Although enrichment in Sr relative to Nd and Ce (Sr/Sr*) is common in both oceanic and continental arc basalts, strong enrichments (Sr/Sr* > 3) appear to be present only in oceanic are basalts. Also, there is a broad positive correlation between Sr/Sr* and Eu/Eu*, particularly in oceanic are basalts. The lack of a correlation in arc basalts between Sr/Sr* and displacement from the mantle array (ΔSr) implies that a source rich in 87Sr relative to 143Nd (e.g., seawater-altered basalts) is not the main cause for enriching are magmas in Sr, an implication that is in agreement with previous studies. Instead, a mechanism is required that would (1) increase Sr (and Eu) contents relative to Nd without severely affecting the Sr isotopic composition of the magma and/or its source and (2) take place more readily in oceanic relative to continental arc magmas and/or sources. Plagioclase resorption by ponded, but dynamic, magma chambers may fulfill both of these requirements.