Geochemical character and tectonic environment of ultramafic to mafic cumulate rocks from the Tekirova (Antalya) ophiolite (southern Turkey)

摘要

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 Cirah-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 Godene 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)) +/- 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 modem 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. Copyright (C) 2006 John Wiley & Sons, Ltd.