Sedimentology and tectonic history of late Archaean sedimentary successions in Zimbabwe

ZusammenfassungSpätarchaische Sedimentgesteine (ca. 2,65 Milliarden Jahre alt) wurden in Grünsteingürteln des Simbabwe Kratons untersucht. In dem Belingwe Grünsteingürtel ist granitoides Grundgebirge von einer allochthonen Einheit aus vulkanischen Gesteinen und Vorlandbeckensedimenten überlagert. Die sedimentäre Abfolge besteht aus Flachwasserkalken und Turbiditen. Unterschiedliche Faziestypen der Kalksteine sind in sedimentäre Verflachungszyklen angeordnet. Eustatische Meeresspiegelschwankungen werden als Ursache der zyklischen Sedimentation angenommen. Sedimentologische, geochemische und strukturelle Analysen zeigen die Bedeutung horizontal-tektonischer Prozesse für die Entstehung dieses Grünsteingürtels an.Sedimentgesteine des Midlands Grünsteingürtels lagern zwischen ozeanischen, mafischen Vulkaniten und kontinentalen, granitoiden Gneisen. Die Art der Abfolge sedimentärer Fazies, beginnend mit Turbiditen und überlagert von flachmarinen Schelfsedimenten und alluvialen Ablagerungen, sowie geologische und geochemische Hinweise aus den benachbarten Gesteinsserien lassen auf Ablagerung während der Kollision zwischen einem ozeanischen Plateau/Inselbogen und einem kontinentalen Krustenfragmentes schließen.In dem Bindura-Shamva Grünsteingürtel können zwei Sedimentgesteinseinheiten unterschieden werden, eine alluvial—flachmarine Abfolge und eine tiefmarin—fluviatile Abfolge. Extensionstektonik verursachte wahrscheinlich die Bildung des Sedimentbeckens. Die spätere Phase der Beckenbildung war jedoch ähnlich jener in modernen Vorlandbecken.Schichtparallele Eisensteinhorizonte sind häufig entlang von Sediment-Vulkanit-Kontakten zu finden. Diese Gesteine werden als silifizierte und von Sulfiden imprägnierte Scherzonen interpretiert. Syntektonische hydrothermale Alteration von Gesteinen entlang der Störungszonen führte zur Bildung dieser 'tektonischen Eisensteine'.

Oceanic crust and island arc formation in Central Asia during late Neoproterozoic times - evidence from petrological and geochemical studies

Die vorliegende Arbeit behandelt die Entwicklung des 570 Ma alten, neoproterozoischen Agardagh - Tes-Chem Ophioliths (ATCO) in Zentralasien. Dieser Ophiolith liegt südwestlich des Baikalsees (50.5° N, 95° E) und wurde im frühen Stadium der Akkretion des Zentralasiatischen Mobilgürtels auf den nordwestlichen Rand des Tuvinisch-Mongolischen Mikrokontinentes aufgeschoben. Bei dem Zentralasiatische Mobilgürtel handelt es sich um einen riesigen Akkretions-Subduktionskomplex, der heute das größte zusammenhängende Orogen der Erde darstellt. Im Rahmen dieser Arbeit wurden eine Reihe plutonischer und vulkanischer Gesteine, sowie verschiedene Mantelgesteine des ATCO mittels mikroanalytischer und geochemischer Verfahren untersucht (Elektronenstrahlmikrosonde, Ionenstrahlmikrosonde, Spurenelement- und Isotopengeochemie). Die Auswertung dieser Daten ermöglichte die Entwicklung eines geodynamisch-petrologischen Modells zur Entstehung des ATCO. Die vulkanischen Gesteine lassen sich aufgrund ihrer Spurenelement- und Isotopenzusammensetzung in inselbogenbezogene und back-arc Becken bezogene Gesteine (IA-Gesteine und BAB-Gesteine) unterscheiden. Darüber hinaus gibt es eine weitere, nicht eindeutig zuzuordnende Gruppe, die hauptsächlich mafische Gänge umfasst. Der grösste Teil der untersuchen Vulkanite gehört zur Gruppe der IA-Gesteine. Es handelt sich um Al-reiche Basalte und basaltische Andesite, welche aus einem evolvierten Stammmagma mit Mg# 0.60, Cr ~ 180 µg/g und Ni ~ 95 µg/g hauptsächlich durch Klinopyroxenfraktionierung entstanden sind. Das Stammmagma selbst entstand durch Fraktionierung von ca. 12 % Olivin und geringen Anteilen von Cr-Spinell aus einer primären, aus dem Mantel abgeleiteten Schmelze. Die IA-Gesteine haben hohe Konzentrationen an inkompatiblen Spurenelementen (leichte-(L)- Seltenerdelement-(SEE)-Konzentrationen etwa 100-fach chondritisch, chondrit-normierte (La/Yb)c von 14.6 - 5.1), negative Nb-Anomalien (Nb/La = 0.37 - 0.62) und niedrige Zr/Nb Verhältnisse (7 - 14) relativ zu den BAB-Gesteinen. Initiale eNd Werte liegen bei etwa +5.5, initiale Bleiisotopenverhältnisse sind: 206Pb/204Pb = 17.39 - 18.45, 207Pb/204Pb = 15.49 - 15.61, 208Pb/204Pb = 37.06 - 38.05. Die Anreicherung lithophiler inkompatibler Spurenelemente (LILE) in dieser Gruppe ist signifikant (Ba/La = 11 - 130) und zeigt den Einfluss subduzierter Komponenten an. Die BAB-Gesteine repräsentieren Schmelzen, die sehr wahrscheinlich aus der gleichen Mantelquelle wie die IA-Gesteine stammen, aber durch höhere Aufschmelzgrade (8 - 15 %) und ohne den Einfluss subduzierter Komponenten entstanden sind. Sie haben niedrigere Konzentrationen an inkompatiblen Spurenelementen, flache SEE-Muster ((La/Yb)c = 0.6 - 2.4) und höhere initiale eNd Werte zwischen +7.8 und +8.5. Nb Anomalien existieren nicht und Zr/Nb Verhältnisse sind hoch (21 - 48). Um die geochemische Entwicklung der vulkanischen Gesteine des ATCO zu erklären, sind mindestens drei Komponenten erforderlich: (1) eine angereicherte, ozeaninselbasalt-ähnliche Komponente mit hoher Nb Konzentration über ~ 30 µg/g, einem niedrigen Zr/Nb Verhältnis (ca. 6.5), einem niedrigen initialen eNd Wert (um 0), aber mit radiogenen 206Pb/204Pb-, 207Pb/204Pb- und 208Pb/204Pb-Verhältnissen; (2) eine N-MORB ähnliche back-arc Becken Komponente mit flachem SEE-Muster und einem hohen initialen eNd Wert von mindestens +8.5, und (3) eine Inselbogen-Komponente aus einer verarmten Mantelquelle, welche durch die abtauchende Platte geochemisch modifiziert wurde. Die geochemische Entstehung der ATCO Vulkanite lässt sich dann am besten durch eine Kombination aus Quellenkontamination, fraktionierte Kristallisation und Magmenmischung erklären. Geodynamisch gesehen entstand der ATCO sehr wahrscheinlich in einem intraozeanischen Inselbogen - back-arc System. Bei den untersuchten Plutoniten handelt es sich um ultramafische Kumulate (Wehrlite und Pyroxenite) sowie um gabbroische Plutonite (Olivin-Gabbros bis Diorite). Die geochemischen Charakteristika der mafischen Plutonite sind deutlich unterschiedlich zu denen der vulkanischen Gesteine, weshalb sie sehr wahrscheinlich ein späteres Entwicklungsstadium des ATCO repräsentieren. Die Spurenelement-Konzentrationen in den Klinopyroxenen der ultramafischen Kumulate sind extrem niedrig, mit etwa 0.1- bis 1-fach chondritischen SEE-Konzentrationen und mit deutlich LSEE-verarmten Mustern ((La/Yb)c = 0.27 - 0.52). Berechnete Gleichgewichtsschmelzen der ultramafischen Kumulate zeigen grosse Ähnlichkeit zu primären boninitischen Schmelzen. Die primären Magmen waren daher boninitischer Zusammensetzung und entstanden in dem durch vorausgegangene Schmelzprozesse stark verarmten Mantelkeil über einer Subduktionszone. Niedrige Spurenelement-Konzentrationen zeigen einen geringen Einfluss der abtauchenden Platte an. Die Spurenelement-Konzentrationen der Gabbros sind ebenfalls niedrig, mit etwa 0.5 - 10-fach chondritischen SEE-Konzentrationen und mit variablen SEE-Mustern ((La/Yb)c = 0.25 - 2.6). Analog zu den Vulkaniten der IA-Gruppe haben alle Gabbros eine negative Nb-Anomalie mit Nb/La = 0.01 - 0.31. Die initialen eNd Werte der Gabbros variieren zwischen +4.8 und +7.1, mit einem Mittelwert von +5.9, und sind damit identisch mit denen der IA-Vulkanite. Bei den untersuchten Mantelgesteinen handelt es sich um teilweise serpentinisierte Dunite und Harzburgite, die alle durch hohe Mg/Si- und niedrige Al/Si-Verhältnisse gekennzeichnet sind. Dies zeigt einen refraktären Charakter an und steht in guter Übereinstimmung mit den hohen Cr-Zahlen (Cr#) der Spinelle (bis zu Cr# = 0.83), auf deren Basis der Aufschmelzgrad der residuellen Mantelgesteine berechnet wurde. Dieser beträgt etwa 25 %. Die geochemische Zusammensetzung und die petrologischen Daten der Ultramafite und Gabbros lassen sich am besten erklären, wenn man für die Entstehung dieser Gesteine einen zweistufigen Prozess annimmt. In einer ersten Stufe entstanden die ultramafischen Kumulate unter hohem Druck in einer Magmenkammer an der Krustenbasis, hauptsächlich durch Klinopyroxen-Fraktionierung. Bei dieser Magmenkammer handelte es sich um ein offenes System, dem von unten laufend neue Schmelze zugeführt wurde, und aus dem im oberen Bereich evolviertere Schmelzen geringerer Dichte entwichen. Diese evolvierten Schmelzen stiegen in flachere krustale Bereiche auf und bildeten dort meist isolierte Intrusionskörper. Diese Intrusionskörper erstarrten ohne Magmen-Nachschub, weshalb petrographisch sehr unterschiedliche Gesteine entstehen konnten. Eine geochemische Modifikation der abkühlenden Schmelzen erfolgte allerdings durch die Assimilation von Nebengestein. Da innerhalb der Gabbros keine signifikante Variation der initalen eNd Werte existiert, handelte es sich bei dem assimilierten Material hauptsächlich um vulkanische Gesteine des ATCO und nicht um ältere, möglicherweise kontinentale Kruste.

Visual scanning in sports actions: comparison between soccer goalkeepers and judo fighters

Visual search and oculomotor behaviour are believed to be very relevant for athlete performance, especially for sports requiring refined visuo-motor coordination skills. Modern coaches believe that a correct visuo-motor strategy may be part of advanced training programs. In this thesis two experiments are reported in which gaze behaviour of expert and novice athletes were investigated while they were doing a real sport specific task. The experiments concern two different sports: judo and soccer. In each experiment, number of fixations, fixation locations and mean fixation duration (ms) were considered. An observational analysis was done at the end of the paper to see perceptual differences between near and far space. Purpose: The aim of the judo study was to delineate differences in gaze behaviour characteristics between a population of athletes and one of non athletes. Aspects specifically investigated were: search rate, search order and viewing time across different conditions in a real-world task. The second study was aimed at identifying gaze behaviour in varsity soccer goalkeepers while facing a penalty kick executed with instep and inside foot. Then an attempt has been done to compare the gaze strategies of expert judoka and soccer goalkeepers in order to delineate possible differences related to the different conditions of reacting to events occurring in near (peripersonal) or far (extrapersonal) space. Judo Methods: A sample of 9 judoka (black belt) and 11 near judoka (white belt) were studied. Eye movements were recorded at 500Hz using a video based eye tracker (EyeLink II). Each subject participated in 40 sessions for about 40 minutes. Gaze behaviour was considered as average number of locations fixated per trial, the average number of fixations per trial, and mean fixation duration. Soccer Methods: Seven (n = 7) intermediate level male volunteered for the experiment. The kickers and goalkeepers, had at least varsity level soccer experience. The vision-in-action (VIA) system (Vickers 1996; Vickers 2007) was used to collect the coupled gaze and motor behaviours of the goalkeepers. This system integrated input from a mobile eye tracking system (Applied Sciences Laboratories) with an external video of the goalkeeper’s saving actions. The goalkeepers took 30 penalty kicks on a synthetic pitch in accordance with FIFA (2008) laws. Judo Results: Results indicate that experts group differed significantly from near expert for fixations duration, and number of fixations per trial. The expert judokas used a less exhaustive search strategy involving fewer fixations of longer duration than their novice counterparts and focused on central regions of the body. The results showed that in defence and attack situation expert group did a greater number of transitions with respect to their novice counterpart. Soccer Results: We found significant main effect for the number of locations fixated across outcome (goal/save) but not for foot contact (instep/inside). Participants spent more time fixating the areas in instep than inside kick and in goal than in save situation. Mean and standard error in search strategy as a result of foot contact and outcome indicate that the most gaze behaviour start and finish on ball interest areas. Conclusions: Expert goalkeepers tend to spend more time in inside-save than instep-save penalty, differences that was opposite in scored penalty kick. Judo results show that differences in visual behaviour related to the level of expertise appear mainly when the test presentation is continuous, last for a relatively long period of time and present a high level of uncertainty with regard to the chronology and the nature of events. Expert judoist performers “anchor” the fovea on central regions of the scene (lapel and face) while using peripheral vision to monitor opponents’ limb movements. The differences between judo and soccer gaze strategies are discussed on the light of physiological and neuropsychological differences between near and far space perception.

The Mavuradonha Layered Complex

Der Mavuradonha Layered Complex repräsentiert einen 862 ? 4 Ma alten Komplex, der in einem tiefkrustalen Milieu intrudierte. Eine mehrphasige magmatische Differentiation ist in macro-rhythmischen Einheiten und kleinmaßstäblichen Lagenbau erkennbar, aus denen die Kristallisationssequenzen Pyroxenite, Gabbros/Norite, Leuko-Gabbros oder Ferro-Gabbro und Anorthosite resultieren. ?Nd-Werte zwischen + 0.3 und + 6.6 zeigen krustale Kontamination eines aus dem verarmten Mantel stammenden, tholeiitischen Ursprungsmagma an. ?Nd-Werte (+ 2.4 bis - 3.5) anderer tholeiitischer Gabbros in unmittelbarer Nähe des Komplexes deuten ebenfalls auf Krustenkontamination hin, jedoch in stärkerem Maße.Der Komplex wurde um 554 ? 13 Ma unter granulitfaziellen Bedingungen von 13 ? 2 kbar und 840 ? 30° C überprägt. Die anschließende retrograde, amphibolitfazielle Metamorphose mit Bedingungen von 11 ? 2 kbar und 680 ? 20° C ereignete sich um 546 ? 9 Ma. Abkühlung bis zur Grünschieferfazies erfolgte spätestens um 501 ? 6 Ma.Die vorgestellten Daten zeigen, dass sich der Sambesi-Gürtel im NE Simbabwes als fehlgeschlagenes Rift oder intrakratonisches Becken während einer frühen Pan-Afrikanischen Extensionsphase entwickelte, während die granulitfazielle Metamorphose um 300 Ma später erfolgte. Somit deutet die Intrusion des Mavuradonha Layered Complex rift-bedingten Magmatismus in einer frühen Riftphase an, während das Becken oder Rift während der Pan-Afrikanischen Orogenese geschlossen wurde.

A structural and metamorphic study of the southern Menderes Massif (Western Turkey)

P-T conditions, paragenetic studies and the relation between mineral growth, deformation and - when possible- isograd minerals have been used to describe the type of metamorphism involved within lower units of the southern Menderes Massif of the Anatolide Belt in western Turkey. The study areas mainly consist of Proterozoic orthogneiss and surrounding schists of presumed Paleozoic age. Both units are seen as nappes in the southern study area, the Çine and the Selimiye nappe, on the whole corresponding to Proterozoic orthogneiss and surrounding schists, respectively. The Çine and Selimiye nappes are part of a complex geological structure within the core series of the Menderes Massif. Their emplacement under lower greenschist facies conditions, would result from closure of the northern Neo-Thethys branch during the Eocene. These two nappes are separated by a major tectonic structure, the Selimiye shear zone, which records top-to-the-S shearing under greenschist facies conditions. Amphibolite to upper amphibolite facies metamorphism is widely developed within the metasedimentary rocks of the Çine nappe whereas no metamorphism exceeding lower amphibolite facies has been observed in the Selimiye nappe. In the southern margin of the Çine Massif, around Selimiye and Millas villages, detailed sampling has been undertaken in order to map mineral isograds within the Selimiye nappe and to specify P-T conditions in this area. The data collected in this area reveals a global prograde normal erosion field gradient from south to north and toward the orthogneiss. The mineralogical parageneses and P-T estimates are correlated with Barrovian-type metamorphism. A jump of P-T conditions across the Selimiye shear zone has been identified and estimated c. 2 kbar and 100 °C which evidences the presence of amphibolite facies metasedimentary rocks near the orthogneiss. Metasedimentary rocks from the overlying Selimiye nappe have maximum P-T conditions of c. 4-5 kbar and c. 525 °C near the base of the nappe. Metasedimentary rocks from the Çine nappe underneath the Selimiye shear zone record maximum P-T conditions of about 7 kbar and >550 °C. Kinematic indicators in both nappes consistently show a top-S shear sense. Metamorphic grade in the Selimiye nappe decreases structurally upwards as indicated by mineral isograds defining the garnet-chlorite zone at the base, the chloritoid-biotite zone and the biotite-chlorite zone at the top of the nappe. The mineral isograds in the Selimiye nappe run parallel to the regional SR foliation. 40Ar/39Ar mica ages indicate an Eocene age of metamorphism in the Selimiye nappe and underneath the Çine nappe in this area. Metasedimentary rocks of the Çine nappe 20-30 km north of the Selimiye shear zone record maximum P-T conditions of 8-11 kbar and 600-650 °C. Kinematic indicators show mainly top-N shear sense associated with prograde amphibolite facies metamorphism. An age of about 550 Ma could be indicated for amphibolite facies metamorphism and associated top-N shear in the orthogneiss and metasedimentary rocks of the Çine nappe. However, there is no evidence for polymetamorphism in the 6 metasedimentary rocks of the Çine nappe, making tectonic interpretations about late Neoproterozoic to Cambrian and Tertiary metamorphic events speculative. In the western margin of the Çine Massif metamorphic mineral parageneses and pressure– temperature conditions lead to similar conclusion regarding the erosion field gradient, prograde normal toward the orthogneiss. The contact between orthogneiss and surrounding metasedimentary rocks is mylonitic and syn-metamorphism. P-T estimates are those already observed within the Selimiye nappe and correlated with lower amphibolite facies parageneses. Finally additional data in the eastern part and a general paragenetic study within the Menderes Massif lower units, the Çine and the Selimiye nappes, strongly suggest a single Barrovian-type metamorphism predating Eocene emplacement of the high pressure–low temperature Lycean and Cycladic blueschist nappes. Metamorphic mineral parageneses and pressure–temperature conditions do not support the recently proposed model of high pressure–low temperature metamorphic overprinting, which implies burial of the lower units of the Menderes Massif up to depth of 30 km, as a result of closure of the Neo-Tethys. According to the geochronological problem outlined during this thesis, there are two possible schemes: either Barrovian-type metamorphism is Proterozoic in age and part of the sediments from Selimiye nappe (lower amphibolite facies) has to be proterozoic of age too, or Barrovian-type metamorphism in Eocene of age. In the first case the structure observed now in the core series would correspond to simple exhumation of Proterozoic basement. In the latter case a possible correlation with closure of Neo-Tethys (sensu stricto, southern branch) is envisaged.

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.

Climate signatures in corals of the tropical-temperate transition zone (Late Miocene, Crete/Greece)

The present study describes a Late Miocene (early Tortonian - early Messinian) transitional carbonate system that combines elements of tropical and cool-water carbonate systems (Irakleion Basin, island of Crete, Greece). As documented by stratal geometries, the submarine topography of the basin was controlled by tilting blocks. Coral reefs formed by Porites and Tarbellastrea occurred in a narrow clastic coastal belt along a „central Cretan landmass“, and steep escarpments formed by faulting. Extensive covers of level-bottom communities existed in a low-energy environment on the gentle dip-slope ramps of the blocks that show the widest geographical distribution within the basin. Consistent patterns of landward and basinward shift of coastal onlap in all outcrop studies reveal an overriding control of 3rd and 4th order sea level changes on sediment dynamics and facies distributions over block movements. An increasingly dry climate and the complex submarine topography of the fault block mosaic kept sediment and nutrient discharge at a minimum. The skeletal limestone facies therefore reflects oligotrophic conditions and a sea surface temperature (SST) near the lower threshold temperature of coral reefs in a climatic position transitional between the tropical coral reef belt and the temperate zone. Stable isotope records (δ18O, δ13C) from massiv, exceptionally preserved Late Miocene aragonite coral skeletons reflect seasonal changes in sea surface temperature and symbiont autotrophy. Spectral analysis of a 69 years coral δ18O record reveals significant variance at interannual time scales (5-6 years) that matches the present-day eastern Mediterranean climate variability controlled by the Arctic Oscillation/North Atlantic Oscillation (AO/NAO), the Northern Hemisphere’s dominant mode of atmospheric variability. Supported by simulations with a complex atmospheric general circulation model coupled to a mixed-layer ocean model, it is suggested, that climate dynamics in the eastern Mediterranean and central Europe reflect atmospheric variability related to the Icelandic Low 10 million years ago. Usually, Miocene corals are transformed in calcite spar in geological time and isotope values are reset by diagenetic alteration. It is demonstrated that the relicts of growth bands represent an intriguing source of information for the growth conditions of fossil corals. Recrystallized growth bands were measured systematically in massive Porites from Crete. The Late Miocene corals were growing slowly with 2-4 mm/yr, compatible with present-day Porites from high latitude reefs, a relationship that fits the position of Crete at the margin of the Miocene tropical reef belt. Over Late Miocene time (Tortonian - early Messinian) growth rates remained remarkably constant, and if the modern growth temperature relationship for massive Porites applies to the Neogene, minimum (winter) SST did not exceed 19-21°C.

Fault delineation and stress orientations from the analysis of background, low magnitude seismicity in Southern Apennines (Italy)

The aim of this work was to show that refined analyses of background, low magnitude seismicity allow to delineate the main active faults and to accurately estimate the directions of the regional tectonic stress that characterize the Southern Apennines (Italy), a structurally complex area with high seismic potential. Thanks the presence in the area of an integrated dense and wide dynamic network, was possible to analyzed an high quality microearthquake data-set consisting of 1312 events that occurred from August 2005 to April 2011 by integrating the data recorded at 42 seismic stations of various networks. The refined seismicity location and focal mechanisms well delineate a system of NW-SE striking normal faults along the Apenninic chain and an approximately E-W oriented, strike-slip fault, transversely cutting the belt. The seismicity along the chain does not occur on a single fault but in a volume, delimited by the faults activated during the 1980 Irpinia M 6.9 earthquake, on sub-parallel predominant normal faults. Results show that the recent low magnitude earthquakes belongs to the background seismicity and they are likely generated along the major fault segments activated during the most recent earthquakes, suggesting that they are still active today thirty years after the mainshock occurrences. In this sense, this study gives a new perspective to the application of the high quality records of low magnitude background seismicity for the identification and characterization of active fault systems. The analysis of the stress tensor inversion provides two equivalent models to explain the microearthquake generation along both the NW-SE striking normal faults and the E- W oriented fault with a dominant dextral strike-slip motion, but having different geological interpretations. We suggest that the NW-SE-striking Africa-Eurasia convergence acts in the background of all these structures, playing a primary and unifying role in the seismotectonics of the whole region.

Caratterizzazione geochimica dei sedimenti di alcuni siti di alimentazione e di riproduzione del Fenicottero (Phoenicopterus roseus) nel Mediterraneo

Il presente lavoro è stato avviato per caratterizzare dal punto di vista geochimico i siti di alimentazione e di riproduzione del Fenicottero ed ottenere così un dataset relativo alle concentrazioni di metalli nei sedimenti di alcune zone umide, utilizzate da questa specie per alimentarsi e riprodursi e scarsamente studiate in passato. Il lavoro di tesi qui presentato si è articolato in due differenti studi: • Un’indagine dettagliata sulla presenza e distribuzione di metalli ed elementi potenzialmente tossici nei sedimenti provenenti da alcune delle principali aree di alimentazione del Fenicottero nell’Alto Adriatico; • Un’indagine preliminare relativa ai metalli contenuti nei sedimenti provenienti da alcuni siti riproduttivi del Fenicottero nel Mediterraneo occidentale. Per quanto riguarda i siti di alimentazione sono state campionate tre zone umide dell’area deltizia del fiume Po: le Valli di Rosolina, Valle Bertuzzi e le Valli di Comacchio. Riguardo i siti riproduttivi sono state campionate cinque aree umide nel Mediterraneo occidentale: le Paludi dell’Odiel nel sud-ovest della Spagna, la Camargue in Francia, lo Stagno di Cagliari in Sardegna, le Valli di Comacchio in Emilia-Romagna e Valle Dogà in Laguna di Venezia. I 57 campioni raccolti sono stati analizzati mediante analisi XRF ed analisi termiche, presso il Dipartimento di Scienze Biologiche, Geologiche e Ambientali, dell’Università di Bologna, e mediante analisi ICP-MS, presso l’AcmeLabs di Vancouver (Canada). Il complesso deltizio del fiume Po ha registrato concentrazioni anomale di Cd, Pb, Sb e Sn mostrando un generale arricchimento nei sedimenti delle aree umide investigate rispetto al valore di riferimento. Analizzando le correlazioni di questo elemento con le frazioni dei sedimenti, si è evidenziata una buona correlazione con la componente organica del sedimento. Ciò potrebbe indicare la presenza di fenomeni di adsorbimento di questo elemento ad opera della matrice organica. L’area di studio non è apparentemente interessata da importanti attività industriali, che potrebbero in parte spiegare le elevate concentrazioni di Cd, Pb, Sb e Sn. Due potenziali sorgenti antropogeniche di contaminazione sono rappresentate da un’estensiva attività agricola nelle zone limitrofe alle valli considerate e da un elevata pressione venatoria esercitata proprio all’interno di queste zone umide. In particolare, quest’ultima attività umana, potrebbe rappresentare una spiegazione più che plausibile per l’elevata presenza di Pb, messa in evidenza dallo studio, dato che fino ad pochissimi anni venivano utilizzate munizioni al Pb con conseguente rilascio in ambiente di ingenti quantitativi di questo metallo. Il Cu e lo Zn si distribuiscono invece in modo relativamente omogeneo nelle tre zone umide investigate, con un debole arricchimento di questi due elementi nei sedimenti delle Valli di Rosolina. Per quanto riguarda l’As, la sua distribuzione nell’area di studio, confrontata con i valori di background, non sembra sollevare particolare preoccupazione, cosi come la presenza di Hg in tutti e tre i siti investigati. Le Valli di Comacchio e Valle Bertuzzi sono inoltre caratterizzate da concentrazioni elevate di Cr e Ni, dati che confermano il naturale arricchimento di questi due elementi nell’area di studio evidenziato da un ampia letteratura e riconducibile ad apporti litologici provenienti dai depositi ofiolitici delle Alpi occidentali trasportati dal fiume Po verso l’Adriatico. Tuttavia, in alcuni campioni la concentrazione di Cr è molto superiore a quella caratteristica delle ofioliti di origine alpina, soprattutto per Valle Bertuzzi. Per spiegare queste anomalie sono necessarie indagini più approfondite sulla presenza e distribuzione di Cr nell’area di Comacchio e Bertuzzi. Riguardo ai 5 siti riproduttivi del Fenicottero, la colonia di Odiel (Spagna) si distingue per essere il sito maggiormente contaminato tra quelli investigati. Si sono infatti riscontrate elevate concentrazioni di As, Cu, Hg, Pb, Sb, Sn e Zn, se confrontate con quelle degli altri siti campionati. Questo risultato non sorprende. Il sito è infatti riconosciuto in letteratura come uno dei sistemi estuarini più inquinati dell’Europa occidentale, in quanto interessato dall’attività mineraria della IPB (Iberian Pyrite Belt), uno dei più importanti siti minerari mondiali, e dall’attività del polo industriale di Huelva. La colonia francese della Camargue si distingue invece per essere il sito meno impattato dall’attività antropica, non mostrando concentrazioni anomale per nessuno degli elementi in traccia analizzati. I sito riproduttivo situato nei pressi di Cagliari, in Sardegna, ha riportato elevate concentrazioni di Cd, Hg e Pb. La contaminazione di questo sito a seguito di ingenti scarichi di rifiuti industriali contenenti Hg e Pb a partire dagli anni ’60 è ben documentata in letteratura. Sebbene negli anni ’90 siano stati realizzati progetti di bonifica del sito, le concentrazioni ottenute nel presente studio sono ancora elevate suggerendo la possibilità che il processo di rimozione di Hg e Pb messo in atto in passato possa aver avuto scarsa efficacia. La colonia riproduttiva di Comacchio ha registrato concentrazioni elevate di Cr, Ni e Pb. Come già detto riguardo ai siti di alimentazione l’abbondanza di Cr e Ni nell’area è da ricondurre a fattori naturali, mentre le elevate concentrazioni di Pb non trovano riscontri in precedenti studi. La presenza di alcuni campioni con concentrazioni anomale di Cr e il generale arricchimento di Pb nel sito suggeriscono la necessità di studi più approfonditi e specifici sulla presenza di questi elementi nell’area di Comacchio. Infine, la colonia situata in Laguna di Venezia si caratterizza per avere concentrazioni relativamente elevate di Cd e Hg riconducibili all’attività del polo industriale di Porto Marghera, come già evidenziato da numerosi studi. Tuttavia, i dati del presente studio non confermano le concentrazioni anomale di Zn messe in evidenza da molti studi effettuati nell’intera laguna veneta. Ciò può trovare una spiegazione nel fatto che il sito indagato in questo studio corrisponde ad un piccola porzione dell’intera laguna, molto raramente investigato negli studi passati. Mediante il presente studio è stato quindi possibile implementare le scarse conoscenze geochimiche relative ai sedimenti di alcune zone umide frequentate dai fenicotteri nell’Alto Adriatico e, al contempo, mettere in luce alcune importanti criticità, in particolar modo riguardo Cd, Cr, Pb, Sb e Sn, la cui presenza e distribuzione nell’area dovrebbero essere ulteriormente investigate da studi futuri.

Geochemistry, petrogenesis and tectonic setting of ophiolites and mafic-ultramafic complexes in the Northeastern Aegean Region

In this study two ophiolites and a mafic-ultramafic complexes of the northeastern Aegean Sea, Greece, have been investigated to re-evaluate their petrogenetic evolution and tectonic setting. These complexes are: the mafic-ultramafic complex of Lesvos Island and the ophiolites of Samothraki Island and the Evros area. In order to examine these complexes in detail whole-rock major- and trace-elements as well as Sr and Nd isotopes, and minerals were analysed and U-Pb SHRIMP ages on zircons were determined. The mafic-ultramafic complex of Lesvos Island consists of mantle peridotite thrusted over a tectonic mélange containing metasediments, metabasalts and a few metagabbros. This succession had previously been interpreted as an ophiolite of Late Jurassic age. The new field and geochemical data allow a reinterpretation of this complex as representing an incipient continental rift setting that led to the subsequent formation of the Meliata-Maliac-Vardar branches of Neotethys in Upper Permian times (253 ± 6 Ma) and the term “Lesvos ophiolite” should be abandoned. With proceeding subduction and closure of the Maliac Ocean in Late Jurassic times (155 Ma) the Lesvos mafic-ultramafic complex was obducted. Zircon ages of 777, 539 and 338 Ma from a gabbro strongly suggest inheritance from the intruded basement and correspond to ages of distinct terranes recently recognized in the Hellenides (e.g. Florina terrane). Geochemical similar complexes which contain rift associations with Permo-Triassic ages can be found elsewhere in Greece and Turkey, namely the Teke Dere Thrust Sheet below the Lycian Nappes (SW Turkey), the Pindos subophiolitic mélange (W Greece), the Volcanosedimentary Complex on Central Evia Island (Greece) and the Karakaya Complex (NW Turkey). This infers that the rift-related rocks from Lesvos belong to an important Permo-Triassic rifting episode in the eastern Mediterranean. The ‘in-situ’ ophiolite of Samothraki Island comprises gabbros, sparse dykes and basalt flows as well as pillows cut by late dolerite dykes and had conventionally been interpreted as having formed in an ensialic back-arc basin. The results of this study revealed that none of the basalts and dolerites resemble mid-ocean ridge or back-arc basin basalts thus suggesting that the Samothraki ophiolite cannot represent mature back-arc basin crust. The age of the complex is regarded to be 160 ± 5 Ma (i.e. Oxfordian; early Upper Jurassic), which precludes any correlation with the Lesvos mafic-ultramafic complex further south (253 ± 6 Ma; Upper Permian). Restoration of the block configuration in NE Greece, before extensional collapse of the Hellenic hinterland and exhumation of the Rhodope Metamorphic Core Complex (mid-Eocene to mid-Miocene), results in a continuous ophiolite belt from Guevgueli in the NW to Samothraki in the SE, thus assigning the latter to the Innermost Hellenic Ophiolite Belt. In view of the data of this study, the Samothraki ophiolite represents a rift propagation of the Sithonia ophiolite spreading ridge into the Chortiatis calc-alkaline arc. The ophiolite of the Evros area consists of a plutonic sequence comprising cumulate and non-cumulate gabbros with plagiogranite veins, and an extrusive sequence of basalt dykes, massive and pillow lavas as well as pyroclastic rocks. Furthermore, in the Rhodope Massif tectonic lenses of harzburgites and dunites can be found. All rocks are spatially separated. The analytical results of this study revealed an intra-oceanic island arc setting for the Evros ophiolitic rocks. During late Middle Jurassic times (169 ± 2 Ma) an intra-oceanic arc has developed above a northwards directed intra-oceanic subduction zone of the Vardar Ocean in front of the Rhodope Massif. The boninitic, island arc tholeiitic and calc-alkaline rocks reflect the evolution of the Evros island arc. The obduction of the ophiolitic rocks onto the Rhodope basement margin took place during closure of the Vardar ocean basins. The harzburgites and dunites of the Rhodope Massif are strongly depleted and resemble harzburgites from recent oceanic island arcs. After melt extraction they underwent enrichment processes by percolating melts and fluids from the subducted slab. The relationship of the peridotites and the Evros ophiolite is still ambiguous, but the stratigraphic positions of the peridotites and the ophiolitic rocks indicate separated origin. The harzburgites and dunites most probably represent remnants of the mantle wedge of the island arc of the Rhodope terrane formed above subducted slab of the Nestos Ocean in late Middle Jurassic times. During collision of the Thracia terrane with the Rhodope terrane thrusting of the Rhodope terrane onto the Thracia terrane took place, whereas the harzburgites and dunites were pushed between the two terranes now cropping out on top of the Thracia terrane of the Rhodope Massif.

Accesorios de indumentaria del regnum visigodo temprano (siglos V-VI)

Los accesorios metálicos de indumentaria constituyen uno de las fuentes materiales principales para aproximarse a la realidad social, cultural y económica de la población del Mediterráneo tardoantiguo. En el caso de los hallazgos de los siglos V y VI procedentes de la Península Ibérica y del suroeste de Francia, numerosos problemas de documentación han impedido extraer y desarrollar todo su potencial, tanto en lo referente al encuadre tipológico y cronológico de estos objetos como en la consiguiente fase interpretativa. Se hacía necesario acometer un nuevo estudio monográfico que actualizara el panorama de la investigación. El trabajo cataloga, data y clasifica tipológicamente más de cuatro millares de fíbulas y accesorios de cinturón recuperados en casi medio millar de yacimientos localizados en los actuales Portugal, España, Andorra y Francia. El resultado permite aproximarse a las áreas de producción y modalidades de circulación y utilización de cada uno de los tipos individualizados. Una veintena de indumentarias distintas, definidas por combinaciones de distintos tipos de accesorios en contextos funerarios, ha sido identificada. Parte de éstas constituye la base principal de un sistema cronológico organizado en seis fases distintas que cubren una cronología situada aproximadamente entre las últimas décadas del siglo IV y las últimas décadas del siglo VI. La investigación acomete asimismo el análisis de la implantación de los accesorios y de las indumentarias relacionadas con ellos en el paisaje tardoantiguo de Hispania y la Galia. El resultado permite reconstruir secuencias regionales de evolución indumentaria y establecer relaciones entre diversas tipologías de contextos funerarios y habitativos y los tipos de indumentaria previamente definidos. Los resultados permiten renovar la mirada sobre este tipo de objetos y el lugar que ocuparon en la vida cotidiana de muchos de los habitantes del regnum visigodo temprano.

Flash floods and their effects on the development in El-Qaá plain area in South Sinai, Egypt

The arid regions are dominated to a much larger degree than humid regions by major catastrophic events. Although most of Egypt lies within the great hot desert belt; it experiences especially in the north some torrential rainfall, which causes flash floods all over Sinai Peninsula. Flash floods in hot deserts are characterized by high velocity and low duration with a sharp discharge peak. Large sediment loads may be carried by floods threatening fields and settlements in the wadis and even people who are living there. The extreme spottiness of rare heavy rainfall, well known to desert people everywhere, precludes any efficient forecasting. Thus, although the limitation of data still reflects pre-satellite methods, chances of developing a warning system for floods in the desert seem remote. The relatively short flood-to-peak interval, a characteristic of desert floods, presents an additional impediment to the efficient use of warning systems. The present thesis contains introduction and five chapters, chapter one points out the physical settings of the study area. There are the geological settings such as outcrop lithology of the study area and the deposits. The alluvial deposits of Wadi Moreikh had been analyzed using OSL dating to know deposits and palaeoclimatic conditions. The chapter points out as well the stratigraphy and the structure geology containing main faults and folds. In addition, it manifests the pesent climate conditions such as temperature, humidity, wind and evaporation. Besides, it presents type of soils and natural vegetation cover of the study area using unsupervised classification for ETM+ images. Chapter two points out the morphometric analysis of the main basins and their drainage network in the study area. It is divided into three parts: The first part manifests the morphometric analysis of the drainage networks which had been extracted from two main sources, topographic maps and DEM images. Basins and drainage networks are considered as major influencing factors on the flash floods; Most of elements were studied which affect the network such as stream order, bifurcation ratio, stream lengths, stream frequency, drainage density, and drainage patterns. The second part of this chapter shows the morphometric analysis of basins such as area, dimensions, shape and surface. Whereas, the third part points the morphometric analysis of alluvial fans which form most of El-Qaá plain. Chapter three manifests the surface runoff through rainfall and losses analysis. The main subject in this chapter is rainfall which has been studied in detail; it is the main reason for runoff. Therefore, all rainfall characteristics are regarded here such as rainfall types, distribution, rainfall intensity, duration, frequency, and the relationship between rainfall and runoff. While the second part of this chapter concerns with water losses estimation by evaporation and infiltration which are together the main losses with direct effect on the high of runoff. Finally, chapter three points out the factors influencing desert runoff and runoff generation mechanism. Chapter four is concerned with assessment of flood hazard, it is important to estimate runoff and tocreate a map of affected areas. Therefore, the chapter consists of four main parts; first part manifests the runoff estimation, the different methods to estimate runoff and its variables such as runoff coefficient lag time, time of concentration, runoff volume, and frequency analysis of flash flood. While the second part points out the extreme event analysis. The third part shows the map of affected areas for every basin and the flash floods degrees. In this point, it has been depending on the DEM to extract the drainage networks and to determine the main streams which are normally more dangerous than others. Finally, part four presets the risk zone map of total study area which is of high inerest for planning activities. Chapter five as the last chapter concerns with flash flood Hazard mitigation. It consists of three main parts. First flood prediction and the method which can be used to predict and forecast the flood. The second part aims to determine the best methods which can be helpful to mitigate flood hazard in the arid zone and especially the study area. Whereas, the third part points out the development perspective for the study area indicating the suitable places in El-Qaá plain for using in economic activities.

Petrogenetic evolution of Uralian-Alaskan-type mafic-ultramafic complexes in the southern and middle Urals, Russia

The PhD thesis at hand consists of three parts and describes the petrogenetic evolution of Uralian-Alaskan-type mafic ultramafic complexes in the Ural Mountains, Russia. Uralian-Alaskan-type mafic-ultramafic complexes are recognized as a distinct class of intrusions. Characteristic petrologic features are the concentric zonation of a central dunite body grading outward into wehrlite, clinopyroxenite and gabbro, the absence of orthopyroxene and frequently occurring platinum group element (PGE) mineralization. In addition, the presence of ferric iron-rich spinel discriminates Uralian-Alaskan-type complexes from most other mafic ultramafic rock assemblages. The studied Uralian-Alaskan-type complexes (Nizhnii Tagil, Kytlym and Svetley Bor) belong to the southern part of a 900 km long, N–S-trending chain of similar intrusions between the Main Uralian Fault to the west and the Serov-Mauk Fault to the east. The first chapter of this thesis studies the evolution of the ultramafic rocks tracing the compositional variations of rock forming and accessory minerals. The comparison of the chemical composition of olivine, clinopyroxene and chromian spinel from the Urals with data from other localities indicates that they are unique intrusions having a characteristic spinel and clinopyroxene chemistry. Laser ablation-ICPMS (LA-ICPMS ) analyses of trace element concentrations in clinopyroxene are used to calculate the composition of their parental melt which is characterized by enriched LREE (0.5-5.2 prim. mantle) and other highly incompatible elements (U, Th, Ba, Rb) relative to the HREE (0.25-2.0 prim. mantle). A subduction-related geotectonic setting is indicated by a positive anomaly for Sr and negative anomalies for Ti, Zr and Hf. The mineral compositions monitor the evolution of the parental magmas and decipher differences between the studied complexes. In addition, the observed variation in LREE/HREE (for example La/Lu = 2-24) can be best explained with the model of an episodically replenished and erupted open magma chamber system with the extensive fractionation of olivine, spinel and clinopyroxene. The data also show that ankaramites in a subduction-related geotectonic setting could represent parental magmas of Uralian-Alaskan-type complexes. The second chapter of the thesis discusses the chemical variation of major and trace elements in rock-forming minerals of the mafic rocks. Electron microprobe and LA-ICPMS analyses are used to quantitatively describe the petrogenetic relationship between the different gabbroic lithologies and their genetic link to the ultramafic rocks. The composition of clinopyroxene identifies the presence of melts with different trace element abundances on the scale of a thin section and suggests the presence of open system crustal magma chambers. Even on a regional scale the large variation of trace element concentrations and ratios in clinopyroxene (e.g. La/Lu = 3-55) is best explained by the interaction of at least two fundamentally different magma types at various stages of fractionation. This requires the existence of a complex magma chamber system fed with multiple pulses of magmas from at least two different coeval sources in a subduction-related environment. One source produces silica saturated Island arc tholeiitic melts. The second source produces silica undersaturated, ultra-calcic, alkaline melts. Taken these data collectively, the mixing of the two different parental magmas is the dominant petrogenetic process explaining the observed chemical variations. The results further imply that this is an intrinsic feature of Uralian-Alaskan-type complexes and probably of many similar mafic-ultramafic complexes world-wide. In the third chapter of this thesis the major element composition of homogeneous and exsolved spinel is used as a petrogenetic indicator. Homogeneous chromian spinel in dunites and wehrlites monitors the fractionation during the early stages of the magma chamber and the onset of clinopyroxene fractionation as well as the reaction of spinel with interstitial liquid. Exsolved spinel is present in mafic and ultramafic rocks from all three studied complexes. Its composition lies along a solvus curve which defines an equilibrium temperature of 600°C, given that spinel coexists with olivine. This temperature is considered to be close to the temperature of the host rocks into which the studied Uralian-Alaskan-type complexes intruded. The similarity of the exsolution temperatures in the different complexes over a distance of several hundred kilometres implies a regional tectonic event that terminated the exsolution process. This event is potentially associated with the final exhumation of the Uralian-Alaskan-type complexes along the Main Uralian Fault and the Serov-Mauk Fault in the Uralian fold belt.

UHP metamorphic rocks of the Eastern Rhodope Massif, NE Greece: new constraints from petrology, geochemistry and zircon ages

In this PhD thesis, a multidisciplinary study has been carried out on metagranitoids and paragneisses from the Eastern Rhodope Massif, northern Greece, to decipher the pre-Alpine magmatic and geodynamic evolution of the Rhodope Massif and to correlate the eastern part with the western/central parts of the orogen. The Rhodope Massif, which occupies the major part of NE Greece and S Bulgaria, represents the easternmost part of the Internal Hellenides. It is regarded as a nappe stack of high-grade units, which is classically subdivided into an upper unit and a lower unit, separated by a SSE-NNW trending thrust plane, the Nestos thrust. Recent research in the central Greek Rhodope Massif revealed that the two units correspond to two distinct terranes of different age, the Permo-Carboniferous Thracia Terrane, which was overthrusted by the Late Jurassic/Early Cretaceous Rhodope Terrane. These terranes are separated by the Nestos suture, a composite zone comprising metapelites, metabasites, metagranitoids and marbles, which record high-pressure and even ultrahigh-pressure metamorphism in places. Similar characteristic rock associations were investigated during this study along several well-constrained cross sections in vincity to the Ada, Sidiro and Kimi villages in the Greek Eastern Rhodope Massif. Field evidence revealed that the contact zone of the two terranes in the Eastern Rhodope Massif is characterized by a mélange of metapelites, migmatitic amphibolites/eclogites, strongly sheared orthogneisses and marbles. The systematical occurrence of this characteristic rock association between the terranes implies that the Nestos suture is a continuous belt throughout the Greek Rhodope Massif. In this study, a new UHP locality could be established and for the first time in the Greek Rhodope, metamorphic microdiamonds were identified in situ in their host zircons using Laser-Raman spectroscopy. The presence of the diamonds as well as element distribution patterns of the zircons, obtained by TOF-SIMS, indicate metamorphic conditions of T > 1000 °C and P > 4 GPa. The high-pressure and ultrahigh-pressure rocks of the mélange zone are considered to have formed during the subduction of the Nestos Ocean in Jurassic times at ~150 Ma. Melting of metapelitic rocks at UHP conditions facilitated the exhumation to lower crustal levels. To identify major crust forming events, basement granitoids were dated by LA-SF-ICPMS and SHRIMP-II U-Pb analyses of zircons. The geochronological results revealed that the Eastern Rhodope Massif consists of two crustal units, a structurally lower Permo-Carboniferous unit corresponding to the Thracia Terrane and a structurally upper Late Jurassic/Early Cretaceous unit corresponding to the Rhodope Terrane, like it was documented for the Central Rhodope Massif. Inherited zircons in the orthogneisses from the Thracia Terrane of the Eastern Rhodope Massif indicate the presence of a pre-existing Neoproterozoic and Ordovician-Silurian basement in this region. Triassic magmatism is witnessed by the zircons of few orthogneisses from the easternmost Rhodope Massif and is interpreted to be related to rifting processes. Whole-rock major and trace element analyses indicate that the metagranitoids from both terranes originated in a subduction-related magmatic-arc environment. The Sr-Nd isotope data for both terranes of the Eastern and Central Rhodope Massif suggest a mixed crust-mantle source with variable contributions of older crustal material as already indicated by the presence of inherited zircons. Geochemical and isotopic similarity of the basement of the Thracia Terrane and the Pelagonian Zone implies that the Thracia Terrane is a fragment of a formerly unique Permo-Carboniferous basement, separated by rifting and opening of the Meliata-Maliac ocean system in Triassic times. A branch of the Meliata-Maliac ocean system, the Nestos Ocean, subducted northwards in Late Jurassic times leading to the formation of the Late Jurassic/Early Cretaceous Rhodope magmatic arc on remnants of the Thracia Terrane as suggested by inherited Permo-Carboniferous zircons. The ~150 Ma zircon ages of the orthogneisses from the Rhodope Terrane indicate that subduction-related magmatism and HP/UHP metamorphism occurred during the same subduction phase. Subduction ceased due to the closure of the Nestos Ocean in the Late Jurassic/Early Cretaceous. The post-Jurassic evolution of the Rhodope Massif is characterized by the exhumation of the Rhodope core complex in the course of extensional tectonics associated with late granite intrusions in Eocene to Miocene times.

Variation of stable silicon isotopes: Analytical developments and applications in Precambrian geochemistry

Die vorliegende Dissertation behandelt die Gesamtgesteinsanalyse stabiler Siliziumisotope mit Hilfe einer „Multi Collector-ICP-MS“. Die Analysen fanden in Kooperation mit dem „Royal Museum for Central Africa“ in Belgien statt. Einer der Schwerpunkte des ersten Kapitels ist die erstmalige Analyse des δ30Si –Wertes an einem konventionellen Nu PlasmaTM „Multi-Collector ICP-MS“ Instrument, durch die Eliminierung der den 30Si “peak” überlagernden 14N16O Interferenz. Die Analyse von δ30Si wurde durch technische Modifikationen der Anlage erreicht, welche eine höherer Massenauflösung ermöglichten. Die sorgsame Charakterisierung eines adäquaten Referenzmaterials ist unabdingbar für die Abschätzung der Genauigkeit einer Messung. Die Bestimmung der „U.S. Geological Survey“ Referenzmaterialien bildet den zweiten Schwerpunkt dieses Kapitales. Die Analyse zweier hawaiianischer Standards (BHVO-1 and BHVO-2), belegt die präzise und genaue δ30Si Bestimmung und bietet Vergleichsdaten als Qualitätskontrolle für andere Labore. Das zweite Kapitel befasst sich mit kombinierter Silizium-/Sauerstoffisotope zur Untersuchung der Entstehung der Silizifizierung vulkanischer Gesteine des „Barberton Greenstone Belt“, Südafrika. Im Gegensatz zu heute, war die Silizifizierung der Oberflächennahen Schichten, einschließlich der „Chert“ Bildung, weitverbreitete Prozesse am präkambrischen Ozeanboden. Diese Horizonte sind Zeugen einer extremen Siliziummobilisierung in der Frühzeit der Erde. Dieses Kapitel behandelt die Analyse von Silizium- und Sauerstoffisotopen an drei unterschiedlichen Gesteinsprofilen mit unterschiedlich stark silizifizierten Basalten und überlagernden geschichteten „Cherts“ der 3.54, 3.45 und 3.33 Mill. Jr. alten Theespruit, Kromberg und Hooggenoeg Formationen. Siliziumisotope, Sauerstoffisotope und die SiO2-Gehalte demonstrieren in allen drei Gesteinsprofilen eine positive Korrelation mit dem Silizifizierungsgrad, jedoch mit unterschiedlichen Steigungen der δ30Si-δ18O-Verhältnisse. Meerwasser wird als Quelle des Siliziums für den Silizifizierungsprozess betrachtet. Berechnungen haben gezeigt, dass eine klassische Wasser-Gestein Wechselwirkung die Siliziumisotopenvariation nicht beeinflussen kann, da die Konzentration von Si im Meerwasser zu gering ist (49 ppm). Die Daten stimmen mit einer Zwei-Endglieder-Komponentenmischung überein, mit Basalt und „Chert“ als jeweilige Endglieder. Unsere gegenwärtigen Daten an den „Cherts“ bestätigen einen Anstieg der Isotopenzusammensetzung über der Zeit. Mögliche Faktoren, die für unterschiedliche Steigungen der δ30Si-δ18O Verhältnisse verantwortlich sein könnten sind Veränderungen in der Meerwasserisotopie, der Wassertemperatur oder sekundäre Alterationseffekte. Das letzte Kapitel beinhaltet potentielle Variationen in der Quellregion archaischer Granitoide: die Si-Isotopen Perspektive. Natriumhaltige Tonalit-Trondhjemit-Granodiorit (TTG) Intrusiva repräsentieren große Anteile der archaischen Kruste. Im Gegensatz dazu ist die heutige Kruste kaliumhaltiger (GMS-Gruppe: Granit-Monzonite-Syenite). Prozesse, die zu dem Wechsel von natriumhaltiger zu kaliumhaltiger Kruste führten sind die Thematik diesen Kapitels. Siliziumisotopenmessungen wurden hier kombiniert mit Haupt- und Spurenelementanalysen an unterschiedlichen Generationen der 3.55 bis 3.10 Mill. Yr. alten TTG und GMS Intrusiva aus dem Arbeitsgebiet. Die δ30Si-Werte in den unterschiedlichen Plutonit Generationen zeigen einen leichten Anstieg der Isotopie mit der Zeit, wobei natriumhaltige Intrusiva die niedrigste Si-Isotopenzusammensetzung aufweisen. Der leichte Anstieg in der Siliziumisotopenzusammensetzung über die Zeit könnte auf unterschiedliche Temperaturbedingungen in der Quellregion der Granitoide hinweisen. Die Entstehung von Na-reichen, leichten d30Si Granitoiden würde demnach bei höheren Temperaturen erfolgen. Die Ähnlichkeit der δ30Si-Werte in archaischen K-reichen Plutoniten und phanerozoischen K-reichen Plutoniten wird ebenfalls deutlich.