No abstract

The late Cretaceous Kızıldağ ophiolite forms one of the best exposures of oceanic lithospheric remnants of southern Neotethys to the north of the Arabian promontory in Turkey. The ultramafic to mafic cumulate rocks, displaying variable thickness (ranging from 165 to 700 m), are ductiley deformed, possibly in response to syn-magmatic extension during sea-floor spreading and characterized by wehrlite, olivine gabbro, olivine gabbronorite and gabbro. The gabbroic cumulates have an intrusive contact with the wehrlitic cumulates in some places. The crystallization order of the cumulus and intercumulus phases is olivine (Fo86–77)± chromian spinel, clinopyroxene (Mg#92–76), plagio-clase(An95–83), orthopyroxene(Mg#87–79). The olivine, clinopyroxene, orthopyroxene and plagioclase in ultramafic and mafic cumulate rocks seem to have similar compositional range. This suggests that these rocks cannot represent a simple crystal line of descent. Instead the overlapping ranges in mineral compositions in different rock types suggest multiple magma generation during crustal accretion for the Kızıldağ ophiolite. The presence of high Mg# of olivine, clinopyroxene, orthopyroxene, and the absence of Ca-rich plagioclase as an early fractionating phase co-precipitating with forsteritic olivine, suggest that the Kızıldağ plutonic suite is not likely to have originated in a mid-ocean ridge environment. Instead the whole-rock and mineral chemistry of the cumulates indicates their derivation from an island arc tholeiitic (IAT) magma. All the evidence indicates that the Kızıldağ ophiolite formed along a slow-spreading centre in a fore-arc region of a suprasubduction zone tectonic setting.

The Upper Cretaceous Tekirova (Antalya) ophiolite derived from the southern branch of the Neotethys is located at the southwestern part of the Antalya Complex along the Tauride belt in southern Turkey. It comprises harzburgitic tectonites, ultramafic to mafic cumulates, isotropic gabbro, sheeted dykes, volcanics and associated sedimentary rocks. The cumulate rocks are located mainly along the Ç iral-Tekirova section to the south and at Doyran to the north. Several isolated blocks of cumulate rocks are also observed in the north-south-trending Gödene zone of the Antalya Complex. The ultramafic and mafic cumulate rocks are represented by wehrlite, lherzolite, olivine clinopyroxenite, olivine gabbronorite, olivine gabbro, gabbronorite and gabbro. The order of crystallization in the cumulates is olivine (Fo 88-76 ) AE chromian spinel ! clinopyroxene (Mg# 92-76 ) ! orthopyroxene (Mg# 86-70 ) ! plagioclase (An 97-84 ). The major and trace element geochemistry of the plutonic rocks suggests that the primary magma generating the Tekirova (Antalya) ophiolite is compositionally similar to those observed in modern island arc tholeiitic sequences. The presence of highly magnesian clino-and orthopyroxenes along with the absence of plagioclase in the ultramafic cumulates suggest their formation as a result of high-pressure crystal fractionation (c. 10 kbar). In contrast, the mafic cumulates in the upper crustal level show evidence of a lower-pressure (2-2.5 kbar) environment within the same tectonic setting. Therefore, it is suggested that the cumulate ultramafic rocks were probably precipitated as a result of in situ crystallization processes along the walls of a conduit system extending downward from a crustal level magma chamber to mantle depths of approximately 30 km. After their formation, the ultramafic cumulates were transported to a shallow-level magma chamber where the remainder of the plutonic section (mafic cumulates) was formed at a lower pressure environment.

The SW Antalya Complex is an assemblage of Mesozoic carbonate platform, margin and ophiolitic rocks which record the formation and tectonic emplacement of a small Mesozoic ocean basin. The late Cretaceous ophiolitic rocks are located at two localities, namely the relatively intact Tekirova ophiolite to the east of Kemer zone and the dismembered Gödene ophiolite to the west of Kemer zone. The Tekirova (Antalya) ophiolite comprises harzburgitic tectonites, ultramafic to mafic cumulates, isotropic gabbros and sheeted dikes. Numerous isolated dikes, ranging in thickness from 5 cm to 10 m, intruded the crustal rocks at different structural levels. The isotropic gabbros are represented by gabbro, diorite and quartz diorite rocks with granular to ophitic-subophitic textures. The isolated dikes are characterized by dolerite, diabase and microdiorite with ophitic, intersertal and microgranular textures. These rocks exhibit tholeiitic to alkaline compositions. New geochemical data presented in this paper from the isolated dikes and isotropic gabbros suggest that there are three main types of parental basic magmas that form the oceanic crustal rocks of the Tekirova (Antalya) ophiolite. These are (1) IAT series which can be referred to the Group I isolated dikes and isotropic gabbros; (2) low-Ti boninitic series characterized by the Group II isolated dike and isotropic gabbros; and (3) OIB-type including the Group III isotropic gabbros. The geochemical evidence suggests that the crustal rocks of the Tekirova (Antalya) ophiolite were generated from a progressive source depletion from island arc tholeiites (IAT) to boninites. Therefore, a fore-arc tectonic setting seems likely for the generation of the crustal rocks from the Tekirova (Antalya) ophiolite in the southern branch of Neotethys during the Late Cretaceous. The OIB-type alkaline isotropic gabbros are thought to have resulted from either (1) a late-stage magmatic activity fed by melts that originated within an asthenospheric window due to slab break-off or (2) subduction of a ridge system which generated OIB source across the asthenospheric window that has been no influence of fluids from the subducted slab into the overlying mantle wedge, shortly before the emplacement of the Tekirova (Antalya) ophiolite onto the Tauride platform.

The İspendere ophiolite forms part of the Tauride active continental margin assemblage in SE Anatolia. The ophiolite exhibits an intact oceanic lithosphere section and is intruded by Late Cretaceous calc-alkaline granites. The ophiolite comprises mantle tectonites, ultramafic to mafic cumulates, isotropic gabbros, isolated diabase dykes, a sheeted dyke complex, plagiogranite and volcanic rocks. The volcanics and the sheeted dyke complex exhibit (1) similar rare earth element patterns, with flat to light rare earth element depletion (La-Yb) N ¼ 0.71-1.14 and 0.65-1.22, (2) negative Nb anomalies and (3) flat-lying high field strength element trends. These features differ from a typical Normal-Mid Ocean Ridge Basalt fractionation trend and could have resulted from c. 15% partial melting of a previously depleted mantle source. The whole-rock chemistry and the mineral chemistry of the ultramafic to mafic cumulates [high Ca plagioclases (An 89 -81 ), magnesian olivines (Fo 88 -81 ) and clinopyroxenes (Mg# 90 -83 )] show that the primary magma of the plutonic suite is compositionally similar to modern island arc tholeiites. The available evidence suggests that the İspendere ophiolite formed at a northerly supra-subduction zone spreading centre of the Southern Neotethys, between the Taurides and the Bitlis-Pütürge metamorphic units, during the Late Cretaceous. Comparison with the adjacent Göksun, Kömürhan and Guleman ophiolites suggests that the İspendere ophiolite represents part of a single regional-scale sheet of oceanic lithosphere that was accreted to the base of Tauride active continental margin where it was cut by arc-type magmatic rocks.