The Ba/La versus La/Yb diagram serves to identify the main melting process in the mantle wedge. The slab input measured by Ba/La controls the degree of melting recorded by La/Yb in the volcanic front (VF) lavas from Tecuamburro and Moyuta. The correlation implies that fluid flux melting generated these magmas. VF lavas from Agua and Pacaya resemble behind-the-front (BVF) cinder cones and show no relationship between slab additions and extent of melting. Decompression melting was more important in the generation of these VF lavas. Diagram from Cameron et al. (2002).