Pa. Floyd, GEOCHEMICAL DISCRIMINATION AND PETROGENESIS OF ALKALIC BASALT SEQUENCES IN PART OF THE ANKARA MELANGE, CENTRAL TURKEY, Journal of the Geological Society, 150, 1993, pp. 541-550
East of Ankara, Turkey, within the major thrust-bound tectonic units o
f the Ankara melange (Karakaya and Anatolian Nappes), are numerous blo
cks of low-grade metamorphosed submarine basaltic lavas. Stable incomp
atible element geochemistry indicates that the majority of these basal
ts 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 (me
tamorphic and limestone block melanges) and the Cretaceous Anatolian N
appe (ophiolitic melange). A complete sequence of submarine alkaline b
asalt lavas was sampled within the ophiolitic melange (the 500 m Kilic
lar section) to illustrate the variation and petrogenesis of a small s
eamount-related crustal segment, prior to tectonic dismemberment. The
basalts can be divided into three chemical groups that relate to discr
ete petrographic segments of the lava pile and probably reflect variab
le 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 en
vironment adjacent to the volcaniclastite debris-filled moats of ocean
ic islands or seamounts and their volcanically-active arches. Dismembe
rment of the seamount-related basalts and pelagic sediments took place
during subduction of the oceanic crust and their eventual accretion w
ithin a forearc platform.