Metabasite Blocks from the Koçyaka HP-LT Metamorphic Rocks, Konya, Central Anatolia: Geochemical Evidence for an Arc-Back-Arc Pair?

Authors: PETER A. FLOYD, L. ÖZGÜL, M. CEMAL GÖNCÜOĞLU

Abstract: The Kütahya-Bolkardağ Belt, situated on the northern margin of the Tauride-Anatolide Platform, includes slices of HP/LT metamorphic rocks adjacent to allochthonous ophiolitic fragments. The Koçyaka Metamorphic Complex is one such thrust slice and is located to the northeast of Konya. The local tectonostratigraphic succession consists of Upper Cretaceous calcareous metasediments overlain respectively by the Altınekin and Akçasar mélanges of ophiolitic character. Both mélanges contain metabasites (pillow lavas and amphibolites) overprinted with HP-LT glaucophanitic assemblages and later low-grade facies associations. The geodynamic significance of the ophiolites prior to dismemberment (as oceanic crust) is in dispute, being either interpreted as a separate Neotethyan oceanic strand or derived from the İzmir-Ankara-Erzincan ocean to the north. Geochemical comparisons suggest that the metasediments are largely admixtures of pelagic and calcareous sediments typical of the ocean floor. The metabasite blocks in both mélanges are incompatible element-depleted, plagioclase-clinopyroxene phyric tholeiites and appear to form a coherent magmatic group. Although the metabasalts have affinities to N-MORB, their range of composition is more typical of a back-arc basin environment. Geochemical comparison, tectonic juxtaposition and similarity of age to the stratiform supra-subduction zone (SSZ) ophiolites of the Central Anatolian Crystalline Complex (CACC) suggest that the Konya metabasite blocks (with back-arc affinity) and the SSZ ophiolites (with arc affinity) could represent an arc-back-arc pair. If this is the case, it removes the need for a separate "Inner Tauride Ocean" between the CACC and the Tauride-Anatolide Platform, both units being initially derived from the northern İzmir-Ankara-Erzincan ocean.

Keywords: metabasite, geochemistry, HP-LT rocks, central Anatolia, back-arc

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