Ion Probe U-Pb Dating of the Central Sakarya Basement: A peri-Gondwana Terrane Intruded by Late Lower Carboniferous Subduction/Collision-related Granitic Rocks

Ion probe dating is used to determine the relative ages of amphibolite-facies meta-clastic sedimentary rocks and crosscutting granitoid rocks within an important 'basement' outcrop in northwestern Turkey. U-Pb ages of 89 detrital zircon grains separated from sillimanite-garnet micaschist from the Central Sakarya basement terrane range from 551 Ma (Ediacaran) to 2738 Ma (Neoarchean). Eighty five percent of the ages are 90-110% concordant. Zircon populations cluster at similar to 550-750 Ma ( 28 grains), similar to 950-1050 Ma (27 grains) and similar to 2000 Ma (5 grains), with smaller groupings at similar to 800 Ma and similar to 1850 Ma. The first, prominent, population (late Neoproterozoic) reflects derivation from a source area related to a Cadomian-Avalonian magmatic arc, or the East African orogen. An alternative Baltica-related origin is unlikely because Baltica was magmatically inactive during much of this period. The early Neoproterozoic ages (0.9-1.0 Ga) deviate significantly from the known age spectra of Cadomian terranes and are instead consistent with derivation from northeast Africa. The detrital zircon age spectrum of the Sakarya basement is similar to that of Cambrian-Ordovician sandstones along the northern periphery of the Arabian-Nubian Shield (Elat sandstones). A sample of crosscutting pink alkali feldspar-rich granitoid yielded an age of 324.3 +/- 1.5 Ma, whilst a grey, well-foliated biotite granitoid was dated at 327.2 +/- 1.9 Ma. A granitoid body with biotite and amphibole yielded an age of 319.5 +/- 1.1 Ma. The granitoid magmatism could thus have persisted for similar to 8 Ma during late Early Carboniferous time, possibly related to subduction or collision of a Central Sakarya terrane with the Eurasian margin. The Central Sakarya terrane is likely to have rifted during the Early Palaeozoic; i.e. relatively early compared to other Eastern Mediterranean, inferred `Minoan terranes' and then accreted to the Eurasian margin, probably during Late Palaeozoic time. The differences in detrital zircon populations suggest that the Central Sakarya terrane was not part of the source area of Lower Carboniferous clastic sediments of the now-adjacent Istanbul terrane, consistent with these two tectonic units being far apart during Late Palaeozoic-Early Mesozoic time

Late Cretaceous-Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey

Six individual tectonostratigraphic units are identified within the Izmir-Ankara-Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayikayasi Formation of Campanian-Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayikayasi Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of similar to 75 % (by volume) serpentinized peridotite (mainly harzburgite), similar to 20 % diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally Occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Melange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadag Formation, of Campanian-Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian-Early Eocene Sutpinar Formation (similar to 1500 m thick) is a coarsening-Upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene-Eocene Sipikor Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic are units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian-Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys

Cadomian (Ediacaran-Cambrian) arc magmatism in the Bitlis Massif, SE Turkey: Magmatism along the developing northern margin of Gondwana

Copyright © 2008 Elsevier B.V. All rights reserved.Small granitic plutons and associated granitic dykes that intrude the pre-Devonian basement of the Bitlis Massif were previously inferred to have a broadly Late Palaeozoic crystallisation age related to the Hercynian orogeny; this was tested during this work. The brittle-ductile-deformed Mutki granite pluton and nearby granitic dykes comprise mainly quartz, alkali feldspar, plagioclase, subordinate biotite, muscovite and rare amphibole. Based on the results of whole-rock major-element and trace-element analysis, the Mutki pluton and associated dykes are inferred to have crystallised from metaluminous, to peraluminous subduction influenced I-type melts. Sm-Nd isotope systematics indicate melting of a mantle source (of notional 1.3 Ga age), with increasing amounts of crustal contamination through time. U/Pb zircon dating of the Mutki granite and a nearby granitic dyke by laser inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded 238U/206Pb crystallisation ages of 545.5 ± 6.1 Ma and 531.4 ± 3.6 Ma, respectively (Ediacaran-Early Cambrian). This shows for the first time that the regionally extensive Bitlis Massif was affected by Cadomian arc-type magmatism. The Ediacaran-Early Cambrian granitic rocks of the Bitlis Massif can be compared with similar-aged metagranitic and metavolcanic rocks within basement units exposed in the Tauride-Anatolide Platform (Menderes-Taurus Block) in western Anatolia and also in NW Turkey. Similar-aged rocks are also exposed in the basement of Iran. All of these magmatic units and their host rocks are interpreted as fragments of a Cadomian active margin bordering the northern margin of Gondwana after its final amalgamation. Formation of the Bitlis Massif granites and contemporaneous granitic units elsewhere in Turkey as fragments of an Andean-type margin adjacent to the Arabian-Nubian Shield is favoured over an alternative explanation as exotic terranes transported > 2000 km eastwards from a Cadomian active margin near West Africa-Amazonia (now NW Africa). © 2008 Elsevier B.V. All rights reserved.P. Ayda Ustaömer, Timur Ustaömer, Alan S. Collins and Alastair H.F. Robertsonhttp://www.elsevier.com/wps/find/journaldescription.cws_home/503362/description#descriptio

Pre-early Ordovician Cadomian arc-type granitoids, the Bolu Massif, West Pontides, northern Turkey: geochemical evidence

The West Pontides tectonic belt of northern Turkey comprises a Lower Ordovician-Lower Carboniferous transgressive sequence. A stratigraphic base ment to this Paleozoic sequence is exposed in the Bolu area. The tectono-stratigraphy of the basement closely resemble that of the Cadomian belt of western Europe. Three rock units forming the basement imply development of an Andean-type active continental margin during the pre-Early Ordovician period. High-grade metamorphics (the Sunnice Group), granitoids (the Bolu Granitoid Complex) and evolved felsic metavolcanic rocks (the Casurtepe Formation) are exposed unconformably beneath the Lower Ordovician fluvial clastics, between the Bolu-Yedigoller area, to the north of Bolu. The Bolu Granitoid Complex comprises a group of intrusive rocks of variable composition and size, generated through multiple episodes of magmatism, and is represented by two separate intrusive bodies within the study area, the Tullukiris Pluton in the west and the Kapikaya Pluton in the east. Both plutons are mainly tonalite and granodiorite in composition. More felsic and mafic compositional varieties also occur. Major and trace element chemical characteristics of the granitoids, as well as biotite chemistry, indicate that these are volcanic are-type granitoids and are products of an immature are developed during early stages of a subduction. Furthermore, textural and chemical characteristics of the plutons show that these are subvolcanic intrusions, emplaced at shallow depths, and are calc-alkaline in composition. The granitoidic plutons intrude the Casurtepe Formation. The Casurtepe Formation is represented by are-type volcanics and volcaniclastics. Both the Casurtepe Formation and the granitoids represent subduction-zone magmatism constructed on a continental crust, represented by the Sunnice Group. The history is very similar to Cadomian active margins as exposed in western Europe (i.e., the North Armorican and Bohemia massifs) and therefore the basement to the Paleozoic of the West Pontides is considered to be a preserved remnant of the Cadomian belt

Eocene continental arc magmatism along the southern Eurasian margin: New U-Pb LA-ICPMS Sm-Nd and whole-rock geochemical data from Marmara Island NW Turkey

Copyright © 2007 European Geosciences Unionhttp://www.cosis.net/abstracts/EGU2007/00670/EGU2007-J-00670.pd

Evidence of Precambrian sedimentation/magmatism and Cambrian metamorphism in the Bitlis Massif, SE Turkey utilising whole-rock geochemistry and U-Pb LA-ICP-MS zircon dating

The Bitlis Massif is a regional-scale, south-vergent allochthon that was finally emplaced by collision of the Eurasian and Afro-Arabian plates during Miocene time. The Bitlis Massif includes a large outcrop of Precambrian continental crust, the closest counterpart to which is the Arabian-Nubian Shield ~1000km to the south. The Massif is sub-divided into two rock associations: a pre-Middle Devonian high-grade basement and a Middle Devonian-Triassic low-grade cover. The pre-Devonian basement comprises meta-granitic plutons emplaced into high-grade metamorphic rocks, including schist, paragneiss, amphibolite and eclogite. New laser-ablation zircon ages obtained for zircons separated from a meta-granite body and its host paragneiss provide constraints on magmatism, sedimentation and metamorphism. Whole-rock geochemical data indicate that the pluton crystallised from peraluminous I-type melts from an arc-type subduction influenced source. Sm-Nd isotope systematics suggest crustal contamination. Zircon dating yielded a 206Pb/ 238U age of 572±4.8Ma, interpreted as the time of crystallisation. Igneous zircons exhibit metamict metamorphic domains dated at 529Ma (Early Cambrian), interpreted as the time of latest Pan-African metamorphism. Nine detrital zircon grains from host paragneiss yielded Neoproterozoic ages (992-627Ma). Combined with the crystallisation age data, this suggests that the sedimentary protolith of the paragneiss was deposited from ~627 to ~572Ma (Ediacaran). The late Neoproterozoic ages suggest the Bitlis Massif is a peri-Gondwanan terrane with a likely origin in northeast Africa where similar early Neoproterozoic (0.9-1.0Ga) ages have been reported. © 2011 International Association for Gondwana Research.P. Ayda Ustaömer, Timur Ustaömer, Axel Gerdes, Alastair H.F. Robertson and Alan S. Collin

The Bolu Massif: remnant of a pre-Early Ordovician active margin in the west Pontides, northern Turkey

The scope of this study is to understand better the pre-Early Ordovician history of the west Pontides of northern Turkey by focusing on the best-exposed part of the Bolu Massif, which is located between Bolu and Yedigoller (Seven Lakes). The Palaeozoic rocks of the west Pontides tectonic belt of northern Turkey comprise a transgressive sedimentary sequence known as 'Palaeozoic of Istanbul.' In a few areas, the basement of the Palaeozoic sequence is exposed, the largest part of which is the Bolu Massif, which is located in the middle of the west Pontides. The lowermost unit of the Palaeozoic of Istanbul in the Bolu area is the Isigandere Formation, which is made up of fluvial red conglomerates and sandstones of Lower Ordovician age. Three different units are exposed unconformably beneath these continental clastics, forming the Bolu Massif. From the structural base to the top, these are as follows: (1) a high-grade metamorphic unit, known as the Sunnice Group); (2) granitoid intrusions, known as the Bolu Granitoid Complex; and (3) a greenschist meta-volcanic sequence (the Casurtepe Formation)