Browsing by Subject "tectonic evolution"

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    Geochemical character and tectonic environment of Neotethyan ophiolitic fragments and metabasites in the Central Anatolian Crystalline Complex, Turkey
    (2000) Floyd P.A.; Göncüoǧlu M.C.; Winchester J.A.; Yaliniz M.K.
    The Central Anatolian Crystalline Complex (CACC) or Kirsehir Block is part of the metamorphosed leading edge of the Tauride-Anatolide Carbonate Platform. It contains oceanic remnants derived from the Neotethys Ocean (Izmir-Ankara-Erzincan branch) which separate it from the Sakarya microcontinent. Two tectonic units are distinguished: an amphibolite facies Mesozoic 'basement', dominated by platform marbles, over which is thrust a younger fragmented Upper Cretaceous ophiolite sequence. Three metabasite horizons were sampled to reconstruct the development of the oceanic components: (1) fragmented Upper Cretaceous (90-85 Ma) stratiform ophiolitic members comprising gabbros, sheeted dykes, basalt lavas and pelagic sediments thrust over all other units; (2) a tectonised admixture of basite, ultramafic and felsic blocks in an ophiolitic melange (Upper Cretaceous matrix) thrust over the basement metamorphic rocks; and (3) amphibolites concordant with 'basement' marbles and minor pelagics of the largely (?)Triassic Kaleboynu Formation in the lower part of the carbonate platform. Metabasalts and metagabbros from isolated fragments of the stratiform ophiolites form geochemically coherent groups and indicate the influence of a subduction component during their development. It is considered that the suprasubduction zone ophiolites record the association of a tholeiitic arc and an adjacent back-arc basin with more mid-ocean ridge basalt (MORB)-like compositions. Metabasite blocks within the tectonised ophiolitic melange slice are MORB like, together with minor ocean island basalt (OIB) and island arc basalts, and may be tectonically related to ophiolitic units within the accretionary wedge of the Ankara Melange. Concordant amphibolites of the Kaleboynu Formation are largely OIB types and reflect an early ensialic rifting stage of the Tauride-Anatolide Carbonate Platform. Small ocean basins also developed at this time, as recorded by the presence of MORB and associated pelagics. The CACC block, together with parts of the Ankara Melange, are considered to represent oceanic lithosphere (comprising both early spreading centre and latter subduction-influenced crust) and continental carbonate platform that were subsequently ejected from an accretionary-subduction complex on collision with the Sakarya microcontinent.
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    Geochemistry of volcanic rocks from the Cicekdag Ophiolite, Central Anatolia, Turkey, and their inferred tectonic setting within the northern branch of the Neotethyan Ocean
    (2000) Yaliniz K.M.; Floyd P.A.; Göncüoǧlu M.C.
    The Central Anatolian Ophiolites (CAO) comprise a number of little studied Upper Cretaceous ophiolitic bodies that originally represented part of the northern branch of the Neotethyan ocean. The Cicekdag Ophiolite (CO) is an dismembered example of this ophiolite group that still retains a partially preserved magmatic pseudostratigraphy. The following units (bottom to top) can be recognized: (1) layered gabbro; (2) isotropic gabbro: (3) plagiogranite; (4) dolerite dyke complex; (5) basaltic volcanic sequence; and (6) a Turonian-Santonian epi-ophiolitic sedimentary cover. The magmatic rock units (gabbro, dolerite and basalt) form part of a dominant comagmatic series of differentiated tholeiites, together with a minor group of primitive unfractionated basalts. The basaltic volcanics mainly consist of pillow lavas with a subordinate amount of massive lavas and rare basaltic breccias. Petrographic data from the least altered pillow lavas indicate that they were originally olivine-poor, plagioclase-clinopyroxene phyric tholeiites. Immobile trace element data from the basalt lavas and dolerite dykes show a strong subduction-related chemical signature. Relative to N-mid-ocean ridge basalt the Cicekdag basaltic rocks (allowing for the effects of alteration) have typical suprasubduction zone features with similarities to the Izu-Bonin Arc, i.e. enriched in most large-ion lithophile elements, depleted in high field strength elements and exhibiting depleted light rare earth element patterns. The geochemical characteristics are similar to other eastern Mediterranean Neotethyan SSZ-type ophiolites and suggest that the CO oceanic crust was generated by partial melting of already depleted oceanic lithosphere within the northern branch of the Neotethyan ocean. The Cicekdag body, along with the other fragmented CAO, is thus representative of the Late Cretaceous development of new oceanic lithosphere within an older oceanic realm.
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    A geotraverse across northwestern Turkey: Tectonic units of the Central Sakarya region and their tectonic evolution
    (2000) Göncüoǧlu M.C.; Turhan N.; Şentürk K.; Özcan A.; Uysal S.; Yaliniz M.K.
    In the Central Sakarya area of Turkey there are two main Alpine continental units, separated by a south verging ophiolitic complex which represents the root zone of the Izmir-Ankara Suture Belt. The Central Sakarya Terrane in the north includes two 'Variscan' tectonic units in its basement. The Sogut Metamorphic rocks represent a Variscan ensimatic arc complex and the Tepekoy Metamorphic rocks are characteristically a forearc-trench complex. The unconformably overlying Triassic Sogukkuyu Metamorphic rocks correspond to a part of the Karakaya Formation and are interpreted as a Triassic rift basin assemblage. These units are unconformably overlain by a transgressive sequence of Liassic-Late Cretaceous age that represents the northeastward deepening carbonate platform of the Sakarya Composite Terrane. The middle tectonic unit (the Central Sakarya Ophiolitic Complex) comprises blocks and slices of dismembered ophiolites, blueschists and basic volcanic rocks with uppermost Jurassic-Lower Cretaceous radiolarite-limestone interlayers. Geochemical data from basalt blocks suggest mid-ocean ridge basalt (MORB)- and suprasubduction-type tectonic settings within the Neotethyan Izmir-Ankara Ocean. The southern tectonic unit includes basal polyphase metamorphosed clastic rocks (Somdiken Metamorphics), intruded by felsic and basic dykes and overlain by thickbedded marbles. This assemblage is unconformably overlain by continental clastic rocks gradually giving way to thick-bedded recrystallized limestones, cherty limestones and pelagic limestones intercalated with radiolarites, and finally by a thick high pressure-low temperature (HP-LT) metamorphic synorogenic flysch sequence. This succession is identical to the passive continental margin sequences of the Tauride Platform. It is suggested that this passive margin was subducted during the Late Cretaceous in an intra-oceanic subduction zone and affected by HP-LT metamorphism. The emplacement of the allochthonous oceanic assemblages and the collision with the Central Sakarya Terrane was complete by the end of the Cretaceous.