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Die Rekonstruktionen der präkambrischen Superkontinente Columbia, Rodinia und Gondwana zeigen, dass der afrikanische Kontinent eine Collage von archaischen kratonischen Kernen ist, welche durch ein Netzwerk von jüngeren Gebirgsgürteln mit paleo-, meso- und neoproterozischen Altern voneinander getrennt sind, die den genannten Superkontinent-Zyklen zugeordnet werden. Durch petrologische Untersuchungen, die mit texturell kontrollierten Monazitdatierungen kombiniert werden, wird in dieser Arbeit versucht, die P-T-t-Entwicklung von ultrahoch temperierten Metamorphoseereignissen in drei verschiedenen afrikanischen Orogenen abzuleiten, um deren Entwicklung und ihre Beziehung zu den Superkontinent-Zyklen besser zu verstehen. 1) Das archaische und paleoproterozoische Grundgebirge im zentralen Teil des ‚East Shara Ghost Craton’ (ESGC) bei Uweinat-Kamil; 2) der neoproterozoisch überprägte östliche Rand des ESGC im Sudan (Sabaloka und Bayuda); 3) der mesoproterozoische ‚Southern Irumide Belt’ in Sambia. Die Texturen in metapelitischen Granuliten des Uweinat-Kamil Inliers, deuten auf eine zweistufige metamorphe Entwicklung hin: Stadium-1 führte zur Bildung von Sapphirin+Quarz+Granat unter ultrahohen Temperaturen (UHT) von ~1050 °C bei ~10 kbar und wurde gefolgt von isobarer Abkühlung. Während Stadium-2 erfuhren die Gesteine eine isotherme Dekompression von etwa 9 auf 6 kbar, ebenfalls unter ultrahohen Temperaturen (900-1000 °C), welche zur Bildung von verschiedenen Symplektiten führte und die von isobarer Abkühlung gefolgt war. Monaziteinschlüsse in Granat-1-Porphyroblasten der Metapelite ergaben ein Alter von ca. 2.6 Ga für des Stadium-1. Stadium-2 fand 700 Ma später als Stadium-1 vor etwa 1.9 Ga statt, wie die Monazitdatierung in der Gesteinsmatrix und in Symmplektiten ergab. Somit wurde durch diese Arbeit erkannt, dass die einzigen archaischen kratonischen Gesteine in Nordost-Afrika eine bisher unbekannte neoarchaische UHT-Metamorphose und eine paläoproterozoische UHT-Überprägung erfuhren. Wegen der Ähnlichkeit mit anderen paläoproterozoischen orogenen Ereignissen auf der Erde, die mit der Bildung Columbias verknüpft waren, sollte die paläoproterozoische Entwicklung in Nordost-Afrika bei zukünftigen Rekonstruktionen dieses Superkontinents berücksichtigt werden. Am Ostrand des ‚East Sahara Ghost Cratons’ erfuhren die Gesteine von Sabaloka und von Bayuda jeweils zwei verschiedene Metamorphosen, die in Bayuda älter und von geringerer Intensität waren als in Sabaloka. In Sabaloka zeigen Monaziteinschlüsse in Granat auf ein frühes neoproterozoisches Hochtemperatur- Krustenverdickungsereignis (700-850 °C, ~6 kbar) vor 780-720 Ma, während Monazitkörner in späten Cordierit-Spinell-Symplektiten auf eine ultrahoch-temperierte Überprägung (850-950 °C) vor ca. 602 Ma hindeuten. In Bayuda deutet die Monazitdatierung von pelitischen Schiefern auf ein krustenverdickendes, amphibolitfazielles Ereignis vor ~890 Ma hin und auf ein späteres Ereignis bei ca. 670 Ma, das zur Rekristallisation von einigen Matrixmineralen führte. Somit waren die tektonometamorphen Ereignissse entlang des Ost-Randes des ESGC sehr heterogen, in zeitlicher Hinsicht und auch in ihrer Intensität. Das bedeutet, dass die panafrikanischen Orogene in Nordost-Afrika während der Bildung von Gondwana durch verschiedene lokale tektonische Ereignisse gebildet wurden. Die neoproterozoischen Ereignisse, welche den Ostrand des ESGC betrafen, wurden nicht im zentralen Teil des ESCG (Uweinat) beobachtet. Wenn man die neuen Erkenntnisse über Uweinat, Sabaloka und Bayuda kombiniert, kommt man zu dem Schluss, dass es wahrscheinlicher ist, dass die vorgeschlagene Delamination des subkontinentalen lithosphärischen Mantels des gesamten ESGC (was eine gleichzeitige orogene Überprägung im gesamten Kraton erfordern würde), nicht gleichzeitig erfolgte, sondern durch verschiedene orogenen Ereignisse in verschiedenen Teilen des Kratons verusacht wurde. Für die metapelitischen Granulite im ‚Southern Irumide Belt’ (SIB) haben die Untersuchungen eine einstufige UHT-Metamorphose ergeben, die während der mesoproterozoischen Irumiden-Orogenese stattfand. Spinell-Quarz-führende Paragenesen und hohe Al-Gehalte (7.9 Gew.%) in Orthopyroxen deuten auf eine UHT-Metamorphose bei 900-1000 °C bei ~6 kbar hin. Monazitkörner in verschiedenen texturellen Positionen (Einschlüsse in Granat, Matixkörner) ergaben Alter zwischen 1067±15 und 1013±4 Ma für das UHT-Ereignis, was also gleichaltrig mit dem assoziierten granitoiden Kontinentalrand-Magmatismus (~1090-1000 Ma) ist. Die Druck-Temperatur-Entwicklung im SIB unterscheidet sich deutlich von den Entwicklungen anderer mesoproterozoischer Orogene in Afrika, welche entweder durch eine sehr lang andauernde (~1200-1000 Ma) oder eine zweistufige Hochtemperatur-Geschichte (mit einer fast 200 Ma andauernden Unterbrechung) gekennzeichnet sind. Der SIB entstand an einem aktiven Kontinentalrand eines südlich gelegenen unbekannten Kratons, der thermisch von subduktionsbezogenem Magmatismus beeinflusst wurde und dann mit dem nördlich gelegenen Bangweulu Kraton während der Irumiden-Orogenese kollidierte. Diese Orogenese stand im Zusammenhang mit der Bildung des Superkontinents Rodinia. Zusammenfassend kann festgestellt werden, dass in dieser Arbeit demonstriert wird, wie texturell kontrollierte Monazitdatierungen in Kombination mit detaillierten petrologischen Untersuchungen in der Lage ist, mit hoher Auflösung die P-T-t Entwicklung von metamorphen Gesteinen zu entziffern. Die genaue Rekonstruktion gelingt sogar für hochgradige Gesteine der tiefen Kruste von Orogenen, die mehrfach überprägt wurden. Reconstructions of the Precambrian supercontinents Columbia, Rodinia and Gondwana reveal that the African continent is a collage of Archean cratonic nuclei, which are separated by a network of orogenic belts of Paleo-, Meso- and Neoproterozoic ages, related to these supercontinent cycles. Using integrated petrological studies and texturally controlled monazite dating, this thesis aims to investigate the metamorphic P-T-t evolution of three ultra high-grade (UHT) terranes from the African continent for a better understanding of orogenic processes related to the various supercontinent cycles. 1) The Archean and Paleoproterozoic basement complex in the central East Sahara Ghost Craton (ESGC) at Uweinat-Kamil; 2) The Neoproterozoic overprinted eastern margin of the ESGC in Sudan at Sabaloka and Bayuda; 3) the Mesoproterozoic Southern Irumide Belt (SIB) of Zambia. Petrographic textures in metapelitic granulites from the Uweinat-Kamil inlier suggest a two-stage metamorphic evolution. Stage-1 saw the growth of sapphirine+quartz+garnet 1 at ultra-high temperatures (UHT) of ~1050 ̊C at ~10 kbar, followed by near isobaric cooling. During stage-2 the rocks experienced near isothermal decompression from ~9 to ~6 kbar at ultra-high temperatures of 900-1000 ̊C, which led to the formation of various symplectitic assemblage, followed again by near isobaric cooling. Monazite inclusions within garnet 1 porphyroblasts from the metapelitic granulites reveals that stage-1 occurred at ~2.6 Ga. Stage-2 occurred 700 million years later at ~1.9 Ga, as indicated by monazite grains in symplectites and the matrix. Thus the study highlights a previously unknown Neoarchean UHT metamorphism and a Paleoproterozoic UHT reworking of the only known Archean cratonic crust of northeast Africa. Owing to its similarity with other Paleoproterozoic orogens around the world, the Paleoproterozoic evolution of the Uweinat-Kamil inlier in northeast Africa should also be taken into account in future Columbia reconstructions. Along the eastern margin of the ESGC, at Sabaloka and Bayuda, four different metamorphic events are recorded. The two events in Bayuda are older and of lower intensity than the two in Sabaloka. At Sabaloka, monazite inclusions in metapelitic garnet record the timing of an early Neoproterozoic (780-720 Ma) high temperature crustal thickening event at ~700–850 °C, ~6 kbar, while monazite grains in cordierite-spinel symplectites indicate the timing of a Neoproterozoic ultra-high temperature overprint (~850–950 °C, 6–3 kbar) at ~602 Ma. Monazite dating of pelitic schists from Bayuda revealed an amphibolite-facies crustal thickening at ~890 Ma and a later event at ~670 Ma. The study thus indicates that the Neoproterozoic tectonometamorphic events along the eastern margin of the ESGC were heterogeneous, both temporally and in their intensity, indicating that the Pan-African “orogeny” in northeast Africa during Gondwana formation, is a complex series of orogenic events of varying intensities controlled by local tectonic elements and that the Neoproterozoic orogenic events, affecting the eastern margin of the ESGC, were not recorded in the central ESGC (Uweinat). Combining the results of Uweinat, Sabaloka and Bayuda, it is more likely that the proposed delamination of the subcontinental lithospheric mantle of the entire ESGC (which requires synchronous collisional events in the entire craton) was not coeval and was likely caused by different orogenic events in different parts of the craton. In southern Africa, similar integrated petrological and geochronological studies of metapelitic granulites from the Chipata Terrane of the SIB revealed a single stage UHT metamorphism during the Mesoproterozoic Irumide orogeny. Spinel + quartz association and high Al2O3 contents in orthopyroxene (7.9 wt%) point to UHT metamorphism at 900-1000°C (UHT) and ∼5-6 kbar. Monazite grains occurring in different textural settings (inclusions in garnet, and matrix) revealed ages between 1067±15 to 1013±4 Ma for the UHT event, synchronous with the continental margin granitoid magmatism (~1090-1000 Ma). The P-T-t evolution of the SIB is in contrast with the evolution of other known Mesoproterozoic belts of Africa, characterized by either a long lasting (1200-1000 Ma) or bimodal (with ~200 Ma time gap) high-temperature history during the Mesoproterozoic. The SIB represents an active continental margin of an unknown craton in the south that was thermally affected by subduction related magmatism and collided with the Bangweulu Craton during the Mesoproterozoic Irumide orogeny, related to the formation of the supercontinent Rodinia. The present study thus demonstrates that texturally controlled in-situ monazite dating, integrated with detailed petrological investigations is an extremely powerful tool in deciphering the P–T–t evolutionary histories, especially for high-grade deep crustal rocks, and allows high-resolution and precise reconstruction of the geodynamic evolution of polyorogenic mountain belts.

Namakwa Sands is a mining company operating on the west coast of South Africa, producing zircon, rutile and ilmenite. Heavy mineral sands are extracted by wet gravity, magnetic and electrostatic separation. In order to maintain their zircon product specifications, particularly with respect to radioactivity, the reject stream may still contain significant grades of zircon but is associated with penalty elements such as titanium dioxide (TiO2), uranium (U) and thorium (Th). The radioactive components U and Th are associated with the mineral monazite and cause issues in handling and disposal of the material.If monazite could be removed from the reject stream, the remaining material could potentially be sold as a low-grade zircon product. Furthermore, monazite is a valuable mineral in itself due to its content of rare earth elements such as cerium and lanthanum, which are valued in the nuclear and wind-power industries. The separation of monazite from the zircon reject stream is therefore desirable to Namakwa Sands from both an economic and an environmental perspective, by reducing the amount of waste and increasing revenue. Flotation of heavy minerals is rarely practiced due to the effectiveness of gravity and electrostatic separation of coarse particles. However, the physical separation at Namakwa Sands is challenged by fine particle sizes and surface coating issues affecting the surface properties and thus the separation. Froth flotation, which operates within finer particle sizes, is a possible separation method that in combination with surface attrition could selectively separate monazite.The objective of this project is to investigate the use of reverse froth flotation to separate monazite from the final zircon reject stream to obtain a higher-grade zircon product that meets product specifications. The accompanying investigation of the mineralogy and surface coatings of the material will also be critical in understanding the effect of the flotation factors on the success of monazite flotation. This project is broadly divided into two phases of flotation experiments with an accompanying mineralogical investigation of the flotation products. In the first phase of the project, the aim was to find flotation conditions where monazite could selectively be removed from the pulp, i.e. by using reverse flotation. A statistical screening design in the statistical software MODDE (©Umetrics) was used to find the significant parameters and the optimum flotation settings. The investigated parameters were pH, collector type, collector dosage, depressant type, depressant dosage and ultrasonication. The most common monazite collectors in flotation were reported to be oleates, hydroxamates and amine based collectors. More specifically, oleate and hydroxamate collectors have been used for the separation of monazite and zircon, and were therefore the collectors that were used in the first phase.In the second phase of the project, fewer parameters, and narrower intervals were used. More intense mechanical attritioning was also applied in this phase using a custom-built mini pin mill. In two full factorial designs, collector dosage, depressant dosage, pH and attrition intensity were studied.The hydroxamate collector was found not to be selective for any of the minerals, but the oleate collector could selectively recover monazite at a pH of 10 and a collector dosage of 180 g/ton. Further investigation showed that an oleate collector dosage of 315 g/ton resulted in a monazite recovery of 55.6%. The best monazite grade was 71.7% with the oleate collector at a dosage of 215 g/ton and a pH of 10, however the recovery was low with 28.4%. Results showed that selectivity was highly dependent on pH. At a pH value of 9, no selectivity was obtained, and more than 50 % of the pulp was recovered to the concentrate in three minutes. An increase of pH to 11 resulted in only foam recovery. Monazite selectivity was obtained between these two extremes, at a pH of 10. The flotation system was extremely pH-sensitive, which indicates that the point of zero charge for the Namakwa Sands zircon and monazite may lie within this narrow pH interval.The accompanying mineralogical study showed that the final zircon reject composed of mainly zircon, between 70% and 83%. The rutile content was around 7% and the monazite grade varied between 3% and 6%. The mineralogy investigation included SEM, QEMSCAN and grain counting results, and besides the bulk mineralogy, surface coatings were studied. Surface coatings on both monazite and zircon were highly associated with SiO2, which has previously been detected as a common surface coating in the deposit in the form of opaline silica. SEM and QEMSCAN were used as tools to detect the degree of surface coatings before and after attritioning. It did not conclusively show any effect of the surface attritioning, which therefore remains unknown. Furthermore, the bulk mineralogy of flotation products was studied. It was shown that the concentrates from the tests with high monazite selectivity were enriched in garnets. The oleate collector may therefore be selective for both monazite and garnets at a pH of 10.The key finding of this project is that monazite can be successfully separated from zircon with an oleate collector at a pH of 10. A monazite recovery of 55.6% was possible; however further research into staged flotation to further improve the zircon-rich tail is needed. The results of surface attritioning are not entirely clear, which gives scope for further investigation into mechanical attritioning methods and intensities. Validerat; 20141020 (global_studentproject_submitter)

This PhD thesis is divided into three parts: (1) the experimental incorporation of Th in monazite and xenotime, (2) the behaviour of the monazite structure under temperature-induced healing, and (3) the experimental resetting of the U-Pb geochronological system in monazite. (1) The Th distribution between monazite and xenotime as a result of the Th + Si = REE + P substitution mechanism was experimentally determined in the T-P-range of 600 to 1100°C and 2Kbar. Starting mixtures consisted of gels and were composed of equal amounts of CePO4 and YPO4 with addition of 10, 20 and 50 mole % of ThSiO4. Run products were analysed using AEM and XRD. At all temperatures, the ThSiO4 component is partitioned almost exclusively into monazite for a ThSiO4 component of 10 and 20 mole %. Xenotime is apparently ThSiO4-free. In the T-range 600°C-900°C and for ThSiO4 = 50 mole %, thorite is additionally formed indicating ThSiO4 saturation within monazite at these conditions. At 1000°C, only monazite and a small amount of xenotime crystallised. No thorite was observed. (2) The healing of radiation damage in a natural and chemically homogeneous concordant (474±1 Ma) monazite has been experimentally investigated (500-1200°C/~7days). XRD, TEM, Raman microprobe and Cathodoluminescence analysis were performed. The unheated monazite has a mosaic structure consisting of two domains corresponding to two monazite crystals with different lattice parameters. (A) domains correspond to well-crystallised areas where He atoms are trapped, thus inducing their lattice expansion. (B) domains are interpreted to exhibit a He-free distorted monazite crystal lattice which can be referred to old alpha-recoil tracks. With increasing temperature, He diffuses out of the monazite lattice, thus inducing its relaxation. Additionally, the nm-sized defect domains (B) are getting healed. The complete healing is achieved at 900°C after 7 days. (3) In order to investigate the influence of fluid composition and temperature on resetting, abraded fragments (200-400 µm) from monazite used in (2) were experimentally treated (800-1000°C/14-39 days) within solutions of different compositions (H2O up to 1200°C/5 days, NaCl, SrCl2 CaCl2-fluids and a Pb-spike-fluid). Products were analysed using SEM, EMP, SIMS and ID-TIMS. For all runs, EMP traverses revealed no Pb-diffusion profiles. Significant overgrowths of newly formed monazite occurred only in the 1000°C experiments when either CaCl2 or Pb-bearing fluids were present. For CaCl2, inherited core and newly formed Ca-rich and Pb-free monazite rim were produced by dissolution/precipitation. Significant discordancy was only observed when grains were treated with SrCl2 (16%) and CaCl2 (68%) solutions at 1000°C. Finally, experiments performed in the presence of Pb-standard produced sub-concordant monazite with a 207Pb/206Pb apparent age older than prior to the experiment indicating Pb-contamination by the fluid., Cette thèse présente les résultats d'étude expérimentales sur (1) le partage du Th entrela monazite et le xenotime, (2) l'effet du recuit sur la structure de la monazite ainsi que (3) laremise à zéro des systèmes géochronologiques U-Pb dans la monazite.(1) Le partage du Th entre la monazite et le xenotime a été déterminéexpérimentallement (600-1100°C/2Kbar) en considérant le mécanisme de substitutionsuivant: Th + Si = REE + P. Le matériel de départ est un gel constitué d'un mélange deCePO4 et YPO4 (1:1) plus 10, 20 ou 50 mole % de ThSiO4. Les produits sont analysés auMET et en DRX. Quelque soit la température et pour une composition initiale de 10 ou 20mole % de ThSiO4, le Th est presque entièrement réparti dans la monazite. Entre 600 et900°C et pour une composition initiale de 50 mole % de ThSiO4, la cristallisation de la thoritemontre une saturation en Th de la monazite. A 1000°C, seuls la monazite et un peu dexénotime sont observés; la thorite est absente.(2) Le recuit des dégats d'irradiation dans une monazite naturelle, homogènechimiquement et concordante à 474 ± 1 Ma, a été étudié expérimentallement (500-1200°C/~7jours). Les produits ont été analysés en DXR, MET, Raman et cathodoluminescence. Lamonazite non-chauffée révèle une structure en “mosaïque” composée de 2 domaines, qui sont2 cristaux de monazites de paramètres de maille différents. Les domaines (A) correspondentaux domaines parfaitement cristallisés, où l'hélium emprisonné provoque une expansion duréseau. Les domaines (B) correspondraient à des domaines exempts d'hélium, où le réseau aété déterioré par les noyaux de recul-alpha. Lors du recuit de la monazite l'hélium diffusehors du cristal, ce qui induit une relaxation du réseau dans les domaines (A). En même temps,les domaines (B), défectueux, sont recuits. A 900°C, le réseau de la monazite est entièrementrecuit.(3) Afin d'étudier l'effet de fluides et de la température sur le “resetting” des systèmesU-Pb dans la monazite, des fragments abrasés (200-400 µm) de l'échantillon utilisé en (2) ontété chauffés (800-1000°C/14-39 jours) en présence de solutions de diverses compositions (eaupure jusqu'à 1200°C/5 jours, fluides à NaCl, SrCl2 CaCl2 et standard de Pb) puis analysés auMEB, EMP, SIMS et ID-TIMS. Quelle que soient les expériences aucun profil de diffusiondu Pb n'est observé (EMP). En présence de fluide à CaCl2 ou à standard de Pb et uniquementpour les expériences réalisées à 1000°C on observe des surcroissances. A 1000°C et dans unfluide à CaCl2 on observe une zonation, coeur hérité et bordure enrichie en Ca et exempt dePb, formée par dissolution/précipitation. Des discordances significatives sont observéesuniquement pour les expériences réalisées à 1000°C dans les fluides à SrCl2 (16%) ou CaCl2(68%). Enfin, l'utilisation du fluide à standard de Pb induit un vieillissement des monazitesinitiales, ce qui indique une contamination de la monazite par ce fluide.

The minor actinides (MA) neptunium, americium, and curium are mainly responsible for the long-term radiotoxicity of the High Active Waste (HAW) generated during thenuclear power operation. If these long-lived radionuclides are removed from the HAW by partitioning and converted by neutron fission (transmutation) into shorter-lived or stable elements, the remaining waste loses most of its long-term radiotoxicity. Thus, partitioning and transmutation (P&T) are considered as attractive options for reducing the burden on geological disposals. As an alternative, these separated MA can also be conditioned (P&C strategy) in specifically adapted ceramics to ensure their safe finaldisposal over long periods. At the moment, spent fuel elements are foreseen either for direct disposal in deep geological repositories or for reprocessing. The highly activeliquid waste that is produced during reprocessing is conditioned industrially using a vitrification process before final disposal. Although the widely used borosilicate glassesmeet most of the specifications needed, ceramic host matrices appear to be even more suitable in terms of resistance to corrosion. The development of new materials based on tailor-made highly specific ceramics with extremely stable behavior would make it possible to improve the final storage of long-lived high-level radiotoxic waste.In the framework of this PhD research project, monazite-type ceramics were chosen as promising host matrices for the conditioning of trivalent actinides. The focus on themonazite-type ceramics is justified by their properties such as high chemical durability. REPO$_{4}$ ceramics are named monazite for RE = La - Gd (monoclinic symmetry) and xenotime for RE = Tb - Lu and Y (tetragonal symmetry). The objective of this study is to contribute to the understanding of the alteration behavior of such ceramics under the repository conditions. REPO$_{4}$ (with RE = La, Eu) is prepared by hydrothermal synthesis at 200°C. Structural and morphological characteristics (using X-ray diffraction (XRD) and scanning electron microscope (SEM)) combined with physical and thermal properties of samples (using thermogravimetry, differential scanning calorimetry (TG-DSC) and dilatometry) are realized in order to study the behavior of monazite-type powder and pellets. The access to short-range-order spectroscopy (time resolved laser fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine structure (EXAFS)) permits to [...]

(Keine Zusammenfassung in englischer Sprache hinterlegt.) Das gekippte Profil durch die kontinentale Kruste im Kalabrischen Massiv Süditaliens, in dem Gesteine aus allen Krustenniveaus aufgeschlossen sind, bietet die seltene Möglichkeit, die thermische, tektonische und magmatische Entwicklung dieser Kruste während der herzynischen Orogenese zu rekonstruieren. Um die thermischen Bedingungen in den unterschiedlichen Krustenniveaus miteinander vergleichen zu können, wurden die grünschiefer- bis amphibolithfaziellen Gesteine der Oberkruste sowie die granulitfaziellen Gesteine der Unterkruste phasenpetrologisch und texturell untersucht. Die Ergebnisse zeigen, daß die Metamorphose in allen Gesteinen dem gleichen orogenen Ereignis zugeordnet werden kann. Isotopische U-Pb Altersdatierungen an Metamorphiten aus allen Krustenstockwerken sowie an Magmatiten, die in die mittlere bis obere Kruste intrudierten, ergänzen diese Untersuchungen. Sie zeigen, daß sowohl die Metamorphose als auch der Magmatismus gleich alt sind (304 - 293 Ma) und damit alle Ereignisse im gesamten aufgeschlossenen Krustenprofil zur selben Zeit stattgefunden haben.

Thailand besteht geologisch aus zwei Krustenblöcken, die ihren Ursprung in Gondwana haben. Sibumasu im Westen und Indochina im Osten. Dazwischen liegen die Inthanon-Zone und der Sukhothai-Arc Gürtel. Während dieses Modell für den Norden des Landes etabliert wurde und mittlerweile gut akzeptiert ist, ist seine Fortsetzung nach Süden immer noch umstritten. Daher wurde der Khanom Komplex untersucht, ein polymetamorpher Komplex auf der Halbinsel Thailands, SE von Surat Thani, der erstmals von Kosuwan (1996) beschrieben wurde. Er enthält Gneise, Schiefer, Calcsilikate, Marmor und wird von postorogenen Graniten durchschnitten. Ziel war es klar zu stellen, ob diese Gesteine eine ähnliche Geschichte wie die hochgradig metamorphen Gesteine im Norden des Landes haben oder nicht. Petrologische Untersuchungen in Kombination mit geochronologischen Untersuchungen wurden an zwei Gneisen in diesem Gebiet durchgeführt (Haad Nai Phlao Gneis und Laem Thong Yang Gneis), um den Zeitpunkt, die metamorphen Bedingungen und die tektonische Entwicklung der Halbinsel Thailands besser zu verstehen. Diese Gneise bestehen hauptsächlich aus Feldspat, Quarz und zwei Glimmern. Granat und Aluminosilicat, welche von Kosuwan (1996) beschrieben wurden, konnten nicht gefunden werden. Während der Laem Thong Yang Gneis grobkörnig ist und große Feldspat-Augen hat, ist der Haad Nai Phlao Gneis fein bis grobkörnig mit Zwischenschichten aus Kalksilikat und feinkörnigem amphibolhaltigem Gneis. In-situ CHIME (chemische Th-U-gesamt-Pb- Isochron-Methode) Monazit-Datierung und 206Pb/238U Zirkon SIMS (Sekundärionen- Massenspektrometrie) Datierung wurden angewendet: Zwei verschiedene Ereignisse konnten bestimmt werden: eines in der späten Trias (~210 Ma), das andere in der späten Kreidezeit (~80 Ma). Zusätzlich wurden Al-in-Hornblende-Barometrie (6,1 ± 0,6kbar) gekoppelt mit Hornblende-Plagioklas-Thermometrie (720 ± 35-40°C) sowie Monazit-Xenotim-Mischbarkeitslückenthermometrie (~400-770°C) durchgeführt. Die Ergebnisse dieser Studie legen nahe, dass der amphibolhaltige Gneis möglicherweise aus dem Khao Dat Fa Granit stammt und dass der Haad Nai Phlao Gneis das Ergebnis einer Kontaktmetamorphose ist, die durch das Eindringen des Khao Pret-Granits verursacht wird. Ähnliche Alter, welche in anderen metamorphen Gesteinen in Thailand gemessen wurden (z.B. metamorpher Kernkomplex von Doi Inthanon), legen nahe, dass sie alle Teil derselben tektonischen Einheit (Sibumasu) sind und daher eine ähnliche tektonometamorphe Geschichte aufweisen., Thailand is part of two main terranes which have their origins in the Gondwana continent, Sibumasu in the west and Indochina in the east. In between are the Inthanon Zone and the Sukhothai arc belt. Whereas this model was established for the northern part of the country and is now well accepted, its continuation to the south is still a matter of debate. Therefore the Khanom complex, a polymetamorphic complex located in Peninsular Thailand SE of Surat Thani first described by Kosuwan (1996) was examined. It contains gneisses, schists, calcsilicates, marbles and is crosscut by postorogenic granites. The objective was to bring more clarity whether these rocks have a similar history to the high-grade metamorphic rocks in the north of the country or not. Petrological investigations combined with geochronological studies were carried out on two gneisses in this area (Haad Nai Phlao gneiss and Laem Thong Yang gneiss), to further understand the timing, metamorphic conditions and tectonic evolution of Peninsular Thailand. These gneisses mainly consist out of feldspar, quartz and two micas. Garnet and aluminosilicate which were described by Kosuwan (1996) could not be found. Whereas the Laem Thong Yang gneiss is coarse-grained and has big feldspar “Augen”, the Haad Nai Phlao gneiss is fine to coarse-grained with interlayers of calcsilicate and fine-grained amphibole-bearing gneiss. In-situ CHIME (chemical Th–U–total Pb isochron method) monazite and 206Pb/238U zircon SIMS (secondary-ion mass spectrometry) dating was applied: two different events could be determined, one in the Late Triassic (~210 Ma) the other in the Late Cretaceous (~80 Ma). In addition Al-in-hornblende barometry (6.1 ± 0.6kbar) coupled with hornblende-plagioclase thermometry (720 ± 35-40°C) as well as Monazite–xenotime miscibility gap thermometry (~400-770°C) were carried out. Results from this study suggest that the amphibolebearing gneiss might be derived from the Khao Dat Fa gneiss and that the Haad Nai Phlao gneiss might be the result of contact metamorphism caused by the intrusion of the Khao Pret granite. Similar ages obtained from other metamorphic basement rocks in Thailand (e.g. Doi Inthanon metamorphic core complex) suggest that they are all part of the same tectonic entity (Sibumasu) and therefore share a similar tectonometamorphic history.

Rare earth elements (REE) are important metals used in green and low-carbon energy and information technologies and are widely used for geological petrogenetic studies. It is becoming increasingly evident that the REE can be mobile in certain hydrothermal fluids and even form hydrothermal REE deposits. This study focuses on the formation of hydrothermal REE deposits rich in the REE-phosphates (monazite [(LREE,Y)PO4] and xenotime [(Y,HREE)PO4]). The main objective of the study was to characterise the Olserum-Djupedal REE-phosphate mineralisation in SE Sweden. Based on this, the study evaluates different sources of REE and P in hydrothermal deposits and assesses how REE and P are transported in hydrothermal fluids. To characterise the Olserum-Djupedal REE mineralisation, this study combines fieldwork, petrographical and textural analysis, major and trace element mineral chemistry of REE-bearing minerals and the main gangue phases, stable Cl isotopic and halogen analysis of fluorapatite, and fluid inclusion microthermometry and LA-ICP-MS analysis. The primary Olserum-Djupedal REE mineralisation comprises co-existing monazite-(Ce), xenotime-(Y) and fluorapatite. These occur mainly within veins dominated by biotite, magnetite, gedrite and quartz forming within metasedimentary rocks in or close to the contact aureole of a peraluminous alkali feldspar granite. The veins are also hosted by the granite within the outermost part of this granite. Primary REE-minerals formed by granitic-derived NaCl-FeCl2-KCl-CaCl2-HF-H2O fluids at high temperatures of ~600 °C at c. 1.8 Ga. Subsequently, the ore assemblages were variably modified during cooling by CaCl2-NaCl to NaCl-CaCl2 brines, and partly, CO2-rich fluids down to temperatures of ~300 °C and to at least 1.75 Ga. Hydrothermal REE deposits rich in REE-phosphates are commonly associated with alkaline magmatism, particularly in silicate-carbonatitic systems. This is because REE and P both exhibit strong chemical affinities with carbonatitic systems and the potential for mobilisation of REE and P are high. This study shows that REE deposits can also form by hydrothermal activity related to subalkaline magmatic rocks. Peraluminous granites exhibit the greatest potential to exsolve fluids carrying REE and P, which can lead to the formation of hydrothermal REE deposits rich in REE-phosphates. The general understanding on how hydrothermal REE-phosphate deposits form is that REE and P are transported in separate fluids and that the REE-phosphates form when these two fluids mix, or the REE-phosphates form when REE-bearing fluids interact with P-rich rocks. The lack of rocks pre-enriched in P in the Olserum-Djupedal district and the co-crystallisation of fluorapatite, monazite-(Ce) and xenotime-(Y), however, suggest that such scenarios not necessarily account for all occurrences of hydrothermal REE-phosphate deposits. As an alternative, REE and P can have been transported by the same fluid. This study demonstrates that the most probable conditions for co-transport of REE and P are at temperatures exceeding 400 °C and with increasing salinity of the fluids, conditions that agree well with that of the Olserum-Djupedal system. The most effective co-transport of REE and P would occur at acidic conditions by REE-Cl, REE-F or REE-SO4 complexes. Yet, co-transport of REE and P may also be feasible at neutral to alkaline conditions by REE-OH complexes. In low-temperature hydrothermal systems, the interaction of REE-bearing fluids with P-rich rocks or fluids is probably the most efficient mechanism for precipitating REE-phosphates. In high-temperature magmatic-hydrothermal systems, REE and P probably share a common origin and were transported by the same fluid. In such systems, pH changes, cooling and the destabilisation of the chief REE transporting complexes jointly contribute to the precipitation of REE-phosphates. De sällsynta jordartsmetallerna (på engelska förkortat REE; Rare Earth Elements) är en grupp grundämnen som idag har en nyckelroll i många högteknologiska applikationer inklusive s.k. grön och fossilfri energiteknik. Över tid har flera REE-mineraliseringar konstaterats ha bildats helt eller delvis av hydrotermala fluider (högtempererade vattenlösningar). Hur sådana förekomster kan bildas är ett idag högaktuellt forskningsområde. Den här studien är fokuserad på bildandet av hydrotermala REE-förekomster innehållande REE-fosfaterna monazit [(LREE,Y)PO4] och xenotim [(Y,HREE)PO4], två viktiga värdmineral för REE i jordskorpan. Studien inriktar sig främst på att karakterisera de nyupptäckta REE-mineraliseringarna i området kring Olserum-Djupedal utanför Västervik i sydöstra Sverige. Fortsättningsvis undersöks ursprunget av REE och P i dessa förekomster, hur REE och P transporteras i de hydrotermala lösningarna och vilka processer som lett fram till bildandet av monazit och xenotim från dem. Den primära mineraliseringen i Olserum-Djupedal domineras av samexisterande monazit-(Ce), xenotim-(Y) och REE-förande fluorapatit i gångar huvudsakligen bestående av biotit, magnetit, gedrit och kvarts. Gångarna förekommer i metasedimentära bergarter kring och i kontaktgården till en peraluminös alkalifältspatgranit. Gångarna uppträder även i utkanten av samma granit. Sammantaget visar resultaten att den primära REE-mineraliseringen har ett hydrotermalt ursprung och bildades för omkring 1,8 miljarder år sedan av högtempererade (ca. 600°C) fluider från den närliggande graniten. De primära associationerna omvandlades därefter under avtagande temperatur till ca. 300°C för åtminstone 1,75 miljarder år sedan. Hydrotermala mineraliseringar med REE-fosfater förknippas vanligtvis med alkalina magmatiska bergarter och karbonatiter eftersom både REE och P i regel uppvisar en stark kemisk affinitet till sådana magmor. Den här studien visar att REE-fosfatförekomster även kan bildas av hydrotermal aktivitet relaterad till magmatiska bergarter av betydligt mindre alkalin karaktär. Av dessa system så har graniter med peraluminös karaktär störst potential att avge fluider anrikade på både REE and P. Den generella uppfattningen om hur hydrotermala REE-fosfatmineraliseringar har bildats är att REE och P transporterats i separata fluider och att REE-fosfater fällts ut som en konsekvens av att dessa fluider blandats, eller att REE-fosfater bildats som ett resultat av att REE-förande fluider reagerat med fosforrika bergarter. Avsaknaden av fosforrika bergarter i området kring Olserum-Djupedal och förekomsten av samexisterande fluorapatit, monazit-(Ce) och xenotim-(Y) visar dock att sådana scenarier inte nödvändigtvis förklarar alla förekomster av hydrotermala REE-fosfatmineraliseringar. Som ett alternativ kan REE och P ha transporterats i samma fluid. De mest troliga förhållanden för samtransport av REE och P är i fluider med temperaturer som överstiger 400°C och som har höga salthalter. Vidare så gynnar låga pH samtransport av REE och P då olika metallkomplex med REE, exempelvis REE-Cl, REE-F eller REE-SO4, är väldigt stabila under dessa förhållanden. Samtransport av REE och P är också möjlig vid ett mer neutralt eller basiskt pH. I ett scenario som innefattar samtransport av REE och P så kan pH-förändringar, sänkta temperaturer och destabilisering av viktiga REE-metallkomplex i kombination bidra till utfällning av REE-fosfater. Sammanfattningsvis kan man säga att i lågtempererade hydrotermala system har REE-fosfaterna sannolikt inte bildats av fluider omfattande samtransport av REE och P, utan genom blandning av två olika fluider eller genom samverkan mellan REE-förande fluider och fosforrika bergarter. I många högtempererade magmatisk-hydrotermala system (> 400°C) så har förmodligen REE och P i REE-fosfaterna däremot haft ett gemensamt ursprung och transporterats i samma fluid.