Geochemical Character and Tectonic Environment of Neotethyan Ophiolitic Fragments and Metabasites in the Central Anatolian Crystalline Complex, Turkey

Abstract

The Central Anatolian Crystalline Complex (CACC) or Kırşehir Block is part of the metamorphosed leading edge of the Tauride-Anatolide Carbonate Platform. It contains oceanic remnants derived from the Neotethys Ocean (İzmir-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 mélange (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 mélange 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 Mélange.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 Mélange, 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.

Geochemistry and origin of plagiogranites from the Eldivan Ophiolite, Çankırı (Central Anatolia, Turkey)

“…The second model assumes hydrous partial melting of gabbro or similar melts in a MOR setting (Gerlach et al 1981;Spulber & Rutherford 1983;Floyd et al 2000). Liquid immiscibility in an evolved MORB liquid has been suggested as third scenario for the plagiogranite generation (Phillpotts 1976;Dixon & Rutherford 1979;Floyd et al 2000). In our subsequent discussion we assess the viability of the first two processes in explaining the major element and REE data of plagiogranites.…”

“…Koepke et al (2007) summarized the generally accepted models. The first one involves late stage differentiation of low-K tholeiitic MORB magmas (Coleman & Peterman 1975;Coleman & Donato 1979;Pallister & Knight 1981;Floyd et al 2000). The second model assumes hydrous partial melting of gabbro or similar melts in a MOR setting (Gerlach et al 1981;Spulber & Rutherford 1983;Floyd et al 2000).…”

“…The first one involves late stage differentiation of low-K tholeiitic MORB magmas (Coleman & Peterman 1975;Coleman & Donato 1979;Pallister & Knight 1981;Floyd et al 2000). The second model assumes hydrous partial melting of gabbro or similar melts in a MOR setting (Gerlach et al 1981;Spulber & Rutherford 1983;Floyd et al 2000). Liquid immiscibility in an evolved MORB liquid has been suggested as third scenario for the plagiogranite generation (Phillpotts 1976;Dixon & Rutherford 1979;Floyd et al 2000).…”

Subduction, ophiolite genesis and collision history of Tethys adjacent to the Eurasian continental margin: new evidence from the Eastern Pontides, Turkey

“…(2) Cretaceous SSZ-type ophiolites are documented from the westward extension of the suture zone into the Central Pontides based on dating of associated deep-sea pelagic carbonates (see above). (3) Upper Cretaceous ophiolites are also recognised overlying the Kırşehir Massif further south, again mainly based on dating of pelagic carbonates associated with ophiolitic volcanic rocks (Floyd et al, 2000). (4) The Late Cretaceous age of metamorphic sole rocks of SSZ-type ophiolites in the northwestern Taurides (Tavşanlı area) implies a Cretaceous age of formation (Önen & Hall, 2000).…”

“…The timing of emplacement of the ophiolitic rocks onto the Pontide continental margin and the final closure of the Tethyan ocean in this region have been regarded as ranging from Late Cretaceous to Eocene in different interpretations (e.g. Floyd, Göncüoğlu, Winchester, & Yalınız, 2000;Göncüoğlu, Turhan, Şentürk, Özcan, & Uysal, 2000;Okay & Şahintürk, l997a;Rice et al, 2006, Rice, Robertson, Ustaömer, İnan, & Taslı, 2009Şengör & Yılmaz, 1981). In addition, Middle Eocene and younger sedimentary and volcanic cover units help to document post-collisional suture tightening and the role of extension related to opening of the Black Sea.…”