Geochemical Implications for Tectonic Setting of the Ophiolitic Rocks From the Ophiolitic Melange Belt of the Ankara Melange

Abstract

Ophiolite melange of Cretaceous age is the youngest belt of the Ankara melange and consists mainly of ophiolitic rock fragments such as serpentinite, gabbro, dolerite and basalt of varying sizes, together with pelagic radiolarites and limestones. The ophiolitic melange includes also large isolated masses which are considered to be preserved slices of oceanic lithosphere. The mafic clasts in the melange and the basic dyke rocks of an oceanic lithosphere fragment, Edige body, have comparable compositions. The petrographic and geochemical characteristics of the ultrabasic rocks of the ophiolite melange are correlated with those of depleted mantle peridotite whereas trace element contents, particularly REE, of the basic rocks are within the range of abyssal tholeiites. These ophiolites are believed to be representative of suboceanic environment. However the basic rocks, with their higher LIL and lower HFS element contents relative to MORB, demonstrate island arc characteristics. Such features imply a marginal basin tectonic setting rather than a major ocean basin for the ophiolitic rocks of the melange. The magmas of the basic rocks have most probably been generated by back arc spreading and have been modified by subduction related fluids later.