Geochemical discrimination and petrogenesis of alkalic basalt sequences in part of the Ankara melange, central Turkey

Publisher Website
Google Scholar
Abstract
East of Ankara, Turkey, within the major thrust-bound tectonic units of the Ankara melange (Karakaya and Anatolian Nappes), are numerous blocks of low-grade metamorphosed submarine basaltic lavas. Stable incompatible element geochemistry indicates that the majority of these basalts are alkaline and exhibit a range of characteristics typical of many within-plate oceanic islands (OIB). There is a broad chemical overlap between alkaline basalts from within the Triassic Karakaya Nappes (metamorphic and limestone block melanges) and the Cretaceous Anatolian Nappe (ophiolitic melange). A complete sequence of submarine alkaline basalt lavas was sampled within the ophiolitic melange (the 500 m Kiliclar section) to illustrate the variation and petrogenesis of a small seamount-related crustal segment, prior to tectonic dismemberment. The basalts can be divided into three chemical groups that relate to discrete petrographic segments of the lava pile and probably reflect variable degrees of partial melting of a garnet-bearing enriched source. The chemistry of alkaline basalts within the ophiolitic melange, together with their sedimentary associations, suggests an initial submarine environment adjacent to the volcaniclastite debris-filled moats of oceanic islands or seamounts and their volcanically-active arches. Dismemberment of the seamount-related basalts and pelagic sediments took place during subduction of the oceanic crust and their eventual accretion within a forearc platform.