Structure and petrology of Tauride ophiolites and mafic dike intrusions (Turkey): Implications for the Neotethyan ocean

Cretaceous Neotethyan ophiolites occur in four east-west-trending subparall el zones within the Tauride tectonic belt in southern Turkey. The ophiolite s of the Inner, Intermediate, and Outer zones tectonically overlie the Meso zoic platform carbonates of the Tauride belt and are commonly underlain by a Cenomanian ophiolitic melange. These ophiolites consist mainly of tectoni zed mantle reeks, mafic-ultramafic cumulates, and gabbros, and commonly lac k sheeted dike complexes and extrusive rocks of a complete ophiolite sequen ce. Metamorphic soles that are several hundred meters thick occur as thrust -faulted slices beneath these ophiolites and show weil-developed metamorphi c held gradients, Ophiolitic units and the metamorphic soles are intruded b y mafic dike swarms that are truncated at the contact with the underlying m elange unit. Dike rocks are made of subalkalic basalt to andesite typical o f evolved island-are tholeiites; they display large compositional variation s, with SiO2 content between 50 and 60 wt% and MgO between 8 and 4 wt%, and contain higher Ti augite phenocrysts and significantly less calcic plagioc lase than their host cumulates, The majority of the analyzed dike rocks sho w a slight depletion in light rare earth elements (REE) with low La/SmN rat ios and are depleted in both high-field strength (HFS) and heavy REEs, whil e enriched in large-ion-lithophile elements (LILE) relative to normal mid-o cean ridge basalt (MORB). These characteristics suggest a mantle source tha t underwent previous melt extractions and subsequent metasomatism by LILE-a nd light REE-enriched fluids. Geochemical modeling of trace elements shows that melting occurred at relatively low pressures under hydrous conditions and that it may have required the existence of an asthenospheric window, in which the dike magmas developed through tapping and mixing of melts genera ted within a rising melting column starting slightly within the garnet stab ility held, or in a transitional zone between the garnet and spinel stabili ty fields at about 60 ion depth. This asthenospheric window was probably cr eated during subduction of a Neotethyan ridge system; magmas ascending from the melt column within this window generated dikes that crosscut the metam orphic soles and were injected into the overlying mantle cr edge and oceani c lithosphere. The new Ar-40/Ar-39 hornblende dates of 92-90 Ma and 90-91 M a from the metamorphic soles and dike swarms, respectively; show that evolu tion of these two geologic units was closely related in time and space and that they formed at the same intraoceanic subduction zone within the Inner Tauride seaway. These data suggest that the Tauride ophiolites within the t hree zones to the north originated from the same root zone situated north o f the Tauride carbonate platform, and that they constitute remnants of a si ngle ophiolitic nappe sheet derived from the Inner Tauride seaway within th e Neotethyan ocean.