The Strandja Massif is a mid-Mesozoic orogenic belt in the Balkans build on a late-Variscan basement of gneisses, migmatites and granites. New single-zircon evaporation ages from the gneisses and granites indicate that the high-grade metamorphism and plutonism is Early Permian in age (~271 Ma). The late-Variscan basement was unconformably overlain by a continental to shallow marine sequence of Early Triassic±Mid-Jurassic age. During the Late Jurassic±Early Cretaceous (Oxfordian±Barremian) the lower Mesozoic cover and the basement were penetratively deformed and regionally metamorphosed in greenschist facies possibly due to a continental collision. An Rb±Sr biotite whole-rock age from a metagranite dates the regional metamorphism as Late Jurassic (155 Ma). Deformation involved north-vergent thrust imbrication of the basement and the emplacement of allochthonous deep marine Triassic series over the Jurassic metasediments. The metamorphic rocks of the Strandja Massif are unconformably overlain by the Cenomanian shallow marine sandstones. During the Senonian, the northern half of the Strandja Massif formed a basement to an intra-arc basin and to a magmatic arc generated above the northward-subducting Tethyan oceanic lithosphere.The Srednogorie arc closed during the early Tertiary through renewed northward thrusting of the Strandja Massif.

The Menderes Massif forms the western of the two large metamorphic culminations within the Turkish Alpide orogen. It has three major lithologic units, with a gneissic “core” at the base and a “schist” and a “marble” envelope overlying it successively, although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the Massif. We present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the Massif to constrain the timing of major tectonic events that shaped the Massif since the late Proterozoic (Pt3). In the southern part of the Massif (sensu stricto) three episodes of deformation and metamorphism are distinguished, whereas in its northern part there are four. The first episode occurred at −500 ± 10 Ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis. In the central part of the Massif, the 470 ± 9 Ma‐old now highly deformed tonalitic and granitic intrusions mark the end of this episode. On a Cambrian reconstruction of continents around the eastern Mediterranean, the Menderes Massif forms the southern end of the Pan‐African orogenic collage of northeastern Africa and Arabia. The area of earliest Palaeozoic deformation in the Menderes may connect with the northwest African orogenic collage along the strike via the Bozburun and Saricicek diabases, arkoses, and schists in the center of the Karacahisar dome interpreted herein as fragments of a Pan‐African suture. The earliest Palaeozoic deformations to affect the rocks were probably related to the last Pan‐African collisions and associated postcollisional convergence. The southern part of the Massif was undeformed from early Ordovician to the early (? later) Eocene, whereas the northern part was deformed, metamorphosed and intruded possibly during the late Triassic, related to the closure of the Karakaya marginal basin of Palaeo‐Tethys. The next major event affecting the whole of the Massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts, and only greenschist grade in the outermost envelope. This metamorphism, here called the “main Menderes metamorphism” (MMM), is biostratigraphically constrained between early Eocene and early Oligocene time. Rb/Sr isotopic data show a spread of ages between 60 Ma and 25 Ma, with the greatest number of determinations around 35 ± 5 Ma. This number is in excellent agreement with the stratigraphic evidence and shows that MMM took place during latest Eocene time or at the transition from Eocene to Oligocene time. Along the northern border of the Massif, deformation and metamorphism had already taken place during the late Cretaceous in a high pressure/low temperature (HP/LT) metamorphic belt (northernmost part of Menderes Massif sensu lato), which was then covered by Palaeocene molasse. The evolution of the HP/LT belt was probably related to the obduction of the Bozkir ophiolites from the Izmi...

A metamorphic core complex of latest Oligocene age crops out in the Kazdağ mountain range in northwest Turkey. The footwall of the core complex consists of gneiss, amphibolite and marble metamorphosed at 5 ± 1 kbar and 640° ± 50 °C. The average muscovite and biotite Rb/Sr ages from the gneisses are 19 Ma and 22 Ma, respectively, and imply high temperature metamorphism during latest Oligocene times. The hangingwall is made up of an unmetamorphosed Lower Tertiary oceanic accretionary melange with Upper Cretaceous eclogite lenses. The hangingwall and footwall are separated by an extensional ductile shear zone, two kilometres thick. Mylonites and underlying high-grade metamorphic rocks show a N-trending mineral lineation with the structural fabrics indicating down-dip, top-to-the-north shear sense. The shear zone, the accretionary melange and the high-grade metamorphic rocks are cut by an undeformed granitoid with a 21 Ma Rb/Sr biotite age, analytically indistinguishable from the Rb/Sr biotite ages in the surrounding footwall gneisses. The estimated pressure of the metamorphism, and that of the granitoid emplacement, indicate that the high-grade metamorphic rocks were rapidly exhumed at ∼ 24 Ma from a depth of ∼ 14 km to ∼ 7 km by activity along the shear zone. The subsequent exhumation of the metamorphic rocks to the surface occurred during Pliocene–Quaternary times in a transpressive ridge between two overstepping fault segments of the North Anatolian Fault zone. The high-grade metamorphic rocks of the Kazdağ range are surrounded by voluminous calc-alkaline volcanic and plutonic rocks of Late Oligocene–Early Miocene age, which formed above the northward-dipping Hellenic subduction zone. The magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest Turkey prior to the onset of extension suggest that the latest Oligocene regional extension was primarily related to the roll-back of the subduction zone rather than to the gravitational collapse.

Ultrahigh‐pressure metamorphic rocks with coesite and diamond form a tectonic slice over 20 km thick, called the eclogite zone, within the Dabie Shan complex in the Qinling orogen in central China. The orogen separates the Sino‐Korean block in the north from the Yangtze block in the south. The Dabie Shan Complex is a composite terrane made up of eclogite facies and amphibolite facies gneiss slices and represents fragments of the lower continental crust of the Yangtze block. The Dabie Shan Complex is bounded in the south by a Triassic foreland fold‐thrust belt and in the north by a greenschist facies metaclastic unit, the Foziling Group, which probably represents the passive continental apron deposits of the Yangtze block. Farther north is a granulite facies gneiss complex, the Qinling Group, which has ultramafic slivers and includes the remnants of an island arc with two bounding suture zones. North of the Qinling Group are early Paleozoic active margin deposits of the Sino‐Korean block. The eclogite zone in the Dabie Shan Complex is sandwiched between amphibolite facies gneiss slices. Dating by Sm‐Nd, Rb‐Sr, and Ar‐Ar of two eclogite samples from the eclogite zone gives early to middle Triassic ages (236–246 Ma); the initial εNd values indicate reworking of a 2.11 and 1.55 Ga continental crust. A Himalayan‐type tectonic evolution is envisaged for the Qinling orogen with the creation of a 100‐km‐thick crustal thrust wedge through continuous underplating during the subduction of the Yangtze continental lithosphere. Exhumation of the ultrahigh‐pressure metamorphic rocks was chiefly achieved by the southward propagation of the thrust planes, thereby isostatically uplifting and eroding the earlier deeply subducted parts of the orogen. A total of 680 km of southward thrusting in front of Dabie Shan is inferred, based on the abrupt termination of the Tanlu fault. Normal faulting possibly caused by gravitational collapse probably also had a role in the exhumation process.

Biostratigraphic, isotopic, and petrologic data from the Central Pontides document major southward growth of the Eurasian continental crust by subduction-accretion during the Cretaceous and Triassic Periods. A major part of the accreted material is represented by a crustal slice, 75 km long and up to 11 km thick, consisting of metabasite, metaophiolite, and mica schist that represent underplated Tethyan oceanic crustal and mantle rocks. They were metamorphosed at 490 °C and 17 kbar in mid-Cretaceous time (ca. 105 Ma). The syn-subduction exhumation occurred in a thrust sheet bounded by a greenschist facies shear zone with a normal sense of movement at the top and a thrust fault at the base. A fl exural foreland basin developed in front of the south-vergent high-pressure-low-temperature (HP-LT) metamorphic thrust sheet; the biostratigraphy of the foreland basin constrains the exhumation of the HP-LT rocks to the Turonian-Coniacian, ~20 m.y. after the HP-LT metamorphism, and ~25 m.y. before the terminal Paleocene continental collision. The Cretaceous subduction-accretion complex is tectonically overlain in the north by oceanic crustal rocks accreted to the southern margin of Eurasia during the latest Triassic-earliest Jurassic. The Triassic subduction-accretion complex is made up of metavolcanic rocks of ensimatic arc origin and has undergone a high pressure, greenschist facies metamorphism with growth of sodic amphibole. Most of the Central Pontides consists of accreted Phanerozoic oceanic crustal material, and hence is comparable to regions such as the Klamath Mountains in the northwestern United States or to the Altaids in Central Asia.

No abstract

No abstract

Earlier geological work in the Istanbul zone, western Pontide tectonic belt, has revealed the presence of extensive basement outcrops exposed underneath Palaeozoic and Mesozoic to Tertiary cover sequences. The basement of suspected Neoproterozoic age plays an important role in understanding the crustal accretion process in NW Turkey. We report the first results of a detailed Pb-Pb and U-Pb zircon study complemented by Nd-Sr whole rock and mineral data from basement rocks exposed in the Karadere valley, Safranbolu area. Five samples were selected for this study, comprising three metagranitoids and two metasediments. Zircon geochronology indicates that the metagranitoids were formed during Late Proterozoic pan-African magmatic events between 590 and 560 Ma. The rocks are of tonalitic and granitic composition and have low Nb/Y ratios and Ti contents, consistent with those of arc rocks. A continental arc setting is supported by their Sr and Nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis. The metasediments can clearly be distinguished from the metagranitoids by their higher 87 Sr/ 86 Sr ratios and lower ε Nd -values at 580 Ma, which supports the suggestion that the arc was underlain by mature continental crust. Zircons from the metasediments yield a range of Pb-Pb ages between 1,860 and 710 Ma. Thirty per cent of them fall between 890 and 710 Ma, possibly suggesting a derivation from Gondwana (Afro-Arabian) regions. A Sm-Nd garnetwhole rock analysis obtained on a metagranite gives an age of 559±8 Ma, which either reflects pre-metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high-temperature metamorphic event. Uplift and cooling of the basement is further constrained by Rb-Sr biotite ages of 548-545 Ma. These lower Cambrian mineral ages demonstrate that the Istanbul zone was not thermally reactivated during the Hercynian, Cimmerian or Alpine orogeny, in contrast to its neighbouring tectonic zones, confirming its role as a suspect terrane in the modern western Pontide tectonic belt.