Abstract <p>This study is concerned with the mineralogical and petrochemical composition of the gabbro sampled on the Esmeralda submarine volcano in the southern Mariana island arc. The dredging was carried out during the 4th and 5th cruises of the research vessel <i>Vulkanolog</i>. It has been found that the gabbro, which belongs to the tholeiitic series, are strongly fractionated rocks, unlike the gabbroids dredged in basins of the southern Mariana island arc system. It is shown that this gabbro typically contains higher concentrations of iron. This higher concentration of iron is confirmed by high concentrations of iron in pyroxenes and plagioclase, which enables us to classify the bulk of dredged gabbro as belonging to the association of arc ferruginous tholeiites. Low concentrations of high charge and heavy rare-earth elements relative to MORB, as well as their interelement relationships, imply the formation of primary melts from a source in a depleted mantle. The enrichment of gabbro in large-ion lithophile elements provides evidence that the magma genesis not only involved high-temperature residual melt, but was also significantly affected by low-temperature fluid components.</p>