Kinematics of faults in the Northern Aegean show three extensional tectonic regimes the tensional directions of which trend (1) WNW-ESE, (2) NE-SW and (3) N-S. These were active during the Upper Miocene, Pliocene-Lower Pleistocene and Mid Pleistocene-Present day, respectively. The main characteristics of the stress patterns (1) and (2) on the overall Aegean is tentatively explained by variations of the horizontal lithospheric stress value txx due to the slab
push and of the vertical lithospheric stress value txx, due to mass heterogeneities. During the Mid Pleistocene-Present, due to the slab push, tectonics were compressional along the arc boundary: txx was t1. In the Aegean basins, tectonics were extensional, tzz was t1 as a consequence of the
thickness of the continental crust and, possibly of an updoming asthenosphere; thus txx, became t2, allowing tension t3 to be orthogonal to the compression along the arc, i.e. to be roughly parallel to the arc trend. During the Pliocene-Lower Pleistocene, the extensional regime was distinctly different. The tensional directions were roughly radial to the arc. It is suggested that
txx was weakly compressional, or eventually tensional, due a seaward migration of the slab so that txx became t3. In the Northern Aegean, the stress pattern has been also controlled by the westward push of the Anatolian landmass. During the Mid Pleistocene-Present day, this was typically extensional (t1 was vertical) and the right lateral strike-slip motion on the North Anatolian Fault transformed into a N-S-stretching, E-W-shortening (of the Northern Aegean.
Dextral strike-slip motions along the North Aegean Trough fault zone were possible on NE-SW-striking faults. During the Pliocene-Lower Pleistocene, normal fault components were higher ; however, because the angle between the NE-SW trend of the tensional axis and the strike of the fault zone was acute, dextral strike-slip components were possible on all the faults striking NE-SW to E-W. A clockwise 15° rotation of Limnos with respect to Samothraki,
Thraki and Thassos, suggested by structural data, was probably associated with these dextral motions. The WNW-ESE trending tension during the Upper Miocene indicates that the dextral North Anatolian Fault had not yet merged into the North Aegean Trough fault zone at that time. We propose that the formation of Aegean basins during the Cenozoic was related to the activity of two major Hellenic arcs. The \\\'Pelagonian-Pindic Arc\\\' resulted in the formation of the
subsident Aegean basins of Middle Eocene-Lower Miocene age and of the older Northern Aegean orogenic volcanism. The \\\'Aegean Arc\\\' resulted in the formation of the subsident Aegean basins of Middie Miocene to Present day age and of the Southern Aegean orogenic volcanism. Were these arcs associated with a unique subduction zone or with two such zones? In the first case, the slab is no more than 16 Myr old, in the second it may be as old as 45-50 Myr. The answer depends on the accuracy of the seismic tomography profiles.

Extensional tectonic regimes in the Aegean basins during the Cenozoic

Rhodope and Vardar: the metamorphic and the olistostromic paired belts related to the Cretaceous subduction under Europe

Jurassic back-arc and Cretaceous hot-spot series In the Armenian ophiolites — Implications for the obduction process

Ophiolites of the Alps, Corsica and the Apennines (ACA) derive from the Jurassic-Cretaceous Ligurian Tethys ocean, which was located between Europe and Africa. They are characterized by a very small volume of gabbros and basalts, by the absence of any dyke complex, and by the frequent stratigraphic contact of sediments resting directly upon mantle-derived peridotites or gabbros. Two types of ACA ophiolites can be distinguished: magma rich (MR) and magma poor (MP). They show strong affinities with the oceanic lithosphere found respectively at the centres and tips of 20–100 km long segments which characterize the suds of the slow-spreading Mid Atlantic Ridge.

Alpine, Corsican and Apennine ophiolites: the slow-spreading ridge model

The Amassia–Stepanavan blueschist-ophiolite complex of the Lesser Caucasus in NW Armenia is part of an Upper Cretaceous-Cenozoic belt, which presents similar metamorphic features as other suture zones from Turkey to Iran. The blueschists include calcschists, metaconglomerates, quartzites, gneisses and metabasites, suggesting a tectonic melange within an accretionary prism. This blueschist melange is tectonically overlain by a low-metamorphic grade ophiolite sequence composed of serpentinites, gabbro-norite pods, plagiogranites, basalts and radiolarites. The metabasites include high-P assemblages (glaucophane–aegirine–clinozoisite–phengite), which indicate maximal burial pressure of ∼1.2 GPa at ∼550°C. Most blueschists show evidence of greenschist retrogression (chlorite—epidote, actinolite), but locally epidote-amphibolite conditions were attained (garnet—epidote, Ca/Na amphibole) at a pressure of ∼0.6 GPa and a temperature of ∼500°C. This LP–MT retrogression is coeval with exhumation and nappe-stacking of lower grade units over higher grade ones. 40Ar/39Ar phengite ages obtained on the high-P assemblages range between 95 and 90 Ma, while ages obtained for epidote-amphibolite retrogression assemblages range within 73.5–71 Ma. These two metamorphic phases are significant of (1) HP metamorphism during a phase of subduction in the Cenomanian–Turonian times followed by (2) exhumation in the greenschist to epidote-amphibolite facies conditions during the Upper Campanian/Maastrichtian due to the onset of continental subduction of the South Armenian block below Eurasia.

M. L. Bazhenov

Papers

Methodes pour l'etablissement de neuf cartes paleogeographiques de l'Atlantique au Pamir depuis le Lias