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Field observations of the Greater Himalayan Sequence in Eastern Nepal demonstrate a ductile, highly strained package of metamorphic rocks that show extensive evidence of crustal anatexis throughout. These can be distinguished from the Lesser Himalayan sequence below by a distinct reduction in metamorphic grade, an inverted metamorphic sequence and a high strain zone corresponding to the Main Central Thrust. Metamorphic studies are combined with geochronology to demonstrate a protracted period of crustal melting followed by rapid decompression from 18.7 Ma to 15.6 Ma. A metamorphic decompression rate is quantified at c.2mm/yr during this period. This is interpreted to represent exhumation of the Greater Himalayan Sequence by a process of ductile, channelised flow from the mid-crust beneath Tibet. Below a prominent band of kyanite gneiss, previously used to locate the Main Central Thrust, but here mapped within the Greater Himalayan Sequence, partial melting is still exhibited. Here monazites are dated at 10.6 Ma. In the Lesser Himalaya below, allanites record a similar 10.1 Ma event. This implies that following channel flow during the mid-Miocene, the channel widened in the lower-Miocene to incorporate a greater structural thickness. Following these two periods of exhumation and ductile extrusion, separated in time and space, Fission Track studies indicate that much slower, erosion driven exhumation proceeded, at <1 mm/yr. This rate increases slightly in the Pliocene, most likely in response to Northern Hemisphere glaciation; no difference in exhumation is seen across the Greater Himalayan Sequence with respect to the different, earlier, phases of ductile channel flow related exhumation. These results demonstrate the episodic nature of channel flow in the Himalaya and reconcile arguments about the position of the MCT in Eastern Nepal.

This thesis employs crystal-specific techniques, combined with field observations, petrology, geochemistry and numerical modelling to reconstruct the magmatic system associated with the ~ 340 ka Whakamaru supereruption, New Zealand. Comparisons are drawn with the ~ 74 ka Youngest Toba Tuff (YTT) supereruption. Whakamaru Group Ignimbrites contain five pumice types, characterised by different mineralogies and crystal contents. Pumice petrography and geochemistry indicate that basaltic magma mixing occurred, possibly triggering eruption. Geothermobarometers suggest an eruption temperature of ~ 770°C and magma storage at ~ 5 km depth. High-resolution thermal records from Ti-in-quartz analysis indicate a thermal pulse of ~ 100°C prior to eruption. Diffusion timescales show multiple recharge events with the most significant event occurring ~ 35 y prior to eruption. Zircon U-Pb data show that most crystallisation occurred at ~ 400 ka, with antecrysts and xenocrysts incorporated. Zircon trace-element data suggest multiple recharge events and complex mixing over ~ 100 ky, consistent with an incrementally growing reservoir. Oxygen-isotope data illustrate that zircon, quartz and feldspar crystallised together in equilibrium, with isotopically homogenous magma sources feeding the reservoir over time. Whakamaru and YTT tephra thickness and grain-size data were used in ash dispersal modelling. Results indicate the YTT eruption had a ~ 35 km column height and erupted volumes of 1500 – 1900 km³, with deposition from a co-ignimbrite phase; whereas Whakamaru had a Plinian column ~ 45 km high with SE dispersal and a minimum volume of ~ 400 km³. The widespread dispersal of large volumes of fine ash from both eruptions would have had global environmental consequences. The data are integrated to reconstruct a new Whakamaru magma reservoir model. The complex crystal records indicate the system was characterised by long periods of incremental assembly, mixing, recycling of material, and reactivation during multiple recharge episodes which perturbed the system and primed the magma for eruption.

Σκοπός της παρούσας εργασίας είναι ο προσδιορισμός της ρύπανσης των ιζημάτων του Αλφειού ποταμού από στερεά σωματίδια, που προέρχονται από την εξόρυξη και την καύση του λιγνίτη Μεγαλόπολης. Βασικό αντικείμενο έρευνας αποτέλεσε η μικροσκοπική εξέταση του οργανικού μέρους, που είναι παρόν στα ιζήματα του Αλφειού ποταμού και η οργανική γεωχημική εξέταση επιλεγμένων δειγμάτων για την ανίχνευση πολυκυκλικών αρωματικών υδρογονανθράκων (polycyclic aromatic hydrocarbons, PAHs). Επιπλέον σε δείγματα λιγνίτη, ιπτάμενης τέφρας, τέφρας εστίας και τέφρας απόθεσης από το Λιγνιτικό Κέντρο Μεγαλόπολης πραγματοποιήθηκε μία σειρά εργαστηριακών προσδιορισμών, που περιέλαβε προσεγγιστική και άμεση ανάλυση, ανθρακοπετρογραφική εξέταση του λιγνίτη, καθώς και ορυκτολογικές και στοιχειακές αναλύσεις. Με βάση τις περιεκτικότητες του λιγνίτη και των παραπροϊόντων της καύσης του σε κύρια στοιχεία και ιχνοστοιχεία μπορεί να εκτιμηθεί η κινητικότητά τους κατά την καύση και το κατά πόσο αυτά διαφεύγουν στο περιβάλλον ή παραμένουν στο χώρο καύσης. Τα πιο ευκίνητα στοιχεία, που περιέχονται στο λιγνίτη Μεγαλόπολης, είναι τα Ba, Li, Mg, Rb και Sn, τα οποία μαζί με τα As και Pb, που συμμετέχουν στο λεπτόκοκκο τμήμα της ιπτάμενης τέφρας αποτελούν δυνητικούς ρυπαντές. Αντίθετα τα στοιχεία Ge, Mn, Th, Ti και Y είναι περιβαλλοντικά λιγότερο επικίνδυνα, καθώς συμμετέχουν στο τμήμα των παραπροϊόντων, που παραμένει στην τέφρα των ατμοηλεκτρικών σταθμών. Από μικροσκοπική παρατήρηση προέκυψε ότι το οργανικό υλικό, που είναι παρόν στα συγκεκριμένα ιζήματα αποτελείται κατά 78,4% κ.ό. από ανθρωπογενή σωματίδια, ενώ το υπόλοιπο 21,6% αποτελείται από φρέσκα φυτικά υπολείμματα. Το 81,5% κ.ό. του συνόλου των ανθρωπογενών σωματιδίων αποτελείται από κόκκους λιγνίτη και το 19,5% κ.ό. συνίσταται από εξανθρακώματα, που μεταφέρονται με την ιπτάμενη τέφρα και αποτίθενται στα ιζήματα. Τα ανθρακούχα σωματίδια στα ιζήματα του Αλφειού αντικατοπτρίζουν την ανθρακοπετρογραφική σύσταση του λιγνίτη Μεγαλόπολης, από την οποία εξαρτάται επίσης και η μορφή των εξανθρακωμάτων. Το επίπεδο των συγκεντρώσεων PAHs στα ιζήματα του Αλφειού είναι σχετικά χαμηλό (10-100 ng/g), ωστόσο η καύση του λιγνίτη συνεισφέρει σε ποσοστό 39,5% στην εκπομπή τους, ενώ το 23,5% προέρχεται από τον ίδιο το λιγνίτη. Η συμμετοχή των PAHs στα συγκεκριμένα ιζήματα φαίνεται να σχετίζεται ως ένα βαθμό με την παρουσία εξανθρακωμάτων, γεγονός που υποδεικνύει διεργασίες ρόφησης. Με την παρούσα εργασία αποδεικνύεται ότι η Οργανική Πετρολογία σε συνδυασμό με δεδομένα Οργανικής και Ανόργανης Γεωχημείας, μπορεί να αποτελέσει σημαντικό εργαλείο σε ό,τι αφορά στον προσδιορισμό της ρύπανσης ιζημάτων και εδαφών από την εκμετάλλευση γαιανθράκων. / The main target of the present study is the assessment of the contamination degree of Alfeios River sediments with solid particles deriving from mining and combustion of Megalopolis lignite. The objectives of the study were the microscopical examination of the organic matter present in these sediments, as well as the determination of the concentration of Polycyclic Aromatic Hydrocarbons (PAHs) in selected samples. Additionally in lignite, fly ash, bottom ash and ash deposit samples, were conducted a string of analyses including, proximate and ultimate analyses along with mineralogical and elemental determinations. The mobility of major and trace elements during the combustion of lignite can be estimated according to the concentration of these elements in bulk lignite and its combustion by-products. Based on these results the most mobile and thus more environmentally "sensitive" elements in Megalopolis lignite are As, Ba, Li, Mg, Pb, Rb and Sn, while Ge, Mn, Th, Ti and Y are the less mobile elements participating mostly in bottom ash. From the microscopical study of the organic matter present in Alfeios sediments it is evident that it consists of 78,4% of anthropogenic particles, while the remaining 21,6% consists of fresh plant remnants. The 81,5% of the anthropogenic particles consists of lignite particles deriving from mining and transportation processes and the remaining 19,5% consists of char particles transported and deposited as portion of the fly ash produced in Megalopolis Lignite Centre. The coal-petrographic composition of lignite particles is similar to the coal-petrographic composition of Megalopolis lignite. The latter is also responsible for the shape and texture of the char particles. The PAHs concentration level is rather low, ranging from 10-100 ng/g. Nevertheless lignite combustion along with the Megalopolis lignite itself are the main emission sources of such compounds accounting for 39,5% and 23,5% respectively. The presence of PAHs is related to the presence of char particles, probably via sortion procedures. The results of this study show that Organic Petrology can be a useful tool in environmental science and particularly in the field of contamination of soils and sediments from coal exploitation, if combined with Organic and Inorganic Geochemical data.

Universiẗat, Diss., 2006--Frankfurt (Main).

La présence de magmas en profondeur permet de contraindre des processus géologiques passés et actuels. Ces magmas (i.e. liquides silicatés) participent aux cycles géochimiques des éléments volatils comme vecteur de matière.Nous étudions deux éléments volatils complémentaires : l'iode (I), un halogène, et le xénon (Xe), un gaz rare. Leur système radioactif éteint 129I/129Xe (T1/2 = 15.7Ma) est utilisé pour dater les processus hadéens et la formation de l'atmosphère, issu de l'évolution d'un océan magmatique. Or on connait peu le comportement de l'iode et du xénon dans les magmas en profondeur à haute pression et température.Notre protocole expérimental vise l'étude de l'incorporation de l'iode et du xénon et de leur solubilité dans les magmas. Pour étudier l'incorporation, la structure des silicates liquides a été caractérisée par diffraction de rayons X avec des expériences in situ réalisées dans des cellules à enclumes de diamant et dans des presses Paris-Édimbourg. Les teneurs de solubilité de l'iode et du xénon ainsi que l'eau ont été mesurés par les méthodes PIXE et ERDA.À hautes pressions, l'iode possède une forte solubilité (quelques %pds) dans les magmas. Les résultats préliminaires sur son incorporation dans du basalte montrent que l'iode ne formerait pas des liaisons covalentes. À haute pression et température (T>300°C - P>1GPa), le xénon forme une liaison covalente Xe-O avec les oxygènes des anneaux de 6 tétraèdres SiO44-. Le xénon a une solubilité élevée dans les magmas (4pds% - 1600°C - 3.5GPa).Les modèles de datation et des cycles géochimiques de l'iode et du xénon doivent être revus en tenant compte de leur comportement différentiel dans les magmas. / The presence of magmas at depth helps to constrain past and actual geological processes. Magmas (i.e. silicate melts) participate in geochemical cycles of volatile elements, as vectors of chemical transfers. We study two complementary volatile elements: iodine (I), a halogen, and xenon (Xe), a noble gas. Their extinct 129I/129Xe isotopic system (half-life of 15.7Ma) is used to date Hadean processes and Earth’s atmosphere formation since the atmosphere originated from the Magma Ocean’s evolution. However, little is known about the behavior of both iodine and xenon in silicate melts at depth, under HT and HP conditions. Our experimental protocol aims at elucidating the incorporation process of xenon and iodine in silicate melts, and their solubility. To understand the incorporation of iodine and xenon in magmas, the structure of silicate melts was investigated by in situ diamond anvil cells and Paris-Edinburgh press experiments coupled with X-ray diffraction characterization. Iodine and xenon’s solubility, along with water content are obtained by PIXE and ERDA methods using a nuclear microprobe. At high pressure, iodine has a high solubility (about few wt.%) in magmas. Preliminary results on iodine incorporation in basaltic melt show an absence of covalent bond. At high pressure and temperature conditions (T>300°C – P>1GPa), xenon forms a Xe-O covalent bond with the oxygens of the 6-membered-rings of the melt network. Its solubility in silicate melts is also high (about 4wt.% in haplogranite melts at 1600°C and 3.5GPa). Considering the xenon and iodine differential behavior in melts at depth, a revision of dating models in xenon and iodine cycles must be considered.

La craie est définie comme étant une roche carbonatée microporeuse. Cette formation est largement exploitée en Mer du Nord pour ses hydrocarbures et constitue un aquifère dans le Bassin de Paris. Les propriétés réservoirs de la Craie (propriétés matricielles) varient considérablement comme Alam et al. (2011) le soulignent pour les craies de surface et de subsurface de Mer du Nord, avec des porosités de 4 à 52 %, des perméabilités de 0,01 à 100 mD et des vitesses des ondes P sur roche saturée de 2,4 à 4,4 km.s-1.Dans le secteur d'étude (Normandie, France), pris comme analogue de terrain, 114 échantillons (Cénomanien- Santonien) ont été prélevés dans le but d'illustrer l'hétérogénéité sédimentaire et pétrophysique de la Craie. Comme en Mer du Nord, les échantillons présentent une grande variabilité des propriétés pétrophysiques : porosités () de 6,1 à 46,5 %, perméabilités matricielles (K) très faibles (0,002 mD) jusqu’à des perméabilités atypiques et très fortes (470 mD, en l’absence de fractures) et des vitesses des ondes P sur échantillon saturé s'étalant selon une gamme très étendue (1,8 à 5,5 km.s-1). Cependant, l’origine de ces hétérogénéités est encore mal comprise. L'objectif de cette étude est donc de comprendre l’influence respective des facteurs contrôlant les propriétés pétrophysiques afin d'optimiser la modélisation de ce type de réservoir.Trois modèles sédimentaires ont ici été définis avec :(1) un modèle de rampes, subdivisé en modèle de rampe argileuse avec des porosités de 34,4 à 46,5 % et des valeurs de perméabilité de 0,02 à 3 mD, et en modèle de rampe carbonatée (mudstone à grainstone) avec des porosités de 26,1 à 46,5 % et des valeurs de perméabilité de 0,04 à 6 mD,(2) un modèle de contourite (mudstone à grainstone et micro-packstone) avec des porosités de 8,3 à 45,5 % et des valeurs de perméabilité de 0,05 à 477 mD,(3) un modèle de surface de hiatus (Soupground à Hardground) avec des porosités de 6 à 36,9 % et des valeurs de perméabilité de 0,002 à 36 mD.Une classification des microtextures, basée sur l’observation au MEB de quatre critères (contenu minéralogique, fraction biogénique, fraction micritique et fraction de ciment), est proposée. À partir de ces critères, deux groupes majeurs ont été définis avec les Pure chalk microtextures et Impure chalk microtextures. Le groupe des Pure chalk microtextures reflète l’intensité des modifications subies par la craie lors de la diagenèse (taux de diagenèse qu’elle soit précoce ou tardive). Une augmentation du taux de diagenèse induit une diminution de la porosité et une augmentation des vitesses de propagation des ondes acoustiques P. En effet, les transformations qui s’opèrent au cours de la diagenèse, d’une part, réduisent la taille des espaces intergranulaires et donc font diminuer la porosité, et d’autre part, renforcent les contacts entre grains, favorisant ainsi la propagation des ondes acoustiques. Pour le groupe des Impure chalk microtextures, la présence de particules insolubles dans la matrice n’affecte pas la porosité, mais diminue la perméabilité du fait de la réduction des tailles d’accès aux pores.Par conséquent, l’héritage sédimentaire et les transformations diagénétiques, qui affectent à différents degrés les faciès sédimentaires primaires, déterminent les propriétés réservoirs et sont donc la cause de la grande variabilité de ces dernières. De plus, la répartition spatiale de ces microtextures, dépendante des conditions de dépôt (e.g. climat, distance des côtes), et des modifications diagénétiques (précoces ou tardives), n’est pas aléatoire. À partir de l’extrapolation combinée des faciès et de l’empreinte diagénétique, il serait ainsi possible de visualiser la distribution des propriétés pétrophysiques sur les falaises, et donc de visualiser l'architecture des réservoirs dans la Craie. / Chalk is defined as a microporous reservoir rock. This formation is a prolific hydrocarbon-bearing reservoir in the North Sea and is one of the main aquifers in the Paris Basin. The heterogeneity of chalk in terms of petrophysical properties (both surface and subsurface) is illustrated by porosity ranging from 4 to 52 %, permeability from 0.01 to 100 mD, and P-wave velocity on water-saturated samples from 2.4 to 4.4 km.s-1 (Alam et al., 2011).In the study area (Normandie, France), taken as an outcrop analogue, 114 samples were collected (Cenomanian – Santonian). As in the North Sea fields, these samples show great petrophysical heterogeneity: total porosity () from 6.1 to 46.5 %, very low permeability (K; 0.002 mD) to atypical high permeability (477 mD; without fractures), and P-wave velocity on water-saturated samples ranging from 1.8 to 5.5 km.s-1. However, the origin(s) of this large variation in petrophysical parameters is poorly understood. Three sedimentary models are defined here for the chalk:(1) Ramp models, subdivided into argillaceous ramp model, with porosity from 34,4 to 46.5%, and permeability from 0.02 to 3 mD, and carbonate ramp model (mudstone to packstone), with porosity from 26.1 to 46.5%, and permeability from 0.04 to 6 mD,(2) Contourite model (mudstone to grainstone and micro-packstone), with porosity from 8.3 to 45.5%, and permeability from 0.05 to 477 mD,(3) Softground to Hardground model, with porosity from 6 to 36.9%, and permeability from 0.002 to 36 mD.Each model has specific distribution in the porosity-permeability plot.A microtexture classification of the chalk is proposed, based on SEM observation of four groups of criteria (mineralogical content, biogenic fraction, micritic fraction and cement fraction). From these criteria, two major groups are defined: Pure chalk microtexture and Impure chalk microtexture. The Pure chalk microtexture group reflects the intensity of chalk modification during diagenesis (rate of diagenesis, whether early stage or not). An increase in the diagenetic rate induces a decrease in porosity and an increase in P-wave velocity. Diagenetic transformation induces a decrease in pore-space size, with better grain contact, explaining the decrease in porosity and the improved propagation of acoustic P-wave velocity. For Impure chalk microtexture group, the presence of insoluble particles in the matrix does not affect porosity but decreases permeability, due to the reduction of pore-throat size.The complex relationships between depositional inheritance and diagenetic transformation lead to variability in chalk petrophysical parameters. Spatio-temporal distribution of depositional facies and associated diagenetic transformation is not random; it depends on sedimentological condition (e.g. climate and distance to shore) and imprint of diagenetic processes (early or late stage). By extrapolating from the combined data on facies and diagenesis, the petrophysical properties of the entire cliff section can be characterised, and used to describe the reservoir architecture of the Chalk.

Les Vosges sont caractérisées par la présence de nombreuses intrusions et extrusions magmatiques d’affinités variées. Elles constituent donc un excellent site d’étude pour contraindre, par la datation et la géochimie, l’évolution des évènements de ce segment de l’orogène Varisque. Ce travail révèle ainsi deux successions d’évènements magmatiques identiques, décalées dans le temps, caractérisent les domaines Moldanubien (360 à 320 Ma) et Saxothuringien (335 à 295 Ma). Ces successions d’évènements magmatiques résultent de deux processus majeurs. L’avancée des croûtes continentales subduites et sous-plaquées au niveau du Moho sous les blocs continentaux permet le passage du magmatisme calco-alcalin au magmatisme calco-alcalin riche en potassium. L’apport de chaleur par désintégration des éléments radiogéniques (K, U et Th) présents dans ces croûtes continentales subduites permet, dans un premier temps, la formation du magmatisme magnésio-potassique en profondeur. Dans un second temps, elle permet la formation du magmatisme d’origine crustale par l’intrusion du magmatisme magnésio-potassique, riche en K, U et Th, à la limite croûte moyenne - croûte supérieure. Ces successions d’évènements magmatiques et particulièrement, la présence des granites magnésio-potassiques, relient clairement les Vosges à la partie Est de l’orogène Varisque (Forêt Noire, Massif de Bohème, Alpes et Corse-Sardaigne). / The Vosges Mountains are characterized by the presence of numerous magmatic intrusions and extrusions of varied affinities. Accordingly, they constitute the best site to investigate, by dating and geochemistry, the evolution of the events affecting this segment of the Variscan orogeny. Two successions of identical magmatic events, shifted in the time, are identified, characterizing both Moldanubian (360 to 320 Ma) and the Saxothuringian (335 to 295 Ma) domains. These successions of magmatic events result of two major process. The progress of subducted and underplated continental crusts at Moho depth under continental blocks permits to shift from calc-alkaline to high potassic calc-alkaline magmatism. The radiogenic heat production from latter underplated continental crusts, in a first time, permits to generate magnesio-potassic magmas at depth. Then, this radiogenic heat permits to generate crustal magmas by intrusion of magnesio-potassic magmas rich in K, U and Th at mid-upper crust boundarie. These successions of magmatic events and particularly, the presence of the magnesio-potassic granites, imply a strong link between the Vosges Mts. and the eastern part of the Variscan orogeny (Black Forest, Bohemian Massif, the Alps and Corsica Batholith).

Three lateritic profiles from different localities and of varying depth and degrees of development were analyzed for precious metals, platinum, palladium, iridium and gold by radiochemical neutron-activation analysis. In addition, the distribution of major, minor and other trace constituents (iron, silicon, magnesium, nickel, cobalt, chromium, copper, manganese, zinc, uranium, sodium, chlorine and scandium) was determined. Instrumental activation analysis, radiochemical analysis and conventional chemical procedures were used. The mineralogy of the samples was studied using electron microscopy. Sufficient analytical data were obtained to justify the use of molecular proportions and net changes plots, and a coefficient correlation method, in order to elucidate the geochemical behaviour of the elements during the weathering processes.

During the Early Cretaceous a regionally extensive cover of dominantly siliciclastic sediments was deposited across the North African continental margin. Historically, these siliciclastic sediments have been considered to be a relatively homogeneous lithofacies known as the ‘Nubian sandstone’. This lithofacies is generally described as coarse grained, cross-bedded sandstone and is ascribed to a braided fluvial depositional environment. However, there have been few detailed sedimentological studies carried out on these sediments. Furthermore, the stratigraphic relationships between regional Early Cretaceous continental strata in different North African countries has only briefly been described and has only locally been related to equivalent marine deposits. In order to address these problems, this study focuses upon two main approaches. Firstly, outcrop analysis of the Messak Fm (SW Libya) and the Sidi Aïch Fm (C Tunisia) details and contrasts the lithofacies variability of Early Cretaceous siliciclastic sediments in North Africa. Secondly, a unified stratigraphic framework is erected for the Early Cretaceous of Algeria, Tunisia, Libya and Egypt and the palaeogeographic evolution is reconstructed. Detailed sedimentological investigation of the Messak Fm has identified greater variation in lithofacies and depositional processes than was previously recognised. By lithostratigraphic correlation with outcrops in northwest Libya, we show a fluvial system transported sediment northward into a wide fluvio-paralic basin covering western Libya. Several episodes of marine influence culminating in a distinct and regionally correlatable transgressive episode are identified. This is the first time that marine influence has been identified in the Murzuq Basin and increases the maximum known extent of marine transgression in the Early Cretaceous of Libya by 600km. The sedimentology of the Messak Fm is contrasted with the sandstone dominated Sidi Aïch Fm which, although showing similar lithofacies, was deposited in a marginal-shallow marine environment.Building upon previous reviews and new insights from the Messak Fm and Sidi Aïch Fm, a synthesis and reinterpretation of the spatial and temporal heterogeneity of sediments and depositional environments in this region throughout the Early Cretaceous is presented. During the Berriasian-Barremian, the North African platform coastline was dominated by a dry subtropical climate with moderate vegetation. The interior of the platform experienced a Savannah-like semi-arid climate with limited vegetation and palaeosol development but was crossed by extensive fluvial networks draining the equatorial tropics. During the Late Barremian-Early Aptian, simultaneous aridification and marine transgression led to a decreased detrital flux to the marginal basins and widespread deposition of marine carbonates and mudstones. During the Late Aptian-Albian the platform returned to a humid tropical climate. Widespread coarse grained fluvial sediments mark the base of this sequence and palaeosols occur locally. The results of this work have implications for the development and controls of large-scale fluvio-paralic systems and illustrate the fact that, in a limited accommodation epicontinental setting, relative sea-level may be the key control on sedimentation and depositional processes for many hundreds of kilometres inland of the lowstand coastline.