Dissertations / Theses: 'Archaean'

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Brown, Isobel Julia. "Geology and geochemistry of Archaean gold mineralization, Arcturus District, Zimbabwe." Thesis, Oxford Brookes University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290402.

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Dougherty-Page, Jon Stanley. "The evolution of the Archaean continental crust of Northern Zimbabwe." Thesis, Open University, 1994. http://oro.open.ac.uk/54877/.

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Granitoid clasts preserved in Late Archaean conglomerates indicate the presence of continental crust in Northern Zimbabwe prior to the ≈ 2.7 to ≈ 2.6Ga "event" which terminated with the stabilisation of the Zimbabwe Craton. The "Kober Technique" (Kober, 1986, 1987) of direct thermal ionisation of zircons has been set up in order to investigate the geochronological record preserved in such clasts. Conglomerates were sampled from two localities, Shamva, within the central part of Northern Zimbabwe, and Chinhoyi, at the north-western boundary of the craton. The results from both localities demonstrate the presence of continental crust in Northern Zimbabwe with a long and complex history prior to the Late Archaean "event". The minimum age of continental crust in the Shamva region is 3.34 Ga (Sm-Nd model age),with further episodes of granitiod intrusion indicated by zircon crystallisation at 3/197 ± 10 Ma, 2,925 ± 10 Ma, and 2,800 ± 20 Ma (Pb-Pb zircon). The Chinhoyi region has a shorter, simpler history, with the earliest recorded continental crust at 2,875 ± 3 Ma and later intrusions of granitoids at 2/800 ± 20 Ma, and2,720 ± 6 Ma (Pb-Pb zircon). Chemically, the early crust was dominated by sodic, Tonalite Trondhjemite-Granodiorite granitoids, whose formation may be modelled by the partial melting of metabasalts with residual hornblende and/or garnet. By contrast, the granitoids formed during the Late Archaean "event" which culminated in the stabilisation of the craton, dominantly follow calc-alkalinetrends, and their formation may be modelled by the fractionation of basaltic magmas (combined with assimilation- of pre-existing continental material) or intra-crustal remelting. This major switch in the origins (and hence chemistry) of granitoids may be attributed to mantle plume activity, the onset of which is recorded by the presence of greens tone belt volcanics derived from anomalously hot mantle, dated at' 2,713 ± 15 Ma (U-Pb zircon Jelsma, 1993).

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Robertson, S. "Late Archaean crustal evolution in the Ivisartoq region, southern west Greenland." Thesis, University of Exeter, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353048.

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Opiyo-Akech, Norbert. "Geology and geochemistry of the late Archaean greenstone associations, Maseno area, Kenya." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/35080.

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The greenstone belt of Kenya is an extension of what is commonly referred to as the Tanganyika "Shield". The two supracrustal sequences recognized in Kenya are the Nyanzian and the Kavirondian. The rocks found in these sequences are diverse, with dominant volcanics in the Nyanzian, whereas the Kavirondian is predominantly sedimentary. The Nyanzian lavas represent a diverse range from basalts and basaltic andesites, through andesites and dacites to rhyolites. From geochemical studies the basalts and basaltic andesites are tholeiitic, whereas the andesites, dacites and rhyolites are calc-alkaline. The sedimentary sequence ranges from mudstone, through shales, sandstones and grits to conglomerates. The plutonic rocks range in composition from gabbro to true granites, but tonalite is the dominant rock type. The chemical differences between the tholeiitic basalts and the calc-alkaline andesitic to rhyolitic sequences suggests that these volcanic suites are derived from different sources and/or through different processes. The granitoids have close chemical similarities with the silicic volcanics. From the geochemical and field relationships, the Nyanzian and Kavirondian sequences are considered to have developed on a continental segment which had not yet attained full stability. The model employed for the generation of these volcanics considers the basalts to have been generated in a region undergoing extension, similar to that of a modern back-arc environment, whereas the calc-alkaline sequences, including the granitoids, are broadly comparable with those found in present day continental arc environments.

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Carles, Patricia 1975. "Constraints on the genesis of the Archaean Troilus gold-copper deposit, Quebec." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31204.

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The Troilus gold-copper deposit lies within the northeastern part of the Archaean Frotet-Evans greenstone belt, in the Opatica sub-province of the Superior Province, northern Quebec, and contains total reserves of 51 Mt at 1.08 g/t gold, 0.11% copper, and 1.4 g/t silver. The largest orebody, Zone 87, has been mined by open pit methods since 1993.
Rocks of the Troilus domain include a coarse- to medium-grained metadiorite, a finer-grained amphibolite, a rock with a brecciated texture and felsic dykes, which crosscut the metadioritic pluton, the amphibolite and the breccia. The amphibolite, breccia, and felsic dykes all locally host ore.
Previous researchers have proposed a porphyry-type model for the genesis of the Troilus deposit. However, evidence that the breccia unit is not hydrothermal but a product of magma mixing, that the felsic dykes predate mineralization, and that mineralization and associated alteration occurred as two discrete events separated by a major episode of regional metamorphism (amphibolite facies), requires that alternative genetic models for the deposit be considered, such as orogenic gold model. (Abstract shortened by UMI.)

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Horstwood, Matthew Simon Anthony. "Stratigraphy, geochemistry and zircon geochronology of the Midlands Greenstone Belt, Zimbabwe." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246222.

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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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Stubbs, Heather M. "The geochemistry and petrogenesis of Archaean and paleoproterozoic dykes and sills of Zimbabwe." Thesis, University of Portsmouth, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440491.

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Wightman, R. T. "Constraints on crustal development and tectonics in the Archaean rocks of south India." Thesis, Open University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374494.

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Taylor, Jeanne. "The anatectic history of Archaean metasedimentary granulites from the Ancient Gneiss Complex, Swaziland." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/20311.

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Thesis (DSc)--Stellenbosch University, 2012
ENGLISH ABSTRACT: This study is an investigation of the anatectic history of high-grade paragneisses from the Ancient Gneiss Complex (AGC) in Swaziland. The work involved an integrated field, metamorphic, geochemical, geochronological and structural study of metasedimentary granulites from three separate, but spatially related areas of outcrop in south-central Swaziland, which were subjected to multiple high-grade partial melting events throughout the Meso- to Neoarchaean. The project has aimed to constrain the age(s) and conditions of metamorphism, so as to contribute to the understanding of geodynamic processes in the Barberton and AGC granite-greenstone terranes, as well as to investigate certain physical and chemical aspects of anatexis in the migmatites. The metamorphic record retained in these rocks, constrained by phase equilibria modelling as well as zircon and monazite SHRIMP and LA-ICP-MS geochronology, informs on the state of the mid- to lower-crust of the southeastern Kaapvaal Craton during key events associated with early lithosphere assembly and crustal differentiation. It also suggests that the region is comprised of more than one high-grade terrane. Two of the areas investigated experienced high-temperature metamorphism at ca. 3.23-3.21 Ga, in addition to a major 830-875º C, 6.5-7.6 kbar anatectic event at ca. 3.11-3.07 Ga. Intermediate and younger high-temperature events are recorded at ca. 3.18 Ga, ca. 3.16 Ga and 2.99 Ga. The timing of these metamorphic events coincided with the amalgamation of the eastern domain of the proto-Craton via subduction and accretion of micro-continental fragments at ca. 3.23 Ga, including the Barberton Greenstone Belt (BGB) and AGC terranes, as well as discrete episodes of crustal differentiation and potassic granitic magmatism between ca. 3.23 and 3.10 Ga. The third area investigated holds no record of Mesoarchaean metamorphism, but instead experienced a 830- 855 ºC, 4.4-6.4 kbar partial melting episode at ca. 2.73 Ga. This broadly coincided with the formation of a large continental flood basalt province, the ca. 2.71 Ga Ventersdorp LIP, and widespread intracratonic granitic magmatism on the Craton towards the end of the Neoarchaean. An explanation for the contrast in metamorphic record in the two terranes may be that the 2.71 Ga granulites represent a much younger sedimentary succession, and that granulites from the older terrane were left too restitic, after substantial partial melting during the Mesoarchaean, to record subsequent high-grade events. Finally, this study documents the details of S-type granitic magma production and extraction from a typical metapelitic source. Using the 2.73 Ga granulites from the AGC as a natural field laboratory, a case is made for the selective entrainment of peritectic garnet to the magma as a mechanism for generating relatively mafic, peraluminous S-type granite compositions. The work demonstrates the evolution of entrained peritectic garnet in such magmas, and is in strong support of a ‘peritectic phase entrainment’ process by which relatively mafic granite magmas are produced from melts which, in theory, should be highly leucocratic.
AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die anatektiese geskiedenis van hoëgraadse metasedimentêre gneise uit die Ancient Gneiss Complex (AGC) in Swaziland. Die werk behels 'n geïntegreerde veld, metamorfiese, geochemiese, geochronologiese en strukturele studie van metasedimentêre granuliete van drie afsonderlike, maar ruimtelik verwante gebiede in suid-sentraal Swaziland, wat aan verskeie hoëgraadse anatektiese gebeure onderworpe was gedurende die Meso-tot Neoargeïese tydsperiode. Die studie is daarop gemik om die ouderdomme en die kondisies van metamorfose vas te stel, om sodoende by te dra tot die begrip van die geodinamiese prosesse in die Barberton en AGC granietgroensteen terrein, asook om sekere fisiese en chemiese aspekte van die anatektiese proses te ondersoek. Die metamorfe rekord, bepaal deur mineraal ewewigsmodellering sowel as sirkoon en monasiet SHRIMP en LA-ICP-MS geochronologie, belig die toestand van die middel-tot laer-kors van die suidoostelike Kaapvaal Kraton tydens vroeë litosfeer samesmelting en differensiasie. Dit stel ook voor dat die streek uit meer as een hoëgraadse terrein bestaan. Twee van die gebiede het hoë-temperatuur metamorfose by 3.23-3.21 Ga ervaar, asook 'n hoof 830-875 ° C, 6.5-7.6 kbar anatektiese gebeurtenis by 3.11-3.07 Ga. Intermediêre en jonger hoë-temperatuur gebeure was ook by 3.18 Ga, 3.16 Ga en 2.99 Ga geregistreer. Die metamorfose van die gebied stem ooreen met die samesmelting van die oos Kaapvaal Kraton domein deur subduksie en aanwas van mikro-kontinente by 3.23 Ga, insluitend die Barberton en AGC terreine, asook diskrete episodes van kors differensiasie en kalium-ryke graniet magmatisme tussen 3.23 en 3.10 Ga. Die derde gebied hou geen rekord van Mesoargeïkum metamorfose nie. In plaas daarvan het dit 'n 830-855 ° C, 4.4-6.4 kbar anatektiese episode by 2.73 Ga ervaar, wat ooreenstem met die vorming van 'n groot kontinentale vloedbasalt provinsie, die 2.71 Ga Ventersdorp Supergroep, en wydverspreide intrakratoniese graniet magmatisme teen die einde van die Neoargeïkum. 'n Moontlike verduideliking vir die kontras in metamorfe rekord in die twee terreine mag wees dat die 2.71 Ga granuliete 'n jonger sedimentêre afsetting verteenwoordig, en dat granuliete van die ouer terrein te restieties gelaat was na aansienlike anateksis in die Mesoargeïkum, om daaropvolgende hoëgraadse gebeure te registreer. Ten slotte, hierdie studie dokumenteer die besonderhede van S-tipe graniet magma produksie en ontginning van 'n tipiese metasedimentêre bron. Die 2.73 Ga granuliete word gebruik as 'n natuurlike veld laboratorium om die selektiewe optel-en-meevoering van peritektiese granaat tot die magma te ondersoek. Die werk toon die evolusie van peritektiese granate in sulke magmas aan, en ondersteun lewering van relatiewe mafiese graniet magmas deur 'n ‘peritektiese fase optel-en-meevoerings’ proses.

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Oak, Keith Alan. "The geology and geochemistry of Closepet granite, Karnataka, South India." Thesis, Oxford Brookes University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278897.

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The Archaean craton of southern India has four main components. The multi-phase Peninsular gneiss, with ages from 3360-2900 Ma, is spatially dominant and grades from granulite facies in the south to greenschist facies in the north. Ages for the Peninsular gneiss range from 3360-2900 Ma. Within the craton are two suites of Greenstone Belts and supracrustal rocks. The older, high-grade Sargur type occur as enclaves in the Peninsular gneiss and are in places older than 3360 Ma. The younger, lower-grade type occur occasionally have unconformable bases with the Peninsular gneiss and have been dated from 3100-2605 Ma. Granitoids form the last major component with the Closepet granite being the largest, ages for the emplacement of the Closepet granite and many of the other granitoids cluster around 2500 Ma. The Closepet granite outcrops from Kabbal Durge in the south to the Deccan Plateau in the north, a distance of some 450 km. A 320 km section from Kabbal Durga to Hospet in the north exposes a linear trending granite. The granite outcrop varies from one of essentially partial melting and melt extraction in the south to a zone of melt accumulation in the central zone to a zone of high level intrusion of large granite bodies. Related to these changes in primary processes are changes in the granite phases, size, shape and intrusive style. The petrography of the granite phases is described. These studies help to constrain phase relationships. The petrography also provides evidence to suggest that the K-feldspar megacrysts are in fact phenocrysts. Analyses of major and trace elements utilised standard X.R.F. methods. However, the analyses of REE on selected samples involved the setting up of the department's "ICP for routine operation. This procedure is outlined. The geochemistry of the granite's is described melting and crystallization models being used to explain their petrogenesis. Harker diagrams indicate that plagioclase, sphene and apatite have strong controls on major element composition and that biotite was a residual or fractionating phase. The removal of restite biotite as granite magmas intrude is thought to be a significant process.Evidence from the petrography agrees with the equilibrium phase diagram at PH2 0 ~ 5 kbar. Plots of Peninsular gneiss in the granite phase diagram have a range of compositions which could provide minimum and non-minimum melts capable of producing the Closepet granite trend. Predicted fractional crystallization would produce a sequence of magma compositions comparable to those of the Closepet granite with an order of phase crystallization that agrees with petrographic evidence. The phase relationships further constrain subsequent melting and crystallization models utilising trace elements and REE.

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Park, J. F. W. "Fault systems in the inner Godthabsfjord region of the Archaean Block, southern west Greenland." Thesis, University of Exeter, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377322.

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Mellqvist, Claes. "Proterozoic crustal growth along the Archaean continental margin in the Luleå area, northern Sweden." Licentiate thesis, Luleå tekniska universitet, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18235.

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Hapugoda, Hapugoda Udage Sarath. "Late Archaean and Early Proterozoic crustal evolution of the Georgetown Block, Northeast Queensland, Australia /." St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16503.pdf.

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Walsh, Carl. "Deep ultra-hot Archaean mantle dynamics; highly depleted residues as cradles for mantle diamond." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235717/1/Carl%2BWalsh%2BThesis.pdf.

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This project investigated the origin of ancient continents (more than 2.5 billion years old) that are often thought to form by shallow melting in the Earth’s mantle. Here, modelling and analysis of rock chemistry show deep melting is much more likely to produce the rocks and minerals observed, including minerals trapped in diamonds. A new formation model for ancient continents is presented that can explain the hottest lavas to ever erupt on Earth, and the association of diamonds with very chemically depleted rocks.

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Silva, Katherine E. "Komatiites from the Belingwe Greenstone Belt, Zimbabwe : constraints on the development of Archaean Greenstone Belts." Thesis, Royal Holloway, University of London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263522.

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Brewer, M. A. "The petrology of the Late Archaean gneisses and granites, Nunatarssuaq, Ivisartoq region, southern West Greenland." Thesis, University of Exeter, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370924.

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Yearron, Lorraine M. "Archaean granite petrogenesis and implications for the evolution of the Barberton mountain land, South Africa." Thesis, Kingston University, 2003. http://eprints.kingston.ac.uk/20723/.

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This research covers the granitoid rocks associated with the Archaean Barberton Greenstone Belt, Kaapvaal Craton, South Africa. The granitoid rocks were emplaced over a 500 Myr interval and can be divided into two suites. The TTG suite (emplaced ea 3.5 - 3.2 Ga) contains tonalites, trondhjemites and granodiorites, and the GMS suite (emplaced ca 3.2 - 3.1 Ga) includes granodiorites, monzogranites and a small syenite-granite complex. These rocks are important as they hold insights into the source rocks from which they were derived, the restitic materials that must have been produced as a result of magma generation, and the tectonic processes that operated during the Archaean. Geochemically, the TTGs are typically low- to medium-K, metaluminous I-type granitoids. Their chondrite-normalised rare-earth-element (REE) patterns show two trends. The majority of plutons are LREE-enriched and HREE-depleted (indicating the presence of garnet during magma genesis), with small or no Eu anomalies. The Steynsdorp and Doornhoek plutons, however, are relatively HREE-undepleted and have significant Eu anomalies. Highly scattered major- and trace-element trends against SiO[sub]2 imply that the TTG magmas were derived from heterogeneous sources. Nd isotope analyses show that the 3.4 Ga TTGs have positive [epsilon][sub]Nd values (O to +3.7), similar to the oldest greenstone belt formations of the Onverwacht. This indicates a juvenile crustal source for these oldest granitoids. In contrast, the 3.2 Ga TTGs have negative [epsilon][sub]Nd (O to -2.48), suggesting input from a more evolved crust. Partial melting experiments on greenstone amphibolite have been used to constrain the source-rocks of the TTGs. The results showed that granodioritic melts can be produced at 1.6 GPa, and 1000 °C, coexisting with eclogitic mineral assemblages of Grt + Opx + Cpx. Furthermore, the minimum pressure for the appearance of garnet has been constrained to 1.52 ± 0.05 GPa, corresponding to a depth of 52 ± 2 km. This has important implications, because it suggests that the majority of the TTG rocks were derived from greenstone amphibolite material at depths that correspond to greatly thickened mafic crust. The GMS rocks are medium- and high-K, metaluminous to slightly-peraluminous, I-type granitoids. They display two different groups of REE patterns. Medium-K GMS rocks (the Dalmein and Heerenveen monzogranite) are LREE-enriched and HREE-depleted, with no Eu-anomalies, whereas the high-K GMS rocks (Heerenveen granodiorites, Mpuluzi and Boesmanskop) are relatively HREE-enriched, with negative Eu anomalies. These indicate that the majority of the GMS magmas were derived at shallower crustal depths than the TTGs, after a period of post-orogenic, crustal thinning. Scattered major- and trace-element trends against SiO[sub]2, particularly in the Dalmein, Heerenveen and Mpuluzi plutons, suggest that their sources were heterogeneous. The Boesmanskop syenite has both positive and negative [epsilon][sub]Nd values (-4.4 to +4.8) implying that its source was mixed, containing both depleted-mantle and crustal components. Material such as alkali basalt magma and TTG-rich crust are considered to be likely source components. Contemporaneous emplacement of the Mpuluzi batholith and the Boesmanskop syenite suggests that the more potassic batholithic granitic magmas must have formed in the same tectonomagmatic setting as the syenite-granite complex. Zircon morphological and geochemical studies were undertaken to determine whether the TTG rocks were involved in the formation of the GMS rocks. However, the results were inconclusive. The local TTG rocks (or materials similar to them) may have been present in the source of the GMS magmas, but this cannot be demonstrated presently. Petrogenetic models for the magmas strongly suggest the operation of subduction in the Archaean, particularly as a driving force for collision and crustal thickening. The generation of TTG magmas is known to have occurred during periods of terrane collision or accretion (at ~3.50 and 3.23 Ga). Additionally, the results of the experimental studies show that the crust must have reached thicknesses of ~ 52 km to produce TTG magmas. The fact that there is strong evidence that mafic greenstone amphibolite rocks are the source-rocks of the TTG magmas implies that the TTG rocks were only derived from mafic oceanic crust. The petrogenesis of GMS rocks is more difficult to constrain. They were generated during periods of crustal thinning and strike-slip activity. The proposed petrogenetic model involves upwelling alkali basaltic magma, which induced partial melting of the TTG crust. Mixing of the crustal and mantle-derived magmas produced hybrids, and subsequent fractional crystallisation generated the monzogranitic/granodioritic magmas, as well as residual syenitic liquids.

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Wiemer, Daniel. "Tectonic evolution of the Early Archaean Doolena Gap Greenstone Belt, East Pilbara Terrane, Western Australia." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/102985/1/Daniel_Wiemer_Thesis.pdf.

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This thesis examined how the oldest core of the Australian continent formed more than 3.5 billion years ago. Unraveling the complex tectonic and petrologic history of ancient rocks of the East Pilbara in Western Australia provided important new insights into how and why continents developed on our hot, young planet. A multifaceted methodology of field-based structural geology, uranium-lead (U-Pb) dating of zircon, whole-rock geochemistry, and petrology improved our understanding of early Archaean mass and heat transfer, including the history of the associated planetary surface environment, which hosted some of the earliest life on Earth.

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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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Mellqvist, Claes. "Proterozoic crustal growth along the archaean continental margin in the Luleå and Jokkmokk areas, northern Sweden /." Luleå, 1999. http://epubl.luth.se/1402-1544/1999/24/index.html.

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Crewe, M. A. "The petrogenesis of Archaean basic and ultrabasic rocks from Ujaragssuit nunat, Ivisartoq region, southern West Greenland." Thesis, University of Exeter, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372574.

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Gilligan, Jonathan Mark. "The geology, geochemistry and genesis of gold mineralization associated with Archaean iron-formation, Lennox mine, Zimbabwe." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292080.

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Snape, Ian. "Geological and geochemical anatomy of Archaean gneisses from the Vestfold Hills and Rauer Group, East Antarctica." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/14437.

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Archaean orthogneisses in the Rauer Group and Vestfold Hills have been examined through a combined field, petrological, geochemical and isotopic study in order to document and evaluate regional terrane correlations in the East Prydz Bay region of East Antarctica, and assess models for early Precambrian crustal growth, both regionally and in general terms. Within the Archaean domain in the Rauer Group, two layered ultramafic-mafic associations, the Torkler-Tango and the Scherbinina Layered Complexes (TTLC & SLC), are hosted in ca. 2800 to 3300-3470 Ma Composite Layered Orthogneiss (CLO). The SLC and TTLC are spatially, compositionally and probably temporally separate metaigneous suites. The TTLC is older than ca. 2800 Ma CLO intrusive sheets, and geochemical similarities between the TTLC and ca. 3300 Ma tonalite-trondhjemite-granite components of the CLO imply that there may be a genetic link between these gneiss units, as both have distinctive arc-like geochemical signatures. The SLC is also cross-cut by ca. 2800 Ma CLO components, but SHRIMP U-Pb zircon dating of the complex reveals that it is only marginally older with a crystallization age of 2844 ± 6 Ma. Geochemically, the SLC has very weak arc-like signatures which are attributed to small amounts of crustal contamination (by CLO), and primary geochemical signatures are inferred to have been derived from an E-MORB-like source. A tectonomagmatic setting similar to that deduced for the early Tertiary East Greenland Margin is envisaged as a possible analogue for events at 2844 Ma in the Rauer Group. However, petrogenetic models for the Rauer Group Archaean domain are tentative, because Sr and Nd isotopes indicate that significant open-system behaviour occurred during fluid infiltration associated with a regionally recognised Pan-African (ca. 500 Ma) event. Detailed mapping of intrusive relations that are preserved in Archaean othogneisses in the Vestfold Hills has allowed a reconstruction of the early high-grade geological history of the terrane. A number of spatially, temporally and compositionally distinct intrusions were emplaced throughout the Crooked Lake magmatic episode between D₁-M₁ and D₂-M₂. The duration of this episode has been precisely defined by SHRIMP U-Pb dating axial planar leucosomes to 2496.3 ± 0.7 Ma (D₁-M₁) and 2475.3 ± 0.7 Ma (D₂-M₂). The distribution of Crooked Lake Gneiss (CLG) indicates that regional-scale tectonic repetition of major units was local rather than regional, and the amount of strain associated with the main folding and fabric producing event (D₂) is heterogeneous.

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Maxlow, James. "Quantification of an Archaean to Recent Earth Expansion Process Using Global Geological and Geophysical Data Sets." Thesis, Curtin University, 2001. http://hdl.handle.net/20.500.11937/2423.

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Global geological and geophysical data, while routinely used in conventional plate tectonic studies, has not been applied to models of an expanding Earth. Crustal reconstructions on Archaean to Recent models of an expanding Earth presented here are the first time that reconstructions have been extended back to the Archaean, and the first time that continental and oceanic geology has been utilised to constrain plate assemblage and palaeoradius of the Earth. A set of twenty four spherical models have been constructed, twenty three covering the Archaean to Recent and one projected to five million years into the future. Construction of these spherical models relies on the fundamental premise that crustal lithosphere is cumulative with time, and historical markers preserved in the oceanic and continental geology accurately constrain both palaeoradius and plate reconstruction from the Archaean to Recent. Post-Triassic reconstructions of oceanic lithosphere demonstrate a plate fit together along each plate margin at better than 99% fit. During the Triassic, continents envelope the Earth as a complete continental shell at a reduced Earth radius, and marginal and epi- continental sedimentary basins merge to form a global network surrounding continental cratons and orogenic zones. Continental crust is reconstructed on Pre-Jurassic models using the primary crustal elements of cratons, orogens and basins, with expansion primarily manifested as crustal extension within an established network of epi-continental rifts, orogens and sedimentary basins. By removing all basin and pre-orogenic sediments a primordial proto-Earth at a palaeoradius of approximately 1700 kilometres is achieved during the Mesoproterozoic, comprising assembled cratons and Proterozoic basement rocks.For all models, an intracratonic to intracontinental spatial integrity is maintained throughout Earth history during processes of Precambrian and Palaeozoic continental crustal extension, Late Palaeozoic crustal rupture, Permo-Triassic continental break-up, and Mesozoic and Cenozoic continental dispersal to the Recent. Palaeomagnetic pole data delineate diametrically opposed palaeomagnetic pole clusters for each era back to the Archaean, without the need to consider random crustal dispersion-amalgamation-dispersal cycles. The palaeopole data is further supported by palaeogeographic, palaeobiogeographic, and palaeoclimatic indicators, which define palaeoequators and palaeoclimatic zones consistent with palaeomagnetic determinations. The distribution of latitude dependent lithofacies including glacigenic strata, carbonates, coal, and faunal and floral species is shown to coincide precisely with established palaeopoles and palaeoequators for all expanding Earth models. For climatic and biotic indicators a distinct latitudinal zonation paralleling the established palaeoequator is evident and a distinct northward shift in climatic zonation suggests that an inclined Earth rotational axis, inclined to the pole of the ecliptic, was well established during the Palaeozoic and persists to the Recent. Coastal geography on expanding Earth models shows that large Panthallassa, Tethys and Iapetus Oceans are not required during reconstruction. Instead, epi-continental Panthallassa and lapetus Seas represent precursors to the modem Pacific and Atlantic Oceans and the Tethys Sea represents a precursor of the present Eurasian continent.Emergent land surfaces during the Precambrian and Phanerozoic equate to the conventional Rodinia, Gondwana and Pangaea supercontinents and smaller subcontinents, and demonstrate a spatial intracratonic and intracontinental integrity throughout Earth history. On each spherical model constructed proto-continental development is evolutionary and defined by a progressive extension of epi-continental sedimentary basins, pulsed orogenesis, eustatic and transgression-regression of epi-continental seas, and opening of modem oceans during the Mesozoic to Recent. Metallogenic modelling of Precambrian and Phanerozoic metal deposits shows a broad global Precambrian metallogenic provinciality coinciding with cratons and intracratonic settings, to regional provinces clustering as specific metal associations. The Phanerozoic metallogenic distribution highlights the abundance of porphyry and granite associated metals concentrated within Phanerozoic orogenic belts, and orogenic belts are shown to crosscut and displace pre-existing Palaeozoic and Precambrian metallogenic provinces. A proposed causal model for Earth expansion has expansion due to an exponential increase in mass with time. Earth expansion then involves an increase in mass by condensation, or segregation of new matter from the Earth's core. This new matter accumulates at the core-mantle interface and the increase in volume results in a swelling of the mantle, which is then manifested in the outer crust as crustal extension. Matter generation within the Earth's core is seen as an endothermic reaction, which will ultimately result in a decay of the matter formation process and cessation of expansion with time.

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Maxlow, James. "Quantification of an archaean to recent earth expansion process using global geological and geophysical data sets /." Full text available, 2001. http://adt.curtin.edu.au/theses/available/adt-WCU20020117.145715.

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Hofmann, Axel. "Sedimentology and tectonic history of late Archaean sedimentary successions in Zimbabwe a study in greenstone belt geology /." [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2002/0026/diss.pdf.

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Woodhouse, Ailsa Jane. "Provenance of late archaean metasedimentary rocks on the southern Gawler craton : implications for its early crustal development /." Title page, table of contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09SB/09sbw889.pdf.

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Zulbati, Petrillo Fabio. "P-T-fluid conditions of an end-Archaean granulite-facies metamorphism in the Vestfold Hills, East Antartica." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/13259.

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Burke, Shyne Duncan Caleb Padraig. "On carbonate alteration zones in a greenstone keel of the East Pilbara Terrane (Doolena Gap Greenstone Belt)." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/107570/1/Duncan_Burke%20-%20Shyne_Thesis.pdf.

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This thesis examines the origin and relative timing of carbonate alteration zones in the poly-deformed Doolena Gap Greenstone Belt in the East Pilbara Terrane, the type locality of Archaean dome-and-keel-terranes. The key findings are: [1] shear-assisted carbonate alteration occurred throughout the entire tectonic history of the greenstone belt; and [2] weak pre- and syntectonic carbonate minerals make up 40 to 60% of the examined greenstone rocks. These outcomes imply that carbonate minerals likely controlled the strength of Archaean lithosphere.

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Rich, Benjamin H. "An investigation of the Archaean Wangary Gneiss and its relevance to the evolution of the southern Gawler Craton /." Title page, abstract and contents only, 2000. http://web4.library.adelaide.edu.au/theses/09SB/09sbr498.pdf.

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Winter, Caroline Jane. "Geology and base-metal mineralization associated with Archaean iron-formation in the Pojuca Corpo Quatro deposit, Carajas, Brazil." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241182.

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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 hoÃ« 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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Bullen, Warwick David. "Gold mineralization in an archaean granite-greenstone remnant west of Melmoth, Natal ore genesis and implications for exploration." Thesis, Rhodes University, 1991. http://hdl.handle.net/10962/d1005579.

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The previously undifferentiated, "Melmoth Granite-Greenstone Remnant" (MGGR¹) crops out over an area of about 360 km² in northern Natal, South Africa. The greenstone sequence is comprised mainly of mafic metalavas with lesser serpentinite, talc schist, dacitic tuff, quartz-muscovite schist, quartzite and calc-silicate rocks. The greenstones are intruded by syntectonic trondhjemitic gneisses, late-tectonic granodioritic gneisses and post-tectonic granite dykes. Four phases of deformation and metamorphism are recognized. Epigenetic, disseminated and quartz vein-hosted gold mineralization is associated with D₂ shearing - a positive correlation existing between the intensity of the shearing, the thickness of the shear zone and the grade of ore it contains. Auriferous quartz veins are distinguished from an earlier generation of barren vein quartz on the basis of mineralogy, texture and relationship to the s-fabric. The mineralization occurs in zones of dilation associated with shear zone refraction. Associated wall rock alteration includes sericitization, argillization and chloritization. An ore genesis model based on the aforementioned parameters, is proposed. Finally, an exploration programme has been devised in order to locate undiscovered gold deposits in the MGGR. The programme could probably be applied, with minor modifications, to shear zone-hosted gold deposits in other granite-greenstone remnants in northern Natal. ¹- Name suggested by writer.

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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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Green, Michael Godfrey. "Early Archaean crustal evolution: evidence from ~3.5million year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia." University of Sydney. Geosciences, 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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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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38

Summers, Michael Alan. "The geochemistry and petrogenesis of palaeoproterozoic mafic and ultramafic intrusions of the central Laramie mountains, Wyoming Archaean Province, USA." Thesis, University of Portsmouth, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310469.

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39

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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40

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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41

Iwaniw, Andrew Mark. "Evidence of recycling of Archaean continental crust : a geochemical and Nd-Sr isotope study of Gawler Craton Granitoids, South Australia /." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09SB/09sbi9663.pdf.

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42

Lundmark, Christina. "Vaikijaur, a palaeoproteroic Cu-Au porphyry style mineralization in the Jokkmokk granitoid at the archaean-proterozoic boundary in northern Sweden." Licentiate thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25764.

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The Jokkmokk granitoid is exposed in a plutonic massif northwest of Jokkmokk in northern Norrbotten. It is light grey to white, fine-grained, with megacrysts of feldspar and glomeroporphyritic hornblende and biotite. Small enclaves of mafic rocks and synplutonic mafic dykes are products of mingling with a coeval and possibly cogenetic mafic magma. A couple of smaller occurrences of Jokkmokk-type granitoid are known south of Jokkmokk. All are spatially associated with metasedimentary rocks of the Norvijaur formation. The Jokkmokk granitoid was previously considered to belong to the c.1.8 Ga Lina S-type intrusive suite, but the Jokkmokk granitoid has a unique calc-alkaline to alkali-calcic, metaluminous to weakly peraluminous character with a steep REE-profile, positive Eu-anomaly, and a low Zr content. U-Pb TIMS zircon dating of the Jokkmokk granitoid gives an age of 1882 +-19 Ma which is within limits the same age as that obtained for the Haparanda suite, but contrary to the Haparanda suite it has a positive epsilon Nd value of 2.8, indicating a more juvenile Palaeoproterozoic character similar to the Jörn suite in the Skellefte district. Compared to other granitoids in the Jokkmokk area it is geochemically most similar to the older 1.93 Ga Norvijaur granitoid. This type of magma seems to be restricted to the palaeoboundary between the Archaean craton in the north and Palaeoproterozoic juvenile crust in the south. Spatial correlation with low angle, south dipping, WNW-trending shear zones and NNE-trending subvertical shear zones, highlight the possibility that this unique magma type is related to transtension in the overriding plate and partial melting in sub-arc mantle wedge during NE directed subduction processes related to the early stages of the Svecokarelian orogen. Possibly magma was ponded in shallow chambers below pull-apart basins in a transtensional regime. This type of setting has been advocated as the potentially most favourable tectonic setting for porphyry copper formation. The Cu-Au-(Mo) mineralization at Vaikijaur northwest of Jokkmokk covers an area of 2 by 3 km within the western part of the Jokkmokk granitoid pluton. The mineralization is characterized by dissemination and veinlets of chalcopyrite, pyrite, molybdenite, magnetite, pyrrhotite, and sphalerite. Quartz stockwork with or without sulphides occur in the mineralization. Gold occurs as free grains in silicate matrix, in contact with chalcopyrite, pyrite and sphalerite, or as inclusions within the chalcopyrite. Porphyritic mafic dykes, with phenocrysts of plagioclase and porphyroblasts of magnetite, follow fractures in an almost concentric pattern in the mineralized area. The fabric in the granitoid, dykes, and mineralization shows that the mineralization predates the main regional deformation. Geophysical ground measurements indicate a strong conductive central zone in the mineralized area bordered by both conductive and magnetic zones. Restricted drilling campaigns were carried out in these zones in 1981-83. Chemical and mineralogical analyses of drillcores and outcrops indicate several stages of alteration and a metal zoning at Vaikijaur. The entire mineralized area is affected by potassic alteration. Hornblende is partly or totally replaced by biotite, and plagioclase is partly replaced by microcline. In irregular propylitic alteration zones that overprint the potassic alteration, epidote has replaced plagioclase and hornblende is replaced by epidote and biotite. Biotite is partly chloritized and calcite is common. Light-coloured, irregular phyllic alteration zones overprint the former alteration types, with quartz and sericite replacing plagioclase. A metal zoning can be seen with a pyrite-rich inner part of the mineralized area surrounded by a zone with pyrite, chalcopyrite and gold. Molybdenite occurs in an irregular pattern within the chalcopyrite zone, magnetite is present in both the pyrite and the chalcopyrite zone.
Godkänd; 2003; 20070215 (ysko)

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43

Linklater, Michael Anthony Leonard Flanders. "The exploration for and possible genesis of, some Archaean granite/gneiss-hosted gold deposits in the Pietersburg granite-greenstone terrane." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005557.

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Abstract The gold mineralization event within Archaean granite-greenstone terranes occurred during the late Archaean, and followed the intrusion of syn- to late-tectonic granitic plutons into previously deformed greenstone belts. An Archaean granite/gneiss-hosted gold deposit, in terms of this project, is classified as having a gold-assay cutoff of 1g/metric ton over widths of at least several metres, or higher grades over narrower widths and/or verbal descriptions that indicate such values. Fluid inclusion studies and isotopic data identify two possible origins for the auriferous fluids; namely magmatic and metamorphic. The exploration target according to the magmatic model, is a late-Archaean, hydrothermally altered, mineralized and fractured granitic intrusion preferably with a granodioritic or quartz-dioritic composition. The exploration target according to the metamorphic replacement model is a granitic stock that has intruded a zone of crustal weakness such as a shear zone, active during the late Archaean. Alternatively, the granitic intrusion should be affected by regionally extensive late-Archaean shearing. It should be hydrothermally altered, deformed and mineralized. Five areas within the Pietersburg granite-greenstone terrane were selected for the 'Regional Area Selection' phase of exploration for Archaean granite/gneiss-hosted gold deposits; namely Roodepoort, Waterval, Ramagoep, Moletsie and Matlala. Roodepoort contains a known granodiorite-hosted gold deposit; the Knight's Pluton, and served as an orientation survey for this project. The use and interpretation of LANDSAT images formed an integral part of exploration techniques; to assess their usefulness in the exploration of Archaean granite/gneiss-hosted gold deposits. Area selection criteria for granite/gneiss-hosted gold mineralization at Roodepoort are the major ENE-trending shear zone, the NNW-trending lineament and hydrothermal alteration, shearing, quartz-stockworks and sulphide mineralization within the Knight's Pluton. The origin of the gold within the Knight's Pluton is uncertain; both magmatic and metamorphic models are possibilities. Ongoing exploration is in progress at Roodepoort. The only area selection criterion for granite/gneiss-hosted gold mineralization at Waterval is the sericitized, subcropping granites located within trenches. Gold mineralization is insignificant. No area selection criteria for Archaean granite/gneiss-hosted gold mineralization were located at Ramagoep, Matlala and Moletsie. No further exploration is recommended for all these areas. The MES image interpretations were successful in identifying lineaments, granitic outcrops, greenstones, vegetation and soil cover. The Clay-iron images adequately differentiated betweeen iron-rich and clay-bearing areas. However, not all clay-bearing areas were associated with hydrothermal alteratian; field checks were necessary to discriminate between weathered granites and hydrothermally altered granites. The Wallis images served to locally enhance the contrasts of the MES and Clay-iron images.

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Wenham, Lana May. "Putting absolute, in-situ U-Pb ages to early-Archaean deformation events in the Muccan Granitic Complex, East Pilbara Terrane." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/120829/2/Lana_Wenham_Thesis.pdf.

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This project dated an Early Archaean partial convective overturn (tectonic) event in the East Pilbara Terrane, giving the first direct age for this event. Petrology, geochemistry and geochemistry techniques were combined in an exemplar case study of how to date deformation events in complex, poly-deformational rocks using the accessory mineral titanite.

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45

Swain, Greg Martin. "Provenance and tectonics of the late Archaean mulgathing complex, central Gawler Craton : geochronological, geochemical and isotopic evidence for plume-arc interaction /." Title page, table of contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09SB/09sbs9715.pdf.

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46

Salimo, Luckmore. "Gold mineralisation at Masumbi Au-Cu Prospect, west Kenya : implication for gold exploration in the Archaean Ndori Greenstone Belt of Kenya." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1020961.

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The Masumbi Au-Cu deposit in the Ndori Greenstone Belt of western Kenya is hosted in dacitic volcanics of the Nyanzian Group (2710 ± 340 Ma) and dioritic to granodioritic felsic intrusives (2504 ± 48 Ma). The deposit is characterised by gold and copper mineralisation that is associated with quartz-sulphide veins and veinlets. The copper mineralisation typically occurs as chalcopyrite. Gold is closely associated with pyrite in mineralogy and its pathfinder elements silver, bismuth, tellurium and selenium in geochemistry. The gold occurs in two forms that may indicate two generations of precipitation: the equant and the elongate forms. Based on Au/Ag ratios, the equant gold grains can be classified as native gold as their gold content is greater than 90 wt%. The elongate gold grains can be classified as electrums as their silver content is greater than 38 wt%. While there is a strong Au-Ag association within individual gold grains supporting an orogenic model for the gold mineralisation, mineralisation at the Masumbi Prospect appears atypical of Archaean orogenic gold deposits because of the abundance of copper (up to 0.43%). The enrichment of silver, copper, bismuth and tellurium in ore assemblages is common in porphyry, VMS and epithermal systems, but their presence at Masumbi does not preclude the formation as an orogenic deposit. Assay results from three Masumbi diamond drill-holes show an apparent correlation between gold and copper. However, petrography and electron probe microanalyses results from this study indicate that chalcopyrite is an earlier phase than pyrite as it occasionally occurs as inclusions in pyrite. This petrogenetic relationship between pyrite and chalcopyrite suggests that there is no temporal relationship between gold and copper mineralisation. Statistical analysis of the assays shows no linear correlation between gold and copper thereby supporting the above findings. The gold and copper mineralisation have been interpreted as forming as two separate events with copper forming first followed by gold. These events are both related to the intrusion of the felsic rocks that are associated with the Aruan metamorphic event that has been responsible for the bulk of the gold mineralisation on the Tanzanian Craton. The common alteration assemblage in the Masumbi rocks comprises chlorite and epidote. This alteration assemblage is typical of regional greenschist metamorphic facies grading into amphibolite metamorphic facies in the Nyanzian Group of Kenya. However, these alteration minerals could possibly be products of propylitic alteration in the rock groundmass. Other alteration mineral assemblages, possibly of hydrothermal origin, comprise muscovite, sericite, quartz, carbonate, associated with the sulphides pyrite and chalcopyrite. Although the occurrence of gold appears to be controlled by the presence of pyrite, it is also associated with silicification. Exploration methods have been proposed to target undiscovered gold deposits in the Ndori Greenstone Belt that are similar to the Masumbi deposit. These methods could probably be applied to vein-type gold deposits in other granite-greenstone terranes in the Lake Victoria Goldfields.

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47

Berger, Stefanie [Verfasser]. "Energy conservation in aceticlastic methanogenic archaea and the human gut archaeon Methanomassiliicoccus luminyensis / Stefanie Berger." Bonn : Universitäts- und Landesbibliothek Bonn, 2015. http://d-nb.info/1077290292/34.

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48

Oliver, Hazel S. "The geochemical and tectono-magmatic evolution of the volcanic and intrusive rocks of the Archaean Shining Tree greenstone belt, Abitibi subprovince, Ontario, Canada." Thesis, University of Portsmouth, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271459.

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49

De, Joux Alexandra. "Cosmos greenstone terrane : insights into an Archaean volcanic arc, associated with komatiite-hosted nickel sulphide mineralisation, from U-Pb dating, volcanic stratigraphy and geochemistry." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8918.

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The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore bodies. These are commonly associated with felsic volcanic successions, many of which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The Cosmos greenstone sequence lies on the western edge of the AWB and this previously unstudied mineralised volcanic succession contrasts markedly in age, geochemistry, emplacement mechanisms and probable tectonic setting to that of the majority of the AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the Cosmos mineralised ultramafic sequence consists of an intricate succession of both fragmental and coherent extrusive lithologies, ranging from basaltic andesites through to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick sequences of amygdaloidal intermediate lavas intercalated with extensive sequences of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic products, indicates the succession was formed in a subaerial environment. Chemical composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional crystallisation modelling has shown that at least two compositionally distinct sources must be invoked to explain the observed basaltic andesite to rhyolite magma suite. High resolution U-Pb dating of several units within the succession underpins stratigraphic relationships established in the field and indicates that the emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma, making it significantly older and longer-lived than most other greenstone successions within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos succession either represents a separate, older terrane in its own right or it has an autochthonous relationship with the AWB but volcanism initiated much earlier in this region than currently considered. Dating of the Cosmos succession has demonstrated that high-resolution geochronology within individual greenstone successions can be achieved and provides more robust platforms for interpreting the evolution of ancient mineralised volcanic successions. The geochemical affinity of the Cosmos succession indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma, much earlier than considered in current regional geodynamic models. The Cosmos volcanic succession provides further evidence that plate tectonics was in operation during the Neoarchaean, contrary to some recently proposed tectonic models.

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Pesch, Katja [Verfasser], Franz Michael [Akademischer Betreuer] Meyer, and Peter A. [Akademischer Betreuer] Kukla. "Processes of seafloor hydrothermal alteration in the Archaean oceanic crust of the Barberton greenstone belt, South Africa / Katja Pesch ; Franz Michael Meyer, Peter A. Kukla." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1158599501/34.

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Dissertations / Theses on the topic 'Archaean'

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