Figure 5. Plot of Th/Yb v. Ta/Yb for the MORB-, OIB- and SSZ-type basaltic lavas from the Tethyan suture zone in western Turkey. Also plotted for comparison are some typical oceanic basaltic and mantle compositions including the depleted MORB mantle, primitive mantle (PM), N-MORB and E-MORB. Partial melting trends predicted using the depleted MORB mantle and PM compositions as the source are shown as solid lines with the calculated degrees of melting on each curve (shown as thick marks). Contours parallel to the mantle array denote the percentage of subduction-derived element Th in the mantle source, assuming that Ta is subduction-immobile (e.g. Pearce et al. 2005).