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.

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.

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Single zircon U-Pb dating combined with 207 Pb/ 206 Pb ages obtained by the evaporation method constrains the emplacement of tonalitic, trondhjemitic, and granodioritic orthogneisses of the Moldanubian zone in the Black Forest between 500 and 510 Ma. Two detrital zircon populations of 1.9 and 1.6 Ga indicate Early-Middle Proterozoic material in the former setting of the basement. The initial Nd values range from -0.1 to -3.4 and mean crustal residence ages of 1.0-1.4 Ga are consistent with involvement of Early-Middle Proterozoic crust, and a subordinate juvenile component probably originating from subduction-related melting of the mantle. The orthogneisses have fractionated REE patterns and slightly higher K 2 O/Na 2 O ratios than typical low-K tonalite-trondhjemite-granite suites. The chemical data are interpreted as evidence for melting of amphibolite and contributions from evolved crust. The emplacement of the orthogneisses was superceded by a high-temperature metamorphic event at F480 Ma which we interpret as a result of lithospheric thinning in a marginal basin behind a Cambrian magmatic arc.

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The Rand Granite is a heterogeneous metamorphosed granitoid rock complex with numerous wallrock inclusions situated in the Moldanubian Zone at the southern margin of the Central Schwarzwald Gneiss Complex. It is a largely mylonitized elongated body and is thrust over the Badenweiler-Lenzkirch Zone forming a nappe with shear zones along its northern and southern boundaries. It comprises meta-granites, meta-trondhjemites and biotite augen gneisses derived from monzogranites to granodiorites. Mineral behaviour indicates that the magmatic body has been deformed under upper greenschist facies conditions. Nappe thrusting, which also affected the South Schwarzwald Gneiss Complex, occurred in Visean time during high-temperature / lowpressure metamorphism. Kinematic indicators in the mylonites document E-to ESE-directed nappe transport, highly transpressive relative to the trend of the nappe boundaries and the foliation. The trondhjemites formed at 351 +5/-4 Ma, predating the Variscan HT metamorphism. They have initial e Nd -values of +6.6 to +6.7 and relatively low initial 87 Sr/ 86 Sr ratios (0.7042 to 0.7063), indicating a predominant mantle origin. The granites and protoliths of the biotite augen gneisses probably crystallised between 436 and 377 Ma, suggested by U-Pb zircon model ages. They are different from the trondhjemites with low initial e Nd -values (4.7 to 3.3) and higher initial 87 Sr/ 86 Sr ratios (0.7068-0.7077), indicating that large part of the Rand Granite originated from anatexis of continental crust. Internal structure of zircons from the Rand Granite reveals mixing of magmas derived from both mantle and crust sources. These new data support an interpretation that the Rand Granite developed along an active continental margin and therefore represents a possible root of a Variscan magmatic arc.

A variety of models has been proposed for the origin of late Devonian low-grade greywacke, juxtaposed with the high-grade Variscan basement of the Black Forest. Here we interpret detrital zircon ages, and geochemical and Sm–Nd isotopic data of greywacke samples as evidence for their sources and tectonic setting of deposition. Detrital zircon ages of 371–384 Ma reveal igneous activity shortly before the deposition of the greywacke sequence at c . 365 Ma. ε Nd values of c . +3 to −10 in the greywacke samples indicate mixing of juvenile and older crustal material. Samples with low MgO concentrations and ε Nd values of −10 to −4 are interpreted as mostly derived from older granite–gneiss basement. Involvement of a juvenile mafic source is documented by samples with up to 7 wt% MgO and ε Nd values up to +3. Assessment of the composition of the juvenile component shows high concentrations of light REE, and low Sm/Nd and Nb/La ratios, all consistent with a subduction-related origin. We conclude that the greywacke sequence was derived from a late Devonian Andean-type continental margin, implying a cryptic suture in the internal high-grade Variscan basement of the southern Black Forest.