The pre-alpine evolution of the basement of the Pelagonian Zone and the Vardar Zone, Greece

The Pelagonian Zone and the Vardar Zone in Greece represent the western part of the Hellenide hinterland (Internal Hellenides). While the Pelagonian Zone comprises predominantly crystalline basement and sedimentary cover rocks, the Vardar Zone has long been regarded as an ophiolite-decorated suture zone separating the Pelagonian Zone from the Serbo-Macedonian Massif to the east. Felsic basement rocks from both areas, with the main focus put on the Pelagonian Zone, were dated in order to identify the major crust-forming episodes and to improve the understanding of the evolutionary history of the region. The interpretation of the single-zircon geochronology results was aided by geochemical investigations. The majority of the basement rocks from the Pelagonian Zone yielded Permo-Carboniferous intrusion ages around 300 Ma, underlining the importance of this crust-forming event for the Internal Hellenides of Greece. Geochemically these basement rocks are classified as subduction-related granitoids, which formed in an active continental margin setting. An important result was the identification of a Precambrian crustal unit within the crystalline basement of the Pelagonian Zone. Orthogneisses from the NW Pelagonian Zone yielded Neoproterozoic ages of c. 700 Ma and are so far the oldest known rocks in Greece. These basement rocks, which are also similar to active margin granitoids, were interpreted as remnants of a terrane, the Florina Terrane, which can be correlated to a Pan-African or Cadomian arc. Since the gneisses contain inherited zircons of Middle to Late Proterozoic ages, the original location of the Florina Terrane was probably at the northwestern margin of Gondwana. In the Vardar Zone an important phase of Upper Jurassic felsic magmatism is documented by igneous formation ages ranging from 155 to 164 Ma. The chemical and isotopic composition of these rocks is also in accord with their formation in a volcanic-arc setting at an active continental margin. Older continental material incorporated in the Vardar Zone is documented by 319-Ma-old gneisses and by inherited zircons of mainly Middle Palaeozoic ages. The prevalence of subduction-related igneous rocks indicates that arc formation and accretion orogeny were the most important processes during the evolution of this part of the Internal Hellenides. The geochronological results demonstrate that most of the Pelagonian Zone and the Vardar Zone crystalline basement formed during distinct pre-Alpine episodes at c. 700, 300 and 160 Ma with a predominance of the Permo-Carboniferous magmatic phase.

Anatomy, phylogeny, and palaeoecology of the basal thalattosuchians (Mesoeucrocodylia) from the Liassic of Central Europe

In the marine Jurassic deposits of Europe, a group of marine crocodilians, the Thalattosuchia, belongs to the frequently found reptiles. Thalattosuchia are widely spread in Central Europe from the Jurassic to Lower Cretaceous, and some taxa are also distributed worldwide. The task of the work was to examine all taxa known from the Liassic of Europe. The most frequently known taxa Steneosaurus bollensis and Pelagosaurus typus are anatomically revised. New discoveries at the skull of Pelagosaurus typus e.g., the fact of a partly paired frontal are described by means of computed tomography investigations. In addition, juvenile specimens of this taxon are studied in detail for the first time. The rarely occurring taxon Platysuchus multiscrobiculatus is anatomically described in detail for the first time. It shows both in the skull and in the postcranial material morphological differences to Steneosaurus bollensis and Pelagosaurus typus. Thus Pl. multiscrobiculatus possesses, e.g., an ilium with a deeper acetabulum and a femur with a distinctly flexed femoral head. A juvenile specimen of Pl. multiscrobiculatus is now discovered and is described in parts for the first time, too. Furthermore, Steneosaurus gracilirostris and Steneosaurus brevior known from Lower Jurassic deposits of England are examined and in parts revised. In this work, Steneosaurs brevior is discovered with one specimen from the Upper Liassic of Holzmaden, Germany for the first time, and provides new evidence for the palaeobiogeographical distribution of the taxon. Because of the high number of investigated specimens, it is possible to study ontogenetic development from juvenile to adult stage in Steneosaurus bollensis, Pelagosaurus typus, and Platysuchus multiscrobiculatus. Biometric data are collected from thalattosuchians and extant crocodilians (e.g. Gavialis gangeticus) to investigate intraspecific variation, ontogenetic development, and taxa differentiation. The skulls of Platysuchus multiscrobiculatus and Steneosaurus bollensis are reconstructed three-dimensionally as wax models. The skull reconstructions form the basis of the jaw muscle restoration of Steneosaurus bollensis in connection with comparative studies at extant crocodilians. By means of functional morphologic analysis of the jaw musculature, the dentition, and the locomotor system of S. bollensis, possible conclusions are drawn for the prey options and the hunting behaviour. To clarify the relationships within the Thalattosuchia, a computer-based cladistic phylogenetic in-group analyse of 25 Thalattosuchia taxa is performed. For the analysis, following Thalattosuchia taxa are studied likewise at original material for comparisons: Metriorhynchus superciliosus, Metriorhynchus hastifer, Metriorhynchus leedsi, Geosaurus gracilis, Geosaurus giganteus, Teleidosaurus calvadosi, Teleidosaurus gaudryi, Teleosaurus cadomensis, Teleosaurus geoffroyi, Steneosaurus priscus, Steneosaurus edwardsi, Steneosaurus heberti, Steneosaurus leedsi, Steneosaurus boutilieri, Steneosaurus megarhinus, Steneosaurus obtusidens, and Machimosaurus hugii. The phylogenetic in-group analyse based on 115 characters, reveals a sister-group relationship of the monophyletic Teleosauridae and monophyletic Metriorhynchidae. Within the groups, some taxa are probably paraphyletic. The taxon Pelagosaurus typus is nested inside the Teleosauridae and not outside or within the Metriorhynchidae, as many authors suggested it so far. Based on these results, a tentative palaeobiogeographical-evolutionary scenario is developed.

Sedimentary rocks of the Internal Hellenides, Greece: age, source, and depositional setting

Ziel der vorliegenden Dissertation war die Untersuchung der Liefergebiete und Ablagerungsräume sedimentärer Gesteine aus ausgewählten Gebieten der inneren Helleniden Griechenlands. Die untersuchten Sedimente Nordgriechenlands gehören zu den Pirgadikia und Vertiskos Einheiten des Serbo-Makedonische Massifs, zu den Examili, Melissochori und Prinochori Formationen der östlichen Vardar Zone und zur Makri Einheit und Melia Formation des östlichen Zirkum-Rhodope-Gürtels in Thrakien. In der östlichen Ägäis lag der Schwerpunkt bei den Sedimenten der Insel Chios. Der Metamorphosegrad der untersuchten Gesteine variiert von der untersten Grünschieferfazies bis hin zur Amphibolitfazies. Das stratigraphische Alter reicht vom Ordovizium bis zur Kreide. Zur Charakterisierung der Gesteine und ihrer Liefgebiete wurden Haupt- und Spurenelementgehalte der Gesamtgesteine bestimmt, mineralchemische Analysen durchgeführt und detritische Zirkone mit U–Pb datiert. An ausgewählten Proben wurden außerdem biostratigraphische Untersuchungen zur Bestimmung des Sedimentationsalters durchgeführt. Die Untersuchungsergebnisse dieser Arbeit sind von großer Bedeutung für paläogeographische Rekonstruktionen der Tethys. Die wichtigsten Ergebnisse lassen sich wie folgt zusammenfassen: Die ältesten Sedimente Nordgriechenlands gehören zur Pirgadikia Einheit des Serbo-Makedonischen Massifs. Es sind sehr reife, quarzreiche, siliziklastische Metasedimente, die auf Grund ihrer Maturität und ihrer detritischen Zirkone mit ordovizischen overlap-Sequenzen vom Nordrand Gondwanas korreliert werden können. Die Metasedimente der Vertiskos Einheit besitzen ein ähnliches stratigraphisches Alter, haben aber einen anderen Ablagerungsraum. Das Altersspektrum detritischer Zirkone lässt auf ein Liefergebiet im Raum NW Afrikas (Hun Superterrane) schließen. Die Gesteinsassoziation der Vertiskos Einheit wird als Teil einer aktiven Kontinentalrandabfolge gesehen. Die ältesten biostratigraphisch datierten Sedimente Griechenlands sind silurische bis karbonische Olistolithe aus einer spätpaläozoischen Turbidit-Olistostrom Einheit auf der Insel Chios. Die Alter detritischer Zirkone und die Liefergebietsanalyse der fossilführenden Olistolithe lassen den Schluss zu, dass die klastischen Sedimente von Chios Material vom Sakarya Mikrokontinent in der West-Türkei und faziellen Äquivalenten zu paläozoischen Gesteinen der Istanbul Zone in der Nord-Türkei und der Balkan Region erhalten haben. Während der Permotrias wurde die Examili Formation der östlichen Vardar Zone in einem intrakontinentalen, sedimentären Becken, nahe der Vertiskos Einheit abgelagert. Untergeordnet wurde auch karbonisches Grundgebirgsmaterial eingetragen. Im frühen bis mittleren Jura wurde die Melissochori Formation der östlichen Vardar Zone am Abhang eines karbonatführenden Kontinentalrandes abgelagert. Der Großteil des detritischen Materials kam von permokarbonischem Grundgebirge vulkanischen Ursprungs, vermutlich von der Pelagonischen Zone und/oder der unteren tektonischen Einheit des Rhodope Massifs. Die Makri Einheit in Thrakien besitzt vermutlich ein ähnliches Alter wie die Melissochori Formation. Beide sedimentären Abfolgen ähneln sich sehr. Der Großteil des detritischen Materials für die Makri Einheit kam vom Grundgebirge der Pelagonischen Zone oder äquivalenten Gesteinen. Während der frühen Kreide wurde die Prinochori Formation der östlichen Vardar Zone im Vorfeld eines heterogenen Deckenstapels abgelagert, der ophiolitisches Material sowie Grundgebirge ähnlich zu dem der Vertiskos Einheit enthielt. Ebenfalls während der Kreidezeit wurde in Thrakien, vermutlich im Vorfeld eines metamorphen Deckenstapels mit Affinitäten zum Grundgebirge der Rhodopen die Melia Formation abgelagert. Zusammenfassend kann festgehalten werden, dass die Subduktion eines Teiles der Paläotethys und die anschließende Akkretion vom Nordrand Gondwanas stammender Mikrokontinente (Terranes) nahe dem südlichen aktiven Kontinentalrand Eurasiens den geodynamischen Rahmen für die Schüttung des detritischen Materials der Sedimente der inneren Helleniden im späten Paläozoikum bildeten. Die darauf folgenden frühmesozoischen Riftprozesse leiteten die Bildung von Ozeanbecken der Neotethys ein. Intraozeanische Subduktion und die Obduzierung von Ophioliten prägten die Zeit des Jura. Die spätjurassische und frühkretazische tektonische Phase wurde durch die Ablagerung von mittelkretazischen Kalksteinen besiegelt. Die endgültige Schließung von Ozeanbecken der Neotethys im Bereich der inneren Helleniden erfolgte schließlich in der späten Kreide und im Tertiär.

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.

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.