En l’absence d’organismes sécrétant un squelette externe en silice, le cycle précambrien du silicium était vraisemblablement très différent de celui que nous connaissons à l’heure actuelle. Notre conception de l’océan archéen est limitée à l’hypothèse d’une concentration en silicium proche de la saturation en silice amorphe. Cette thèse vise à une meilleure compréhension des processus qui contrôlaient le cycle géochimique externe du silicium à l’archéen (3.8-2.5 Ga). Dans cette optique, le rapport germanium/silicium (Ge/Si) et les isotopes stables du silicium (δ30Si) représentent des traceurs idéaux pour démêler les différents processus contrôlant le cycle du Si.
Dans un premier temps, cette étude se focalise sur les apports et les exports de silicium à l’océan sur une période de temps restreinte (~2.95 Ga Pongola Supergroup, Afrique du Sud) via l’étude d’un paléosol et d’un dépôt sédimentaire de précipitation chimique quasi-contemporain. L’étude du paléosol apporte de précieux indices quant aux processus d’altération archéens et aux transferts de silicium des continents vers l’océan. Ainsi, la désilicification et le lessivage du fer apparaissent comme des processus majeurs de l’altération archéenne. La présence de résidus issus de ces processus d’altération en tant que composants majeurs de dépôts détritiques (shales) atteste de la globalité de ces processus et suggère des flux significatifs en silicium dissout des continents vers l’océan. En parallèle, les « banded iron formations » (BIFs), caractérisés par une alternance de niveaux riches en fer et en silice, représentent un enregistrement extraordinaire et caractéristique du précambrien de précipitation de silice à partir de l’océan. Une étude détaillée d’un dépôt de BIFs permet d’identifier une contribution importante des eaux douces dans la masse d’eau à partir de laquelle ces roches sont précipitées. Par ailleurs, un mécanisme d’export de silicium via absorption sur des oxyhydroxydes de fer est mis en évidence. Ainsi, les niveaux riches en fer et riche en silice constituant les BIFs auraient une même origine, un réservoir d’eau de mer mélangée avec des eaux douces et une contribution minime de fluides hydrothermaux de haute température, et un même précurseur commun. Dès lors, tant les paléosols que les BIFs mettent en évidence l’importance des apports continentaux à l’océan, souvent négligés ou sous estimés, ainsi que le lien étroit entre les cycles du fer et du silicium.
Dans un second temps, cette étude explore l’évolution du cycle du silicium au cours du précambrien. Durant cette période, l’océan voit les apports hydrothermaux ainsi que sa température diminuer. Dans l’intervalle de temps 3.8-2.5 Ga, les effets de tels changements sur le cycle du silicium sont marqués par un alourdissement progressif des signatures isotopiques des cherts et des BIFs. Le fort parallélisme entre l’évolution temporelle des compositions isotopiques des deux précipités met en évidence leur origine commune, l’océan. Cependant, les compositions isotopiques des BIFs sont systématiquement plus légères d’environ 1.5‰ que les signatures enregistrées pas les cherts. Cette différence est interprétée comme le reflet de mécanismes de dépôts différents. L’alourdissement progressif des compositions isotopiques concomitant à une diminution des rapports Ge/Si reflètent une diminution des apports hydrothermaux ainsi que la mise en place d’une désilicification de plus en plus importante et/ou généralisée lors de l’altération des continents.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Said, Nuru. "Geochemistry of the Neoarchean mafic volcanic and intrusive rocks in the Kalgoorlie Terrane, eastern Yilgarn, Western Australia : implications for geodynamic setting." University of Western Australia. School of Earth and Environment, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0156.
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[Truncated abstract] The Neoarchean (2800 to 2600 Ma) Eastern Goldfields Superterrane (EGST) comprises elongated belts of deformed and metamorphosed volcanic and sedimentary rocks intruded by granitoids. The Superterrane is made up of five distinct tectonostratigraphic terranes. From west to east these are the Kalgoorlie, Gindalbie, Kurnalpi, Laverton and Duketon Terranes. The Kalgoorlie Terrane is characterised by 2720 to 2680 Ma marine mafic-ultramafic volcanic successions interlayered with, and overlain by, 2710 to 2660 Ma dominantly trondhjemite-tonalite-dacite (TTD) dacititic volcaniclastic rocks (Black Flag Group). The adjacent Gindalbie and Kurnalpi terranes are characterised by 2720 to 2680 Ma calc-alkaline volcanic successions representing oceanic island arcs. To the west of the EGST, the Youanmi Terrane is characterised by older, dominantly 3000 to 2900 Ma greenstone rocks and complex granitoid batholiths derived from older crustal sources. The southern Kalgoorlie Terrane comprises five elongate NNW-trending tectono-stratigraphic domains. Three principal marine komatiitic to basaltic suites, collectively referred to as the Kambalda Sequence, are present, including the wellpreserved massive to pillowed Lower and Upper Basalt Sequences, separated by the Komatiite Unit, as well as numerous dyke suites. The Lower Basalt Sequence comprises the Woolyeenyer Formation, Lunnon, Wongi, Scotia, Missouri Basalts and Burbanks and Penneshaw Formations, whereas the Upper Basalt Sequence contains the Paringa, Coolgardie, Big Dick, Devon Consols, Bent Tree, and Victorious basalts. ... Instead, the data suggest that discrete PGE-bearing phase (s) fractionated from the basaltic magmas. Such phases could be platinum group minerals (PGM; e.g. laurite) and/or alloys, or discrete PGE-rich nuggets. In summary, data on the three magmatic sequences record decompression melting of three distinct mantle sources: (1) long-term depleted asthenosphere for prevalent depleted tholeiitic and komatiitic basalts, and komatiites; (2) long-term enriched asthenosphere for Paringa Basalts and similarly enriched rocks; and (3) shortterm enriched continental lithospheric mantle (CLM) for HREE and Al-depleted dykes. Some of these rocks were contaminated by TTD-type melts. Taken with the existing geophysical and xenocrystic zircon data, the most straightforward interpretation is eruption of a zoned mantle plume at the margin of rifted continental lithosphere. The Kalgoorlie Terrane extensional basin was subsequently tectonically juxtaposed with the adjacent arc-like Gindalbie and Kurnalpi Terranes at approximately 2660 Ma at the start of orogeny in a Cordilleran-style orogen to form the EGST. Collectively, uncontaminated basalts have Nb/Th of 8-16, compared to 8-12 reported for the Lunnon basalts in a previous study. To a first approximation these asthenosphere melts are complementary to average Archean upper continental crust with Nb/Th =2, consistent with early growth of large volumes of continental crust rather than models of steady progressive growth.
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Kranidiotis, Prokopis. "Geology, geochemistry and hydrothermal alteration at the Phelps Dodge massive sulfide deposit, Matagami, Québec." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66033.
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Salier, Brock Peter. "The timing and source of gold-bearing fluids in the Laverton Greenstone Belt, Yilgarn Craton, with emphasis on the Wallaby gold deposit." University of Western Australia. School of Earth and Geographical Sciences, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0013.
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[Truncated abstract] The Laverton Greenstone Belt (LGB), located in the northeastern part of the Eastern Goldfields Province (EGP) of the Yilgarn Craton, Western Australia, has a total contained gold endowment of over 690t. An important feature of the gold deposits in the LGB is their close spatial association with granitoids, with many gold deposits located adjacent to, or hosted by, granitoids. Recently-proposed genetic models for Archaean orogenic gold deposits have emphasised the role of granitoids in the formation of ore-deposits, but differ significantly in the nature of that role. Some models suggest that the granitoids are a source of ore-fluids and solutes, whereas others suggest that granitoids exert an important structural control on gold mineralisation. Such competing genetic models for gold mineralisation variably propose either a proximal-magmatic or distal-metamorphic, or less commonly distal-magmatic, source for goldbearing fluids, or mixing of fluids from multiple sources. Isotope geochemistry and geochronological studies are used to constrain the source and timing of auriferous fluids at nine gold deposits in the LGB in an attempt to differentiate between conflicting genetic models. To overcome the lack of detailed deposit-scale geological constraints inherent to any regional study, hypotheses generated from regional datasets are tested in a detailed case-study of the Wallaby gold deposit. The Pb-isotope compositions of ore-related sulphides from deposits in the LGB plot along the line representing crustal-Pb in the Norseman-Wiluna Belt of the EGP, with individual deposits clustering with other nearby deposits based on their geographic location. This trend is similar to that recorded in the Kalgoorlie-Norseman region in the southern EGP, and is consistent with a basement Pb reservoir for gold-bearing fluids. As such, data are consistent with a similar fluid source for all gold deposits. The Nd and Sr isotopic composition of goldrelated scheelite in the LGB clusters very tightly. The inferred ore-fluid composition has a slightly positive εNd, similar to ore fluids at other gold deposits in the EGP for which a proximal magmatic source is highly improbable. As such, Sr and Nd data are consistent with a similar fluid source for the gold deposits analysed in the LGB, but cannot unequivocally define that source. The median S, C and O isotopic compositions of ore minerals from all nine different gold deposits studied in the LGB fall in a very narrow range
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Laurie, Angelique. "The formation of Earth’s early felsic continental crust by water-present eclogite melting." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80214.
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Thesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: The sodic and leucocratic Tonalite, Trondhjemite and Granodiorite (TTG) granitoid series of rocks characterise Paleo- to Meso- Archaean felsic continental crust, yet are uncommon in the post-Archaean rock record. Consequently, petrogenetic studies on these rocks provide valuable insight into the creation and evolution of Earth’s early continental crust. The highpressure (HP)-type of Archaean TTG magmas are particularly important in this regard as their geochemistry requires that they are formed by high-pressure melting of a garnet-rich eclogitic source. This has been interpreted as evidence for the formation of these magmas by anatexis of the upper portions of slabs within Archaean subduction zones. In general, TTG magmas have been assumed to arise through fluid-absent partial melting of metamafic source rocks. Therefore, very little experimental data on fluid-present eclogite melting to produce Archaean TTG exist, despite the fact that water drives magmatism in modern arcs. Consequently, this study experimentally investigates the role of fluid-present partial melting of eclogite-facies metabasaltic rock in the production of Paleo- to Meso-Archaean HP-type TTG melts. Experiments are conducted between 1.6 GPa and 3.0 GPa and 700 ºC and 900 ºC using natural and synthetic eclogite, and gel starting materials of low-K2O basaltic composition. Partial melting of the natural and synthetic eclogite occurred between 850 ºC and 870 ºC at pressures above 1.8 GPa, and the melting reaction is characterised by the breakdown of sodic clinopyroxene, quartz and water: Qtz + Cpx1 + H2O ± Grt1 = Melt + Cpx2 ± Grt2. The experimental melts have the compositions of sodic peraluminous trondhjemites and have compositions that are similar to the major, trace and rare earth element composition of HPtype Archaean TTG. This study suggests that fluid-present eclogite melting is a viable petrogenetic model for this component of Paleo- to Meso-Archaean TTG crust. The nature of the wet low-K2O eclogite-facies metamafic rock solidus has been experimentally defined and inflects towards higher temperatures at the position of the plagioclase-out reaction. Therefore, the results indicate that a crystalline starting material is necessary to define this solidus to avoid metastable melting beyond temperatures of the Pl + H2O + Qtz solidus at pressures above plagioclase stability. Furthermore, this study uses numerical and metamorphic models to demonstrate that for reasonable Archaean mantle wedge temperatures within a potential Archaean subduction zone, the bulk of the water produced by metamorphic reactions within the slabs is captured by an anatectic zone near the slab surface. Therefore, this geodynamic model may account for HP-type Archaean TTG production and additionally provides constraints for likely Archaean subduction. The shape of the relevant fluid-present solidus is similar to the shape of the pressure-temperature paths followed by upper levels of the proposed Archaean subducting slab, which makes water-fluxed slab anatexis is very dependant on the temperature in the mantle wedge. I propose that cooling of the upper mantle by only a small amount during the late Archaean ended fluid-present melting of the slab. This allowed slab water to migrate into the wedge and produce intermediate composition magmatism which has since been associated with subduction zones.
AFRIKAANSE OPSOMMING: Die reeks natruimhoudende en leukokraties Tonaliet, Trondhjemiet en Granodioriet (TTG) felsiese stollingsgesteentes is kenmerkend in die Paleo- tot Meso-Argeïkum felsiese kontinentale kors, maar is ongewoon in die post-Argeïese rots rekord. Gevolglik, petrogenetiese studies op hierdie rotse verskaf waardevolle insig in die skepping en evolusie van die aarde se vroeë kontinentale kors. Die hoë-druk (HD)-tipe van die Argeïkum TTG magmas is veral belangrik in hierdie verband as hulle geochemie vereis dat hulle gevorm word deur hoë druk smelting van 'n granaat-ryk eklogitiese bron. Dit word interpreteer as bewys vir die vorming van hierdie magmas deur smelting van die boonste gedeeltes van die blaaie in Argeïese subduksie sones. TTG magmas in die algemeen, is veronderstel om op te staan deur middel van water-afwesig gedeeltelike smelting van metamafiese bron rotse. Daarom bestaan baie min eksperimentele data op water-teenwoordig eklogiet smelting om Argeïkum TTG te produseer, ten spyte van die feit dat water magmatisme dryf in moderne boë. Gevolglik is hierdie studie ‘n eksperimentele ondersoek in die rol van water-teenwoordig gedeeltelike smelting van eklogiet-fasies metamafiese rots in die produksie van Paleo- tot Meso-Argeïkum HD-tipe TTG smelte. Eksperimente word uitgevoer tussen 1.6 GPa en 3.0 GPa en 700 ºC en 900 ºC met behulp van natuurlike en sintetiese eklogiet, en gel begin materiaal van lae-K2O basaltiese samestelling. Gedeeltelike smelting van die natuurlike en sintetiese eklogiet het plaasgevind tussen 850 ºC en 870 ºC te druk bo 1.8 GPa, en die smeltings reaksie is gekenmerk deur die afbreek van natruimhoudende klinopirokseen, kwarts en water: Qtz + Cpx1 + H2O ± Grt1 = Smelt + Cpx2 ± Grt2. Die eksperimentele smelte het die komposisies van natruimhoudende trondhjemites en is soortgelyk aan die hoof-, spoor- en seldsame aard element samestelling van HD-tipe Argeïkum TTG. Hierdie studie dui daarop dat water-teenwoordig eklogiet smelting 'n lewensvatbare petrogenetiese model is vir hierdie komponent van Paleo- tot Meso-Argeïkum TTG kors. Die aard van die nat lae-K2O eklogietfasies metamafiese rock solidus is eksperimenteel gedefinieër en beweeg na hoër temperature by die posisie van die plagioklaas-out reaksie. Daarom dui die resultate daarop dat 'n kristallyne materiaal nodig is om hierdie solidus te definieër en metastabiele smelting buite temperature van die Pl + H2O + Qtz solidus druk bo plagioklaas stabiliteit te vermy. Verder maak hierdie studie gebruik van numeriese en metamorfiese modelle om aan te dui dat die grootste deel van die water geproduseer deur metamorfiese reaksies binne die blaaie bestaan vir redelike Argeïkum mantel wig temperature binne 'n potensiële Argeïkum subduksie sone, en word opgevang deur 'n smelting sone naby die blad oppervlak. Daarom kan hierdie geodinamies model rekenskap gee vir HD-tipe Argeïkum TTG produksie en dit bied ook die beperkinge vir waarskynlik Argeïese subduksie. Die vorm van die betrokke waterteenwoordig solidus is soortgelyk aan die vorm van die druk-temperatuur paaie gevolg deur die boonste vlakke van die voorgestelde Argeïkum subderende blad, wat water-vloeiing blad smeltingbaie afhanklik maak van die temperatuur in die mantel wig. Ons stel voor dat afkoeling van die boonste mantel met slegs 'n klein hoeveelheid gedurende die laat Argeïese, die water-vloeiing smelting van die blad beëindig. Dit het toegelaat dat die blad water in die wig migreer en intermediêre samestelling magmatisme produseer wat sedert geassosieer word met subduksie sones.
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Drieberg, Susan L. "The magmatic-hydrothermal architecture of the Archean Volcanic Massive Sulfide (VMS) System at Panorama, Pilbara, Western Australia." University of Western Australia. School of Earth and Geographical Sciences, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0064.
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[Truncated abstract. Formulae and special characters can only be approximated here. Please see the pdf version of this abstract for an accurate representation.] The 3.24 Ga Panorama VMS District, located in the Pilbara Craton of Western Australia, is exposed as a cross-section through subvolcanic granite intrusions and a coeval submarine volcanic sequence that hosts Zn-Cu mineralization. The near-complete exposure across the district, the very low metamorphic grade, and the remarkable preservation of primary igneous and volcanic textures provides an unparalleled opportunity to examine the P-T-X-source evolution of a VMS ore-forming system and to assess the role of the subvolcanic intrusions as heat sources and/or metal contributors to the overlying VMS hydrothermal system. Detailed mapping of the Panorama VMS District has revealed seven major vein types related to the VMS hydrothermal system or to the subvolcanic intrusions. (1) Quartz-chalcopyrite veins, hosted in granophyric granite immediately beneath the granite-volcanic contact, formed prior to main stage VMS hydrothermal convection, and were precipitated from mixed H2OCO 2-NaCl-KCl fluids with variable salinities (2.5 to 8.5 wt% NaCl equiv). (2) Quartz-sericite veins, ubiquitous across the top 50m of the volcanic sequence, were formed from an Archean seawater with a salinity of 9.7 to 11.2 wt% NaCl equiv at temperatures of 90° to 135°C. These veins formed synchronous with the regional feldspar-sericite-quartz-ankerite alteration during seawater recharge into the main stage VMS hydrothermal convection cells. (3) Quartz-pyrite veins hosted in granophyric granite, and (4) quartz-carbonate-pyrite veins hosted in andesitebasalt, also formed from relatively unevolved Archean seawater (5.5 to 10.1 wt% NaCl equiv; 150° to 225°C), but during the collapse of the VMS hydrothermal system when cool, unmodified seawater invaded the top of the subvolcanic intrusions. (5) Quartz-topaz-muscovite greisen, (6) quartz-chlorite-chalcopyrite vein greisen, and (7) hydrothermal Cu-Zn-Sn veins are hosted in the subvolcanic intrusions. Primary H2O-NaCl-CaCl2 fluid inclusions in the vein greisens were complex high temperature hypersaline inclusions (up to 590°C and up to 56 wt% NaCl equiv). The H2O-CO2-NaCl fluid inclusions in the Cu-Zn-Sn veins have variable salinities, ranging from 4.9 to 14.1 wt% NaCl equiv, and homogenization temperatures ranging from 160° to 325°C. The hydrothermal quartz veins and magmatic metasomatic phases in the subvolcanic intrusions were formed from a magmatic-hydrothermal fluid that had evolved through wallrock reactions, cooling, and finally mixing with seawater-derived VMS hydrothermal fluids.
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Liu, Mian. "Migmatization and volcanic petrogenesis in the La Grande greenstone belt, Quebec." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63353.
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Nicoli, Gautier. "The metamorphic and anatectic history of Archaean metapelitic granulites from the South Marginal Zone, Limpopo Belt, South Africa." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97041.
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Thesis (DSc)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Anatexis is the first step in granite genesis. Partial melting in the lower crust may produce leucoratic features of unusual chemical compositions, very different from the final products of crustal differentiation. Therefore, the links that exists between some migmatites and crustal-derived granites can be ambiguous. This study is an investigation of the anatectic history of a high-grade terrain: the Southern Marginal Zone of the Limpopo Belt (SMZ), north to the Kaapvaal Craton in South Africa. The work involved an integrated field, metamorphic, geochemical and geochronogical study of the metasedimentary granulites from two separate quarries in the northern zone of the Southern Marginal Zone, the Bandelierkop quarry and the Brakspruit quarry, where Neoarchean high-grade partial melting features can be observed. The project has aimed to address two main issues: (1) to accurately constrain the pressuretemperature conditions and the age of the metamorphic episode in the SMZ, with implication for the geodynamic processes near the end of the Archean, (2) to investigate the fluid-absent partial melting reactions that control formation of K2O-poor leucosomes and to understand the chemical relationships in the system source-leucosome-melt–S-type granite. The P-T-t record retained in the Bandelierkop Formation metapelites, constrained by phase equilibria modelling as well as zircon LA-ICP-MS geochronology, gives an insight into crustal differentiation processes in the lower crust. Rocks in both quarries indicate high-temperature metamorphism episodes with peak conditions of 840-860 oC and 9-11 kbar at c. 2.71 Ga with formation of leucosomes (L1) during the prograde path. Minor leucocratic features (L2) were produced during decompression to 6-7 kbar. The end of the metamorphic event is marked by the granulites/amphibolites facies transition (< 640 oC) at c. 2.68 Ga. The maximum deposit age for the detrital zircons in the metapelites (c. 2.73 Ga) indicates a rapid burial process ( 0.17 cm.y1). Those evidences strongly support that the Southern Marginal Zone contains sediments deposited in an active margin during convergence, and that the metapelites were metamorphosed and partially melted as a consequence of continental collision along the northern margin of the Kaapvaal Craton at c. 2.7 Ga. The leucocratic features generated along this P-T-t path display an unusual chemistry with low K2O and FeO+MgO content and high CaO content. The combination of field observations, chemical mapping and geochemical analyses leads to the conclusion the major part of the leucosomes (L1) crystallized prior to syn-peak of metamorphism concurrent with melt extraction from the source. This study documents the details of leucosomes formation using field observations in the Southern Marginal Zone and numerical modelling. This work demonstrates that the formation of K2O-poor leucosome in the metasedimentary lower crust is controlled by the difference in volume of equilibration and heterogeneities within the migmatites. The partial melting of the source coupled with melt loss and water diffusivity within the melt transfer site is a potential mechanism to explain the chemical link in the sytem residuum– melt–S-type granite.
AFRIKAANSE OPSOMMING: Anateksis is die eerste stap in granietgenese. Meganismes wat in die onderste kors aan die werk is, is verantwoordelik vir korsdifferensiasie en bepaal die chemiese samestelling van die graniet. Hierdie studie het’n ondersoek behels van die anatektiese geskiedenis van ’n ho egraadse terrein: die suidelike randstreek van die Limpopo-gordel, noord van die Kaapvaal-kraton in Suid-Afrika. Die werk het ’n ge integreerde veld- , metamorfiese, geochemiese en geochronologiese studie van die metasedimentêre granuliete van twee afsonderlike groewe in die noordelike sone van die suidelike randstreek (SRS), die Bandelierkop-groef en die Brakspruit-groef, waar Neoarge iese ho egraadse gedeeltelike smeltkenmerke waargeneem kan word, ingesluit. Die projek was gerig op die ondersoek van twee belangrike kwessies: (1) om die drukâtemperatuurtoestande en die ouderdom van die metamorfiese episode in die SRS akkuraat te beheer, met implikasie vir die geodinamiese prosesse naby die einde van die Arge ikum, en (2) om die reaksies onder gedeeltelik gesmelte toestande wat die vorming van migmatiete beheer, te ondersoek en die chemiese verwantskappe in die stelsel bron - leukosoom - smelt - S-tipe graniet te begryp. Die P-T-t-rekord wat in die Bandelierkop-formasie metapeliete behoue is, ingeperk deur modellering van fase-ekwilibria asook sirkoon LA-ICP-MS-geochronologie, gee insig in korsdifferensiasieprosesse in die onderste kors. Rotse in albei groewe dui op metamorfismeepisodes teen hoë temperature met piektoestande van 840â860 oC en 9â11 kbar teen ongeveer 2.71 Ga met vorming van leukosome (L1) gedurende die progradeerpad. Geringe leukokratiese eienskappe (L2) het tydens dekompressie tot 6â7 kbar ontstaan. Die einde van die metamorfiese voorval word gekenmerk deur die fasiesoorgang van granuliete / amfiboliete (<640 oC) by ongeveer 2.68 Ga. Die maksimum afsettingsouderdom vir die detitrale sirkone in die metapeliete (ongeveer 2.73 Ga) dui op Å snelle begrawingsproses ( 0.17 cm.y1). Daardie bewyse bied sterk ondersteuning daarvoor dat die SRS sedimente bevat wat gedurende konvergensie in Å aktiewe rand afgeset is, en dat die metapeliete gemetamorfoseer en gedeeltelik gesmelt het as gevolg van kontinentbotsing langs die noordelike rand van die Kaapvaal-kraton teen ongeveer 2.7 Ga. Die leukokratiese eienskappe wat langs hierdie P-T-t-pad opgewek word, toon Å ongewone chemiese samestelling met lae K2O en FeO+MgO-inhoud en ho e CaO-inhoud. Die kombinasie van veldwaarnemings, chemiese kartering en geochemiese ontledings lei tot die gevolgtrekking dat die grootste deel van die leukosome (L1) gekristalliseer het voor die syn-piek van metamorfisme tesame met smeltekstraksie van die bron. Hierdie studie het die besonderhede van leukosoomformasie met behulp van veldwaarnemings in die SRS en numeriese modellering opgeteken. Hierdie werk toon aan dat korsdifferensiasie in die metasedimentêre onderste kors deur Å ander volume van ekwilibrasie en heterogeniteite in die migmatiete beheer word. Die gedeeltelike smelting van die bron gepaard met smeltverlies en waterdiffusiwiteit tot in die smeltoordragterrein is ’n potensiele meganisme om die chemiese skakel in die stelsel residuum-smelt-S-tipe graniet te verklaar.
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Mengel, Flemming Cai. "Thermotectonic evolution of the Proterozoic-Archaean boundary in the Saglek area, northern Labrador /." 1987. http://collections.mun.ca/u?/theses,91862.
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Langsford, N. "Long structural zones in the Archaean Yilgarn Craton, Western Australia." Thesis, 1994. https://eprints.utas.edu.au/20343/7/whole_LangsfordNick1995.pdf.
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Eight structural zones from 250km to 800km long, traverse the granite-greenstone
terrane of the Eastern Goldfields and Murchison districts of the Yilgam Craton. The
structural zones, herein called LSZ, (long structural zones) have been traced using
1 :500,000 geological compilations and AGSO (Australian Geological Survey
Organisation) aeromagnetic and gravity data.
LSZ are complex linear deformation zones, resulting in the reactivation of structures
formed prior to a craton wide shortening episode. Some of the pre-existing structures
are interpreted as low angle extensional features, post dating the formation of much of
the supracrustals; others as still earlier structures controlling original volcanic and
sedimentary greenstone belt architecture.
The structural corridors reactivated by the shortening event are overprinted by strikeslip
faults which formed relatively narrow shear zones within the corridors.
Most of the LSZ contain or abut linear belts of relatively coarse, immature, locally
derived elastic sediments, which have been in turn overprinted by shear zones.
Carbonate and alkali metasomatism is commonly strongly developed within the local
sediment troughs.
Numerous alkalic syenitic plugs have been intruded within and adjacent to the LSZ. At I
larger scales, several LSZ are associated with K-Th-U rare metal (W-Sn-Be-Li)rich
granitoids, or alkali rich syenites in belts up to 250km long. LSZ contain a record of the youngest events related to the evolution of the greenstonegranite
terrane; the youngest sediments, the belts of elastics; the youngest shear zones;
and the youngest intrusive suites.
LSZ are direct hosts to only a few large Yilgarn gold deposits. Several major deposits ·
occur within structures directly connected to LSZ. Although major, deeply penetrating
crustal scale structures, LSZ are not a necessary or sufficient condition for the
formation of major gold deposits in the Yilgarn.
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"An integrated field, geochemical and geochronological study of archaean rock units in Southern Swaziland." Thesis, 2015. http://hdl.handle.net/10210/13700.
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M.Sc. (Geology)This study represents the first detailed field, geochemical and geochronological study of Archaean rock units that crop out along the Ncotshane River in the southern part of Swaziland. These rock units were mapped as Mahamba Gneiss in the geological map of Swaziland (Wilson, 1982). However, field examination indicated that the area consists of a heterogeneous assemblage of serpentinite, amphibolite, gabbroic gneiss, quartzite, meta-ironstone, augen gneiss, granitic gneiss and diorite, all of which are intimately associated with weakly foliated granite and dolerite. Serpentinite is regarded to represent the metamorphosed equivalent of komatiite found in the Dwalile Supracrustal Suite, a correlate of the Onverwacht Group, on the basis of similar geochemical characteristics. The silicified part of the serpentinite may compare with silicified komatiite that are widely observed in the Onverwacht Group. It is equally possible however that the ultramafic rocks originated as intrusions that are widespread in the SE Kaapvaal craton and which include both Palaeoarchaean and Mesoarchaean layered complexes. No contacts with neighbouring rocks were observed, thus not allowing unequivocal differentiation between the different possibilities. Amphibolites represent metamorphosed equivalents of the Mozaan Group basalts based on their association with Mozaan quartzite. Gabbroic gneiss, which occurs in association with amphibolite, likely represents an intrusive equivalent of amphibolite.....
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Nhleko, Noah. "Stratigraphy of the Archean Mozaan Group in the Kubuta-Mooihoek area, Swaziland." Thesis, 2012. http://hdl.handle.net/10210/6405.
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M.Sc.Known outcrops of the supracrustal Mesoarchean Mozaan Group of the Pongola Supergroup occur in north-eastern Kwazulu-Natal and southern Mpumalanga in South Africa, and southern Swaziland. Outcrops of the Mozaan succession in Swaziland are preserved in the Ntungulu-Mahlangatsha and Kubuta-Mooihoek areas. The succession is composed of polymictic conglomerate, poorly sorted scour based quartzite, orthoquartzite, shale, iron-formation, polymictic diamictite and lava. In the Kubuta- Mooihoek area a 3000m thick succession is preserved and correlates almost bed for bed with that in the Hartland area in South Africa. The succession is preserved from the Dipka member of the Sinqeni Formation at the base to the Tobolsk lava at the top. The depositional environment ranges essentially between fluvial and marine with two distinct glaciogenic diamictite units and one unit of lava near the top of the succession. Seven unconformity bounded sequences are recognised in the succession and from these a relative sea-level curve could be constructed. Trace element geochemistry of the shale reveals that the source area was predominantly felsic with a mafic component probably derived from the uplifted pre-Pongola granitoids and Nsuze Group. The petrography of the quartzite in the succession suggests a change in provenance from a low-lying deeply weathered to uplifted moderately weathered source area higher up in the stratigraphy. Part of the tectonic uplift may have been associated with isostatic rebound related to melting of continental glaciers. The Tobolsk lava is a continental flood basalt also possibly related to a tectonic uplift event. There are indications of sediment recycling in the upper part of the succession where conglomerates are predominantly composed of chert clasts A pretectonic quartz porphyry sill, folded with the strata, provides an upper age limit of 2837±5 Ma for the deposition of the Mozaan Group. The Mooihoek granite (2824±6 Ma) that intrudes and deforms the synclinal structure along its eastern flank, provides an upper age limit of the folding event. This suggests that the deformation of the Mozaan succession took place in the intervening 13 Ma period between 2824 and 2837 Ma ago.
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Kohler, Ernest Alfred. "The geology of the archaean granitoid-greenstone terrane in the vicinity of three Sisters, Barberton greenstone Belt." Thesis, 1994. https://hdl.handle.net/10539/24354.
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A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Doctor of PhilosophyThis 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
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Kohler, Ernst Alfred. "The geology of the Archaean granitoid-greenstone terrane in the vicinity of Three Sisters, Barberton Greenstone Belt." Thesis, 1994. https://hdl.handle.net/10539/24352.
Full textAbstract:
A thesis submitted to the Faculty of Science,
University of the Witwatersrand, Johannesburg, for
the degree of Doctor of PhilosophyThis 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
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Finn, Gregory Clement. "Geochemical and isotopic evolution of the Maggo Gneiss component from the Hopedale Block, Labrador : evidence for Late-Middle Archaean crustal reworking /." 1988. http://collections.mun.ca/u?/theses,109660.
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Blane, Craig Harry. "Composition and provenance of quartzites of the Mesoarchean Witwatersrand supergroup, South Africa." Thesis, 2013. http://hdl.handle.net/10210/8712.
Full textAbstract:
M.Sc.(Geology)The Mesoarchean Witwatersrand Supergroup is a remarkably well preserved siliciclastic dominated cratonic platform succession located on the Kaapvaal Craton in South Africa. The vast gold resources which have been mined since 1886 make it relevant for study. The study aimed to identify significant provenance shifts throughout the depositional life of the basin which should be reflected in the in heavy mineral populations and the geochemical composition of the siliciclastic rocks. The study identified major changes in the source rock compositions through the basin lifespan and inferred major tectonic events during the life of the basin. It was found that the mechanical effects of sorting in different depositional environments tended to obscure provenance shifts, but with careful evaluation of the various factors in play significant provenance shifts could be identified. It was found that these provenance shifts corresponded closely with major unconformity sequence boundaries identified by Beukes (1995). These major provenance shifts are a record of a major tectonic event during the development of the basin. The Hospital Subgroup records a passive trailing margin, fed by a combination of felsic and ultra-mafic source rocks. Within the Hospital Hill Subgroup, there is a trend of increasing ultramafic components in the source area with increasing stratigraphic height. This trend is believed to reflect progressive unroofing of tonalite and greenstone belt complexes over the life of the Hospital Hill Subgroup. At the base of the Promise Formation a basin wide unconformity is present, which marks a shift from mature shallow marine and outer shelf sediments of the Hospital Hill Subgroup to immature fluvial quartzites for the Government and Jeppestown Subgroups (Beukes, 1995). In addition to the major change in depofacies that was recognised by Beukes (1995), this study found evidence for a shift in provenance to generally more fractionated source rocks, that were heterogeneous, but well mixed. The presence of lithoclasts indicates a possible metamorphic component was also present in the source area. This is consistent with a source area containing granitoid batholiths, and granite plutonism which is associated with early subduction tectonics and volcanic arc formation during the deposition of the Government and Jeppestown Subgroups (Wronkiewicz and Condie, 1987 and Poujol, et al., 2003, Kositcin and Krapez, 2004). Another important basin wide unconformity is present at the base of the Johannesburg Subgroup, and marks another major provenance change. These rocks are chemically more mature than the Government and Jeppestown Subgroups and represent a shift to an immature fluvial depositional setting related to basin closure (Beukes, 1995). A shift to moderate Th:Sc and La:Sc suggests a less fractionated mix of source rocks. The disappearance of the lithoclasts indicates that the metamorphic source rocks no longer supplied material to the basin. A small increase in the chromite to zircon ratio also suggests that some unfractionated source rocks were present. The narrow range in Th:Sc, La:Sc, Nb:Y ratios suggests that a homogeneous source area is present, but this is contradicted by the highly variable zircon ages measured by Kositcin and Krapez (2004), so the narrow spread might indicate that the rocks are very well mixed. Zircon populations measured by Kositcin and Krapez (2004) suggest that source terrain of the Johannesburg Subgroup probably consisted of a mixture of the granitoid batholiths from which the Government and Jeppestown Subgroups are a derived as well as some intermediate igneous material with ages of 3000-2870 ma. This would reflect incorporation of syntectonic granitoid plutons into the source areas, Kositcin and Krapez, (2004). The Turffontein Subgroup rocks are very coarse and chemically mature, but they display poor to moderate sorting and rounding. The rocks were deposited in a fluvial environment but marine quartzites are not uncommon. It is believed that these rocks were transported in a high energy environment, but the duration of transportation was short. This allows for effective winnowing but insufficient time for physically mature rocks with well-rounded grains to develop, explaining the mature chemical composition but immature physical composition. The source rocks of the Turffontein Subgroup were probably the same as the Johannesburg Subgroup with the higher energy mode of transportation responsible for the observed increase in Zr:Ti ratio. It would also explain the scarcity of feldspars and chlorite in the Turffontein Subgroup. Th:Sc and Nb:Y ratios suggest highly fractionated source rocks, but care must be taken because the mature nature and coarse grainsize of these rocks make trace element analyses unreliable. The zircon population indicates the presence of 3090-3060ma (Kositcin and Krapez, 2004) granite batholiths, as well as 3000-2870 Ma (Kositcin and Krapez, 2004) syntectonic granite plutons, as well as ancient granitoid gneiss (Kositcin and Krapez, 2004) in the source area. This study has provided new support for a foreland basin origin of the Witwatersrand Supergroup, proposed by Beukes (1995), Beukes and Nelson (1995) and Nhleko (2003), resulting from orogenic collision of the Witwatersrand and Kimberley blocks along the western margin of the Witwatersrand block. The Amalia, Kraaipan and Madibe greenstone belts and Colesberg Magnetic Anomaly are probably the only remaining remnants of this orogeny today.
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Mathe, Humphrey Lawrence Mbendeni. "Tectonostratigraphy, structure and metamorphism of the Archaean Ilangwe granite - greenstone belt south of Melmoth, Kwazulu-Natal." Thesis, 1997. http://hdl.handle.net/10413/5033.
Full textAbstract:
The mapped area, measuring about 400m2, is situated along the southern margin of the
Archaean Kaapvaal Craton south of Melmoth in KwaZulu-Natal and comprises greenstones
and metasediments forming a narrow, linear E-W trending and dominantly northerly
inclined belt flanked to the north and south by various granitoids and granitoid gneisses
which have been differentiated for the first time in this study. This belt is here referred to as
the ILANGWE GREENSTONE BELT.
The lIangwe Belt rocks are grouped into the Umhlathuze Subgroup (a lower metavolcanic
suite) and the Nkandla Subgroup (an upper metasedimentary suite). The former consists
of:
(a) the Sabiza Formation: a lower amphibolite association occurring along the
southern margin of the greenstone belt;
(b) the Matshansundu Formation: an eastern amphibolite-BIF association;
(c) the Olwenjini Formation: an upper or northern amphibolite-banded chert-BIF
association.
whereas the latter is sub-divided into:
(a) the Entembeni Formation: a distinctive phyllite-banded chert-BIF association
occurring in the central and the eastern parts of the belt;
(b) the Simbagwezi Formation: a phyllite-banded chert-amphibolite association
occurring in the western part of the belt, south-east of Nkandla;
(c) the Nomangci Formation: a dominantly quartzite and quartz schist formation
occurring in the western part of the belt, south-east of Nkandla.
The contacts between the six major tectonostratigraphic formations are tectonic.
In the eastern sector of the lIangwe Belt, the lowermost metasedimentary formation, the
Entembeni Formation, cuts across both the Sabiza and Matshansundu Formations (the
lower formations of the Umhlathuze Subgroup) in a major deformed angular unconformity
referred to as the Ndloziyana angular unconformity. In the central parts of the belt, the
Entembeni Formation structurally overlies the Olwenjini Formation in what seems to be a
major local unconformity (disconformity). In the western sector of the belt, the Simbagwezi
Formation occurs as a structural wedge between the lower and upper formations of the
Umhlathuze Subgroup. That is, it structurally overlies the Sabiza Formation and structurally
underlies the Olwenjini Formation. The uppermost metasedimentary unit, the Nomangci
Formation occurs as a complex series of finger-like wedges cutting and extending into the
Simbagwezi Formation and in each case showing that the Nomangci Formation structurally
underlies the Simbagwezi Formation. This structural repetition of lithological units is
suggestive of normal dip-slip duplex structures.
Palimpsest volcanic features, such as pillow structures and minor ocelli, indicate that many
of the amphibolitic rocks represent metavolcanics, possibly transformed oceanic crust. This
is also supported by limited major element geochemistry which suggests that the original
rocks were ocean tholeiites. Evidence suggests that the talc-tremolite schists and the
serpentinitic talc schists represent altered komatiites. The nature of the metasediments
(represented by banded metacherts, quartzites and banded iron formations) and their
similarity to those of the Barberton, Pietersburg and Nondweni greenstone complexes
suggests that they were formed in relatively shallow water environments.
The lIangwe magmatism is represented by different types of granitoids and granitoid
gneisses and basic-ultrabasic intrusive bodies. Based on similar geochemical and
mineralogical characteristics and on regional distribution, mutual associations and contact
relationships, these granitoids and granitoid gneisses can be divided into three broad
associations, viz:
(a) The Amazula Gneiss - Nkwa/ini Mylonitic Gneiss - Nkwalini Quartzofeldspathic
Flaser Gneiss Association: a migmatitic paragneiss and mylonitic to
flaser gneiss association of older gneisses of Nondweni age occurring in several
widely separated areas and intruded by younger granitoids.
(b) The early post-Nondweni Granitoids comprising the Nkwalinye Tonalitic
Gneiss (a distinctive grey gneiss intrusive into the greenstones and older
gneisses) and the Nsengeni Granitoid Suite (an association of three granitoid
units of batholithic proportions flanking the greenstone belt and intrusive into the
greenstones, older gneisses and Nkwalinye Tonalitic Gneiss).
(c) The late post-Nondweni Granitoids comprising the Impisi-Umgabhi Granitoid
Suite, a batholithic microcrystic to megacrystic association of five granitoid
phases/units occurring to the north and south of the greenstone belt and intrusive
into the greenstones, older gneisses and early post-Nondweni granitoids.
Limited major element geochemistry suggests that the granitoids and granitoid gneisses
are of calc-alkaline origin and are of tonalitic, granodioritic, adamellitic and granitic
composition. An igneous derivation from material located possibly at the lower crust or
upper mantle is suggested.
At least three major episodes of deformation (01, O2 and 03) have been recognized in the
greenstones. During 01, a strong penetrative S1 tectonic foliation developed parallel to the
So primary layering and bedding. This period was characterized by intense transpositional
layering, recumbent and isoclinal intrafolial folding with associated shearing,thrusting and
structural repetition of greenstone lithologies. These processes took place in an essentially
horizontal, high strain tectonic regime.
The first phase of deformation (OG1) in the migmatitic and mylonitic gneisses was also
characterized by recumbent and isoclinal intrafolial folding and is remarkably similar to the
01deformational phase in the lIangwe greenstones.
Structural features of the first phase of deformation suggest that it was dominated by
formation of fold nappes and thrusts and was accompanied by prograde M1 medium-grade
middle to upper amphibolite facies metamorphism.
During D2 deformation, the subhorizontal D1 structures were refolded by new structures with
steeply inclined axial planes. This resulted in the formation of superimposed Type 3
interference folding in the amphibolitic rocks and large-scale, E-W trending, doublyplunging
periclinal folds in the metasediments. These periclinal folds have steeply inclined
and overturned limbs and are characterized by narrow, closed elliptical outcrop patterns
well-defined by extensive banded ironstones and metacherts.
The second phase of deformation in the granitoids (DG
2) was characterized by steeply
plunging and steeply inclined small-scale tight to isoclinal similar folds. Large-scale folds
are not present in the granitoids.
Evidence suggests that the second phase of deformation was a major compressional event
which resulted in the large-scale upright, flattened flexural folds. It was accompanied by
widespread regional greenschist metamorphism and the intrusion of the early postNondweni
granitoids.
The third phase of deformation produced steeply plunging small-scale folds on the limbs
and axial planes of the pre-existing large-scale F2 folds and upright open folds in the
granitoid terrain. This episode was characterized by the emplacement of the late postNondweni
granitoids (along the D2 greenstone boundary faults) and is associated with two
significant events of prograde M3 upper greenschist facies metamorphism and retrograde
M3 lower greenschist facies metamorphism.
Post-D3 deformation is characterized by late cross-cutting faults and the emplacement of
younger basic - ultrabasic bodies.Thesis (Ph.D.)-University of Natal, 1997.
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Cole, Edward George. "Lithostratigraphy and depositional environment of the Archaean Nsuze Group, Pongola Supergroup." Thesis, 2014. http://hdl.handle.net/10210/11447.
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Jenner, Frances Elaine. "Geochemistry and petrogenesis of Archean mafic and ultramafic rocks, Southern West Greenland." Phd thesis, 2006. http://hdl.handle.net/1885/151671.
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Kent, Adam John Reginald. "Geochronological constraints on the timing of Archaean gold mineralisation in the Yilgarn Craton, Western Australia." Phd thesis, 1994. http://hdl.handle.net/1885/140164.
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Hiess, Joseph. "Early crustal petrogenesis : integrated in situ U-Pb, O, Hf and Ti isotopic systematics of zircon from Archaean rocks, West Greenland." Phd thesis, 2008. http://hdl.handle.net/1885/150388.
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Stoltze, Amanda M. "Is proximal carbonatite magmatism the source of gold at the Wallaby Deposit, Western Australia?" Phd thesis, 2006. http://hdl.handle.net/1885/150079.
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Ghaderi, Majid. "Sources of Archaean gold mineralisation in the Kalgoorlie-Norseman region of western Australia, determined from strontium-neodymium istotopes and trace elements in scheelite and host rocks." Phd thesis, 1998. http://hdl.handle.net/1885/145165.
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Xu, Yinghuai. "The stable isotope and trace element geochemistry of the Victory gold deposit, Western Australia." Phd thesis, 1999. http://hdl.handle.net/1885/147403.
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Tomkins, Andrew George. "Evolution of the granulite-hosted Challenger gold deposit, South Australia : implications for ore genesis." Phd thesis, 2002. http://hdl.handle.net/1885/146024.
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Crawford, Matthew Adam. "Dynamic coupling between deformation processes, fluid-rock interaction, and gold deposition in the Argo gold deposit, St Ives, Western Australia." Phd thesis, 2011. http://hdl.handle.net/1885/150787.
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Johnson, Geoffrey I. (Geoffrey Ian). "The petrology, geochemistry and geochronology of the felsic alkaline suite of the eastern Yilgarn Block, Western Australia / Geoffrey I. Johnson." 1991. http://hdl.handle.net/2440/19697.
Full textAbstract:
Typescript (Photocopy)Includes copies of 4 papers by the author as appendix 4 (v. 1)
Errata slip inserted
Bibliography: leaves 170-192 (v. 1)
2 v. : ill., maps ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--Dept. of Geology and Geophysics, University of Adelaide, 1992