Geochemistry of volcanic rocks from the Cicekdag Ophiolite, Central Anatolia, Turkey, and their inferred tectonic setting within the northern branch of the Neotethyan Ocean
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2000
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Abstract
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.