Kolios, Antonios (2001) Stratigraphy, origin, mineralogy, geochemistry and paleotectonic significance of the volcaniclastic sediments of the Kannaviou Formation, Cyprus. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 118 pp.

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Abstract

This study concerns the tectonic setting of the Troodos Ophiolite. The volcaniclastic sediments of the Kannaviou Formation, accumulated in westem Cyprus, are the main geological criteria to find a solution to this question. The Kannaviou Formation is subdivided into eight different volcaniclastic facies which are distinguished from each other by bedding characteristics and grain size in massive sandstone to claystone (facies 1, 2, 3, 6, 7, 8) and bedded (up to 4 cm thick) to laminated (<1 cm thick) sandstone to siltstone (facies 4 and 5). The sediments are accumulated either on the Javas of the Troodos Ophiolite or locally on the younger Fe-Mn-rich umbers and radiolarian claystones overlying the ophiolitic body. The volcaniclastic deposits are distributed mainly in western Cyprus, particularly on the westem periphery of the Troodos Ophiolite making up a succession of more than 700 m based on the geological maps, but less than half is exposed. Facies 1 and 2 form the top of the succession whereas the base is characterized by the facies 6 and 7. Highly vesicular rhyolitic glass (pumice) is the main component reaching in the pumice-rich layers of facies 5 >50 vol% and in the massive sediments <10->50 vol%. Glass shards (mainly rhyolitic, minor basaltic to basaltic andesitic) reach up to 20 volo/o. Wherever basal and fine grained massive beds are exposed (facies 6 and 7), the pumice concentration is lower than 5 vol%. Plagioclase (An32_95) is less than 25 vol% in the massive sediments and <10-20 vol% in the bedded sediments. Other igneous components are quartz ( <5-< 10 vol%), clinopyroxene (mainly augite, minor diopside), amphibole (edenite, hastingsite), minor orthopyroxene (hypersthene) (mafic mineral phases up to 5 vol%) and opaque minerals (up to 5 vol%). Lithic fragments (radiolarian claystones, volcanic and metamorphic lithics (<5 to >15 vol%) and fauna (mostly radiolaria and calcareous nannofossils reaching up to 10 vol%) are other important components. Minor metamorphic assemblage includes chiefly polycrystalline quartz, pargasite, epidote/zoisite, minor chromian spinel and white mica. Pumice clasts of facies 1 are characterized by large "lapilli" (up to 3 cm) whereas basal beds of facies 6, in contrast, are characterized by ash-sized pumice clasts. The sediments are interpreted to be accumulated either as turbidity currents (sharp contacts of the bedded sediments e.g. facies 5) or as debris flows. The sedimentation takes place in form of small channels. The Kannaviou Formation is possibly autochthonous. Abundance of highly vesicular ash to lapilli-sized particles in the sediments higher in the uccession suggests a successively shallowing of the water depth during the volcaniclastic deposition. The eruptions possibly continued under subaerial conditions, as shown by pyroclastic flows which are nearly monomineralic. Lithological criteria together with the faunal assemblage suggest that the sedimentation place was deep-marine (1000-2500 m) and the position of the CCD was higher than that during the Troodos emplacement (<5000 m). The majority of the examined crystals are placed in the Late Campanian (c. 75 Ma) suggesting a short life-time of the accumulation. Magma mixing is the reason for inhomogeneous concentration of anorthite and sieve-like structures in the plagioclases. Calc-alkaline composition suggests the activity of a subduction zone beneath the Troodos Ophiolite leading to the Kannaviou volcanic sources. Ta/Yb versus Th/Yb in the Kannaviou sediments further suggests an island arc setting. Such a composition is dissimilar to coeval volcanoes erupted in Turkey, Israel and Lebanon. Chemical data of the Kannaviou Formation and the Mariana arc volcanoes overlap. The comparison between the compositional data between the Mariana backarc volcanoes and the Troodos Ophiolite reveals geochemical similarities as well, suggesting that the Troodos Ophiolite represents possibly a backarc setting. The Kannaviou eruptions derived possibly from arc volcanoes located in the sea area close to Troodos Ophiolite.

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