Isotope geochemical and geochronologic studies of basement units in the Central Western Carpathians (Slovakia)

In dieser Arbeit werden geochronologische und isotopen-geochemische Daten zur Entwicklung der Zentralen Westlichen Karpathen präsentiert. Die Karpathen bilden die östliche Fortsetzung der Alpen und können in drei Alpine Grundgebirgsdecken unterteilt werden, von denen zwei, die Veporische und die Gemerische, bearbeitet wurden. In der Veporischen Einheit wurden polymetamorphe Grundgebirgseinheiten untersucht, um deren genaue Altersstellung zu definieren und sie isotopengeochemisch zu klassifizieren. Dagegen wurde in der der Gemerischen Einheit, welche die Veporische Einheit überlagert, ein spezialisierter S-Typ Granit im Detail untersucht, um die petrogenetischen Prozesse, die zur magmatischen Entwicklung dieses Granits geführt haben, zu identifizieren. U-Pb Datierungen an Zirkonen der Veporischen Grundgebirgseinheiten zeigen für die gesamte Veporische Einheit ordovizische Entsehungsalter an (440-470 Ma). Diese Datierungen revidieren publizierte kambrische Entstehungsalter dieses Grundgebirges. Die Isotopensignatur (epsilon Nd und 87Sr/86Sr) der ordovizischen Grundgebirgseinheiten, bestehend aus stark überprägten Amphiboliten und Gneissen, ist von der Signatur der sich im Norden anschliessenden Tatrischen Einheit gut unterscheidbar. Die Bleiisotopenzusammensetzung dieser Gesteine ist stark krustal geprägt und überschneidet sich mit der der Tatrischen Einheit. Zusammen mit den T-DM Altern sind diese Einheiten vergleichbar mit prävariskischen Einheiten der Alpen. Somit kann das ordovizische Grundgebirge zu den peri-Gondwana Terranen gezählt werden, die an einem aktiven Kontinentalrand im Norden von Gondwana gebildet wurden. In den Gesteinen der Veporischen Einheit wurde im Weiteren eine starke metamorphe überprägung und intensiver felsischer Magmatismus karbonischen Alters erkannt (320-350 Ma). Dieses Ereignis ist zeitgleich mit dem Magmatismus, welcher hauptsächlich in der sich im Norden anschliessenden Tatrischen Einheit beobachtet wird. Dieser gehört der variskischen Orogenese an. Intensive alpine Deformation und Metamorphose konnte in der südlichen Veporischen Einheit anhand der Einzelzirkondatierungen und der Isotopendaten der ordovizischen Einheiten nachgewiesen werden. Am Dlha Dolina Granit in der Gemerischen Einheit können starke Fraktionierungs- und Auto-Metasomatose-Effekte beobachtet werden. Durch die magmatische Fraktionierung wird eine Anreicherung der SEE erzeugt, wogegen die Metasomatose die SEE stark verarmt. Es kommt sogar zur Ausbildung eines Tetraden Effektes im SEE Muster, welche den starken Einfluss von Fluiden während der spät-magmatischen Phase belegt. Gesamtgesteins Pb-Pb Daten beschränken das minimale Intrusionsalter dieses Granites auf 240 Ma. Dieses Alter ist in guter übereinstimmung mit den Sr-Isotopendaten der magmatisch dominierten Gesteine, wohingegen die stark metasomatisch geprägten Gesteine ein zu radiogenes 87Sr/86Sri aufweisen. Während dieser Arbeit wurde intensiv mit der Blei-Isotopenzusammensetzung von Gesamtgesteinsproben gearbeitet. Um die Auswertung dieser Daten optimieren zu können wurde ein Computerscript für das GPL Programm Octave erstellt. Die Hauptaufgabe dieses Scripts besteht darin, Regressionen für geochronologische Anwendungen gemäss York (1969) zu berechnen. Ausserdem können mu und kappa-Werte für diese Regressionen berechnet und eine Hauptkomponentenanalyse, welche hilfreich für den Vergleich von zwei Datensätzen ist, durchgeführt werden. Am Ende der vorliegenden Arbeit wird die analytische Methode für einen Mikrowellen beschleunigten Säureaufschluss von granitoidem Material zur Bestimmung der Sr- und Nd-Isotopenzusammensetzung und der Elementkonzentrationen vorgestellt. Diese kombinierte Methode nutzt ein TIMS für die Sr und Nd Isotopenmessungen und eine Einzelkollektor-ICPMS zur Bestimmung der SEE, Rb und Sr Konzentrationen, welche mithilfe von relativen Sensitivitätsfaktoren gegenüber einem internen Standard quantifiziert werden. Diese Methode wird durch Messungen von internationalen Referenzmaterialien bewertet. Die Ergebnisse zeigen eine Reproduzierbarkeit von <10% für die Elementkonzentrationen und von <5% für Elementverhältnisse.

Characterization of igneous terranes by zircon dating: implications for the UHP relicts occurrences and suture identification in the Central Rhodope, Northern Greece

One of the key for the understanding of an orogenic belt is the characterization of the terranes involved and the identification of the suture(s) separating crustal blocks: these are essential information for large-scale paleo-reconstructions. In addition, the structural relationships between the terranes involved in the collisional processes and the eventual UHP relicts may provide first order inputs to exhumation models of subducted rocks. The structure of the Rhodope Massif (northern Greece and southern Bulgaria) results from the stacking of high-grade nappes during a continental collision, which age is comprised between Latest-Jurassic and Early-Cenozoic. UHP and HP relicts, associated with oceanic and ultramafic material, suggest the presence of a dismembered suture zone within the massif. The location of this suture remains unclear; furthermore, up to now, the UHP and eclogitic localities represent isolated spots and no synthesis on their structural position within the massif has been proposed. The first aim of this work is to define the relationships between HP-UHP relicts, crustal blocks, shear zones and amphibolitic material. To achieve this objective, we characterized the accreted blocks in terms of protoliths ages of the orthogneisses mainly along two cross sections on the Greek part of the belt. Geochemical affinities of meta-igneous rocks served as a complementary tool for terrane characterization and geodynamic interpretation. Single-zircon Pb-Pb evaporation and zircon U-Pb SHRIMP dating of orthogneiss protoliths define two groups of intrusion-ages: Permo-Carboniferous and Late Jurassic-Early Cretaceous. Structurally, these two groups correspond to distinct units: the Late Jurassic gneissic complex overthrusts the one bearing the Permo-Carboniferous orthogneisses. Mylonites, eclogites, amphibolites of oceanic affinities, and UHP micaschists, mark a “melange” zone, intensively sheared towards the SW, which separates the two units. Thus, we interpret them as two distinct terranes, the Rhodope and Thracia terranes, separated by the Nestos suture. The correlation of our findings in northern Greece to the Bulgarian part of the Massif suggests a northern rooting of the Nestos Suture. This configuration results of the closure of a marginal oceanic basin of the Tethys system by a north-directed subduction. This interpretation is supported by the geochemical affinities of the orthogneisses: the Late-Jurassic igneous rocks formed by subduction-related magmatism, pprobably the same north-directed subduction that gave rise to the UHP metamorphism of the metasediments of the “melange” zone. It is noteworthy that the UHP-HP relicts seem to be restricted to the contact between the two terranes suggesting that the UHP relicts are exhumed only within the suture zone. Furthermore, the singularity of the suture suggests that the Late-Jurassic subduction explains the occurrence of UHP and eclogite relicts in the Central Rhodope despite the large age range previously attributed the UHP and/or HP stage.

High-resolution reconstruction of Holocene climate variability and environmental changes in the North Pacific using bivalve shells

Bivalve mollusk shells are useful tools for multi-species and multi-proxy paleoenvironmental reconstructions with a high temporal and spatial resolution. Past environmental conditions can be reconstructed from shell growth and stable oxygen and carbon isotope ratios, which present an archive for temperature, freshwater fluxes and primary productivity. The purpose of this thesis is the reconstruction of Holocene climate and environmental variations in the North Pacific with a high spatial and temporal resolution using marine bivalve shells. This thesis focuses on several different Holocene time periods and multiple regions in the North Pacific, including: Japan, Alaska (AK), British Columbia (BC) and Washington State, which are affected by the monsoon, Pacific Decadal Oscillation (PDO) and El Niño/Southern Oscillation (ENSO). Such high-resolution proxy data from the marine realm of mid- and high-latitudes are still rare. Therefore, this study contributes to the optimization and verification of climate models. However, before using bivalves for environmental reconstructions and seasonality studies, life history traits must be well studied to temporally align and interpret the geochemical record. These calibration studies are essential to ascertain the usefulness of selected bivalve species as paleoclimate proxy archives. This work focuses on two bivalve species, the short-lived Saxidomus gigantea and the long-lived Panopea abrupta. Sclerochronology and oxygen isotope ratios of different shell layers of P. abrupta were studied in order to test the reliability of this species as a climate archive. The annual increments are clearly discernable in umbonal shell portions and the increments widths should be measured in these shell portions. A reliable reconstruction of paleotemperatures may only be achieved by exclusively sampling the outer shell layer of multiple contemporaneous specimens. Life history traits (e.g., timing of growth line formation, duration of the growing season and growth rates) and stable isotope ratios of recent S. gigantea from AK and BC were analyzed in detail. Furthermore, a growth-temperature model based on S. gigantea shells from Alaska was established, which provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). This approach allows the independent measurement of water temperature and salinity from variations in the width of lunar daily growth increments of S. gigantea. Temperature explains 70% of the variability in shell growth. The model was calibrated and tested with modern shells and then applied to archaeological specimens. The time period between 988 and 1447 cal yrs BP was characterized by colder (~1-2°C) and much drier (2-5 PSU) summers, and a likely much slower flowing ACC than at present. In contrast, the summers during the time interval of 599-1014 cal yrs BP were colder (up to 3°C) and fresher (1-2 PSU) than today. The Aleutian Low may have been stronger and the ACC was probably flowing faster during this time.

Aircraft-based in-situ aerosol mass spectrometry: Chemical characterization and source identification of submicron particulate matter in the free and upper troposphere and lower stratosphere

The composition of the atmosphere is frequently perturbed by the emission of gaseous and particulate matter from natural as well as anthropogenic sources. While the impact of trace gases on the radiative forcing of the climate is relatively well understood the role of aerosol is far more uncertain. Therefore, the study of the vertical distribution of particulate matter in the atmosphere and its chemical composition contribute valuable information to bridge this gap of knowledge. The chemical composition of aerosol reveals information on properties such as radiative behavior and hygroscopicity and therefore cloud condensation or ice nucleus potential. rnThis thesis focuses on aerosol pollution plumes observed in 2008 during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) campaign over Greenland in June/July and CONCERT (Contrail and Cirrus Experiment) campaign over Central and Western Europe in October/November. Measurements were performed with an Aerodyne compact time-of-flight aerosol mass spectrometer (AMS) capable of online size-resolved chemical characterization of non-refractory submicron particles. In addition, the origins of pollution plumes were determined by means of modeling tools. The characterized pollution episodes originated from a large variety of sources and were encountered at distinct altitudes. They included pure natural emissions from two volcanic eruptions in 2008. By the time of detection over Western Europe between 10 and 12 km altitude the plume was about 3 months old and composed to 71 % of particulate sulfate and 21 % of carbonaceous compounds. Also, biomass burning (BB) plumes were observed over Greenland between 4 and 7 km altitude (free troposphere) originating from Canada and East Siberia. The long-range transport took roughly one and two weeks, respectively. The aerosol was composed of 78 % organic matter and 22 % particulate sulfate. Some Canadian and all Siberian BB plumes were mixed with anthropogenic emissions from fossil fuel combustion (FF) in North America and East Asia. It was found that the contribution of particulate sulfate increased with growing influences from anthropogenic activity and Asia reaching up to 37 % after more than two weeks of transport time. The most exclusively anthropogenic emission source probed in the upper troposphere was engine exhaust from commercial aircraft liners over Germany. However, in-situ characterization of this aerosol type during aircraft chasing was not possible. All long-range transport aerosol was found to have an O:C ratio close to or greater than 1 implying that low-volatility oxygenated organic aerosol was present in each case despite the variety of origins and the large range in age from 3 to 100 days. This leads to the conclusion that organic particulate matter reaches a final and uniform state of oxygenation after at least 3 days in the free troposphere. rnExcept for aircraft exhaust all emission sources mentioned above are surface-bound and thus rely on different types of vertical transport mechanisms, such as direct high altitude injection in the case of a volcanic eruption, or severe BB, or uplift by convection, to reach higher altitudes where particles can travel long distances before removal mainly caused by cloud scavenging. A lifetime for North American mixed BB and FF aerosol of 7 to 11 days was derived. This in consequence means that emission from surface point sources, e.g. volcanoes, or regions, e.g. East Asia, do not only have a relevant impact on the immediate surroundings but rather on a hemispheric scale including such climate sensitive zones as the tropopause or the Arctic.