Boron contents were measured in predominantly mafic Quaternary lavas from the Central American Volcanic Arc to evaluate along-strike variations in subduction processes. Despite the significant range in B concentrations (∼2 to 46 ppm), B/La ratios vary in a systematic fashion along the arc: Higher values (>1) are typical between Guatemala and northern Costa Rica, whereas low values (most <0.5) typify central Costa Rica and western Panama. Because B/La is highly correlated with ¹⁰Be/Be (r² = 0.94, excluding one sample), B/La may be a useful indicator of subduction contributions to the magma sources. If enrichments of both B and...