The Aegean region is a concentrate of the main geodynamic processes that shaped the Mediterranean region: oceanic and continental subduction, mountain building, high-pressure and low-temperature metamorphism, backarc extension, post-orogenic collapse, metamorphic core complexes, gneiss domes are the ingredients of a complex evolution that started at the end of the Cretaceous with the closure of the Tethyan ocean along the Vardar suture zone. Using available plate kinematic, geophysical, petrological and structural data, we present a synthetic tectonic map of the whole region encompassing the Balkans, Western Turkey, the Aegean Sea, the Hellenic Arc, the Mediterranean Ridge and continental Greece and we build a lithospheric-scale N-S cross-section from Crete to the Rhodope massif. We then describe the tectonic evolution of this cross-section with a series of reconstructions from ~70 Ma to the Present. We follow on the hypothesis that a single subduction has been active throughout most of the Mesozoic and the entire Cenozoic, and we show that the geological record is compatible with this hypothesis. The reconstructions show that continental subduction (Apulian and Pelagonian continental blocks) did not induce slab break-off in this case. Using this evolution, we discuss the mechanisms leading to the exhumation of metamorphic rocks and the subsequent formation of extensional metamorphic domes in the backarc region during slab retreat. The tectonic histories of the two regions showing large-scale extension, the Rhodope and the Cyclades are then compared. The respective contributions to slab retreat, post-orogenic extension and lower crust partial melting of changes in kinematic boundary conditions and in nature of subducting material, from continental to oceanic, are discussed.

/pdf/cenozoic-geodynamic-evolution-of-the-aegean-2w6i0upj7j.pdf

Cenozoic geodynamic evolution of the Aegean

A full-plate global reconstruction of the Neoproterozoic

http://perso.numericable.com/laetitia.le.pourhiet/publications_files/Jolivetetal2012.pdf

Aegean tectonics: Strain localisation, slab tearing and trench retreat

At subduction zones, crustal material enters the mantle. Some of this material, however, is returned to the overriding plate through volcanic and plutonic activity. Magmas erupted above subduction zones show a characteristic range of compositions that reflect mixing in the magma source region between three components: hydrous fluids derived from the subducted oceanic crust, components of the thin veneer of subducted sediments and peridotite mantle rocks. The mechanism for mixing and transport of these components has been enigmatic. A combination of results from the fields of petrology, numerical modelling, geophysics and geochemistry suggests a two-step process. First, intensely mixed metamorphic rock formations—melanges—form along the interface between the subducted slab and the mantle. As the melange contains the characteristic three-component geochemical pattern of subduction-zone magmas, we suggest that melange formation provides the physical mixing process. Then, blobs of low-density melange material—diapirs—rise buoyantly from the surface of the subducting slab and transport the well-mixed melange material into the mantle beneath the volcanoes. Magma erupted at subduction-zone volcanoes contains mantle rocks and a mixture of fluids and sediments derived from the subducted slab. A synthesis of work over past years provides an integrated physico-chemical framework for subduction zones with mixing at the slab–mantle interface and transport towards the surface volcanoes by buoyant diapirs.

/pdf/arc-magmas-sourced-from-melange-diapirs-in-subduction-zones-3l20i6ie3n.pdf

Arc magmas sourced from melange diapirs in subduction zones

https://cyberleninka.org/article/n/651108.pdf

Application of organic petrography in North American shale petroleum systems: A review

During the Devonian, the Svalbard Archipelago lay at low latitudes, occupying a paleogeographic position at the intersection of Caledonian and Ellesmerian orogens. Provenance analysis, including detrital zircon U‐Pb age studies, of Devonian (ca. 420–360 Ma) strata from the Andrée Land Basin, Svalbard, help reconstruct sediment sources to understand the assembly of the three basement provinces that make up Svalbard, which are presently separated by Devonian sedimentary basins and(or) faults with syn‐to post‐Devonian displacement. The studied Andrée Land Group strata, which are part of the North Atlantic's Old Red Sandstone, consist of the Early Devonian Wood Bay Formation and Middle to Late Devonian Mimerdalen subgroup. Paleocurrent indicators from Lower to lower‐Middle Devonian strata record north‐directed sediment transport. Detrital zircon U‐Pb ages indicate a prominent “Caledonian” signal and include sources from Svalbard's Northwestern and(or) Southwestern basement provinces. In Middle and Upper Devonian strata, paleocurrents and detrital zircon ages record a shift to a predominantly eastern‐northeastern provenance, likely from the uplifting Ny‐Friesland block along the Billefjorden Fault Zone. Late Ediacaran‐early Cambrian detrital zircons in the uppermost Planteryggen Formation (Frasnian) indicate extrabasinal sources possibly associated with the Timanian orogen of Northern Baltica. The combined provenance data suggest Svalbard may have already been assembled, similar to the modern block, with the Andrée Land Basin located between modern exposures of the Southwestern/Northwestern and the Northeastern basement provinces. Comparison of detrital zircon ages from Andrée Land Group strata with those from other circum Arctic Devonian strata provides constraints on Svalbard's paleogeographic position in the Devonian.

Provenance Analysis of the Andrée Land Basin and Implications for the Paleogeography of Svalbard in the Devonian

Structural evolution and paleostress pattern of the New Siberian Islands and De Long Islands, NE Russia

New multicellular microfossil eukaryotes from the ca. 950–820-million-year-old veteranen group of svalbard

The sedimentary deposits of the central Sverdrup Basin on Ellef Ringnes Island were affected by both salt diapirism and igneous activity of the Cretaceous High Arctic Large Igneous Province (HALIP). Occurrences of mafic igneous rocks on the centre of salt domes are usually assigned to the Cretaceous magmatism. Petrographic, geochemical, Sr–Nd isotope, and geochronological (Ar–Ar dating) studies on six rock fragments collected on the top of Isachsen Dome reveal a larger variability in the composition and the age compared to HALIP-related rocks from elsewhere on Ellef Ringnes Island. A blocky fragment of tholeiitic hornblende dolerite with an Ar–Ar age of 121 Ma is interpreted to originate from an in-situ intrusion and was uplifted by evaporite diapirism. The other samples are small, sub-rounded pebbles, which represent three different parent rock types. A kaersutite-bearing alkali basalt was possibly formed during the Triassic or Permian. A leucocratic, albitised rock fragment has experienced contact metasomatism at 102 Ma, and three very similar tholeiitic basalt fragments probably derived from the margin of a dyke were auto-hydrothermally affected at 69 Ma. The inferred source area of these exotic pebbles is the segment of the Arctic continental margin in the northeast that was repeatedly affected by igneous events between the Carboniferous and latest Cretaceous and that was uplifted and eroded during the Eocene. The rock fragments were probably deposited as Palaeogene sediments above the rising Isachsen diapir shortly before or as the head of the salt dome has pierced the Earth’s surface. Glacial transport up the top of Isachsen Dome during the Late Wisconsinan glaciation is not very likely due to the contrast between the north to northwest directed ice-flow direction reported in the literature and the assumed northeastern source area of the pebbles; however, it cannot be completely excluded.

Diversity of igneous rocks from the Isachsen Dome, Ellef Ringnes Island, Canadian High Arctic

Tectonic models for development of the Svalbard Caledonides depend on reliable assessment of the metamorphic evolution of the various basement provinces involved. The Mosselhalvøya Group (MG) and the Atomfjella Complex (AC) have previously been assigned to the Nordaustlandet and West Ny-Friesland terranes, respectively. New analytical data and petrographic observations indicate that both units experienced 2-stage metamorphism under similar pressure-temperature (P-T) conditions. Two stages of amphibolite facies metamorphism (M1 and M2) are clearly recorded by garnet and staurolite porphyroblast textures. The results of thermodynamic phase equilibrium modelling indicate that peak M2 metamorphism occurred at ~7-7.5 kbar and 590-600°C in both units. Zirconium-in-rutile trace element thermometry confirms the temperature estimates for M1 and M2 stages of metamorphism. Monazite chemical Th-U-Pb dates from the MG resolve a 2-stage garnet growth at 444 ± 7 Ma (M1) and 423 ± 6 Ma (M2). In contrast, monazite dated in the AC define a single age of 420 ± 4 Ma interpreted as M2 growth. We suggest M2 was coeval with early strike-slip motion along the Billefjorden Fault Zone, whereas M1 reflects initial tectonic burial of the studied units. The similarity in metamorphic history between the both units suggest that the boundary between them is a subordinate thrust fault within the Atomfjella thrust stack rather than a major boundary separating the Nordaustlandet and West Ny-Friesland terranes. The MG is included within West Ny-Friesland terrane and the tectonic boundary with the Nordaustlandet terrane is likely the Eolussletta Shear Zone.

Karsten Piepjohn

Papers

Provenance Analysis of the Andrée Land Basin and Implications for the Paleogeography of Svalbard in the Devonian

Structural evolution and paleostress pattern of the New Siberian Islands and De Long Islands, NE Russia

New multicellular microfossil eukaryotes from the ca. 950–820-million-year-old veteranen group of svalbard

Diversity of igneous rocks from the Isachsen Dome, Ellef Ringnes Island, Canadian High Arctic

Reinterpretation of a major terrane boundary in the northern Svalbard Caledonides based on metamorphic fingerprinting of rocks in northern Spitsbergen