The three metamorphic belts of the Hellenides: A review and a kinematic interpretation

New results obtained in the three metamorphic belts of the Hellenides suggest that each belt has a different structure, geotectonic setting and evolution. The external metamorphic belt of Peloponnesus-Crete has probably resulted from nappe movement in the vicinity of an evolving island arc system. The blueschists occurring within this external belt are allochthonous and have been transported with other nappes over the external carbonate platform of the Pre-Apulian-Plattenkalk-Ionian-Tripolitza-Almyropotamos Units. This implies that there was only one true blueschist domain, initiated in the Cycladic area during ?Early Eocene. The kinematic interpretation is based on the distinction of a- and b-structures and on the nature of the shear zones between the different domains, especially that between the metamorphic Hellenides below and the non-metamorphic Hellenides above. The existence of the probably Lower Palaeozoic meta-sedimentary sequence of Kastoria in the northern Pelagonian zone indicates that the overlying, ophiolite-bearing Almopias unit has been derived from within the Hercynian domain. The Kastoria sedimentary sequence, the ophiolites of Vertiskos and the carbonate platform of Pangeon are considered to be most likely elements of a probable Hercynian orogeny. © 1984 The Geological Society

Disruption of the Hellenic arc: Late Miocene extensional detachment faults and steep Pliocene-Quaternary normal faults - Or what happened at Corinth?

Extensional faults exposed in the Peloponnesus and mainland Greece, most of which are described here for the first time, record a transition from regional extension of the Aegean domain to the modern tectonic system. The East Peloponnesus Detachment System trends north-northwest from the southern Peloponnesus to ∼30 km north of the Gulf of Corinth, dips gently northeast, and is late Miocene-early Pliocene in age. It has a minimum displacement of 25-30 km and appears to be the youngest of the regional-scale extensional systems with significant displacement that formed parallel to the Hellenic are. The partially coeval East Sterea Extensional System, which extends from the Gulf of Corinth to the Aegean Sea, contains low-angle normal faults that both crosscut and trend parallel to older structures of the Hellenic arc. Late Miocene to early Pliocene displacement within this zone disrupted the arc-parallel structures of the Hellenides. Upper Pliocene-Quaternary normal faults, which trend approximately east-west and generally dip steeply at the surface, continue the disruption of the Hellenic arc. Much of the subsidence within the Gulf of Corinth appears to be unrelated to the younger faults and is instead related to the motion on the East Peloponnesus Detachment, which crosscuts the modern graben. Copyright 2007 by the American Geophysical Union

Slab segmentation and late Cenozoic disruption of the Hellenic arc

The Hellenic subduction zone displays well-defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy, subduction rate, and tectonic deformation. In space, the active Hellenic subduction front is dextrally offset by 100-120 km across the Kephalonia Transform Zone, coinciding with the junction of a slowly subducting Adriatic continental lithosphere in the north (5-10 mm/yr) and a rapidly subducting Ionian oceanic lithosphere in the south (∼35 mm/yr). Subduction rates can be shown to have decreased from late Eocene time onward, reaching 5-12 mm/yr by late Miocene time, before increasing again along the southern portion of the subduction system. Geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic (Pindos) lithosphere until late Eocene time, followed by subduction of a broad tract of continental or transitional lithosphere (Hellenic external carbonate platform) and then by Miocene entry of high-density oceanic (Ionian) lithosphere into the southern Hellenic trench. Model results yield an initiation age for the Kephalonia Transform of 6-8 Ma, in good agreement with observations. Consistency between geodynamic model results and geologic observations suggest that the middle Miocene and younger deformation of the Hellenic upper plate, including formation of the Central Hellenic Shear Zone, can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab. Using this assumption, we make late Eocene, middle Miocene, and Pliocene reconstructions of the Hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation. Copyright 2011 by the American Geophysical Union

Paleomagnetic results from the Pindos, Paxos, and Ionian zones of Greece

Maastrichtian to Miocene sediments were sampled at 12 sites in central Greece (Meso-Hellenic basin, Pindos zone and Western Thessaly unit) and four sites on Lefkas island (Paxos and Ionian zones). The samples were subjected in the laboratory to thermal and alternating field (AF) cleaning. As a result, characteristic remanent magnetizations (ChRMs) were obtained for 11 sites. In comparing these paleomagnetic directions with others already obtained for the external Hellenides, the following points are noteworthy. 1. (1)|In post-Alpine times a slight clockwise rotation seems to be common to the zones of the external Hellenides in Western Greece; 2. (2)|independent movement of the Pindos flysch and the Ionian Paleogene sediments is plausible as the sampled sites from the former exhibit large counter-clockwise declination rotation with respect to the latter; 3. (3)|the net rotation of the Mesozoic sediments of both Pindos and Ionian zones is similar. These observations may indicate that the two zones rotated independently as 'blocks' before the Miocene, for the detachment of the Paleogene from the Mesozoic sediments is opposed on geological grounds. Thus the similar declinations observed for the Mesozoic sediments of the Pindos and Ionian zones must be regarded as coincidence. © 1990

Paleomagnetic results from the Pindos, Paxos, and Ionian zones of Greece

Maastrichtian to Miocene sediments were sampled at 12 sites in central Greece (Meso-Hellenic basin, Pindos zone and Western Thessaly unit) and four sites on Lefkas island (Paxos and Ionian zones). The samples were subjected in the laboratory to thermal and alternating field (AF) cleaning. As a result, characteristic remanent magnetizations (ChRMs) were obtained for 11 sites. In comparing these paleomagnetic directions with others already obtained for the external Hellenides, the following points are noteworthy. 1. (1)|In post-Alpine times a slight clockwise rotation seems to be common to the zones of the external Hellenides in Western Greece; 2. (2)|independent movement of the Pindos flysch and the Ionian Paleogene sediments is plausible as the sampled sites from the former exhibit large counter-clockwise declination rotation with respect to the latter; 3. (3)|the net rotation of the Mesozoic sediments of both Pindos and Ionian zones is similar. These observations may indicate that the two zones rotated independently as 'blocks' before the Miocene, for the detachment of the Paleogene from the Mesozoic sediments is opposed on geological grounds. Thus the similar declinations observed for the Mesozoic sediments of the Pindos and Ionian zones must be regarded as coincidence. © 1990

Critical elasticity at zero and finite temperature

Elastic phase transitions of crystals and phase transitions whose order parameter couples linearly to elastic degrees of freedom are reviewed with particular focus on instabilities at zero temperature. A characteristic feature of these transitions is the suppression of critical fluctuations by long-range shear forces. As a consequence, at an elastic crystal symmetry-breaking quantum phase transition the phonon velocity vanishes only along certain crystallographic directions giving rise to critical phonon thermodynamics described by a stable Gaussian fixed point. At an isostructural solid-solid quantum critical end point, on the other hand, the complete suppression of critical fluctuations results in true mean-field critical behavior without a diverging correlation length. Whenever an order parameter couples bilinearly to the strain tensor, the critical properties are eventually governed by critical crystal elasticity. This is, for example, the case for quantum critical metamagnetism but also for the classical critical Mott end point at finite T. We discuss and compare the solid-solid end points expected close to the Mott transition in V2O3 and κ-(BEDT-TTF)2X